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Effects of livestock grazing on pollination on a steppe in eastern Mongolia
Abstract
Widespread degradation of Mongolian grasslands by overgrazing is of global concern. The objective of this study was to reveal the effects of grazing on pollination as an example of interaction biodiversity in Mongolian grasslands. We established three plots according to grazing intensity on the eastern steppe of Mongolia. In each plot, we recorded the numbers of insect-pollinated plants and observed the foraging behavior of pollinators in June and August. The richness of insect-pollinated species was high and these species were most abundant in lightly grazed plots, and formed complex relations with diverse pollinators. But, frequency of flower visitation and pollination index were greater in heavily grazed plots. All pollination properties were poorest in intermediately grazed plots. These results suggest that the forb-biased foraging of sheep and goats reduces the floral diversity of insect-pollinated species, and consequently reduces pollinators in the intermediately grazed plots. In the heavily grazed plots, only limited ruderal species could survive under heavy cattle grazing, and such simple vegetation formed unbalanced but strong bonds with pollinators. Removal simulation showed that the mutual network was more fragile with respect to the extinction of certain species.
... While insect herbivory research covered all categories, most large herbivore research focused on resource abundance and availability, while no studies have indirectly tied large herbivore grazing to pollinators via plant chemistry changes. References Yoshihara et al. (2008) Content courtesy of Springer Nature, terms of use apply. Rights reserved. ...
... However, cattle preference for grasses may impact the resource availability for juvenile pollinator life stages-e.g., butterfly larvaeconsuming grasses. Other large herbivores such as sheep, goats, deer, and giraffes have all shown a preference for forbs, and these species would be expected to negatively impact pollinators indirectly by removing important plants that provide nectar and pollen (Hatfield and LeBuhn 2007;Yoshihara et al. 2008;Cutter et al. 2021) (Fig. 1). ...
... Large herbivores may have dietary overlaps with pollinators at the individual plant level (Yoshihara et al. 2008;DeBano et al. 2016), which would set the expectation that effects on pollinators are primarily negative. However, the variable indirect effects to pollinators (see Fig. 1) implies that at least under the right conditions, grazing lands at broader scales may provide ample resources for herbivores while limiting negative indirect effects on pollinators (Wilkerson et al. 2013). ...
Globally, large herbivores (e.g., cattle, elk) graze over 2.6 billion hectares of land. These lands can also be used to conserve pollinators that rely on similar resources, specifically diverse plant communities. Pollinator conservation will benefit from management in lands that are used for livestock grazing and wildlife conservation. However, maximizing ecosystem services provided in these areas is often nuanced and difficult. To improve our ability to support multiple ecosystem services in grazing lands, we reviewed published literature to investigate the mechanisms of indirect effects of large herbivores on pollinators via their resources (food plants, nesting sites). We used a framework from previous research on indirect effects of insect herbivores to explore and interpret how plant responses mediate large herbivore effects on pollinators through three mechanistic categories: resource abundance and availability, plant appearance, and plant chemistry. Using the broader conceptual model, we conducted a targeted literature review that found ~ 95% of studies investigating pollinators and large herbivores focused on resource abundance and availability. Consequently, more research is necessary to understand how large herbivores impact pollinators through multiple mechanisms. Future research could also test responses with both large herbivores and insect herbivores to determine their combined ecological consequences. This research will provide insights for managing large herbivores and pollinators simultaneously, while connecting concepts of pollinator ecology and grazing ecology. Filling research gaps on the mechanisms of indirect effects of large herbivores on pollinators will ultimately improve management of multiple ecosystem services and our ability to conserve declining pollinator species.
... Long-term grazing can be related to decreased vegetation cover, plant height and number of open flowers, thus influencing floral display and the reproductive success of plants in desert steppes [2][3][4]. Heavy grazing alters plant and insect communities, and the plant-pollinator relationship is sensibility to the anthropogenic effects of habitat change [5]. Grazing influences individual plant growth and population dynamics and can change vegetation characteristics in desert steppe ecosystems, resulting in different grazing intensities that may exhibit variation in plant floral display [6]. ...
... chenm@lzb.ac.cn plants with high-density flowers [8]. The higher livestock grazing intensity can even negatively affect pollinator species richness and abundance [5]. In that regard, understanding the mechanisms through which grazing may affect pollinator assemblage is critical for informed management decisions and insect-pollinated conservation planning. ...
... Pollen limitation occurs when plants receive insufficient pollen, reducing the reproductive success of the plant [9]. The global expansion of livestock grazing, particularly in desert areas, is considered a major threat to pollination services [5]. The plant-pollinator relationship is a good barometer of interaction biodiversity under anthropogenic effects due to its sensibility to habitat change [10]. ...
Background
Grazing disturbance usually affects floral display and pollination efficiency in the desert steppe, which may cause pollen limitation in insect-pollinated plants. Effective pollination is essential for the reproductive success of insect-pollinated plants and insufficient pollen transfer may result in pollen limitation. Caragana microphylla Lam is an arid region shrub with ecological importance. Few studies have been conducted on how grazing disturbance influences pollen limitation and pollination efficiency of C. microphylla . Here, we quantify the effect of different grazing intensities on floral display, pollinator visitation frequency and seed production in the Urat desert steppe.
Results
In C. microphylla , supplemental hand pollination increased the seed set, and pollen limitation was the predominant limiting factor. As the heavy grazing significantly reduced the seed set in plants that underwent open-pollination, but there was no significant difference in the seed set between plants in the control plots and plants in the moderate grazing plots. Furthermore, there was a higher pollinator visitation frequency in plants in the control plots than in plants in the heavy grazing plots.
Conclusions
We found that pollinator visitation frequency was significantly associated with the number of open flowers. Our findings also demonstrated that seed production is associated with pollinator visitation frequency, as indicated by increased seed production in flowers with higher pollinator visitation frequency. Therefore, this study provides insight into the effect of different grazing intensities on floral display that are important for influencing pollinator visitation frequency and pollination efficiency in desert steppes.
... It is known that intensive grazing can act as a strong filter, reducing plant diversity and altering community composition, but the parallel effect of grazing on functional groups, insects and plant-insect interactions has received less attention (but see [27,38,71,72]). Our results show that, in contrast to traditional hay meadows, intensive pasture management reduces the taxonomic and functional diversity of pollinating insects and strongly shifts community composition towards the dominance of a single plant species with specialized floral traits. As the majority of the interactions in the intensive pastures shifted towards this single specialized plant species, its importance within the network increased and plant-pollinator networks became more specialized and less modular, features that have been linked with lower robustness of networks towards future perturbations [73][74][75]. ...
... The rewiring of interaction towards T. repens also led to a reduction of modularity from several relatively large modules in hay meadows, to just two main modules in pastures. Such simplified networks with lower diversity of species and interactions, higher specialization and niche overlap and lower modularity are expected to be less robust to perturbations [27,71,86,87]. This is underlined by the fact that the loss or decline of a single species, of T. repens could lead to the collapse of the network, unless other flowering species take over its role. ...
... Our study joins a limited body of research on the effect of intensive grazing on plant-pollinator networks (i.e. [27,36,38,71,89]), and provides insights into some of the potential mechanisms that drive changes of ecological communities under intensive grassland management. Grazing is an essential management tool in conservation in Europe (i.e. ...
Complex socio-economic, political and demographic factors have driven the increased conversion of Europe’s semi-natural grasslands to intensive pastures. This trend is particularly strong in some of the most biodiverse regions of the continent, such as Central and Eastern Europe. Intensive grazing is known to decrease species diversity and alter the composition of plant and insect communities. Comparatively little is known, however, about how intensive grazing influences plant functional traits related to pollination and the structure of plant-pollinator interactions. In traditional hay meadows and intensive pastures in Central Europe, we contrasted the taxonomic and functional group diversity and composition, the structure of plant-pollinator interactions and the roles of individual species in networks. We found mostly lower taxonomic and functional diversity of plants and insects in intensive pastures, as well as strong compositional differences among the two grassland management types. Intensive pastures were dominated by a single plant with a specialized flower structure that is only accessible to a few pollinator groups. As a result, intensive pastures have lower diversity and specificity of interactions, higher amount of resource overlap, more uniform interaction strength and lower network modularity. These findings stand in contrast to studies in which plants with more generalized flower traits dominated pastures. Our results thus highlight the importance of the functional traits of dominant species in mediating the consequences of intensive pasture management on plant-pollinator networks. These findings could further contribute to strategies aimed at mitigating the impact of intensive grazing on plant and pollinator communities.
... Grazing intensity has an impact on plant species composition and traits by favouring those which can cope with the grazing pressure, for example, by growing shorter or having less biomass, in order to be less attractive to grazers (Díaz et al., 2001;Dupré and Diekmann, 2001;Moog et al., 2005;Pykälä, 2004;Díaz et al., 2007). Grazing intensity also affects the diversity of plants, with highest plant richness at intermediate grazing levels (see also Intermediate Disturbance Hypothesis; Tadey, 2015;Lázaro et al., 2016) and lowest plant richness in intensive pastures (Yoshihara et al., 2008;Rakosy et al., 2022). As a result, the diversity of pollinators in heavily grazed areas is reduced to a few species, letting the plant-pollinator network become more fragile due to its diminished modularity (Yoshihara et al., 2008;Rakosy et al., 2022). ...
... Grazing intensity also affects the diversity of plants, with highest plant richness at intermediate grazing levels (see also Intermediate Disturbance Hypothesis; Tadey, 2015;Lázaro et al., 2016) and lowest plant richness in intensive pastures (Yoshihara et al., 2008;Rakosy et al., 2022). As a result, the diversity of pollinators in heavily grazed areas is reduced to a few species, letting the plant-pollinator network become more fragile due to its diminished modularity (Yoshihara et al., 2008;Rakosy et al., 2022). However, there is a knowledge gap in understanding why these patterns emerge and how they affect other ecosystem functions. ...
Semi-natural grasslands are key habitats for biodiversity, yet are negatively affected by intensified land-use. To mitigate such adverse effects, effective subsidies systems encouraging extensified production need to be developed that focus not only on species richness and functional diversity. We evaluated the effect of two grazing intensities and the effects of landscape complexity on plant functional traits in three grassland types in the Great Hungarian Plain. Regarding plant traits responding to grazing, we found shorter-statured and earlier flowering species in intensively grazed pastures and more disturbance-tolerant species with increasing boundary length. For pollination-related plant traits, there were more later flowering species in extensively grazed sites, while flowering duration and flower colour revealed complex relations between landscape complexity and grazing intensity. Generally, local low-intensity grazing (0.5 cattle/ha) supports specialist plant species, and increasing boundary length promotes generalist disturbance-tolerant species with traits beneficial for pollinators. Especially when designing new agri-environment schemes for low-intensity grazing systems, understanding the complex functional relationships is crucial to maintaining and restoring farmland biodiversity.
... More importantly, most of those studies were conducted in Europe (>65%), North America (21%), and Africa (5%) (van Klink et al. 2015), and only one of the 140 papers assessed was related to Central Asia (Mongolia). This paper studied, however, only butterflies, bees, and hoverflies (Yoshihara et al. 2008). Two additional papers concerned similar studies in China (Xie et al. 2008;Zhu et al. 2012). ...
... However, all these studies were carried out in Central Europe (Hungary). Considering only the studies conducted in Mongolia, Enkhtur et al. (2017) tested the responses of moths to grazing, Yadamsuren et al. (2015) in crane flies, while Yoshihara et al. (2008) in a few pollinator groups (mainly in bumblebees, butterflies, and beetles). The selection of such narrow indicator groups is most likely related to the limited availability of taxonomists specialising in these arthropod taxa and, consequently, to the difficulties in identifying diverse and abundant material. ...
Arthropods play an essential role in steppe ecosystems. However, studies testing the overall response of terrestrial arthropods to overgrazing are scarce. The problem is particularly worrisome in Central Asia, while, to date, only a very few broader studies have been conducted in this region. We investigated how epigeic terrestrial arthropod assemblages respond to different livestock grazing pressure in two ecozones in SE Mongolia by examining their structure using pitfall traps. We also assessed which groups can be utilised as the most efficient indicators of grazing intensity. Our analyses demonstrated that the habitat type, grazing intensity, and the interaction of these variables had a significant effect on the overall species composition and abundance. However, the grazing intensity caused different changes in the composition of arthropod communities in both studied ecozones. Contrary to the semi- desert, in the steppe habitat, the grazing had the strongest impact in the moderately grazed site. It is most likely because steppe- dwelling species are more sensitive to loss of plant biomass and changes in habitat structure. We also found that the most representative species within and from different groups can react differently to changing grazing intensities, indicating with their presence the characteristics of the respective habitat. Such differences should also be considered when elaborating the management plan of conserved species but also when applying grazing management in different habitat types. Our survey is one of the most comprehensive in Central Asia and should help implement further, more targeted studies in the corresponding habitats.
... However, the two management types have been shown to support different plant species compositions (Fantinato et al., 2019;Fontana et al., 2014). Grazing is a selective management type as grazers selectively remove functional groups of plant species (Oleques et al., 2019) and promote resistant, ruderal species (Vázquez & Simberloff, 2003;Yoshihara et al., 2008). Mowing, on the other hand, is an unselective management type that involves the periodic removal of all plant material, which prevents the spread of dominant plant species (Catorci et al., 2011). ...
... For instance, the mowing management promoted the mass flowering of the partial-shade-adapted plant M. nemorosum, despite mowing usually preventing species' dominance (Catorci et al., 2011). Grazing may also influence the compositional differences by directly influencing plant species abundance (i.e., through the selective removal of particular plant species; Vázquez & Simberloff, 2003, Yoshihara et al., 2008. The compositional differences of sites within management types were small for wooded meadows, but quite large for alvar pastures. ...
In the face of global pollinator decline, extensively managed grasslands play an important role in supporting stable pollinator communities. However, different types of extensive management may promote particular plant species and thus particular functional traits. As the functional traits of flowering plant species (e.g., flower size and shape) in a habitat help determine the identity and frequency of pollinator visitors, they can also influence the structures of plant−pollinator interaction networks (i.e., pollination networks). The aim of this study was to examine how the type of low-intensity traditional management influences plant and pollinator composition, the structure of plant−pollinator interactions, and their mediation by floral and insect functional traits. Specifically, we compared mown wooded meadows to grazed alvar pastures in western Estonia. We found that both management types fostered equal diversity of plants and pollinators, and overlapping, though still distinct, plant and pollinator compositions. Wooded meadow pollination networks had significantly higher connectance and specialization, while alvar pasture networks achieved higher interaction diversity at a standardized sampling of interactions. Pollinators with small body sizes and short proboscis lengths were more specialized in their preference for particular plant species and the specialization of individual pollinators was higher in alvar pastures than in wooded meadows. All in all, the two management types promoted diverse plant and pollinator communities, which enabled the development of equally even and nested pollination networks. The same generalist plant and pollinator species were important for the pollination networks of both wooded meadows and alvar pastures; however, they were complemented by management-specific species, which accounted for differences in network structure. Therefore, the implementation of both management types in the same landscape helps to maintain high species and interaction diversity.
... Grazing has a negative impact on abundance and richness of the bee community in both exotic and native grass communities (Campbell et al. 2021 p. 1). Domestic grazing animals can harm bumble bees by trampling soil, removing floral resources, and degrading bumble bee habitat (Hatfield & LeBuhn 2007 p. 153;Yoshihara et al. 2008Yoshihara et al. p. 2384 which can lead to a linear decline in bee abundance and richness (Yoshihara et al. 2008(Yoshihara et al. p. 2384Tadey 2015 p. 455;Lázaro et al. 2016 p. 408). Grazing livestock have considerable, adverse effects on grassland ecosystems by altering plant species composition and reducing flowering forb species diversity (Fleischner 1994 p. 631;Black et al. 2011 p. 10). ...
... Grazing has a negative impact on abundance and richness of the bee community in both exotic and native grass communities (Campbell et al. 2021 p. 1). Domestic grazing animals can harm bumble bees by trampling soil, removing floral resources, and degrading bumble bee habitat (Hatfield & LeBuhn 2007 p. 153;Yoshihara et al. 2008Yoshihara et al. p. 2384 which can lead to a linear decline in bee abundance and richness (Yoshihara et al. 2008(Yoshihara et al. p. 2384Tadey 2015 p. 455;Lázaro et al. 2016 p. 408). Grazing livestock have considerable, adverse effects on grassland ecosystems by altering plant species composition and reducing flowering forb species diversity (Fleischner 1994 p. 631;Black et al. 2011 p. 10). ...
Petition to list the variable cuckoo bumble bee (Bombus variabilis) to the Endangered Species Act.
... The numbers of domestic livestock have been dramatically increasing during the last three decades (Mongolian Statistical Information Service, 2019), threatening this long-term existing co-existence. In recent years, several studies have shown how competition, pasture degradation and overgrazing influence the populations of wild ungulates (Campos-Arceiz, Takatsuki, & Lkhagvasuren., 2004;Olson et al., 2011;Sheremetev et al., 2017;Sugimoto et al., 2018;Takatsuki, Sato, & Morinaga., 2018;Yoshihara, Chimeddorj, Buuveibaatar, Lhagvasuren, & Takatsuki., 2008). Few of them have considered further potential impacts on other wildlife species, like predators, or though modifications in the ecosystems. ...
... On the other hand, the predictions for the two fox species were particularly contrasting: corsac fox, a small arid-adapted carnivore, was predicted to decrease substantially, while red fox, the larger of these two foxes with a wide ecological niche, was predicted to increase. Both species compete for food resources that, in turn, are susceptible to livestock grazing intensities (Kang, Han, Zhang, & Sun, 2007;Yoshihara et al., 2008), while red foxes are able to outcompete and kill the smaller Corsac foxes. Moreover, Corsac foxes are using marmot burrows for shelter (Geptner, Nasimovich, Hoffmann, & Bannikov, 1988;Murdoch, Munkhzul, Buyandelger, Reading, & Sillero-Zubiri., 2009; but see Townsend & Zahler, 2006), thus, the local extinction of marmots might influence the population of Corsac foxes making them more vulnerable to predation and hunt (Murdoch et al., 2009). ...
The Mongolian plateau is a hotspot for mammals and a perfect environment for nomadic herding. The long-term co-existence with the local wildlife is nowadays threatened by a recent drastic increase of livestock numbers, and associated modifications in the ecosystems. Official hunting and livestock data were used to understand historical links between certain selected species (grey wolf, red fox, corsac fox, ground squirrels and marmots, vs. cattle, sheep, goat, horses and camels), during the period 1941-1985. Significant interactions appeared, like negative effects of goat numbers on wolves hunting. These models were thereafter used to predict the consequences of the increase of livestock in the period 1986-2015 on wildlife. A sharp decrease of wolves and corsac foxes was predicted, and positive effects on marmots, squirrels and red fox; i.e., beneficial for ecosystem-engineering borrowing species, but negative for predators. These predictions agree with the current situation, except for marmots which are currently declining.
... Domestic grazing animals can harm bumble bees by trampling soil, removing floral resources, and degrading bumble bee habitat (Hatfield & LeBuhn 2007 pp. 153, 156;Yoshihara et al. 2008Yoshihara et al. p. 2384 which can lead to a linear decline in bee abundance and richness (Yoshihara et al. 2008(Yoshihara et al. p. 2384Tadey 2015 p. 455;Lázaro et al. 2016 p. 408). ...
... Domestic grazing animals can harm bumble bees by trampling soil, removing floral resources, and degrading bumble bee habitat (Hatfield & LeBuhn 2007 pp. 153, 156;Yoshihara et al. 2008Yoshihara et al. p. 2384 which can lead to a linear decline in bee abundance and richness (Yoshihara et al. 2008(Yoshihara et al. p. 2384Tadey 2015 p. 455;Lázaro et al. 2016 p. 408). ...
... In shrublands in northern Scotland, the diversity of both floral visitors and plants was higher at moderate and higher grazing intensities (Vulliamy et al. 2006;Vanbergen et al. 2013). Contrastingly, a pollination network in a Mongolian steppe presented lower diversity and generalization at moderate grazing intensities (Yoshihara et al. 2008). Thus, the effects of grazing vary among different ecosystems, and generalizations may be difficult. ...
... In addition, grazer feeding preferences may influence species composition and indirectly determine network structure. In the Mediteranean phrygana (Lázaro et al. 2016) and Mongolian steppe (Yoshihara et al. 2008), goats and sheep were the main herbivores. These species present forb-biased foraging and therefore reduce diversity of insect-pollinated species at high and intermediated grazing intensities (Lázaro et al. 2016). ...
Understanding how disturbances influence interaction networks is a central but still poorly explored issue in ecology and management. The goal of this study was to test how the structure of plant-pollinator networks and the structuring processes are influenced by grazing in a subtropical grassland community on the southern hemisphere. Twelve sampling plots were allocated in order to cover a grazing gradient ranging from overgrazed to ungrazed sites. For each plot, we created a quantitative matrix containing all observed pairwise insect-plant interactions and described morphology, phenology and abundances of each species. We fitted a series of models to test the influence of grazing intensity on metrics describing networks structure. We finally used probabilistic matrices, maximum likelihood and model selection to investigate the processes influencing frequencies of interactions across the gradient of disturbance. Grazing intensity influenced connectance, specialization and interaction evenness, while the number of species and links, nestedness and modularity were less variable. Species abundance was the most important determinant of interaction frequencies regardless of grazing intensity. In contrast to northern hemisphere pollination networks studied so far, these subtropical plant-pollinator networks and their structuring processes were remarkably consistent along the grazing gradient. We argue that this results from the dominance of generalist Asteraceae species, which are selectively avoided by cattle and play a core role in attracting a wide range of pollinators and thereby structuring plant-pollinator interactions, providing therefore stability.
... Vanbergen et al. (2014) compararon sitios sin pastoreo y con pastoreo en Escocia y mostraron que el pastoreo aumentaba el tamaño, la diversidad, y la generalización de las redes. Un resultado similar fue encontrado por Yoshihara et al. (2008) cuando compararon sitios sin pastoreo con sitios fuertemente pastoreados en Mongolia, mientras que a niveles intermedios de pastoreo encontraron una menor diversidad y generalización de la red de polinización (Yoshihara et al. 2008). En este último estudio, sin embargo, los gradientes de pastoreo se asociaron con diferentes tipos de herbívoros (ovejas y cabras frente a las vacas y caballos) y, por lo tanto, estos dos efectos no pudieron ser separados. ...
... Vanbergen et al. (2014) compararon sitios sin pastoreo y con pastoreo en Escocia y mostraron que el pastoreo aumentaba el tamaño, la diversidad, y la generalización de las redes. Un resultado similar fue encontrado por Yoshihara et al. (2008) cuando compararon sitios sin pastoreo con sitios fuertemente pastoreados en Mongolia, mientras que a niveles intermedios de pastoreo encontraron una menor diversidad y generalización de la red de polinización (Yoshihara et al. 2008). En este último estudio, sin embargo, los gradientes de pastoreo se asociaron con diferentes tipos de herbívoros (ovejas y cabras frente a las vacas y caballos) y, por lo tanto, estos dos efectos no pudieron ser separados. ...
The loss, fragmentation and degradation of natural and semi-natural habitats due to land-use changes is one of the fundamental causes of worldwide pollinator declines. In this paper, we review how land-use changes affect wild native pollinator insects, as well as the particular effects of the three main types of land-use (agriculture, livestock grazing and urbanization) on pollinator abundance and diversity, plant-pollinator networks, and pollination service. Land-use changes may vary in intensity, but all of them involve habitat disturbances affecting pollinator populations, especially through modification of their floral and nesting resources. In general, regardless of the land-use type, changes whose intensity increases the availability of resources and the heterogeneity of microhabitats tend to have positive effects on the abundance and diversity of pollinators, whereas changes that reduce resource availability usually have negative effects. Moreover, the response of pollinators depends on their specific traits (specialization, mobility, sociability, nesting site, phenology). Some species or groups may be favoured while others disadvantaged by different land-uses. Although the negative effects of land-use changes are ubiquitous, anthropogenic habitats may still be suitable for pollinators if appropriate conservation, restoration and management measures are taken.
... Grazers can also indirectly impact other grassland organisms, such as birds (Vickery et al. 2001;Bleho et al. 2014) and mammals (Jones 2000), through habitat structural changes caused by herbivory and trampling. However, invertebrates, particularly pollinators, have been given less attention in grazing impact studies (Debano 2006;Yoshihara et al. 2008), especially in North America, even though pollinators have critical roles in grassland ecosystem functioning (Losey and Vaughan 2006). ...
... Carvell 2002;Vulliamy et al. 2006), negatively (e.g. Xie et al. 2008;Yoshihara et al. 2008), and not at all (e.g. Sjodin et al. 2008;Batary et al. 2010) to grazing. ...
Livestock grazing is a widespread grassland disturbance and can negatively impact biodiversity. Pollinators constitute a vital component of grassland ecosystems, but the impact of grazing on pollinator diversity has seldom been evaluated in North America. We assessed vegetation structure, and pollinator and flowering plant abundance, richness, diversity, and community composition in four pairs of spring-grazed/ungrazed sites in south-central British Columbia, Canada. We also investigated whether pollinator or floral communities differed between the two threatened shrubsteppe habitat types we sampled—antelope-brush and big sagebrush shrubsteppe. Pan-trapping surveys captured 5907 bees, flies, beetles, wasps and butterflies constituting 253 species. We found that the percent cover of shrubs and bare soil increased with grazing, while the height of grasses and forbs decreased. In contrast, pollinator and flowering plant abundance, richness, diversity, and community composition were not significantly affected by grazing. Flowering plant and pollinator community composition did differ significantly between shrubsteppe habitats. Our results indicate that grasslands in North America, when managed responsibly, can maintain pollinator and flowering plant diversity under grazing pressure. The continued effort of land managers to balance ecological integrity and economic viability will be important for the conservation of grassland pollination systems.
... This may be related to the high diversity of plant species. High diversities of plants and pollinators in the grassland ecosystems are maintained by the light level of grazing pressure (Yoshihara et al. 2008). Hustai National Park, located in the conservation area of introduced wild horse (takh), experiences disturbance by livestock and marmots, which could contribute to the high species diversity of plants and ower visitors (Yoshihara et al. 2010). ...
Flowering phenology of alpine-plant communities is determined by the interaction between abiotic and biological factors. Bees (especially bumble bees) and flies are major pollinators in alpine ecosystems. The abundance of bumble bees consistently increases with seasonal progress reflecting the colony development cycle, while the abundance of flies often fluctuates unpredictably. Responding to the seasonal dynamics of pollinators, flowering phenology of alpine-plant communities may also vary between bee-visited and fly-visited plants within and among regions. We compared the relationship between flower-visitor composition and flowering phenology across geographic regions: fly-dominated alpine in New Zealand, subtropical alpine in Taiwan, mid-latitudinal alpine in central and northern Japan, and high-elevation grassland in Mongolia. Thermal gradient was a fundamental factor regulating flowering patterns across regions, and clear seasonality at higher latitudes created diverse flowering patterns at a community scale. Flower production of fly-visited plants was less predictable with large variation, whereas that of bee-visited plants showed consistent patterns across regions reflecting the seasonality of bees. In New Zealand, most plant species were linked to syrphid and/or non-syrphid flies, but the network structure between insects and plants varied between sites. The network structures of the East Asian alpines were commonly constituted by syrphid flies, non-syrphid flies, and bumble bees, and these groups had specific niche width. In the Mongolian grassland, many insect groups formed diverse networks with small niche overlap. These results suggest that the flowering phenology of alpine-plant communities is influenced by the seasonal activity of bee pollinators under the climatic restriction in each region.
... Across rangelands, grazing can not only influence ecosystem health, function, and structure ( Jones 20 0 0 ;Freilich et al. 2003 ;Krausman et al. 2009 ;Schönbach et al. 2011 ;Bailey et al. 2019 ;Goosey et al. 2019 ) but can also affect pollinators, including bees. In some systems, livestock grazing has been found to improve outcomes for bee populations ( Vulliamy et al. 2006 ;Lázaro et al. 2016 ;Shapira et al. 2020 ;Lasway et al., 2022 ), whereas other studies have found grazing can negatively affect some bees ( Kruess and Tscharntke 2002 ;Sjödin 2007 ;Xie et al. 2008 ;Yoshihara et al. 2008 ;Kimoto et al. 2012b ). The variability in responses of native bees to livestock grazing may be due to myriad factors, including differences in the type of grazer, the intensity of grazing, the timing of grazing, plant growth stage, and the species traits of the particular bee species in the system ( Kimoto et al. 2012b ;Cutter et al., 2021 ). ...
Rangelands may offer valuable habitat for invertebrate wildlife, helping conserve ecologically and economically significant organisms, like native bees. In some systems, livestock may affect bees by consuming or trampling blooming plants that bees rely on for food. One potential way to reduce potential negative effects of livestock on bees is to delay grazing on floristically rich parts of the landscape until after peak bloom (i.e., phenologically targeted grazing). To test the outcome of this method, we collected bees using pan traps and counted blooming stems from May to September in grazed and ungrazed sites. Our sites were located in two experimental cattle grazing systems in the Pacific Northwest, United States, in which cattle turnout did not occur until after peak forb bloom. One system was located in bunchgrass prairie, and the other was located in riparian meadows. Our objectives were to 1) quantify seasonal variation in bee and blooming plant communities and 2) measure how or if these communities responded to grazing. In both systems, bee and bloom species richness peaked in June and bloom abundance and diversity were highest in May and June. Bee abundance and diversity were more variable throughout the season. We observed significantly lower abundance, richness, and diversity of blooming species in the riparian system in response to grazing, potentially decreasing floral resource availability for bees, but did not detect a concomitant negative effect on bees. In the bunchgrass system, we observed no significant negative effects of grazing on bees or blooming plants. This suggests that for areas with high-quality
bee habitat, site-specific, phenologically targeted grazing may moderate negative effects of livestock on bee and plant communities. Range managers could use alternative grazing locations (e.g., old fields, early senescing sites, more intensively managed pastures), if available, during peak bloom to mitigate potential herbivory effects on bees and blooms.
... 3. Incentives (nectar) offered by the plant may not be viable enough for pollinators to waste their energy on or may attract animals that would eat the whole flower (Yoshihara et al., 2008). ...
Euphorbia groenewaldii R.A Dyer is threatened with extinction, yet virtually nothing is known about this attractive succulent species apart from a 40-year-old study. Conservation and management of threatened species require a thorough understanding of their ecological requirements and spatial. In order to understand the ecology of this species, the study investigated its population structure, identified biotic and abiotic features that influence its ecology, as well as the threats facing the different populations in the Limpopo Province of South Africa. One square metre plots containing E. groenewaldii plants were assessed for six micro-habitat features, of which three were biotic and three abiotic, i.e. grass, forbs, dead material, stones, fixed rock and bare ground. A population census was done by collecting data on adults, juveniles, and senescent individuals. Results indicate that there was a clear correlation between aspects within populations (P < 0.0001). There was a clear correlation between the slope degrees within populations (P < 0.0001). Population densities per slope position support the statistical analysis that the majority of E. groenewaldii's plants occur on the middle slope. Soil samples from all the E. groenewaldii sites were acidic. The mean canopy size occurring on the northwestern aspect was at least 2500 cm 2 larger than on any other aspect. Adults were the most prominent in all populations; except De Put who had on average 20% fewer adults than the other populations. When comparing the maximum canopy areas, a significant difference existed between populations (one-way ANOVA test, P < 0.0001). The populations of E. groenewaldii differed from each other with respect to the number of plants in each population that carried flowers or fruit or both. About 87% of all measured plants were non-reproductive. All threats and agents of damage that were noted were of a biotic nature. These included trampling, herbivory, and anthills/termites. Major threats were residential and commercial (office and mining) developments, which had a once-off destructive effect on the small geographical areas in which relatively large numbers of E. groenewaldii grew.
... Following fire, species richness and floral abundance rebound over time and can exceed levels in adjacent unburned areas (Mola & Williams, 2018;Potts, Vulliamy, Dafni, N'eeman, et al., 2003). In a similar fashion, grazing can decrease floral resources through herbivory, but a total absence of grazing can decrease floral resources by favouring grasses and promoting litter build-up (Buckles & Harmon-Threatt, 2019;Carvell, 2002;Cutter et al., 2021;Palit et al., 2021;Yoshihara et al., 2008). In both cases, floral resources benefit from both focal disturbances and refuge from said disturbances, suggesting that a patchy disturbance regime might be beneficial. ...
Grasslands provide essential floral resources for both managed and wild pollinators. However, grassland flowers in remaining native landscapes are threatened due to non‐native plant invasions and alterations to historic disturbance regimes such as fire and grazing. The potential for managed disturbance to promote grassland floral resources remains unclear. Fire and grazing historically occurred interactively, but uniform application of each may be a detriment to floral resources and the pollinators depending on them. Though fire can increase resources available to plants and stimulate flowering, it initially destroys floral resources and may delay flower availability. Similarly, grazing removes competitors of flowering plants, but destroys flower heads.
To address this knowledge gap, we investigated the impacts of rotational fire and cattle grazing (patch‐burn grazing with one and two seasons of fire per year) versus traditional season‐long grazing with no fire on floral resources in mixed‐grass prairie. In patch‐burn treatments, part of each pasture is burned each year, which focuses grazing activity due to the high‐quality regrowth. We aimed to use fire to remove litter around flowering plants while also sheltering established flower heads from grazing pressure by directing cattle away from regenerating forbs in unburned portions of the landscape. Over two summers, we performed weekly flower surveys in season‐long grazing and patch‐burn grazing pastures. We analysed total seasonal floral resources, maximum floral abundance and seasonal species richness between treatments.
Over 2 years, we surveyed 1,238,241 ramets of 160 species, focusing on 36 common species for individual analysis. We found broad positive associations between patch‐burn grazing and total seasonal flower abundance, maximum flower abundance and species richness compared to traditional management. In most cases, patch‐burn grazing with dormant and growing season fires produced higher floral abundance, total seasonal floral resources and species richness than patch‐burning with dormant season fires alone, suggesting benefits of increased levels of pyrodiversity.
Synthesis and applications . Under increasing pressure to manage for declining pollinators, rangeland managers must consider strategies to enhance floral resources within the context of livestock production goals. The spatiotemporal interaction of cattle grazing and fire shows promise for promoting floral resource abundance and diversity.
... America. Likewise, in eastern Mongolia, heavy grazing pressure was found to be associated with an increase in the number of plantpollinator interactions, even though overall forb diversity was reduced (Yoshihara et al., 2008). However, a study from the Inner Mongolia region of China (Ma et al., 2017) showed that over-grazing can reduce abundances of primary and secondary (arthropod) consumers over time. ...
A variety of habitat‐associated factors moderate effects of grazing on insect biodiversity. Here, we examine how aridity, evolutionary history of grazing and grazing intensity individually and interactively mediate the effect of livestock grazing on pollinator biodiversity (native bees and butterflies).
Using a meta‐analysis of 59 studies published in the primary literature, we characterized the response of pollinator communities to grazing across several continents.
In very humid habitats, high grazing intensities generally had negative impacts on pollinator abundance and richness, but these effects were not found in semi‐arid habitats, where livestock grazing intensity did not interact with aridity to impact pollinator abundance or richness. However, within semi‐arid habitats livestock grazing was associated with reduced pollinator richness in areas with short evolutionary histories grazing.
Pollinator life history mediated effects of livestock grazing on pollinator communities: livestock grazing had negative impacts on richness of social bees and butterflies but not solitary bees, though abundances of all three pollinator categories were consistently reduced under livestock grazing.
Our synthesis suggests that effects of cattle on pollinators may be driven by impacts on nesting habitats (e.g. soil compaction), rather than consumption or alteration of forb cover. Our collective findings have importance for coordinating grazing management and pollinator conservation efforts and help to distinguish how grazing practices could impact pollinator biodiversity across ecoclimatic regions.
... Despite that livestock grazing constitutes the major land use type in the drylands of Afrotropical grasslands and is expected to further increase in the near future, (Basu et al., 2016;Bystriakova et al., 2018;Rojas-Downing et al., 2017), there is no single well-replicated study that has attempted to elucidate the effect of livestock grazing intensity on the bee abundance and diversity of the Afrotropical savannah. Hitherto, most of the studies have been conducted in temperate regions (Davidson et al., 2020;Kearns & Oliveras, 2009;Kimoto et al., 2012;Lazaro et al., 2016;Minckley, 2014;Shapira et al., 2020;Tadey, 2015;Van Klink et al., 2016;Vulliamy et al., 2006;Yoshihara et al., 2008) leaving the effects of grazing intensity on bee assemblage in Afrotropical savannah largely unknown. In this study, we examined the effect of livestock grazing intensity on bee species richness and abundance along a temperature gradient in the Afrotropical savannah of northern Tanzania. ...
One of the pronounced global challenges facing ecologists is how to feed the current growing human population while sustaining biodiversity and ecosystem services. To shed light on this, I investigated the impact of human land use on bee diversity and plant-pollinator interactions in Tanzania Savannah ecosystems. The thesis comprises the following chapters:
Chapter I: General Introduction
This chapter provides the background information including the study objectives and hypotheses. It highlights the ecological importance of bees and the main threats facing bee pollinators with a focus on two land-use practices namely livestock grazing and agriculture. It also highlights the diversity and global distribution of bees. It further introduces the tropical savannah ecosystem, its climate, and vegetation characteristics and explains spectacular megafauna species of the system that form centers of wildlife tourism and inadequacy knowledge on pollinators diversity of the system. Finally, this chapter describes the study methodology including, the description of the study area, study design, and data collection.
Chapter II: Positive effects of low livestock grazing intensity on East African bee assemblages mediated by increases in floral resources
The impact of livestock grazing intensity on bee assemblage has been subjected to research over decades. Moreover, most of these studies have been conducted in temperate Europe and America leaving the huge tropical savannah of East Africa less studied. Using sweep netting and pan traps, a total of 183 species (from 2,691 individuals) representing 55 genera and five families were collected from 24 study sites representing three levels of livestock grazing intensity in savannah ecosystem of northern Tanzania. Results have shown that moderate livestock grazing slightly increased bee species richness. However, high livestock grazing intensity led to a strong decline. Besides, results revealed a unimodal distribution pattern of bee species richness and mean annual temperature. It was also found that the effect of livestock grazing and environmental temperature on bee species richness was mediated by a positive effect of moderate grazing on floral resource richness. The study, therefore, reveals that bee communities of the African savannah zone may benefit from low levels of livestock grazing as this favors the growth of flowering plant species. A high level of livestock grazing intensity will cause significant species losses, an effect that may increase with climatic warming.
Chapter III: Agricultural intensification with seasonal fallow land promotes high bee diversity in Afrotropical drylands
This study investigated the impact of local agriculture intensification on bee diversity in the Afro tropical drylands of northern Tanzania. Using sweep netting and pan traps, a total of 219 species (from 3,428 individuals) representing 58 genera and six families were collected from 24 study sites (distributed from 702 to 1708 m. asl) representing three levels of agriculture intensity spanning an extensive gradient of mean annual temperature. Results showed that bee species richness increased with agricultural intensity and with increasing temperature. However, the effects of agriculture intensity and temperature on bee species richness were mediated by the positive effects of agriculture and temperature on floral resource richness used by bee pollinators. Moreover, results showed that variation of bee body sizes increases with agricultural intensification, “that effect”, however, diminished in environments with higher temperatures. This study reveals that bee assemblages in Afrotropical drylands benefit from agriculture intensification in the way it is currently practiced. Further intensification, including year-round irrigated crop monocultures and extensive use of agrochemicals, is likely to exert a negative impact on bee diversity and pollination services, as reported in temperate regions. Moreover, several bee species were restricted to natural savannah habitats. Therefore, to conserve bee communities in Afro tropical drylands and guarantee pollination services, a mixture of savannah and agriculture, with long periods of fallow land should be maintained.
Chapter IV: Impact of land use intensification and local features on plants and pollinators in Sub-Saharan smallholder farms
For the first time in the region, this study explores the impact of land-use intensification on plants and pollinators in Sub-Saharan smallholder farms. The study complemented field surveys of bees with a modern DNA metabarcoding approach to characterize the foraged plants and thus built networks describing plant-pollinator interactions at the individual insect level. This information was coupled with quantitative traits of landscape composition and floral availability surrounding each farm. The study found that pollinator richness decreased with increasing impervious and agricultural cover in the landscape, whereas the flower density at each farm correlated with pollinator richness. The intensification of agricultural land use and urbanization correlated with a higher foraging niche overlap among pollinators due to the convergence of individuals' flower-visiting strategies. Furthermore, within farms, the higher availability of floral resources drove lower niche overlap among individuals, greater abundance of flower visitors shaped higher generalization at the networks level (H2I), possibly due to increased competition. These mechanistic understandings leading to individuals’ foraging niche overlap and generalism at the network level, could imply stability of interactions and the pollination ecosystem service. The integrative survey proved that plant-pollinator systems are largely affected by land use intensification and by local factors in smallholder farms of Sub-Saharan Africa. Thus, policies promoting nature-based solutions, among which the introduction of more pollinator-friendly practices by smallholder farmers, could be effective in mitigating the intensification of both urban and rural landscapes in this region, as well as in similar Sub-Saharan contexts.
Chapter V: A synopsis of the Bee occurrence data of northern Tanzania
This study represents a synopsis of the bee occurrence data of northern Tanzania obtained from a survey in the Kilimanjaro, Arusha, and Manyara regions. Bees were sampled using two standardized methods, sweep netting and colored pan traps. The study summed up 953 species occurrences of 45 species belonging to 20 genera and four families (Halictidae, Apidae, Megachilidae, and andrenidae) A. This study serves as the baseline information in understanding the diversity and distribution of bees in the northern parts of the country. Understanding the richness and distribution of bees is a critical step in devising robust conservation and monitoring strategies for their populations since limited taxonomic information of the existing and unidentified bee species makes their conservation haphazard.
Chapter VI: General discussion
In general, findings obtained in these studies suggest that livestock grazing and agriculture intensification affects bee assemblages and floral resources used by bee pollinators. Results have shown that moderate livestock grazing intensity may be important in preserving bee diversity. However, high level of livestock grazing intensity may result in a strong decline in bee species richness and abundance. Moreover, findings indicate that agriculture intensification with seasonal fallow lands supports high floral resource richness promoting high bee diversity in Afrotropical drylands. Nonetheless, natural savannahs were found to contain unique bee species. Therefore, agriculture intensification with seasonal fallow should go in hand with conserving remnant savannah in the landscapes to increase bee diversity and ensure pollination services. Likewise, findings suggest that increasing urbanization and agriculture cover at the landscape level reduce plant and pollinator biodiversity with negative impacts on their complex interactions with plants. Conversely, local scale availability of floral resources has shown the positive effects in buffering pollinators decline and mitigating all detrimental effects induced by land-use intensification. Moreover, findings suggest that the impact of human land use (livestock grazing and agriculture) do not act in isolation but synergistically interacts with climatic factors such as mean annual temperature, MAT. The impact of MAT on bee species richness in grazing gradient showed to be more detrimental than in agriculture habitats. This could probably be explained by the remaining vegetation cover following anthropogenic disturbance. Meaning that the remaining vegetation cover in the agricultural gradient probably absorbs the solar radiations hence reducing detrimental effect of mean annual temperature on bee species richness. This one is not the case in grazing gradient since the impact of livestock grazing is severe, leaving the bare land with no vegetation cover. Finally, our findings conclude that understanding the interplay of multiple anthropogenic activities and their interaction with MAT as a consequence of ongoing climate change is necessary for mitigating their potential consequences on bee assemblages and the provision of ecosystem services. Moreover, future increases in livestock grazing and agriculture intensification (including year-round crop irrigated monocultures and excessive use of agrochemicals) may lead to undesirable consequences such as species loss and impair the provision of pollination services.
... were shared among the studied sites regardless of the disturbance level or type. These remnants have allowed the network of bee-plant interactions to remain nested despite the high level of human disturbance these sites have and continue to experience (Vázquez & Simberloff, 2003;Yoshihara et al., 2008); (5) some blooming plants that are attractive to bees are common in disturbed areas. For instance, different Asteraceae thrive in the roads along agricultural landscapes attracting then more bee species than the crops (Montagnana & Campos, 2020); and (6) given that we only sampled a small portion of the AZQH over 10 months and in 1 year, it is possible that more intensive surveys may reveal disturbance effects that we did not find. ...
The maintenance of interactions between plants and their floral visitors depends on factors such as resource variability, seasonality, and population dynamics. Changes in water availability along with different types and levels of anthropogenic disturbance may influence how plants and pollinators interact, especially in arid environments.
In a semi‐arid area of the southernmost Chihuahuan Desert (Mexico), we surveyed bee–plant interactions in the dry and rainy season at sites that differed in disturbance type. We used a mutualistic network approach to analyse our data.
We collected 946 bee individuals belonging to 32 bee species, almost a third of the total richness previously reported for Querétaro state. We detected a strong impact of seasonality on the structure of ecological interactions, with more complex and robust interactions among bee and plant species in the rainy season.
We did not find statistical support for a relationship among disturbance, nestedness, or niche overlap. We did find disturbance negatively affected plant robustness to secondary extinctions.
Four plants: Echinocactus platyacanthus , Opuntia stenopetala , Senna wislizeni var. painteri and Cylindropuntia imbricata comprised the core species that were primarily responsible for the resilience of the bee communities. The following bees conformed the generalist core of species: Diadasia rinconis , Lasioglossum ( Dialictus ) sp. 1, Apis mellifera , and Augochlorella pomoniella .
Overall, network nestedness and robustness differed significantly between seasons but not among sites with different levels of disturbance.
... Despite that livestock grazing constitutes the major land-use type in the drylands of Afrotropical grasslands and is expected to further increase in the near future, (Basu et al., 2016;Bystriakova et al., 2018;Rojas-Downing et al., 2017), there is no single well-replicated study that has attempted to elucidate the effect of livestock grazing intensity on the bee abundance and diversity of the Afrotropical savannah. Hitherto, most of the studies have been conducted mainly in temperate regions (Davidson et al., 2020;Kearns and Oliveras, 2009;Kimoto et al., 2012;Lazaro et al., 2016;Minckley, 2014;Shapira et al., 2020;Tadey, 2015;Van Klink, 2016;Vulliamy et al., 2006;Yoshihara et al., 2008) leaving the effects of grazing intensity on bee assemblage in Afrotropical savannah largely unknown. In this study, we examined the effect of livestock grazing intensity on bee species richness and abundance along a temperature gradient in the Afrotropical savannah of northern Tanzania. ...
Livestock grazing is widespread and increasing in the African grasslands, with largely unknown consequences for bee pollinators. Here we assessed the direct and indirect impacts of livestock grazing intensity on bee assemblages in East African grasslands and tested if the effect of grazing intensity on bee assemblages depends on temperature. We collected data on 24 study sites representing three different levels of livestock grazing intensity in northern Tanzania. Ordinary linear models and path analysis were used to test the effect of grazing and temperature on floral resources and bee diversity. Non-metric multidimensional scaling (NMDS) and permutational MANOVA were used to analyze changes in bee community composition and bee-visited plant community with grazing intensity and temperature. We found that moderate livestock grazing slightly increased bee species richness while high grazing intensity led to a strong decline. Further, bee species richness was highest at moderate temperatures and significantly lower in colder and very hot environments. Path analysis results showed that the effect of livestock grazing and environmental temperature on bee species richness is mediated by a positive effect of moderate grazing on floral resource richness. Livestock grazing led to a significant change in the species composition of bee communities, this effect was stronger in environments with very high temperatures. Our study reveals that bee communities of the African savannah zone may benefit from low levels of livestock grazing as this proliferates the growth of flowering plant species. However, livestock grazing at high intensity will cause significant species losses and turnover of bee species communities; effects which may increase with climatic warming.
... The pastures in Central Asia are often ecologically vulnerable because of unreliable rainfall, overgrazing, degradation, and soil erosion at many places (Ykhanbai et al., 2004;Sternberg et al., 2011). While effects of livestock grazing on the diversity and productivity of the ground vegetation have been studied repeat-edly in grasslands (Yoshihara et al., 2008;Wu et al., 2009;Wesche et al., 2010), there are not many studies dealing with the responses of forest vegetation to mobile livestock breeding in Central Asia (Blaser et al., 1998). ...
The intensive grazing in forbs-Stipa pasture
were reduced by the increasing participation of annual species bad eaten by animals and also
increasing area of bare ground, which is reason to increase the individual number of the
Xanthoparmelia camtscha-dalis (Ach.) Hale, it might be explained that all indi-vidual cover of lichens could be disrupted by animal drop even it could be destroyed completely at the end
... The details of grazing intensity from May to September in the year of 2013 and 2014 are presented in Table S1. Based on the grazing intensity classification from literatures (Yoshihara et al. 2008;Schönbach et al. 2011;Ma et al. 2017), both rotational and continuous grazing in this study belong to overgrazing. Each treatment has three replicates, and each replicated plots had an area of 33.3 m × 33.3 m. ...
In situ 13CO2 pulse labeling was conducted in temperate grasslands, managed by no grazing, rotational, or continuous overgrazing, to trace the allocation pattern and the dynamics of newly assimilated C into the plant-soil system. Forty-eight days after the labeling, the belowground 13C allocations under overgrazing were substantially lower than those under no grazing (55% for no grazing, 29% for rotational grazing, 36% for continuous grazing). Overgrazing reduced the relative amount of C incorporation into soil organic C (SOC). Overgrazing led to more C losses through shoot respiration (23%, 54%, 46% by no, rotational, and continuous grazing, respectively), but fewer losses via soil respiration (33%, 12%, 13% by no, rotational, and continuous grazing, respectively). Continuous grazing produced more C allocation to roots than rotational grazing (12% vs 4%), indicating that plants had stronger root C storage capacity under continuous than rotational grazing. The mean C residence time of the belowground rhizodeposits and C used for root respiration under rotational grazing (2.08 days) was longer than that under no grazing (1.47 days) or continuous grazing (1.37 days). Overgrazing decreased the C stocks in shoots but remained stable in roots. Meanwhile, overgrazing decreased the newly assimilated C allocation to belowground, creating a negative effect on C sequestration. Under overgrazing regimes, continuous grazing is more preferable in the investigated temperate grasslands than rotational grazing for C allocation and sequestration in soil.
... By selectively targeting plants with specific functional traits, small ruminants may also affect vegetation composition and community-level phenology. For example, sheep and goats' preferential herbivory on forbs reduced floral diversity in Mongolian grasslands (Yoshihara et al., 2008), while sheep preferences for late-flowering plants in alpine pastures in Norway led to an increase in late-flowering species when sheep were removed (Evju et al., 2009). Although graminoids comprise the largest proportion of yak diets, they also consume forb flowers and maximize their consumption of forbs during the summer, when most high-elevation forbs are flowering (Cincotta et al., 1991;Shrestha and Wegge, 2008). ...
Changes in the seasonal timing of plant flowering are hypothesized to alter the number of flowers plants produce , which contributes to reproductive success. However, empirical evidence linking specific aspects of plant flowering phenology to the number of flowers produced is limited, particularly under future global climate change. We used phenology measurements after 2, 3, 6, and 7 years of a fully factorial, climate change field experiment in an alpine meadow pasture on the central Tibetan Plateau to understand: 1) how experimental warming and snow addition affect the date of first and last flowering in related forb and shrub species, Potentilla saundersiana Royle and Potentilla fruticosa L.; and 2) how these changes in the timing of phenological events alter flowering duration and production, as a proxy for reproductive effort. We found that warming significantly advanced the date of first flowering in both P. fruticosa and P. saundersiana, with no other significant effects on flowering duration or production. In contrast to warming, simulated snowstorms delayed the date of first flowering in P. saundersiana, but had no significant effect on P. fruticosa. There were no significant treatment interactions. For both species, flower production increased as the last date of flowering occurred later. These results indicate that as climate change alters alpine plant phenology, advances in the timing of first flowering alone will not necessarily translate to increases in flowering duration and enhanced reproductive effort. Instead, these findings demonstrate the importance of the date of last flowering in mediating plant reproductive effort and success.
... Most of the studies investigating the effects of livestock grazing on bee and flower communities have been conducted in temperate grasslands, and have found that increased intensity of cattle grazing (from no to heavy grazing) negatively affects bee abundance and/or richness due to decreased flower diversity and altered plant species composition (Kruess and Tscharntke 2002, Sjodin 2007, Xie et al. 2008, Kearns and Oliveras 2009, Minckley 2014, Tadey 2015. A few studies have shown positive impacts of increased grazing intensity compared to low-or no-grazing sites, on both bee and flower communities (Carvell 2002, Yoshihara et al. 2008, Kovacs-Hostyanszki et al. 2013, van Klink et al. 2016, whereas others did not find any such effects (Sjodin et al. 2008, Batary et al. 2010, Elwell et al. 2016 or found a mix of effects depending on the season and pollinator guild (Kimoto et al. 2012). The differences among these studies are likely the result of differences in habitat type and land-use history, grazing level, and additional interacting management practices such as fire. ...
Rangelands are a dominant anthropogenic land use and a main driver of natural habitat loss worldwide. Land sharing, the integration of agricultural production and biodiversity conservation, may provide a platform for managing rangelands to fulfill multiple ecosystem services. However, livestock grazing can greatly affect biodiversity and little is known about its effects on providers of focal ecosystem services, such as pollinators. We investigated the effect of cattle grazing on bee communities and their foraging and nesting resources in Mediterranean rangelands. Specifically, we explored the effect of moderate cattle grazing on flowering plant abundance, species richness and composition, the diversity of nesting substrates, and consequently, the possible effects on wild bee and honey bee foraging activity, species diversity, and community composition. We conducted field research in the Mediterranean rangelands of Israel during the main bee activity season, in the spring of 2012 and 2013, comparing paired cattle‐grazed and ungrazed areas. The availability of floral and nesting resources for bees was unaffected or positively affected by grazing. Similarly, wild bee abundance, species richness, and composition were not affected by grazing, but were instead shaped by spatiotemporal factors. Nor was honey bee activity level impaired by grazing. The foraging preferences of bees, as well as flower species composition and peak bloom differed between grazed and ungrazed areas. Therefore, in our studied rangelands, grazing had its main effect on the foraging choices of honey bees and wild bees, rather than on their abundance and diversity. Moreover, our results indicate the potentially important role of ungrazed patches in increasing nectar and pollen diversity and availability in rangelands for both honey bees and wild bees in the spring. Hence, maintaining a mosaic of moderately grazed and ungrazed patches is expected to provide the greatest benefits for wild bee conservation and honey bee activity in Mediterranean rangelands. Our findings support the notion of rangeland sharing by cattle and bees in Mediterranean ecosystems under moderate grazing intensities, mimicking the coexistence of honey bees, wild bees, and cattle in Mediterranean ecosystems on an evolutionary timescale.
... Effects of grazing on pollinators are mixed, but there is evidence it changes the way pollinators select plants for visitation (V� azquez and Simberloff, 2003;Vanbergen et al., 2014). Research supports that grazing at an intensity appropriate for the habitat can enhance bee and flower richness and diversity (Vulliamy et al., 2006;Yoshihara et al., 2008;Wilkerson et al., 2013) and can be used as a tool to enhance biodiversity (Darkoh, 2003). However, overgrazed (Darkoh, 2003), heavily grazed (Vulliamy et al., 2006), and intensively managed grassland pastures (Kruess and Tscharntke, 2002;Cole et al., 2015) can result in poor floral resources and corresponding low diversity of plants and pollinators (Darkoh, 2003;Vulliamy et al., 2006;Cole et al., 2012). ...
Numerous studies have documented that invertebrate pollinator services are critical to the world economy. Factors including habitat loss and agricultural practices, however, threaten pollinator populations. Many counties in the Southern High Plains were identified as at risk for a shortage of pollination service from wild bees. This region also has one of the highest concentrations of Conservation Reserve Program (CRP) contracts in the US. The CRP is the largest, voluntary, private lands conservation program in the US and was targeted as a program to improve pollinator habitat. Our objective was to determine how the predominant land uses in the SHP (native grassland, CRP, and cropland) affect pollinator abundance and species richness, and more specifically if the CRP can provide quality habitat for pollinators. We also examined how the keystone habitat, playa wetlands, embedded within these land uses contribute to pollinator habitat (land type: uplands vs. wetland). We used blue vane traps placed in playa basins and adjacent uplands to determine Hymenoptera abundance and richness from April to October in 2013 and 2014. The CRP had lower abundance than cropland and native grassland, and generally less richness. Uplands and playa wetlands had little difference in Hymenoptera abundance and richness. Patch size negatively influenced abundance but had a positive influence on richness. The interaction of vegetation height and percent bare ground positively influenced abundance in cropland and native grasslands, and positively influenced richness in all land uses. In the CRP, vegetation height negatively influenced Hymenoptera abundance and percent bare ground had a positive influence. The years sampled in this study were during a severe extended drought; therefore, these results may be reflective of poor floral resources. The CRP has potential to create valuable habitat for pollinators if land managers incorporate a diversity of native grasses and native forbs into plantings to enhance pollinator foraging and nesting habitat.
... Grazing not only reduces floral density but also simplifies plant diversity and alters floral composition (Debano, 2006;Kruess and Tscharntke, 2002;Xie et al., 2008). Changes in plant communities can then induce changes in pollinator communities causing shifts in plant-pollinator interactions, such as reducing the number of floral specialists within the community and ultimately weakening important ecological functions (Debano, 2006;Kimoto et al., 2012aKimoto et al., , 2012bYoshihara et al., 2008). The low abundance and richness of wild bees found at our grazed sites indicate that the bee community is responding negatively to grazing pressures. ...
Changes in land use and management intensification, especially in agriculture, have led to alarming declines in bee populations and the important ecological services they provide. Little is known how wild bee communities respond to these landscape changes at the phylogenetic level. Phylogenetic diversity was found to be correlated to functional trait diversity, since the former reflects a species evolutionary history while the later reflects the traits a species has accumulated. Here we use a mix of traditional measures of biodiversity and phylogenetic methods to examine differences in wild bee assemblages at six landscapes associated with grazing pressure and different management schemes. We found that grazing pressure strongly influences bee abundance, species richness and functional trait diversity while management intensity has little effect. Interestingly, wild bee phylogenetic diversity was not highly affected by land use, management, or grazing pressure as landscapes retained high levels of phylogenetic evenness. We additionally found evidence of phylogenetic signaling of examined traits. Our findings reveal that wild bee communities can maintain functional trait diversity even with low abundance and species richness. Furthermore, our study supports the notion that trait conservation through evolutionary lineages may only occur for some traits.
... The situation got fundamentally worse after 1990´s with political and economic changes in Mongolia. The planned economy turned into market economy and, therefore, the number of livestock increased (Yoshihara et al. 2008;Saizen et al. 2010). In 1992, the number of livestock was 25.6 million in Mongolia. ...
This paper provides information on long-term suppression of natural forest regeneration due to the livestock grazing in the vicinity of one of the world largest open-pit ore mine close the city of Erdenet in Mongolia. The area is characterized by high concentration of herder’s households where the 52% were found only up to 1 km distance from the forest edge. Forest grazing causes extensive damage to seedlings and significant reduction of their growth. Within the 30–99 cm height category, up to 61% Larix sibirica, 90% Betula platyphylla and 68% Populus tremula individuals are grazingdamaged. L. sibirica and P. tremula seedlings with heights over 99 cm were absent, and no individuals of any species were found within 136–200 cm height category. In addition to the seedlings, only 7 or more meters high L. sibirica individuals are found in the forest structure, which means the absence of successfully growing forest regeneration for at least 40 years. In 2017, the defoliation of L. sibirica, reaching locally up to 100%, occurred in the stands east of the mine. Total defoliation represents a high risk of mortality of affected individuals. The stands cannot be successfully regenerated under the conditions of current intensive grazing. Mine metal stocks are calculated to provide for at least another 25 years of mining. Over that time, neither significant population decline nor decreasing grazing pressure on forests can be expected. If effective protection measures are not implemented, there is a risk of transforming threatened forest into steppe.
... Simultaneously, however, grazing exposed a greater proportion of the soil surface relative to cattle exclosures, which, particularly in dryland systems, can increase erosion rates, deplete soil nutrients, and reduce water infiltration (Belnap, 2006;Frank and Evans, 1997;Schlesinger et al., 1990;Yong-Zhong et al., 2005). These findings suggest that grazing could both benefit aspects of ecosystem function, like pollinator services, that are positively related to native plant diversity, while compromising hydrological systems or nutrient cycling by disturbing and exposing soil ( Fig. 10) (Jerrentrup et al., 2014;Kammerer et al., 2016;L azaro et al., 2016;Sj€ odin et al., 2007;Yoshihara et al., 2008). Such differing and potentially antagonistic effects of grazing on ecological services indicate that, unsurprisingly, no single management recommendation should be uniformly applied to semi-arid grasslands, if observed Fig. 10. ...
Management of domesticated ungulates on grasslands has the potential to affect ecosystem function at landscape to global scales. In the southwestern United States, introduction of livestock in the 1800s corresponded with grassland degradation and dramatic shifts in vegetation, including the rapid spread of invasive plant species. In contemporary grasslands, however, evidence increasingly suggests that responsible grazing may enhance plant diversity in the region, though positive effects on diversity may or may not offer corresponding benefits to ecosystem function. Here, we examined the effects of grazing on land cover and functional composition of a semiarid grassland over a 20-year period. We found that high intensity grazing increased exposed soil and shifted community composition toward a greater proportion of annual and exotic species. This was particularly apparent following a severe drought event that initiated a significant loss of perennial plant cover, especially forbs, and was followed by a nearly 4-fold expansion of exotic species. Plots that were grazed at moderate levels consistently exhibited the lowest proportion of exotic species and were similar in functional group composition to exclosure plots. However, moderate grazing did increase soil exposure relative to exclosure plots. These findings suggest that moderate grazing could provide benefits to grassland ecosystem diversity and correlated ecosystem services like invasive species control and pollination services, while simultaneously increasing erosion, reducing water infiltration and altering nutrient cycling, due to increased soil exposure and disturbance. The potential for grazing to exert antagonistic effects on ecosystem services, depending on site conditions and grazing intensity, suggests that livestock management decisions should be tailored to individual management and conservation goals that address the inherent spatiotemporal variability of arid grasslands. Keywords: Plant functional groups, Climate change, Southwestern United States, Exotic species, Ecosystem services, Livestock management
... Similar to our work, a wide variety of past work has found evidence that herbivores alter plant community composition ( numbers and assemblages of floral visitors. Consistent with these results, a variety of previous studies have found that herbivores affect insect and pollinator abundance and assemblages via topdown effects (Carvell 2002, Warren 1993, Yoshihara et al. 2008. ...
Cascading effects of high trophic levels onto lower trophic levels have been documented in many ecosystems. Some studies also show evidence of extended trophic cascades, in which guilds dependent on lower trophic levels, but uninvolved in the trophic cascade themselves, are affected by the trophic cascade due to their dependence on lower trophic levels. Top-down effects of large mammals on plants could lead to a variety of extended trophic cascades on the many guilds dependent on plants, such as pollinators. In this study, floral-visitor and floral abundances and assemblages were quantified within a series of 1-ha manipulations of large-mammalian herbivore density in an African savanna. Top-down effects of large mammals on the composition of flowers available for floral visitors are first shown, using regressions of herbivore activity on metrics of floral and floral-visitor assemblages. An extended trophic cascade is also shown: the floral assemblage further altered the assemblage of floral visitors, according to a variety of approaches, including a structural equation modelling approach (model with an extended trophic cascade was supported over a model without, AICc weight = 0.984). Our study provides support for extended trophic cascades affecting floral visitors, suggesting that trophic cascades can have impacts throughout entire communities.
... The Mongolian government has transferred all its state- owned livestock to the herders at the very beginning of the 1990s which was the economic shifting period of Mongolia from a planned economy to market economy. Many scholars (Nixson & Walter, 2006;Yoshihara, Chimeddorj, Buuveibaatar, Lhagvasuren, & Takatsuki, 2008;Zinsstag et al., 2005) have focused their study on animal husbandry during this period as it was not only due to the transferred of national wealth but also due to its probable influences on livestock and grassland management. Many studies during that time were focused on environmental degradation rather than on socio-economic characteristics of ...
This study examines the relationship between the number of livestock domesticated in Mongolia and socioeconomic status of Mongolian nomads. A major assumption of this study is higher the number of livestock, higher the livestock product and vice-versa. Human Development Index of Mongolia is taken as a measurement scale for socioeconomic status of Mongolian nomads and Gross Livestock Product is taken as measurement scale for the number of livestock in Mongolia. Impact of livestock output on the socioeconomic status of Mongolian nomads is analysed through log-log and semi-log regression module. The statistical output shows a strong and positive relationship between the socioeconomic status of Mongolian people and gross livestock output. Mongolian government should be prepared for urgent distribution of livestock fodder packages, immediate veterinary services in the dzud and drought-affected areas, development of pre dzud risk mapping system, and special plan to upgrade economic status of small and middle level herders in order to maximize the livestock output which result in positive changes in socioeconomic status of Mongolian people. Implementation of the social protection programme can be beneficial for the Mongolian government to control rural to urban migration due to livestock loss. Education regarding sanitation and development of technologically advanced slaughterhouse can be supportive for the Mongolian government to increase the export level of their livestock product.
... Concentrated grazing affects the soil, vegetation, water resources, insects and other animal species that form part of the steppe. Prolonged heavy grazing in one location, for example, changes the types of plant species that predominate in an area and shapes the number and diversity of pollinating insects, which can cumulatively create enduring changes in the land (Yoshihara et al. 2008). Grasses and shrubs frequently decline in number while other plant species, such as variants of Artemisia that livestock find distasteful, come to predominate (Fujita and Amartuvshin 2013). ...
Examines the discourses and practices of climate change adaptation in the context of pastoralist herders in contemporary Mongolia. Uses a historical political ecology approach to critique narratives of vulnerability and resilience that naturalise hazards on the Mongolian steppe. Examines issues of changing herd compositions, indebtedness and class differentiations within herders.
... Tallgrass prairie is ideal for studying disturbance effects as it is characterized and maintained by frequent disturbance from the interaction between ungulate grazing and fire (Vinton et al. 1993;Fuhlendorf and Engle 2004;Collins and Calabrese 2012). Community response to habitat state resulting from naturally occurring and varying disturbance regimes has only occasionally been examined in the context of network structure, an approach which offers significant insight into community resistance to species loss (Yoshihara et al. 2008;Vanbergen et al. 2014;Lázaro et al. 2016). ...
Significant loss of pollinator taxa and their interactions with flowering plants has resulted in growing reductions to pollination services globally. Ecological network analysis is a useful tool for evaluating factors that alter the interaction structure and resistance of systems to species loss, but is rarely applied across multiple empirical networks sampled within the same study. The non-random arrangement of species interactions within a community, or “network structure” such as nested or modular organization, is predicted to prevent extinction cascades in ecological networks. How ecological gradients such as disturbance regimes shape network structural properties remains poorly understood despite significant efforts to quantify interaction structure in natural systems. Here, we examine changes in the structure of plant–floral visitor networks in a tallgrass prairie using a decadal and landscape-scale experiment that manipulates prescribed burn frequency and ungulate grazing, resulting in different grassland states. Plant and floral visitor communities and accompanying network structure were impacted by grassland fire and grazing regimes. The presence of grazers increased flowering plant species richness, network floral visitor species richness, and decreased network nestedness. Fire frequency affected flowering plant and floral visitor community composition; community composition impacted network specialization and modularity. Grassland state resulting from fire-grazing interactions has important implications for the resistance of flowering plant and floral visitor communities to species loss.
... Gonz alez-Meg ıas, Huntzinger et al., 2008;Rothenw€ ohrer et al., 2013). Additionally, disruption of plant-insect networks by livestock has also been shown for plant-pollinator networks ( Vazquez & Simberloff, 2003;Yoshihara et al., 2008). This suggests that the disruption of plant-insect interactions by means of asymmetrical competition may be a common phenomenon which can explain the often observed negative relation between vertebrate grazing and the abundance and species richness of herbivorous insects. ...
Studies of grassland communities have demonstrated that increasing vertebrate grazing decreases the diversity of specialised herbivorous insects, while plant diversity is maintained or increased. However, we still have a limited understanding of the causal mechanisms underlying these contrasting observations of two tightly linked groups of organisms.
We used spatially linked plant and moth observations from salt marshes, sampled for 3 years along an experimental sheep‐grazing gradient (0, 1–2, 3–4 and 10 sheep ha ⁻¹ ), to test whether the disruption of plant–insect interactions by large herbivores accounts for these contrasting grazing effects. Moths were caught using emergence traps, which were moved and repositioned every 3 weeks.
Firstly, we quantified species turnover between the grazing regimes for both taxa (measured as Sørensen dissimilarity) using a null‐model approach. Secondly, we analysed the number of observed insect ̶ host associations under the different regimes.
Species turnover between grazing regimes was significant (after correcting for rarefaction effects) for moth species, but not for plants, indicating very few and random effects of grazing on plant species composition. The percentage of realised plant–moth associations decreased from 37% in the absence of grazing to 6.5% under high stocking densities.
We thus conclude that vertebrate grazing caused a disruption of plant–moth associations, probably by rendering the host‐plants unsuitable for most of the moth species. Our findings provide further mechanistic understanding on how large herbivores shape arthropod communities and illustrate the importance of host‐plant associations in explaining effects of natural or anthropogenic habitat modification.
... Grazing affects pollinators and pollination in complex ways ( Agren et al. 2013) that depend on the grazing intensity, selectivity, timing, climate, habitat type, etc. (Asner et al. 2004;Kimoto et al. 2012;Tadey 2015). For instance, the intensity of herbivory can shape the attractiveness of flowers to pollinators ( Agren et al. 2013), with highly intensive grazing able to lower forb coverage or diversity with concomitant impacts on pollinator densities, diversity and network structure (Kruess & Tscharntke 2002;Yoshihara et al. 2008;Potts et al. 2009). Grazing livestock (e.g. ...
Worldwide, human appropriation of ecosystems is disrupting plant–pollinator communities and pollination function through habitat conversion and landscape homogenisation. Conversion to agriculture is destroying and degrading semi-natural ecosystems while conventional land-use intensification (e.g. industrial management of large-scale monocultures with high chemical inputs) homogenises landscape structure and quality. Together, these anthropogenic processes reduce the connectivity of populations and erode floral and nesting resources to undermine pollinator abundance and diversity, and ultimately pollination services. Ecological intensification of agriculture represents a strategic alternative to ameliorate these drivers of pollinator decline while supporting sustainable food production, by promoting biodiversity beneficial to agricultural production through management practices such as intercropping, crop rotations, farm-level diversification and reduced agrochemical use. We critically evaluate its potential to address and reverse the land use and management trends currently degrading pollinator communities and potentially causing widespread pollination deficits. We find that many of the practices that constitute ecological intensification can contribute to mitigating the drivers of polli-nator decline. Our findings support ecological intensification as a solution to pollinator declines, and we discuss ways to promote it in agricultural policy and practice.
... Since, in studied species, seed weight represents the major component of fruit weight (Tadey 2007), low fruit weight may reflect insufficient reserves in their endosperm affecting germination and plant development (Zaidman et al. 2010). Alternatively, livestock may increase plant isolation decreasing pollination levels (i.e., pollen quantity) or pollen quality (i.e., endogamic pollen) resulting in poor fruit quality (Ramsey and Vaughton 2000;Tadey 2008;Yoshihara et al. 2008). Within each species, heavier fruits from less grazed paddocks (Fig. 3, black symbols) significantly germinated more than lighter fruits from heavily grazed paddocks (Fig. 3, white symbols; Table 2). ...
Grazing intensification with non-native livestock is known to degrade vegetation cover, particularly in arid environments where low resource availability strongly limits plant recovery after damage. However, it remains unclear whether the effect of grazing on consumed plants is transmitted to plant offspring. We hypothesized that grazing would reduce fruit weight, germination percentage, and seedling vigor of consumed vegetation. Therefore, we collected mature fruits from six dominant shrub species in seven independent paddocks with increasing livestock densities. Fruits were air-dried and weighed before seed sowing. After seedling emergence, we measured the percentage of germination and seedling vigor, i.e., height and number of leaves. Hierarchical models were used to account for the effects of plant species and year of collection. Results show that, in general, increasing livestock density reduced fruit weight and percentage of germination of consumed plants. However, surprisingly, increasing livestock density enhanced seedling vigor. Overall, increasing livestock density has both negative and positive effects on consumed plantsʼ offspring.
... Results of these studies vary depending on several factors, including plant and bee community composition, intensity of grazing, type of grazer, timing and duration of grazing, and land use. Several studies of livestock grazing and native bees have found significant effects, some negative (Kruess and Tscharntke 2002;Hatfield and LeBuhn 2007;Sjödin 2007;Xie et al. 2008;Kearns and Oliveras 2009) and some positive (Carvell 2002;Vulliamy et al. 2006;Yoshihara et al. 2008). Most studies have been observational, but a large scale manipulation in the Pacific Northwest showed cattle grazing altered native bee abundance, richness, diversity, and community composition, with taxa varying in their sensitivity to grazing (Kimoto et al. 2012b). ...
Many federal, state, and tribal agencies, as well as nonprofit organizations, have recently increased efforts to understand how natural areas can be managed to enhance native pollinators and the ecosystem services they provide. However, managing this important group must be balanced with other services that natural areas provide including hunting, timber production, and livestock grazing. Significant knowledge gaps exist about how to effectively manage habitats used by large ungulates (e.g., cattle (Bos taurus), elk (Cervus elaphus), mule deer (Odocoileus hemionus)) in ways that also enhance pollinators. One key gap is understanding the degree to which diets of mammalian herbivores overlap with floral resources used by bees, and how this overlap varies spatially and temporally. Invertebrate pollinators, including bees, rely on flowering forbs and shrubs for nectar and pollen. Ungulates also feed on flowering plants, although preferences vary by ungulate species, vegetation community, and season. Here we review existing literature on ungulate diets relative to flowering plants and compare this information with flower preferences of bees, drawing on studies of bee abundance and diversity at the Starkey Experimental Forest and Range in northeastern Oregon. Our review can inform managers about the potential dietary overlap between ungulates and native bees and aid planning efforts aimed at biodiversity conservation of pollinators. We discuss management implications relative to seasonal habitat use and dietary preferences of ungulates and variation in bee phenology, and conclude with guidance about timing and intensity of ungulate grazing when managing for multiple conservation objectives, especially in sensitive habitats like riparian areas.
Human‐induced nutrient eutrophication is a major threat to grassland biodiversity, because it promotes the dominance of fast‐growing plants. Negative impacts of fertilization on plant biodiversity may be offset by grazing by large vertebrate herbivores. However, whether grazers also mitigate impacts of nutrient addition on insects is less well understood. We use a field experiment to test how plant communities and abundances of pollinators and grasshoppers respond to nutrient addition and grazing by different assemblages of large herbivores, i.e. access by all herbivores (including cattle and horses), access by wild herbivores only (wild boar and deer), no access by large herbivores. Plant biomass increased, plant diversity decreased and community composition shifted towards lower forb cover in response to fertilization, but only in the absence of all herbivores. Flower visitation by Hymenoptera (bees and wasps), i.e. the most abundant pollinator group, was reduced by nutrient addition only in the absence of all herbivores and was positively related to flowering plant richness. In contrast, flower visitation by Diptera (e.g. hoverflies) was enhanced by fertilization, but not affected by grazing. Orthoptera (grasshopper) abundance was reduced by grazing and enhanced by nutrient addition, with positive impacts of fertilization tending to be stronger in plots with only wild or no herbivores. The abundance of grasshoppers was positively related to grass biomass. We conclude that vertebrate herbivores can offset impacts of fertilization on both plant and insect communities, making grazing by large mammals an essential tool to protect insects, particularly pollinators. Most responses to nutrient addition were only apparent in plots without any large herbivores, suggesting that wild herbivores alone could already mitigate nutrient impacts. We also show that insects with contrasting feeding guilds may be favoured by fertilized, ungrazed conditions. Therefore, creating a mosaic of patches grazed at different intensities will enhance overall insect biodiversity.
Background & Aims: Overgrazing poses a dominant threat to the biodiversity of most grassland communities. Bees are the primary pollinator group in the grassland ecosystem. Grazing has generally negative effects on bee diversity by affecting floral and nesting resources in grassland communities. However, in communities with long grazing history and reasonable grazing management, grazing may have a positive or neutral impact on bee diversity. Therefore, how grazing affects bee diversity and its role in ecological restoration needs further study.
Progress: In this study, we integrate the recent literature and research practice, and propose that the efficacy of bee restoration can be more accurately assessed through the integration of bee species richness, functional diversity, phylogenetic diversity and full plant-pollinator interaction networks, which provide comprehensive and quantitative information on the structure and function of grassland communities. For grasslands with low degradation, bees can be gradually recovered by effective grazing management, which uses the natural recovery potential of the communities. For grasslands with greater degradation, it is necessary to accelerate the bee restoration through active interventions on the basis of grazing management, such as sowing wildflower species that cannot migrate into the restoration area without assistance and enhancing the availability of nesting habitat for bees. To ensure that bees can obtain enough floral rewards in different flowering periods, the selection and combination of the sown flower species should take into account their roles in the pollination network, floral traits and flowering phenology.
Perspective: It is of great practical significance to investigate the mechanism of bee loss in different types of grasslands in southern and northern China, and to guide the development of targeted ecological restoration strategies for bees.
Background
Land use change is a key catalyst of global biodiversity loss and ecosystem degradation. Deforestation and conversion of natural habitats to agricultural or urban areas can profoundly disrupt plant-flower visitor interactions by altering their abundances and distribution. Yet, specific studies analyzing the effects of land use change on the structure of networks of the interactions between particular groups of flower visitors and their plants are still scarce. Here, we aimed to analyze how converting native habitats affects the species composition of butterfly communities and their plants, and whether this, in turn, leads to changes in the structure of interaction networks in the modified habitats.
Methods
We performed bi-monthly censuses for a year to record plant-butterfly interactions and assess species diversity across three habitat types, reflecting a land-use change gradient. From original native juniper forest to urban and agricultural zones in central Mexico, one site per land use type was surveyed. Interactions were summarized in matrices on which we calculated network descriptors: connectance, nestedness and modularity.
Results
We found highest butterfly diversity in native forest, with the most unique species ( i.e. , species not shared with the other two sites). Agricultural and urban sites had similar diversity, yet the urban site featured more unique species. The plant species richness was highest in the urban site, and the native forest site had the lowest plant species richness, with most of the plants being unique to this site. Butterfly and plant compositions contrasted most between native forest and modified sites. Network analysis showed differences between sites in the mean number of links and interactions. The urban network surpassed agriculture and native forest networks in links, while the native forest network had more interactions than the agriculture and urban networks. Native plants had more interactions than alien species. All networks exhibited low connectance and significant nestedness and modularity, with the urban network featuring the most modules ( i.e. , 10 modules).
Conclusions
Converting native habitats to urban or agricultural areas reshapes species composition, diversity and interaction network structure for butterfly communities and plants. The urban network showed more links and modules, suggesting intricate urban ecosystems due to diverse species, enhanced resources, and ecological niches encouraging interactions and coexistence. These findings emphasize the impacts of land use change on plant-butterfly interactions and the structure of their interaction networks.
La respuesta de las plantas a los disturbios se relaciona con sus características fisiológicas, sus formas de vida y su función dentro de la comunidad. Evaluamos la respuesta, en términos de biomasa y fecundidad, de los distintos tipos sucesionales de especies (colonizadoras, intermedias y tardías) del Monte Patagónico a un gradiente de carga ganadera (unidades ganaderas.año.ha-1). La biomasa la estimamos mediante el tamaño de las plantas consumidas (diámetro x altura) y la fecundidad a través del esfuerzo reproductivo (% de ramas reproductivas) y del porcentaje de semillas viables producido. Observamos que el ramoneo disminuyó la biomasa y la fecundidad de las plantas, tanto ramas reproductivas como semillas viables. Sin embargo, los tipos sucesionales de especies mostraron diferente producción de semillas viables en respuesta a la intensidad de pastoreo. Con el aumento del ganado se redujo el tamaño de especies colonizadoras, aumentó el de las intermedias, y el tamaño de las tardías no cambió significativamente. En general, el aumento del ramoneo afectó negativamente el esfuerzo reproductivo de todas las especies. A pesar de ello, las colonizadoras e intermedias aumentaron la producción de semillas viables, mientras que las tardías la disminuyeron. Estos resultados sugieren que las especies tardías son las más afectadas por el ganado en términos de fecundidad, lo que podría reducir su reclutamiento. El aumento de su biomasa con la carga ganadera en especies intermedias sugiere una respuesta compensatoria que podría otorgarles una ventaja a corto plazo. La pérdida de tejido que sufren las plantas por consumo del ganado impacta en la cantidad de semillas, pero, además, podría tener consecuencias en la tasa y el momento de germinación de la progenie. Los resultados ayudan a comprender la dinámica de las comunidades frente a los disturbios, y aportan información útil para elaborar estrategias de manejo y restauración de ecosistemas áridos.
The Center for Biological Diversity and Bombus Pollinator Association of Law Students of Albany Law School have written a petition to the US Fish and Wildlife Service to list the American bumble be under the Endangered Species Act.
Ecosystem functions are threatened by continuing global loss of biodiversity. We simultaneously investigated three ecosystem functions and forage nutrient values following potential species extinction scenarios (dominant species removal, rare species removal, end-member species removal and random species removal) in a Mongolian grassland. ANPP, forage nutrient values, litter decomposition, and soil respiration were measured one and/or two years after plant removal. DNA samples of microorganisms extracted from the soil were subjected to metagenomics analysis. Finally, we calculated the multifunctionality, and examined the relationship of multifunctionality with plant and microorganism diversity. Among ecosystem functions, ANPP and litter decomposition rate decreased under random and rare species extinction scenarios, respectively, and forage quality increased when only dominant species had been removed. Diversity and species composition of soil microorganism were not affected by plant species richness or removal scenario. Only genus-level diversity of bacteria and ANPP were significantly and positively correlated with microbial diversity. Taken together, decreasing species richness of plants and soil organisms rarely impaired multifunctionality. Ecosystem functions were relatively robust to realistic disturbances and species extinction in natural grasslands. However, as each function responded differently to the different sets of species removed, the consequences of a realistic non-random extinction scenario for multiple ecosystem functions should be critical to the management of biodiversity loss caused by different disturbances.
Towns and villages are sometimes viewed as minor, even quaint, spots, whereas this book boldly reconceptualizes these places as important dynamic environmental 'hotspots'. Multitudes of towns and villages with nearly half the world's population characterize perhaps half the global land surface. The book's pages feature ecological patterns, processes, and change, as well as human dimensions, both within towns and in strong connections and effects on surrounding agricultural land, forest land, and arid land. Towns, small to large, and villages are examined with spatial and cultural lenses. Ecological dimensions - water, soil and air systems, together with habitats, plants, wildlife and biodiversity - are highlighted. A concluding section presents concepts for making better towns and better land. From a pioneer in both landscape ecology and urban ecology, this highly international town ecology book opens an important frontier for researchers, students, professors, and professionals including environmental, town, and conservation planners.
Summary:
The relationship between pollinators and flowering plants plays a crucial role in the function of terrestrial ecosystems. The ecological and co-evolutionary interactions in plant-pollinator systems can be studied in many aspects, at very different spatio-temporal scales. Pollinator communities are influenced by a lot of plant and animal traits (e.g. floral colour, size and morphology and pollinator mouth-part morphology), as well as environmental conditions. Thus to understand plant-pollinator interactions, researchers should monitor these at different levels by using appropriate and reliable field methods.
Pollinators visit plants for floral food resources (nectar, pollen, etc.), and they pollinate plants. Floral food resources may be rapidly changing in space and time. Foraging affects survival and reproductive success in animals, including flower visiting insects, such as butterflies. Among insect pollinators, butterflies are suitable model organisms to investigate foraging behaviour, because they can be easily monitored under natural circumstances. Adult butterflies mostly feed on floral nectar, and besides larval food intake, adult nectar-feeding was proved to significantly affect the longevity and reproductive success of several species. Furthermore, studying resource-use can yield basic information for conserving vulnerable species. Floral species selectivity and the spatio-temporal changes of foraging behaviour are still understudied in butterflies. Studies investigating foraging behaviour in insect pollinators on many spatio-temporal scales are also scarce.
In the first section of the thesis, we reviewed the floral resource sampling methods frequently used in pollination studies and highlighted the potential methodological biases. We selected studies investigating flowering plant abundance for insect pollinators in temperate grasslands. From these publications, we extracted specific information on methodologies. The focus was on how representative vegetation samples were both spatially and temporally. We also searched for trade-offs between different aspects of sampling investment. Furthermore, in a case study we compared scanning and quadrat sampling procedures to estimate floral resources in a small meadow. We showed that the two methods, and the two sampling persons differed in finding species, estimating flower abundance and flowering phenologies. We suggest that these differences can be explained by the procedures' biases estimating the spatially heterogeneous and rapidly changing floral resources. Although further field work on optimising sampling techniques is mandatory, based on the methodological literature review and the case study, we recommend a guideline for more appropriate sampling designs, e.g. the need to increase sampling coverage and frequency.
In the second section of the thesis, we studied spatio-temporal changes in flower visitation in the Clouded Apollo butterfly (Parnassius mnemosyne, Linnaeus, 1758; Lepidoptera: Papilionidae), a species spending considerable time on feeding. We studied its flower visitation behaviour at population and individual levels in relation to the abundance of available floral resources. Our aim were to reveal natural patterns in flower visitation. The collected field observational data were primarily suitable for descriptive analyses, rather than statistical hypothesis driven. Plant species differ in their flower traits (e.g. colour, nectar amount, flower type, etc.) and in flower abundances. Clouded Apollo butterflies may select between nectar plant species based on these traits. They visited a few nectar-plants frequently, while many others rarely, and did not visit several abundant species. Flower abundance and visit ratio varied among years and within flight periods. The number of visits increased with flower abundance in the most frequently visited plant species. Furthermore, we found considerable differences among individuals in their resource-use, i.e. remarkable individual specialisation. This variation was partly explained by changing floral resource availability over time, together with individual butterflies occurring in different time windows during the flight period. We found that the individuals' resource-use changed during their lifetimes, indicating that butterflies can adjust foraging to varying resource availability. Spatial occurrence of Clouded Apollo butterflies within one habitat were explained by the spatial distribution of the most frequently visited nectar-plant and habitat openness. Butterfly spatial occurrence changed over time, and this can be explained by the temporal changes in nectar-plant spatial distribution. Taken together, Clouded Apollo butterflies, beside their choosiness, are able to flexibly adjust their foraging behaviour to the resource distributions rapidly changing in space and time. We suggest that Clouded Apollo butterflies are sequential specialists, i.e. short-term specialists (individuals are specialists at narrow time windows) and long-term generalists at the levels of the individual during its lifetime, the population as well as the species, i.e. change flexibly among resources. Diet selectivity in adults might increase the vulnerability of this species. However, visitation plasticity may mitigate the effect of the lack of some nectar-plants, as complementary resources can be used as alternatives. This foraging plasticity can be essential for short-living insect pollinators in rapidly changing environments. Ultimately, the relative pace of environmental change compared to individual lifespan may be a key factor in resource-use plasticity.
The sum of fruit and seed predation by multiple species may strongly affect plant reproduction and population dynamics. We evaluated the combined effects of ungulates, seed-eating rodents and insect pre-dispersal seed predators on the reproductive success of the Mediterranean gum cistus shrub (Cistus ladanifer), over two consecutive years within a long-term ungulate-exclusion experiment. We compared fruiting success in shrubs exposed and protected from ungulates by examining fruit abortion and fruit production. We also investigated the effect of insect predation on seed production (i.e. proportion of depredated fruit and seed loss) and measured fruit weight, seed number per fruit, and seed weight of unpredated fruits. Ungulate browsing directly removed 42.3% of the plant reproductive structures, early in the reproductive season and insect predation reduced mature seeds by over 40%. Results also emphasize the additive effects of ungulate browsing on pre-dispersal insect predation and fruit abortion which increased by 74.7% and 60.9%, respectively. Rodents, which only occurred in ungulate excluding plots, had a limited and later effect on seed production with 6% of mature fruit loss. Fruit weight, seed weight and number were higher in shrubs protected from ungulates. Our study indicated that seed predation by mice was irrelevant, but ungulate and invertebrate seed predation interacted to strongly limit the reproductive success of C. ladanifer, potentially affecting plant population dynamics in the long-term.
Despite the importance of wild pollination as an ecosystem service, little is known about the spatial and temporal variation of pollination services. Variation in insect pollinator emergence or forb flowers can lead to inconsistent delivery of pollination service to the forb community. A variety of factors, such as air temperature, flower abundance, pollinator abundance, and forb species richness influence the stability of pollination service. All of these factors exhibit spatial and temporal variability. Furthermore, anthropogenic disturbances endanger the persistence of pollination service. To assess the variability of pollination we compared the number of insect flower visits at different locations throughout the summer for two consecutive years in Dalbay Valley, Mongolia. Within this spatio-temporal framework, we investigated the stability of plant-pollinator networks and the effect of ungulate grazing cessation on pollinator visits.
Flower visits, forb flower abundance, and measures of plant-pollinator network stability varied greatly over space and time. Hymenoptera visits were positively correlated with only network specialization and Diptera visits were positively correlated with only network nestedness. The exclusion of ungulate grazing altered the composition and abundance of both the forb species and flower visitor communities, but there was no difference in total flower visits between grazed and ungrazed plots. Our results suggest the forb and pollinator community may persist despite the removal of the consistent ungulate grazing pressure. Furthermore, the contribution towards network stability may not be synergistic. Hymenoptera visits were associated with increased network specialization, which tends to lower plant-pollinator network resilience against perturbations, while Diptera visits were associated with increased nestedness, which tends to increase network resilience.
In terms of the sustainable management of grasslands in Mongolia, the rapid change in the livestock population since the beginning of the 1990s has been a very important issue. For this chapter, the spatial distribution and changes in the populations of Mongolian livestock were investigated for the years 1992, 1999, 2002, and 2006 using GIS datasets based on administrative units. Although the total livestock population had changed drastically owing to the shift from a planned economy to a free market economy from 1992 to 1999 and 2002 to 2006—as well as the impact of the Zud, an adverse combination of summer drought followed by a harsh winter, between 1999 and 2002—no significant change in the spatial association of any livestock other than goats was detected by the local indicators of spatial autocorrelation (LISA) statistics. Goats were the only animals to show a significant change in their spatial association, and the goat population is increasing in areas surrounded by a high density of livestock. Considering that of all Mongolian domestic animals, goats have the greatest impact on grasslands, policymakers should pay attention to these areas to ensure the sustainability of grasslands in the future.
We explored the combined effects of seasonal variation in both pollinator assemblage and availability of pollen donors on pollination in a gynodioecious species, Sidalcea oregana ssp. spicata (Malvaceae). Hermaphrodites produced flowers with significantly larger petals but maintained fewer open flowers per inflorescence than females. Flowers of hermaphrodites produced 50% more nectar sugar in the 24 h after anthesis than the flowers of females. Nectar sugar production was also significantly and positively correlated with petal length. Pollinator visitation rates were influenced more by differences in petal length than by differences in flower number per inflorescence. Consequently, hermaphrodites experienced higher visitation rates on a per-flower basis. Female flowers tended to receive pollen at a lower rate than hermaphrodites, but remained in the receptive female-phase longer than hermaphrodites. On average, the length of the period of flower receptivitiy declined as pollen deposition rate increased. These opposing processes resulted in the sex morphs receiving equivalent levels of pollination. Seasonal variation in the rate of pollen reception was more strongly influenced by the efficiency of the available pollinator pool than by rates of visitation. Dramatic seasonal shifts in the composition of the pollinator assemblage and pollen availability were correlated with increased pollination intensity as the season progressed. Not only were more pollen grains received, but they arrived in a shorter period of time and the number of potential pollen donors (hermaphrodites) increased. These findings suggest that pollen competition in both sex morphs may be more intense late in the season.
The number of bumblebee approaches to viper's bugloss (Echium vulgare L.) plants increased with the number of flowers per plant. The proportion of the number of flowers visited after an approach was smaller in plants with many flowers. Individual flowers on large plants received significantly fewer visits than flowers on small plants. Compared with plants in dense parts of a population, isolated plants received fewer approaches that lasted longer. The result of this was that the number of visits to individual flowers did not differ between plants in dense parts of a population and isolated plants. The protandrous flowers lasted for two to three days. During the male phase the flowers presented a higher nectar reward and were more frequently visisted than during the female phase.
We conducted a 3-yr field experiment that manipulated the presence of ungulates (domestic sheep and Spanish ibex Capra pyrenaica, Bovidae) and the monophagous beetle Timarcha lugens (Chrysomelidae) to evaluate (1) the effects on beetle abundance and interaction with the woody crucifer Hormathophylla spinosa; (2) the reciprocal effect of this insect on the interaction between ungulates and the plant; (3) their impact on H. spinosa reproductive output; and (4) the abundance of an associated taxon, Ceutorhynchus sp. nov. (Curculionidae). Our experiment showed that ungulate exclusion increased Timarcha abundance, whereas Timarcha had no effect on ungulates. H. spinosa reproductive output increased threefold promptly when ungulates were excluded, although in the third year Timarcha began to have effects on shrub reproduction. Ungulates affected weevils both by exploitative competition and by incidental predation, with the total number of weevils emerging per shrub being more than fourfold higher in shrubs excluded from these mammals than in shrubs open to them. In addition, during the last year, the abundance of weevils was also affected by Timarcha removal. Our study demonstrated that phytophagous insects can compete with other herbivores highly dissimilar in size, ecology, and taxonomy, such as ungulates. These interactions usually produce asymmetrical results, sometimes closer to amensalism or predation than to pure competition.
The classic Jaccard and Sørensen indices of compositional similarity (and other indices that depend upon the same variables) are notoriously sensitive to sample size, especially for assemblages with numerous rare species. Further, because these indices are based solely on presence–absence data, accurate estimators for them are unattainable. We provide a probabilistic derivation for the classic, incidence-based forms of these indices and extend this approach to formulate new Jaccard-type or Sørensen-type indices based on species abundance data. We then propose estimators for these indices that include the effect of unseen shared species, based on either (replicated) incidence-or abundance-based sample data. In sampling simulations, these new estimators prove to be considerably less biased than classic indices when a substantial proportion of species are missing from samples. Based on species-rich empirical datasets, we show how incorporating the effect of unseen shared species not only increases accuracy but also can change the interpretation of results.
The Mongolian gazelle (Procapra gutturosa) is often sympatric with livestock. After the political regime changed in 1990 in Mongolia, the human population and consequent livestock populations increased, resulting in overgrazing. If food preferences overlap and food supply is limited, ungulates may compete. We analyzed summer (2004) food habits of the Mongolian gazelle and sympatric livestock (sheep, goats, cattle, and horses) in three areas (Dornod, Dorno-Gobi, and Omno-Gobi) in eastern and southern Mongolia by the fecal analysis method. The food resource composition of the ungulates largely supported the prediction of the Jarman–Bell principle: the horse, a large nonruminant, was a grazer, the Mongolian gazelle and sheep/goats, small ruminants, were browsers, and cattle, large ruminants, were intermediate. The food composition of the Mongolian gazelle was consistent among the areas, and fed on more forbs and less grasses. The foods of sheep/goats varied greatly among the areas, suggesting their foods were strongly affected by herding. Food resource used by horses and cattle showed some variations among the areas. Since heavy grazing of livestock results in reductions in plant biomass, the similarity found in food resources strongly suggests the possibility of competition between Mongolian gazelle and sheep and goats.
Plant-animal mutualistic networks can be described as bipartite graphs depicting the interactions between two distinct sets: plants and animals. These mutualistic networks have been found to be highly structured. Specifically, they show a nested pattern in which specialists interact with proper subsets of the species generalists interact with. This pattern is important for understanding coevolution in species-rich communities which can be reduced neither to pairs of coevolving species nor to diffuse, randomly-interacting assemblages. We discuss the dynamic implications of network structure from the points of view of coevolution, community ecology, and conservation biology.
1. The species composition and spatial distribution of small insects (Hemiptera, Coleoptera, Lepidoptera) and arachnids (Araneae, Opiliones, and Pseudoscorpiones) were investigated in three indigenous, upland grasslands identified as the National Vegetation Classification Festuca–Agrostis–Galium typical subcommunity (code U4a), Festuca–Agrostis–Galium, Vaccinium–Deschampsia subcommunity (code U4e), and Nardus stricta species‐poor sub‐community (code U5a), on which grazing management was manipulated experimentally.
2. Two hypotheses were tested that predicted arthropod diversity in upland grasslands. The habitat heterogeneity hypothesis predicts that the species number and abundance of arthropods will have an asymptotic relationship with increasing numbers of plant species and greater structural heterogeneity in the vegetation. The symbiosis between patches hypothesis states that the species number and abundance of arthropods will express a unimodal relationship with the grain size of sward patches created by grazing. The sward patches must be large enough to be apparent to, and support populations of, arthropods, but small enough that interspersed tussocks provide shelter from weather and a deterrent to disturbance by grazers.
3. The hypotheses were tested by sampling arthropods from the geometrical patterns represented by the individual tussocks and intermediate sward components of three indigenous grasslands produced by different grazing treatments. Paired samples of arthropods were taken by motorized suction sampler, the first of the pair from the grazed sward and the second, the accumulated samples from the surrounding triad of tussocks (U4a and U5a grasslands) or hummocks (U4e grassland). The paired samples were taken from six randomly‐selected locations across both replicates of each of the grazing treatments.
4. Arthropod species composition and abundance were compared between the paired sward and tussock samples and in turn with measures of the vertical and horizontal components of vegetation structure, i.e. the variance in vegetation height per unit area and the area covered by tussock compared with sward.
5. There were consistently more species and a greater abundance of arthropods associated with tussocks than with swards and the average species number and abundance for the combined pair of samples declined with increased grazing pressure. The relationship between vertical and horizontal components of vegetation structure and the species number and abundance of selected arthropods was asymptotic as opposed to unimodal, supporting the habitat heterogeneity hypothesis, rather than the symbiosis between patches hypothesis.
6. Small and relatively sedentary insects and arachnids are more sensitive to grazing intensity and species of grazer in these upland, indigenous grasslands than are larger Coleoptera and Araneae, which respond less directly to varied grazing management. The overall linear reduction of small herbivorous and predatory arthropods with increased grazing intensity was buffered in grasslands with substantial tussock patches.
Recent reviews of plant–pollinator mutualistic networks showed that gen-eralization is a common pattern in this type of interaction. Here we examine the ecological correlates of generalization patterns in plant–pollinator networks, especially how interaction patterns covary with latitude, elevation, and insularity. We review the few published anal-yses of whole networks and include unpublished material, analyzing 29 complete plant– pollinator networks that encompass arctic, alpine, temperate, Mediterranean, and subtrop-ical–tropical areas. The number of interactions observed (I) was a linear function of network size (M) the maximum number of interactions: ln I 0.575 0.61 ln M; R 2 0.946. The connectance (C), the fraction of observed interactions relative to the total possible, decreased exponentially with species richness, the sum of animal and plant species in each community (A P): C 13.83 exp[0.003(A P)]. After controlling for species richness, the residual connectance was significantly lower in highland (1500 m elevation) than in lowland networks and differed marginally among biogeographic regions, with both alpine and trop-ical networks showing a trend for lower residual connectance. The two Mediterranean networks showed the highest residual connectance. After correcting for variation in network size, plant species were shown to be more generalized at higher latitude and lowland habitats, but showed increased specialization on islands. Oceanic island networks showed an im-poverishment of potential animal pollinators (lower ratio of animal to plant species, A : P, compared to mainland networks) associated with this trend of increased specialization. Plants, but not their flower-visiting animals, supported the often-repeated statements about higher specificity in the tropics than at higher latitudes. The pattern of interaction build-up as diversity increases in pollination networks does not differ appreciably from other mutualisms, such as plant–seed disperser networks or more complex food webs.
Foliar cover of plant species; grass, forb and total herbaceous biomass; soil P, K, N and C; and percent coarse fraction of soils were sampled over two years along grazing gradients from livestock water sources in three grazed Mongolian steppe ecosystems of varying productivity. Samples within each of the three systems (mountain-steppe, and desert-steppe) were classified into plant communities using TWINSPAN and species-environment relationships in each system were examined using CCA. Community classifications were driven by the presence/absence of ruderal species and highly palatable grasses in the steppe and mountain-steppe and by the presence/absence of salt-shrub or Caragana shrub species and associated Iris species in the desert-steppe. Ordinations were largely driven by soil nutrient concentrations, particularly P and K, in all three zones. Bulk density and percent coarse fraction to 10 cm were also important in the desert-steppe. Distance from water, which we assumed to be inversely related to grazing pressure, was a significant driving factor in steppe and mountain-steppe ordinations, and was negatively correlated with P and K. We speculate that elevated nutrient concentrations near water sources result from livestock redistributing nutrients in the landscape by voiding urine and feces in the areas where they congregate. Livestock may thus influence species composition in these systems both through the direct effects of defoliation and trampling, and the indirect effects of nutrient enrichment and depletion over the broader landscape. This hypothesis deserves further testing under controlled conditions.
A system comprising 2 species of bumblebess (Bombus appositus and Bombus flavifrons) and 2 species of flowers (Delphinium barbeyi and Aconitum columbianum) in Gothic, Colorado, USA, was manipulated to determine whether resource utilization by each bumblebee species was influenced by the presence of the other species of bumblebee. Each bumblebee species concentrated its foraging efforts on a different flower species, apparently choosing the species whose corolla tube length matched its proboscis length most closely. When each bumblebee species was temporarily removed from its preferred flower species, the remaining bumblebee species increased visitation to the other, previously less-utilized, flower species. The remaining bumblebees visited more flowers per stay in the patch, suggesting that they were finding greater amounts of nectar in the absence of other bumblebee species. These removal experiments demonstrated that the bumblebees were sampling flowers frequently enough and were flexible enough in their foraging behavior to respond rapidly to short-term changes in nectar availability. In another area, where its preferred flower species and the other bumblebee species were absent, B. flavifrons foraged actively on the flower species it rarely used in Gothic. This observation and the experiments demonstrate that resource utilization by a bumblebee species is influenced by the presence of other species and suggest that the phenomenon of competitive release can be observed in bumblebees. In this system,interspecific exploitation competition appears to be the primary mechanism involved in resource partitioning.
The pollination of flowering plants by animals represents a critical ecosystem service of great value to humanity, both monetary and otherwise. However, the need for active conservation of pollination interactions is only now being appreciated. Pollination systems are under increasing threat from anthropogenic sources, including fragmentation of habitat, changes in land use, modem agricultural practices, use of chemicals such as pesticides and herbicides, and invasions of non-native plants and animals. Honeybees, which themselves are non-native pollinators on most continents, and which may harm native bees and other pollinators, are nonetheless critically important for crop pollination. Recent declines in honeybee numbers in the United States and Europe bring home the importance of healthy pollination systems, and the need to further develop native bees and other animals as crop pollinators. The 'pollination crisis' that is evident in declines of honeybees and native bees, and in damage to webs of plant-pollinator interaction, may be ameliorated not only by cultivation of a diversity of crop pollinators, but also by changes in habitat use and agricultural practices, species reintroductions and removals, and other means. In addition, ecologists must redouble efforts to study basic aspects of plant-pollinator interactions if optimal management decisions are to be made for conservation of these interactions in natural and agricultural ecosystems.
Livestock grazing is the most widespread land management practice in western North America. Seventy percent of the western United States is grazed, including wilderness areas, wildlife refuges, national forests, and even some national parks. The ecological costs of this nearly ubiquitous form of land use can be dramatic. Examples of such costs include loss of biodiversity; lowering of population densities for a wide variety of taxa; disruption of ecosystem functions, including nutrient cycling and succession; change in community organization; and change in the physical characteristics of both terrestrial and aquatic habitats. Because livestock congregate in riparian ecosystems, which are among the biologically richest habitats in arid and semiarid regions, the ecological costs of grazing are magnified in these sites. Range science has traditionally been laden with economic assumptions favoring resource use. Conservation biologists are encouraged to contribute to the ongoing social and scientific dialogue on grazing issues.
INTRODUCTION
Here we will describe and discuss the effects of large herbivores on animal community composition, diversity and abundance, using examples from different taxonomic and functional groups in different habitats. The main focus is the effect of wild ungulates in natural or semi‐natural habitats, but when relevant we will also cover the effects of domestic grazers in agricultural systems. Less attention will be given to the effects of large herbivores on groups which recently have been reviewed (e.g. birds) (McShea & Rappole 1997, Van Wieren 1998, Fuller 2001), less studied groups (e.g. reptiles and aquatic communities) (but see e.g. Strand & Merritt 1999) and on the consequences following the transfer of forests into grasslands by large herbivores (e.g. Van Wieren 1998, see also Chapter 7).
Our focus will be on ecological processes affecting animal communities, e.g. impacts of competition for food with other herbivores, and indirect impacts via changes in habitat structure on seemingly unrelated taxa. The possible differences between introduced and native wild herbivores as well as between wild and domestic grazers will be discussed; parasitism and the role of dung will only briefly be mentioned. By impacts, or effects, we mean observed changes in animal community composition, or abundance in response to changes in presence, density or species composition of large herbivores. The last part of the chapter summarizes the observed impacts on other biota, and discusses some theoretical and practical issues associated with the effects of large herbivores on other animals.
The most important floral visitors to Nepeta cataria were honey bees Apis mellifera, solitary bees (Halictidae) and bumble bees (Bombus spp.). Visitation rate was higher in larger patches for honey bees and bumble bees, but lower for solitary bees. Patch size explained 74-83% of the variation in visitation rate. Intraspecific isolation also had an effect: isolated patches received relatively few visits. Visitation rate depended both on visitor abundance and on the proportion of flowers entered during one visit. All three visitor types were more abundant in larger patches, ie flowers showed mutual attraction of pollinators. Relative to a visit to a small patch, during a visit to a large patch, honey bees visited more flowers but a lower proportion of flowers; solitary bees visited fewer flowers and thus a lower proportion of flowers; and bumble bees visited not only more flowers but a higher proportion of flowers as well. Thus, within patches, flowers competed for visits from honey bees and solitary bees but showed facilitation regarding bumble bee visits. Patch size explained 63% of the variation in pollinator limitation.-from Authors
(1) In the subalpine region of Central Switzerland (Tavetsch Valley) studies were made of the day-active Lepidoptera faunas in different types of cultivated grassland, in various stages in the development of abandoned grassland and in woodlands (climax vegetation). (2) The results show a close correlation between bufferfly fauna and vegetation type concerning species composition and species richness of Lepidoptera. (3) Species richness of butterflies is highest in early abandoned stages and falls rapidly with the arrival of shrubs and trees. It is also high in traditionally lightly cultivated grassland (unfertilized mown and lightly grazed meadows), but it declines drastically with increasing intensity of cultivation. (4) In general, species richness of butterflies is closely correlated with species richness of vascular plants, but cultivation methods and the short time since abandonment (<5 years) of lightly cultivated grassland have strongly different influences on species richness of Lepidoptera and vascular plants. (5) The results are in contrast to former studies in Central Europe and parallel studies in England. (6) The natural primary habitats of butterflies living in the anthropogenetic types of vegetation investigated and the consequences for nature conservation are discussed.
An introductory discussion traces the development of the concept of community structure, and defines its content. Life form is recognized as the basis upon which community structure is analysed, and the trends in the development of systems of classifying life form are briefly reviewed. The values and limitations of Raunkiaer's system are mentioned and, together with an extended system of classifying growth form, it is adopted for the purpose of comparing community structure in two sand dune systems. This comparison is carried out as an illustration of the relationships between structure and environment discussed in the introduction, and as a contribution to the investigation of the dune habitat and its plant community. Analysis is based solely upon floristic lists with estimates of frequency. The dune communities examined are situated at Luskentyre Banks, Isle of Harris (West Scotland), and at St Cyrus, Kincardineshire (East Scotland). The association between the typical structure of the dune community and the exacting environment is discussed; the importance of vegetative spread and dense growth forms is linked with the mobile substratum, and the high proportions of dwarf growth forms with wind exposure. Under more sheltered conditions taller growth forms may become important. From the general indications of community structure provided by Raunkiaer's system and the additional details from the growth form classification, the influences of climate and of the physical nature of the substratum are regarded as of primary importance. Where these are similar community structure will show a basic similarity, while minor variations will be referable to local variations in climate or substratum.
(1) Pollination relationships were investigated for fourteen months in a southern Spanish Mediterranean coastal scrub community, composed of thirty plant species, at Reserva Biologica de Donana, Donana National Park. (2) Flowering encompassed the whole year, as did insect visits to flowers. Distinct seasonal changes, however, in both the number and identity of insect taxa, and in the number of plant species in bloom were apparent: maximum plant and insect richness occurred in spring. (3) Insect visitors mainly included small beetles, honeybees, small halictid bees, syrphids and bombylids. The overall species richness of the pollinator array was very high (187 taxa). (4) Plant species with specialized pollination mechanisms were relatively infrequent. Most plants had non-restrictive or small flowers, or both. Species relying on pollen to attract pollinators outweighed those relying on nectar as the main reward. (5) Joint analysis of flower attributes, blooming phenology and pollination vectors demonstrated that species flowering at about the same time of year tend to have their flowers visited by the same insects, irrespective of floral features. (6) It is hypothesized that fruit set is more resource-than pollen-limited and that to achieve maximum fruit set most plants have unspecialized pollination relationships. The generalized nature of pollination systems may have been a major factor contributing to the survival and weedy behaviour of many Mediterranean scrub species.
We monitored breeding eastern meadowlarks, dickcissels, Henslow's sparrows, grasshopper sparrows and field sparrows using strip transect surveys in 1995 and 1996. The 473-ha study area was an array of 3-ha management units of burned, mowed, hayed, grazed and undisturbed (> 1 year) cool- and warm-season grasses and annual weeds. Management units grouped by habitat type (management regime and grass type) had different (P < 0.05) abundances of each species. Eastern meadowlarks and dickcissels were most frequently observed in grazed warm-season grasses. Observation rates of Henslow's sparrows and field sparrows were highest in undisturbed warm-season grasses, whereas eastern meadowlarks and grasshopper sparrows were observed least often in this habitat type. Grasshopper sparrows were observed most frequently in annual weeds, Henslow's sparrows and field sparrows were not observed in this habitat type. Overall avian abundance was lowest in recently burned cool-season grasses. The low-intensity, late-season grazing system was important for creating a heterogeneous habitat mosaic attractive to the five species studied.
Herbivores can affect plants not only directly through browsing and tram- pling, but also indirectly through other species. For example, herbivores could affect the interaction between plants and their pollinators. Because plant population density may affect plant-pollinator interactions and plant reproductive success, we hypothesized that herbi- vores could affect pollination and plant reproduction indirectly by modifying plant popu- lation density. Unlike previous hypotheses, which concerned individual-level effects on vegetative and reproductive traits, our hypothesis focuses on population-level effects and involves a feedback mechanism. To test this hypothesis, we conducted field studies in the temperate forest of the southern Andes, where introduced ungulates are a major source of anthropogenic alteration. For 10 animal-pollinated understory plants, we compared popu- lation density, pollinator visitation, pollen deposition in stigmas, and reproduction in four pairs of grazed and ungrazed sites. We found evidence of indirect effects of ungulates on pollination and reproduction only for the herb Alstroemeria aurea(Alstroemeriaceae). The general lack of evidence for indirect effects on most of the species may result from resistance to cattle browsing and trampling, or low statistical power. For A. aurea, we present additional evidence from trampling and hand-pollination experiments, plus path analyses of the effect of density on pollination and reproduction showing that: (1) cattle decrease the absolute and relative population density of this species through trampling; (2) density, particularly relative density, affects pollen deposition on stigmas; and (3) conspecific pollen deposition affects reproduction. Thus, our results indicate that, by directly reducing the population density of A. aurea, cattle are indirectly affecting its reproduction.
Floral display and reward production may affect the attractiveness of a plant to a range of interacting animals including pollinators, herbivores, and vectors of pathogenic fungi. The optimal floral phenotype should therefore depend on the relative importance of selection exerted by both mutualistic and antagonistic animals. The perennial, rosette herb Primula farinosa is polymorphic for scape length. Natural populations may include both plants with flowers displayed well above the ground (the long-scaped morph) and those with flowers positioned very close to the ground (the short-scaped morph). In this study, we conducted a field experiment to examine how the relative fitness of the two scape morphs is affected by interactions with pollinators and fruit predators in two different microhabitats (high and low vegetation). As predicted based on the difference in floral display, supplemental hand-pollination showed that fruit initiation was more strongly pollen-limited in the short-scaped than in the long-scaped morph, and that this difference was significantly larger in high than in low vegetation. Moreover, plants with a short scape experienced lower levels of fruit predation than plants with a long scape. Among open-pollinated controls, there was no significant difference in seed output between the two scape morphs. However, among plants receiving supplemental hand-pollination, short-scaped plants produced significantly more seeds than long-scaped plants. The results suggest that the positive and negative effects of a prominent floral display (increased pollination and seed predation, respectively) balance in the study population, but also that the short-scaped morph would have an advantage at higher pollination intensities. Spatial and temporal variation in pollinator activity and seed predation should result in associated variation in the relative fecundity of the two scape morphs.
Moorlands dominated by heather Calluna vulgaris are of international conservation importance, but are declining as a result of increased grazing pressure and deposition of atmospheric pollutants. Grazing and nutrient deposition can alter the composition, structure and nutritional quality of the vegetation, which may affect the diversity of herbivorous insects. However, the drivers of insect community diversity in moorlands remain poorly understood.
Here we quantify the changes in moorland vegetation caused by grazing and nutrient addition, together with the effects of these changes on the community structure of a major group of herbivorous insects on moorlands, the Hemiptera. Fencing and fertilizer treatments were used to test the hypotheses that: (1) hemipteran species richness is related to plant species richness; (2) fertilizer addition increases host plant quality and hence the abundance and diversity of Hemiptera; and (3) a reduction in grazing alters vegetation structure and hence the composition of the hemipteran community.
Sites with more mineral soils had the most plant species and the largest species richness and abundance of Hemiptera, supporting hypothesis 1. Fertilizer increased the nitrogen content of both grasses and Calluna and significantly increased Hemiptera abundance and species richness (hypothesis 2), although the effect of fertilizer on diversity was smaller than that of site‐based factors such as plant species richness.
Grazing altered vegetation structure (hypothesis 3): fenced plots increased Calluna ground cover, height and canopy occupancy but reduced grass cover. Four months after the fencing and fertilizer treatments, the level of grazing on Calluna was the prime factor influencing the composition of the hemipteran community. However, after 2 years of the treatments, soil organic content and prevalence of Nardus and new‐growth Calluna had become the greatest influence on community composition.
Synthesis and applications. Grazing and nitrogen deposition alter the vegetation of moorland landscapes and this study shows that these factors also have significant effects on the abundance, species richness and species composition of moorland invertebrates. However, site‐based factors such as soil organic content and plant species richness had the greatest impact on the hemipteran community because plant diversity appears to be the most important driver of hemipteran diversity. Moorland managers may be able to maximize hemipteran species richness using a grazing regime that maintains a mosaic of dwarf shrub and grass cover. Site‐specific factors such as soil type need to be considered when managing moorlands for conservation.
We compared species diversity of plants and insects among grazed and ungrazed areas of Ponderosa pine–grassland communities in Arizona. Plant species richness was higher in two of three grassland communities that were grazed by native elk and deer and domestic cattle than in ungrazed areas inside a series of three large (approximately 40-ha) grazing exclosures. Similarly, plant species richness was higher in grazed areas relative to ungrazed areas at one of two series of smaller (approximately 25-m²) and short-term exclosure sites. Evenness of plant distribution, however, was greater inside ungrazed long-term exclosures but was reduced inside ungrazed short-term exclosures relative to grazed areas. Relative abundances of forbs, grasses, trees, and shrubs, and native and introduced plants did not differ between the long- and short-term grazing exclosures and their grazed counterparts. Relative abundances of some plant species changed when grazers were excluded, however. In contrast, insect species richness was not different between grazed and ungrazed habitats, although insect abundance increased 4- to 10-fold in ungrazed vegetation. Our results suggest that vertebrate grazing may increase plant richness, even in nutrient-poor, semi-arid grasslands, but may decrease insect abundances.
The main aims of this study were to assess grazing impacts on bee communities in fragmented mediterranean shrubland (phrygana) and woodland habitats that also experience frequent wildfires, and to explain the mechanisms by which these impacts occur. Fieldwork was carried out in 1999 and 2000 on Mount Carmel, in northern Israel, a known hot-spot for bee diversity. Habitats with a range of post-burn ages and varying intensities of cattle grazing were surveyed by transect recording, grazing levels, and the diversity and abundance of both flowers and bees were measured. The species richness of both bees and flowers were highest at moderate to high grazing intensities, and path-analysis indicated that the effects of both grazing and fire on bee diversity were mediated mainly through changes in flower diversity, herb flowers being more important than shrubs. The abundance of bees increased with intensified grazing pressure even at the highest levels surveyed. Surprisingly though, changes in bee abundance at high grazing levels were not caused directly by changes in flower cover. The variation in bee abundance may have been due to higher numbers of solitary bees from the family Halictidae in grazed sites, where compacted ground (nesting resource) and composites (forage resource) were abundant. The effects of grazing on plants were clearest in the intermediate-aged sites, where cattle inhibited the growth of some of the dominant shrubs, creating or maintaining more open patches where light-demanding herbs could grow, thus allowing a diverse flora to develop. Overall, bee communities benefit from a relatively high level of grazing in phrygana. Although bee and flower diversity may decrease under very heavy grazing, the present levels of grazing on Mount Carmel appear to have only beneficial effects on the bee community.
The maintenance of grasslands as distinct habitats depends on regular management, usually through grazing or mowing, but their species diversity is known to decline with increasing management intensity. The reduction of management intensity can be a useful tool for the long-term conservation of the biological diversity of grasslands. We analyzed floral and faunal diversity on intensively and extensively ( unintensively) grazed pastures and on 5- to 10-year-old ungrazed grasslands in northern Germany. Each of the three grassland habitats differing in grazing intensity was replicated six times. We related diverse taxa such as grasshoppers, butterfly adults and lepidopteran larvae, and trap-nesting solitary bees and wasps to vegetation structure. There was an increase of species richness and abundance from pastures to ungrazed grasslands. The percentage of parasitism of the most abundant trap-nesting species, the digger-wasp ( Trypoxylon figulus), was also higher on ungrazed grasslands. Decreased grazing on pastures enhanced species richness for adult butterflies only, whereas the abundance of adult butterflies, solitary bees and wasps, and their natural enemies increased. Although the differences in insect diversity between pastures and ungrazed grassland could be attributed to a greater vegetation height and heterogeneity (bottom-up effects) on ungrazed areas, the differences between intensively and extensively grazed pastures could not be explained by changes in vegetation characteristics. Hence, intensive grazing appeared to affect the insect communities through the disruption of plant-insect interactions. A mosaic of extensively grazed grassland and grassland left ungrazed for a few years may be a good means by which to maintain biodiversity and the strength of trophic interactions.
The effects of agricultural intensification on biodiversity in arable systems of western Europe have received a great deal of attention. However, the recent transformation of grassland systems has been just as profound.
In Britain, the management of grassland has changed substantially in the second half of the 20th century. A high proportion of lowland grassland is managed intensively. The major changes include a doubling in the use of inorganic nitrogen, a switch from hay to silage, and increased stocking densities, particularly of sheep. Structurally diverse and species‐rich swards have been largely replaced by relatively dense, fast‐growing and structurally uniform swards, dominated by competitive species.
Most of these changes have reduced the suitability of grassland as feeding and breeding habitat for birds.
The most important direct effects have been deterioration of the sward as nesting and wintering habitat, and loss of seed resources as food. Short uniform swards afford poor shelter and camouflage from predators, whereas increased mowing intensities and trampling by stock will destroy nests and young. Increased frequency of sward defoliation reduces flowering and seed set, and hence food availability for seed‐eating birds.
The indirect effects of intensification of management on birds relate largely to changes in the abundance and availability of invertebrate prey. The effects of management vary with its type, timing and intensity, and with invertebrate ecology and phenology, but, in general, the abundance and diversity of invertebrates declines with reductions in sward diversity and structural complexity.
Low input livestock systems are likely to be central to any future management strategies designed to maintain and restore the ecological diversity of semi‐natural lowland grasslands. Low additions of organic fertilizer benefit some invertebrate prey species, and moderate levels of grazing encourage sward heterogeneity.
There is now a need to improve understanding of how grassland management affects bird population dynamics. Particularly important areas of research include: (i) the interaction between changes in food abundance, due to changes in fertilizer inputs, and food accessibility, due to changes in sward structure; (ii) the interaction between predation rates and management‐related changes in habitat; and (iii) the impact of alternative anti‐helminithic treatments for livestock on invertebrates and birds.
Because of changing land‐use practices and abandonment, many European calcareous grasslands are under increasing threat. In order to protect those grasslands that remain, better insights into how plant populations respond to different management scenarios are needed.
Using transition matrix models and life‐table response experiment (LTRE) analysis, the effects of different management strategies (grazing, summer and autumn mowing, and no management) on plant performance and population dynamics of the perennial herb Primula veris (Primulaceae) were experimentally studied. Data were collected between 1999 and 2003 in a species‐rich calcareous grassland.
Early grazing (May) resulted in low population growth rates (λ < 0·860) and a mean annual population decline of 11%. Under these conditions, both the proportion of flowering individuals and flower and seed production per plant were low, resulting in seed limitation overall. However, when grazing started later in the growing season (early July) flowering probability and overall seed set increased, as did population growth rates (λ > 1).
Mowing in autumn (October) was the most favourable management scenario (mean λ= 1·213), resulting in high proportions of flowering individuals and a large seed output. Furthermore, this management yielded optimal conditions for recruitment and seedling establishment during the next growing season.
Summer mowing (mid‐July) resulted in a similar increase of flowering and overall seed shed to autumn mowing, but recruitment rates were lower because of a dense and tall vegetation structure at the time of germination. Consequently, population growth rates (mean λ= 1·045) were lower compared with the autumn mowing regime.
No management of the grassland resulted in low growth rates (λ < 0·843) and a mean annual population decline of 35%, because of high mortality rates of each life stage and a lack of recruitment. Recruitment rates were strongly reduced by lowered flowering probabilities and limited germination possibilities.
Synthesis and applications . This study may enable conservation managers to understand better the effects of time and type of management on population dynamics of P. veris . In order to preserve the remaining populations of this long‐lived species, management interventions can promote flowering and seed shed and reduce productivity of the vegetation by mowing in autumn. Finally, this study has clearly shown that the lack of any management, which is the fate of many abandoned calcareous grassland relicts, will seriously restrict the long‐term survival of P. veris .
Declining populations of UK grassland flora and fauna have been attributed to intensification of agricultural management practices, including changes in cutting, fertilizer, grazing and drainage regimes. We aimed to develop field margin management practices that could reverse declines in intensively managed grassland biodiversity that would have application in the UK and Europe. Here we focus on one aspect of grassland biodiversity, the beetles.
In four intensively managed livestock farms in south‐west England, 10‐m wide field margins in existing grasslands were managed to create seven treatments of increasing sward architectural complexity. This was achieved through combinations of inorganic (NPK) fertilizer, cattle grazing, and timing and height of cutting. To examine the potential influence of complexity on faunal diversity, beetles were identified to species level from suction samples taken between 2003 and 2005, and their assemblage structure was related to margin management, floral assemblages and sward architecture.
Beetle abundance, and species richness and evenness were influenced by margin management treatment and its interaction with year. Correlations with sward architecture and the percentage cover of dominant forbs and grasses were also found. Functional groups of the beetles showed different responses to the management treatments. In particular, higher proportional abundances of seed/flower‐feeding guilds were found in treatments not receiving NPK fertilizer.
The assemblage structure was shown to respond to margin management treatments, sward architecture and the percentage cover of dominant forbs and grasses. The most extensively managed treatments were characterized by distinct successional trajectories from the control treatment.
Synthesis and applications. This study provides management options suitable for use within agri‐environment schemes intended to improve faunal diversity associated with intensively managed lowland grasslands. Field margins receiving either no management or a single July silage cut were shown to support greater abundances and species richness of beetles, although subtler modifications of conventional management may also be beneficial, for example the absence of NPK fertilizer while maintaining grazing and silage cutting systems.
Species richness is a fundamental measurement of community and regional diversity, and it underlies many ecological models and conservation strategies. In spite of its importance, ecologists have not always appreciated the effects of abundance and sampling effort on richness measures and comparisons. We survey a series of common pitfalls in quantifying and comparing taxon richness. These pitfalls can be largely avoided by using accumulation and rarefaction curves, which may be based on either individuals or samples. These taxon sampling curves contain the basic information for valid richness comparisons, including category–subcategory ratios (species-to-genus and species-to-individual ratios). Rarefaction methods – both sample-based and individual-based – allow for meaningful standardization and comparison of datasets. Standardizing data sets by area or sampling effort may produce very different results compared to standardizing by number of individuals collected, and it is not always clear which measure of diversity is more appropriate. Asymptotic richness estimators provide lower-bound estimates for taxon-rich groups such as tropical arthropods, in which observed richness rarely reaches an asymptote, despite intensive sampling. Recent examples of diversity studies of tropical trees, stream invertebrates, and herbaceous plants emphasize the importance of carefully quantifying species richness using taxon sampling curves.
Food-web structure mediates dramatic effects of biodiversity loss including secondary and `cascading' extinctions. We studied these effects by simulating primary species loss in 16 food webs from terrestrial and aquatic ecosystems and measuring robustness in terms of the secondary extinctions that followed. As observed in other networks, food webs are more robust to random removal of species than to selective removal of species with the most trophic links to other species. More surprisingly, robustness increases with food-web connectance but appears independent of species richness and omnivory. In particular, food webs experience `rivet-like' thresholds past which they display extreme sensitivity to removal of highly connected species. Higher connectance delays the onset of this threshold. Removing species with few trophic connections generally has little effect though there are several striking exceptions. These findings emphasize how the number of species removed affects ecosystems differently depending on the trophic functions of species removed.
Long-term conservation of biodiversity may depend not only on the maintenance of its component parts but also on their interactions. Here we provide strong evidence that an introduced species is able to affect the network of interactions among coexisting species. We studied plant–pollinator interactions in native forest sites with and without domestic cattle and used these data to construct plant–pollinator interaction networks. Results from nonmetric multidimensional scaling and permutation tests suggest that the presence of cattle has significantly modified the structure of the plant–pollinator interaction network. The effect of cattle on network structure was mainly because of the modification of a few highly frequent interactions, which are likely important from a functional perspective. This overwhelming influence of a few interactions on observed community patterns should serve as a caution to those studying community and ecosystem properties.
I analyse the effects of habitat fragmentation on the pollination success of a perennial, butterfly‐pollinated, caryophyllaceous herb, the maiden pink, Dianthus deltoides L. The study was conducted in July 1986 and July 1987 at two different sites in southwest Sweden, an undisturbed “mainland” site and a fragmented site consisting of “habitat islands” within a heavily utilized agricultural area The fragmented area had a lower diversity and abundance of both flowering plants and flower‐visiting insects. Dianthus flowers received fewer visits in the fragmented area than in the mainland area, and the seed set was much lower. Hand pollination increased seed set up to 4.1 times in the fragmented area, but no significant differences were found between hand‐pollinated and control flowers at the mainland site. There were no differences between the two sites in standing crop of nectar, ovule number per flowers, or seed set of bagged flowers, band‐pollinated flowers, and hand‐pollinated fertilized flowers Thus, the difference in natural seed set between the two sites can be explained by differences in pollinator service.
1. The Mongolian gazelle Procapra guttorosa is legally hunted, but has no scientifically-based management strategy. It has suffered a range contraction in recent years, but the reasons for this are unclear. This paper addresses both of these issues.
2. The available data on the population dynamics and human influences on the Mongolian gazelle are presented and evaluated. Districts which currently contain Mongolian gazelles had a significantly lower human population density in 1969 than those which no longer contain gazelles.
3. A discrete-time age- and sex-structured model is developed for the Mongolian gazelle. The model includes stochastically determined mortality rates, depending on whether the winter is harsh and/or the summer has a disease epidemic. The model results suggest that given the poor data available, a relatively safe strategy for managers, producing reasonable yields, would be to hunt at a low hunting mortality rate, taking up to 6% of the population each year, while selecting strongly for males.
4. A simpler lumped-parameter model is developed using the climate and disease-determined rates of population increase derived from the age- and sex-structured model. Comparison between the two models shows that the lumped parameter model is an adequate simplification of the age- and sex-structured model, although it underestimates equilibrium population sizes somewhat.
5. The simplified model is used to investigate the available data on the Mongolian gazelle. It is shown that the population must have been larger than previous estimates in order to have sustained the level of recorded hunting over the last 64 years.
6. The model suggests that the population declined rapidly from 1979 to 1986, then stabilized. Variation in natural mortality rates has had an effect on the rate of decline since 1932, but recorded hunting has not. It is not possible to tell whether the rates of unrecorded hunting or habitat degradation have changed since 1932. The results are robust to parameter variation.
The relationships between rosette size, vernalization, and photoperiod in bolting induction of Oenothera erythrosepala (a facultative biennial) were examined. A natural population of O. erythrosepala in a sand dune system at Azigaura, Japan, behaves as a monocarpic perennial, while a population treated with fertilizer showed the life cycle of a winter annual. In both natural and fertilized populations, bolting was restricted to size classes with rosette diameter greater than 9 cm, regardless of the chronological age and the amount of food reserves accumulated in the tap root. Pot culture experiments showed that the species requires both vernalization and long-day photoperiod for bolting induction, and has a critical leaf area for receiving photoperiodic stimuli. The amount of food reserves in the plant per se does not contribute to the size-dependent flowering of the species.
It has been suggested that intensive grazing management, aimed at maintaining plant diversity, might not be the optimal choice
to preserve diversity of insects in semi-natural pastures. In the present study the behaviour of flower visiting insects was
studied in two semi-natural pastures in central Sweden. Two grazing treatments were established with one grazed from mid-May,
“continuous”, and one grazed from mid-July, “late”. Flower visitors were followed for 9weeks in summer 2003 in 7 pairs of
5×5m plots on two sides of a fence dividing the two grazing treatments. Visitor behaviour was studied on three decision
levels between: (1) habitats, (2) flowers and (3) activities on flowers. The pattern varied between decision levels: More
species and individual visitors chose to forage in the late grazing treatment. Visitation rate and flower constancy did not
differ between treatments and was related, to a large extent, to plant species richness. In relation to flowers, insects utilized
a broader diversity of activities in the late grazing treatment. All patterns were consistent across sites and during the
whole study period. The differences in pollinator abundance and activities on flowers were best explained by the higher abundance
of flowers. It is suggested that studies of insect behaviour may be a useful tool when deciding on management recommendations.
Late grazing is recommended as a useful management regime and might potentially function as a substitute for mowing in the
future.
Declines in the natural populations of several bumblebee species across Britain and Europe are an increasing cause for concern. In this study the habitat use of bumblebees was investigated on Salisbury Plain Training Area, the largest remaining area of unimproved chalk grassland in north-west Europe. Habitat characteristics influencing the overall abundance, species richness and foraging activity of bumblebees included the diversity and abundance of flowering plant species (particularly of favoured forage plants such as Trifolium pratense), vegetation structure and height. It is suggested that different Bombus species respond to these habitat characteristics depending on their specific foraging and nesting requirements, the case of Bombus humilis being especially relevant. The effects of several grassland management practices were considered in terms of their suitability for the conservation of bumblebee habitats. Cattle grazing was shown to be preferable to both sheep grazing and the absence of any management, although the timing and intensity of such grazing was important. Small-scale disturbances caused by vehicle activity were also of value in producing locally abundant forage resources in less intensively managed grasslands.
This is a keynote paper focusing on regional perspectives on agriculture and biodiversity by exploring the situation in Northern Africa, the West African Sahel, East Africa and the Horn, and Southern Africa. The paper establishes that in all these regions agriculture accelerates loss of biodiversity because of attempts by farmers to increase crop and animal production to feed the increasing population and contribute to the growth of the national economies. Harmful agricultural practices, such as overcultivation, overgrazing, bush fires, cultivation of marginal and easily eroded land, mechanization and the widespread use of chemicals and pesticides, have intensified the degradation of the soil and vegetation and led to rapid decline of species types and their numbers. Agriculture and biodiversity can be complementary activities. If properly managed, agriculture should enhance and not be the enemy of biodiversity in the drylands of Africa. There is need to assess the agricultural potential of the semi-arid environments and develop specific agricultural policies or programmes to enhance their sustainable utilization and conservation of biodiversity. Information contained in this paper was gathered from the existing literature
The importance of structure in grasslands to arthropods is emphasised. Community dynamics below ground are briefly described. The characteristics of stenophagous, polyphagous, predacious and parasitoid arthropods in relation to structure are outlined. Tall grassland supports more species, individuals and a greater diversity of arthropods than short swards, but some species are characteristic of the latter. The classification of structure in grassland is briefly reviewed. Change in grassland structure occurs through the opposing forces of succession and, in most cases, management. The commonest method of management is grazing, which is characterised by selectivity in the foliage eaten, treading of the sward and deposition of dung. Cutting is sudden, but its effects of defoliation are similar to those of grazing. Burning is considered in less detail. Ploughing, rotovating, re-seeding, fertiliser application, translocation and set-aside are generally forms of agricultural or ‘creative’ management. Human treading can have severe effects on invertebrate diversity and abundance. Management interacts with other factors, such as seasonality, timing, topography, site-specific characteristics and connectivity to produce varied effects on arthropods. The various types of management systems, reclamation, maintenance, agricultural, rotational and others are discussed in relation to management plans and objectives in conservation. It is concluded that conservationists need to be more aware of grassland dynamics, that management by reference to past land-use must be tempered by full consideration of ecological factors and conservation aims and that ‘practical’ and ‘theoretical’ conservationists need to interact more effectively.
The effects of grazing intensity on plant and insect diversity were examined in four different types of grassland (intensively and extensively cattle-grazed pastures, short-term and long-term ungrazed grassland; 24 study sites). Vegetation complexity (plant species richness, vegetation height, vegetation heterogeneity) was significantly higher on ungrazed grasslands compared to pastures but did not differ between intensively and extensively grazed pastures. However, insect species richness was higher on extensively than on intensively grazed pastures, established by suction sampling of four insect taxa (Auchenorrhyncha, Heteroptera, Coleoptera, Hymenoptera Parasitica). This may be due to intensive grazing disrupting plant–insect associations as predicted by a “trophic-level” hypothesis. Local persistence and small-scale recolonization of insects on plants appeared to be difficult in the highly disturbed environment of intensive grazing. Insect diversity increased across the four treatments in the following order: intensively grazed<extensively grazed<short-term ungrazed<long-term ungrazed. The major predictor variable of differences in species diversity was found to be vegetation height. Predator–prey ratios within the investigated insect groups were not affected by grazing intensity.
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