Article

Promotion of Seed Set in Yellow Star-Thistle by Honey Bees: Evidence of an Invasive Mutualism

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Abstract

We examined the role of nonnative honey bees (Apis mellifera) as pollinators of the invasive, nonnative plant species yellow star-thistle (Centaurea solstitialis), both introduced to the western United States in the early to middle 1800s. Using four different treatments (three exclosure types) at flower heads, we observed visitation rates of different pollinators. Honey bees were the most common visitors at each of three transects established at three study locales in California: University of California at Davis, Cosumnes River Preserve. and Santa Cruz Island. A significant correlation existed between honey bee visitation levels monitored in all these transects and the average number of viable seeds per seed head for the same transects. Selective exclusion of honey bees at flower heads using a 3 mm diameter mesh significantly reduced seed set per seed head at all locales. Seed set depression was less dramatic at the island locale because of high visitation rates by generalist halictid bees Augochlorella pomoniella and Agapostemon texanus that penetrated the 3-mm mesh. The introduced megachilid bee Megachile apicalis occurred at all three locales as well (though in much lower numbers) and may contribute to pollination. In an ancillary study, seed set of plants with bagged heads was compared with that of plants without any bagged heads to test for resource shunting effects. These results showed that seed set differences observed between treatments within a single plant were not exaggerated due to resource shunting induced by the bagging technique. Yellow star-thistle may have low or variable levels of self-compatibility (as reflected by low seed set levels in small-mesh bags), increasing the importance of pollination in its breeding system. These results suggest that honey bees and yellow star-thistle may act as invasive mutualists, an association that may extend to other normative plant and pollinator species from Eurasia.

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... When the other two options are unavailable, establishing mutualistic associations with native pollinators may greatly enhance an invading species' ability to establish (Simberloff andVon Holle 1999, Jesse et al. 2006). Pollination and the competition for pollinators has been studied for a number of invasive plants (Grabas and Laverty 1999, Barthell et al. 2001, Chittka and Schürkens 2001, Brown et al. 2002, Larson et al. 2002, Parker and Haubensak 2002, Jesse et al. 2006, Morales and Aizen 2006. Invasive plants that have showier flowers, higher quality nectar, or more nectar may cause problems for native species in two ways. ...
... The plant can either have been introduced to the new habitat along with its associated pollinators from its native region, it can wait for those previously associated pollinators to be independently introduced, or it can attempt to compete for resident pollinating species (Parker and Haubensak 2002). The establishment and competition for mutualistic associations with native pollinators has been studied for a number of invasive plants (Grabas and Laverty 1999, Barthell et al. 2001, Chittka and Schürkens 2001, Brown et al. 2002, Larson et al. 2002, Parker and Haubensak 2002, Jesse et al. 2006, Morales and Aizen 2006. With costs of preventing and controlling invasive species estimated at $137 billion per year, it is increasingly important to understand the reproductive biology of these pest species (Pimentel et al. 2000). ...
... Managed bees could also affect resource availability for wild bees by changing plant community composition. Previous studies have shown that in some regions where managed bees are exotic, they preferentially forage on exotic plants [28][29][30]. These foraging preferences can form invasive mutualisms whereby exotic pollinators and plants facilitate each other's spread in non-native regions, subsequently reducing populations of native plants [29]. ...
... For example, some studies compared managed bee and wild bee foraging behaviors, in particular their preferences for native vs. exotic plants, but did not measure the effects of such preferences on plant reproduction, abundance, or diversity. Even among studies that measured plant reproductive output as a function of managed bees, individual-level responses such as fruit and seed set were not followed to population-level responses such as plant abundance or geographic range expansion (e.g., [29][30][64][65][66][67], but see [68]). Furthermore, while it was generally outside the scope of these studies, the consequences of such changes in plant community composition for wild bees has not been well examined, and will likely vary across plant communities and bee species, especially between generalists and specialists [1,69]. ...
Article
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Managed bees are critical for crop pollination worldwide. As the demand for pollinator-dependent crops increases, so does the use of managed bees. Concern has arisen that managed bees may have unintended negative impacts on native wild bees, which are important pollinators in both agricultural and natural ecosystems. The goal of this study was to synthesize the literature documenting the effects of managed honey bees and bumble bees on wild bees in three areas: (1) competition for floral and nesting resources, (2) indirect effects via changes in plant communities, including the spread of exotic plants and decline of native plants, and (3) transmission of pathogens. The majority of reviewed studies reported negative effects of managed bees, but trends differed across topical areas. Of studies examining competition, results were highly variable with 53% reporting negative effects on wild bees, while 28% reported no effects and 19% reported mixed effects (varying with the bee species or variables examined). Equal numbers of studies examining plant communities reported positive (36%) and negative (36%) effects, with the remainder reporting no or mixed effects. Finally, the majority of studies on pathogen transmission (70%) reported potential negative effects of managed bees on wild bees. However, most studies across all topical areas documented the potential for impact (e.g. reporting the occurrence of competition or pathogens), but did not measure direct effects on wild bee fitness, abundance, or diversity. Furthermore, we found that results varied depending on whether managed bees were in their native or non-native range; managed bees within their native range had lesser competitive effects, but potentially greater effects on wild bees via pathogen transmission. We conclude that while this field has expanded considerably in recent decades, additional research measuring direct, long-term, and population-level effects of managed bees is needed to understand their potential impact on wild bees.
... Documented positive relationships between honey bee abundance and fruit set of the invader suggest that honey bees may facilitate the population growth of the invader (Goulson & Derwent, 2004). Barthell et al. (2001) posited that honey bees have facilitated the invasion of non-native yellow star thistle, Centaurea solstitialis, in the state of California. Not only were honey bees the most frequent visitors to flowers, but their exclusion from flowers also significantly reduced seed production. ...
... Whether honey bees were responsible for the invasion of yellow star thistle depends on whether native visitors might pollinate this species adequately in regions in which honey bees are not the numerically dominant pollinator. Interestingly, the non-native bee species Megachile apicalis that specializes on yellow star thistle did not appear to contribute substantially to its seed set, despite its occurrence at some of the study sites (Barthell et al., 2001). Because most invasive plants receive pollinator services from multiple species, their interactions with any one bee species are likely to be weak (Traveset & Richardson, 2006). ...
Article
This chapter examines the interactions between exotic invasive plants focusing on the following questions: How do bees contribute to invasive plant establishment and spread? How do resident bee communities respond to the invasion? What are the indirect effects of the invasion mediated by pollinator communities? New data on the frequency of insect pollinatordependent invasive plant species in US natural areas confirm that pollinator interactions are likely to play a role in the outcome of many invasions. Generalizations are sought regarding which invasive plant-bee interactions likely contribute most to reproduction of invasive plants and negative indirect effects on native plant communities. Finally, mechanisms behind pollinator-mediated indirect effects of invasive plants on native plants are examined by considering invasive plants as resources that contribute to bee population abundance and community structure.
... In its invasive range, some populations of C. solstitialis (e.g., Santa Cruz Island) produce relatively high volumes of nectar per floret, on average usually exceeding 0.050 lL (Barthell et al. 2009(Barthell et al. , 2012 and, although it might be visited by more than 80 species of native bees at a given location, the exotic honey bee (Apis mellifera L.) and introduced leafcutting bee Megachile apicalis Spinola are major pollinators (Thorp et al. 1994;McIver et al. 2009). This relationship between C. solstitialis and both exotic bees, but particularly with honey bees, has been described as ''an invasive mutualism'' (Barthell et al. 2001). Greater seed production occurs whenever honey bees are present and, because of the high volumes of nectar, managed honey bee colonies produce yellow star-thistle honey, which is commercially available in the northwestern USA (Dalby 2004). ...
... Our observations on the nectar availability, composition, and visitation pattern of bees on the weedy population of C. solstitialis at the Uludag University largely agree with those of Barthell et al. (2009) on a non-weedy population of this plant from Lesvos. At both sites standing crop nectar volume, on average, is relatively low, inflorescences are visited by a large number of bee species, and honey bees are uncommon visitors relative to the western USA (Barthell et al. 2001). At our study sites, honey bees were always present in great numbers at flowers of other plants because at least a dozen hives were located within a 5 km radius, yet they did not frequently visit our observational patches. ...
Article
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Information on the pollination ecology and floral visitors of the noxious weed Centaurea solstitialis is available for several populations in its invasive range, but limited information is available in its native range, with most studies conducted on the Greek island of Lesvos. Herein, we document the visitation pattern of bees and explore the relationship of bee body size and nectar availability in weedy populations of C. solstitialis from an urban environment within its native range in northwestern Turkey. Studies were conducted at patches of C. solstitialis in abandoned lots at the Uludağ University near the city of Bursa. A total of 41 species, including honey bees, belonging to five families and 19 genera were recorded. Small megachilid and halictid bee species were the most common visitors. Average nectar standing crop volume per floret was low (0.003–0.117 μL) and did not significantly vary throughout the day. Average bee head width significantly correlated with average nectar standing crop volume but did not significantly change throughout the day. Analyses of pollen loads as well as direct observations of bee foraging behavior indicate that a large number of bees visit C. solstitialis, primarily in search of nectar while carrying a large percentage of pollen grains of this plant species on their bodies. These results are similar to previous observations on a non-weedy population of C. solstitialis from the island of Lesvos.
... Moreover, honey bee could reduce the germination ability of pollen due to their inhibitory effects of their glandular L. ROPARS 2016-2020 CHAPITRE III -146 -secretions. As honey bee could preferentially forage on invasive plant species (Barthell et al. 2001), they could also modify the plant species community. ...
... 54. Barthell J, Randall J, Thorp RW, Wenner A. 2001 Promotion of seed set in yellow starthistle by honey bees : evidence of an invasive mutualism. Ecol. ...
Thesis
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Confrontés aux demandes grandissantes d’installations de ruches, les gestionnaires d’aires protégées s’interrogent sur les conséquences d’une densité élevée d’abeilles domestiques sur les communautés d’abeilles sauvages. Pour répondre à cette question, au sein du Parc national des Calanques, nous avons inventorié la diversité des espèces de pollinisateurs, leurs traits écologiques, et leurs interactions avec la flore sauvage. À travers un bilan des campagnes de terrain réalisées sur une période de 10 ans, près de 250 espèces de pollinisateurs (Apoidea, Syrphidae et Bombyliidae) ont été répertoriées. Les communautés d'abeilles sauvages étaient sensibles à l’occupation du sol à l’échelle du paysage à 1km. La richesse spécifique et l’abondance des grandes abeilles sauvages diminuaient avec l’augmentation de la densité de colonies d’abeilles domestiques suggérant une compétition pour les ressources florales. Ce résultat a été confirmé à travers l’observation des comportements de butinage des abeilles domestiques et sauvages et s’est manifesté par une exclusion compétitive des grandes abeilles sauvages et un changement de régime alimentaire des petites abeilles sauvages et des bourdons. Enfin, la quantité de ressources florales disponibles (nectar et pollen) estimée à l’échelle du Parc national des Calanques n’est pas suffisante pour couvrir les besoins alimentaires des abeilles domestiques déjà installées. Aux vues de l’importance des habitats protégés méditerranéens pour les communautés de pollinisateurs sauvages, cette thèse propose des préconisations de gestion visant à concilier la pratique de l’apiculture avec le maintien de la faune de pollinisateurs sauvages.
... These species were (to an extent) both pollinator-limited and competitively inferior, meaning invasion would not be successful until disturbance changed competitive networks and increased pollination services. Any species directly altering properties of recipient ecosystems has the potential to indirectly facilitate a previously inhibited species(Figure 3interaction 2).Exotic species can also form strong associations that will directly facilitate persistence and prevalence within a community(Barthell, Randall, Thorp, & Wenner, 2001;Constible, Sweitzer, Van Vuren, Schuyler, & Knapp, 2005;Ricciardi, Whoriskey, & Rasmussen, 1997).Common direct facilitative interactions include pollination, such as exotic honey bees increasing seed set of an exotic plant(Barthell et al., 2001), and dispersal, such as introduced bison increasing the spread of seeds of exotic plants(Constible et al., 2005). Direct mutualistic relationships between invasive ants and honeydew-secreting insects are common, resulting in significant population increases of both(Bach, 1991). ...
... These species were (to an extent) both pollinator-limited and competitively inferior, meaning invasion would not be successful until disturbance changed competitive networks and increased pollination services. Any species directly altering properties of recipient ecosystems has the potential to indirectly facilitate a previously inhibited species(Figure 3interaction 2).Exotic species can also form strong associations that will directly facilitate persistence and prevalence within a community(Barthell, Randall, Thorp, & Wenner, 2001;Constible, Sweitzer, Van Vuren, Schuyler, & Knapp, 2005;Ricciardi, Whoriskey, & Rasmussen, 1997).Common direct facilitative interactions include pollination, such as exotic honey bees increasing seed set of an exotic plant(Barthell et al., 2001), and dispersal, such as introduced bison increasing the spread of seeds of exotic plants(Constible et al., 2005). Direct mutualistic relationships between invasive ants and honeydew-secreting insects are common, resulting in significant population increases of both(Bach, 1991). ...
Article
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Positive interactions between exotic species may increase ecosystem-level impacts and potentially facilitate the entry and spread of other exotic species. Invader-facilitated invasion success—”secondary invasion”—is a key conceptual aspect of the well-known invasional meltdown hypothesis, but remains poorly defined and empirically underexplored. Drawing from heuristic models and published empirical studies, we explore this form of “secondary invasion” and discuss the phenomenon within the recognized conceptual framework of the determinants of invasion success. The term “secondary invasion” has been used haphazardly in the literature to refer to multiple invasion phenomena, most of which have other more accepted titles. Our usage of the term secondary invasion is akin to “invader-facilitated invasion,” which we define as the phenomenon in which the invasion success of one exotic species is contingent on the presence, influence, and impacts of one or more other exotic species. We present case studies of secondary invasion whereby primary invaders facilitate the entry or establishment of exotic species into communities where they were previously excluded from becoming invasive. Our synthesis, discussion, and conceptual framework of this type of secondary invasion provides a useful reference to better explain how invasive species can alter key properties of recipient ecosystems that can ultimately determine the invasion success of other species. This study increases our appreciation for complex interactions following invasion and highlights the impacts of invasive species themselves as possible determinants of invasion success. We anticipate that highlighting “secondary invasion” in this way will enable studies reporting similar phenomena to be identified and linked through consistent terminology.
... Broad environmental tolerances that enable non-native plants to establish and persist across a wide range of geographic areas was probably a major factor that promoted their use in highly disturbed habitats and resulted in their commercialization as some of the most available and inexpensive choices for seeding (Green and Franz 1986). However, non-native plant species can reduce native floral resources available to pollinators (Moro n et al. 2009), may support non-native pollinators that compete with native counterparts (Barthell et al. 2001), and can actually reduce populations of pollinators such as lepidopterans, the larvae of which feed on the foliage of native plants (Graves andShapiro 2003, Burghardt andTallamy 2009). Therefore, restoration efforts must carefully consider the costs and benefits of both adding and removing non-native flowering species, and the tradeoffs among different pollinator groups that may result from each management decision. ...
Article
Plant-pollinator interactions represent a crucial ecosystem function threatened by anthropogenic landscape alterations. Disturbances that reduce plant diversity are associated with floral resource and pollinator declines. Establishing wildflower plantings is a major conservation strategy targeting pollinators, the success of which depends on long-term persistence of seeded floral communities. However, most pollinator-oriented seeding projects are monitored for a few years, making it difficult to evaluate the longevity of such interventions. Selecting plant species to provide pollinators diverse arrays of floral resources throughout their activity season is often limited by budgetary constraints and other conservation priorities. To evaluate the long-term persistence of prairie vegetation seeded to support pollinators, we sowed wildflower seed mixes into plots on a degraded reclaimed strip-mine landscape in central Ohio, USA. We examined how pollinator habitat quality, measured as floral abundance and diversity, changed over 10 years (2009-2019) in the absence of management, over the course of the blooming season within each year, and across three seed mixes containing different numbers and combinations of flowering plant species. Seeded species floral abundance declined by more than 75% over the study, with the largest decline occurring between the fifth and seventh summers. Native and non-native adventive flowering plants quickly colonized the plots and represented > 50% of floral community abundances on average. Floral richness remained relatively constant throughout the study, with a small peak one year after plot establishment. Plots seeded with high-diversity mixes averaged 2-3 more species per plot compared to a low-diversity mix, despite having been seeded with twice as many plant species. Within years, the abundance and diversity of seeded species were lowest early in the blooming season and increased monotonically from June to August. Adventive species exhibited the opposite trend, such that complementary abundance patterns of seeded and adventive species blooms resulted in a relatively constant floral abundance across the growing season. Seeded plant communities followed classic successional patterns in which annual species quickly established and flowered but were replaced by perennial species after the first few summers. Long-term data on establishment and persistence of flower species can guide species selection for future-oriented pollinator habitat restorations.
... En algunos casos su presencia ha provocado el desplazamiento de polinizadores nativos (Waser et al. 1996) y a veces la producción de semillas de las plantas visitadas por la abeja melífera ha sido mayor, en especial cuando se trata de especies también invasoras o exóticas (Aizen & Feinsinger 1994;Degrandi-Hoffman & Watkins 2000). Cabe destacar que, en el sitio de estudio, A. mellifera interactuó con especies nativas pero también con especies adventicias, como Carduus thoermeri, Taraxacum officinale o Cosmos sulphureus, en cuyos casos se podrían considerar como "mutualismos invasores" (Barthell et al. 2001). Sería por lo tanto de gran interés indagar sobre las consecuencias de esta interacción en la viabilidad y conservación de las poblaciones, sobre todo en algunas especies que son endémicas del centro de Argentina (Gaillardia megapotamica, Flourensia campestris, Wedelia buphthalmiflora). ...
Article
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The diversity of floral visitors (DFV) and the frequency of visits (FV) were related to some reproductive traits, in 30 co-occurring Asteraceae species of Chaco forests from Córdoba (Argentina). DFV and FV were very different between species and Apis mellifera was the most frequent visitor of flowers. The DFV and the FV showed significant correlations: negative with flowering period and positive with the number of open flowers per plant. Results suggest that the reproductive assurance by autonomous selfing may be limited, since pollinator activity plays an important role in plant reproduction. Both, species with and without autonomous selfing, showed an increase in the number and size of the fruits produced.
... To date, few studies have addressed the issue of the introduction of honeybee hives on the dynamics of native plant communities. It has been documented that introduced colonies enhance the visitation frequency of honeybees on invasive plant species, enhancing their reproduction (e.g. the effect on the purple loosestrife, Lythrum salicaria, in America: Barthell et al., 2001;Mal et al., 1992). By contrast, other studies have demonstrated that the introduction of honeybee hives can negatively affect the reproductive success of plants through increased pollen theft (Hargreaves et al., 2009), nectar robbing , physical damage to the flowers (Dohzono et al., 2008) or through the disruptive influence of honeybee workers on the patterns of pollen transfer among compatible plants that have otherwise evolved highly specialized interactions with native pollinators (Gross and Mackay, 1998;Vaughton, 1996;Watts et al., 2012). ...
Chapter
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Since the rise of agriculture, human populations have domesticated plant and animal species to fulfil their needs. With modern agriculture, a limited number of these species has been massively produced over large areas at high local densities. Like invasive species, these Massively Introduced Managed Species (MIMS) integrate local communities and can trigger cascading effects on the structure and functioning of ecosystems. Here, we focus on plant and insect MIMS in the context of plant–pollinator systems. Several crop species such as mass flowering crops (e.g. Brassica napus) and domesticated pollinating insects (e.g. Apis mellifera, Bombus terrestris) have been increasingly introduced worldwide and their impact on natural communities is addressed by an increasing number of scientific studies.
... European honey bees are reported to assist introduced plant species in their reproduction through mutualism. This has been observed in the association of European honey bee with several invasive weeds including scotch broom (Cytisus scoparius) (Simpson et al., 2005) and yellow star-thistle (Centaurea solstitialis) (Barthell et al., 2001). Additional studies on insect pollinator interactions may be helpful in gaining a better understanding of the factors supporting successful reproduction and spread of Cucumis myriocarpus in Australia. ...
... G.Don, but not its native congeners, was visited frequently by A. mellifera (Woods et al. 2012). In California and Oregon, A. mellifera is the principal pollinator of the nonnative Centaurea solstitialis L. (Barthell et al. 2001;Mciver et al. 2009; Swope and Parker 2010), a major rangeland invader. In South Africa, A. mellifera is the primary pollinator of nonnative Araujia sericifera Brot. ...
Article
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The western or European honey bee (Apis mellifera) is the primary managed pollinator in US agricultural systems, and its importance for food production is widely recognized. However, the role of A. mellifera as an introduced species in natural areas is potentially more complicated. The impact of A. mellifera on native insect pollinators can depend on broad community context, as can the relative effectiveness of A. mellifera in pollination of both native and nonnative plant species outside of agricultural systems. Apis mellifera is highly generalist and able to interact with hundreds of native plant species following its naturalization. It is unlikely to wholly replace native pollinators as visitors of specialized plant species, and its behavioral characteristics tend to reduce A. mellifera's per-visit efficiency, even when its overall effectiveness is high. Preliminary results of our case study exploring the importance of A. mellifera vs. native bees as pollinators of native plants in Hawai'i indicate that A. mellifera is less important than native Hylaeus bees as a flower visitor of focal native plant species. In light of current global declines in A. mellifera populations, maintenance of a diversity of pollinators and pollinator habitat are critical conservation needs in natural areas.
... Honeybees may also have large impacts on native plant communities and natural ecosystems. For example, honeybees can help non-native plants outcompete native plants by enhancing seed set through pollination (Barthell et al. 2001). Spread of invasive plants can distract native bees from their native plant mutualisms, which can lead to further negative effects on biodiversity (Traveset & Richardson 2006). ...
Article
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Global pollinator declines have resulted in an increasing number of policies and actions to help bee populations. In North America, there is strong public engagement, but also growing controversies over how to address declines. This is fueled by complex scientific evidence across species, habitat types, geographic regions, as well as intense lobbying by NGOs, beekeeping, agro-chemical and farming industries. Policy and conservation initiatives often focus on the Western Honeybee, Apis mellifera Linnaeus, a domesticated species not native to North America. Although losses of managed honeybee colonies are recorded annually, we argue that honeybee losses are not a conservation problem, but instead a domesticated animal management issue. By focusing attention on honeybees, policies and subsequent resources may undermine native bee conservation and have negative impacts ecologically and socially. This article is protected by copyright. All rights reserved.
... In California, yellow starthistle (Centauria solstitialis) attracts bees too, but mostly exotic species that are also of European origin. 7 Otherwise, the disruptive exotic weeds of North American rangelands are mostly wind-(or self-) pollinated grasses (e.g., cheatgrass [Bromus tectorum] and buffelgrass [Cenchrus ciliaris]) and forbs (e.g., Russian thistle [Salsola kali]). Most of the exotic forbs of the Great Basin with somewhat more showy fl owers, such as red storksbill (Erodium cicutarium), tumblemustard (Sisymbrium altissimum), and white top (Cardaria draba), do not seem to attract many native pollinators. ...
... Simberloff and Von Holle (1999) coined the term "invasional meltdown" to describe the process by which this facilitation leads to the increased success and further establishment of invasive species and an eventual shift in community composition (Simberloff 2006). Examples of such positive invader-invader interactions among plants and animals fall into two basic categories: (1) pollination/dispersal such as by an invasive pollinator improving the reproduction of an invasive plant, or an invasive animal preferentially eating and dispersing the seeds of an invasive plant (Simberloff and Von Holle 1999;Richardson et al. 2000; Barthell et al. 2001;Goulson 2003;Traveset and Richardson 2006;Aizen et al. 2008;Lafleur et al. 2009;Nuñez et al. 2013;Beavon and Kelly 2015;Prior et al. 2015) and (2) disturbance whereby invasive animals alter habitat so that it favors invasive plants (Hobbs and Huenneke 1992;Kotanen 1995;Lozon and MacIsaac 1997;Schiffman 1997;Simberloff and Von Holle 1999;DiTomaso 2000;Vavra et al. 2007;Knight et al. 2009). Many examples of facilitation through disturbance involve feral animals, particularly the invasive non-native Sus scrofa Linnaeus, 1758 (wild hog) (Spatz and Mueller-Dombois 1972;Stone 1985;Loope et al. 1988;Vavra et al. 2007;Walter and Levin 2008;Spear and Chown 2009;Firn et al. 2010). ...
Article
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Invasive animals can facilitate the success of invasive plant populations through disturbance. We examined the relationship between the repeated foraging disturbance of an invasive animal and the population maintenance of an invasive plant in a coastal dune ecosystem. We hypothesized that feral wild hog (Sus scrofa) populations repeatedly utilized tubers of the clonal perennial, yellow nutsedge (Cyperus esculentus) as a food source and evaluated whether hog activity promoted the long-term maintenance of yellow nutsedge populations on St. Catherine's Island, Georgia, United States. Using generalized linear mixed models, we tested the effect of wild hog disturbance on permanent sites for yellow nutsedge culm density, tuber density, and percent cover of native plant species over a 12-year period. We found that disturbance plots had a higher number of culms and tubers and a lower percentage of native live plant cover than undisturbed control plots. Wild hogs redisturbed the disturbed plots approximately every 5 years. Our research provides demographic evidence that repeated foraging disturbances by an invasive animal promote the long-term population maintenance of an invasive clonal plant. Opportunistic facultative interactions such as we demonstrate in this study are likely to become more commonplace as greater numbers of introduced species are integrated into ecological communities around the world.
... Finally, patterns of pollen limitation must be attributable to lack of activity of pollinators. Although plant-pollinator interactions are known to play a large role in plant reproductive success ( Ashman et al., 2004 ), and even plant community assembly ( Sargent and Ackerly, 2008 ), few examples outside of studies on invasive species consider the role of pollinators in plant range expansions or contractions ( Parker, 1997 ;Barthell et al., 2001 ;Stout et al., 2002 ;Liu et al., 2006 ; but see Chalcoff et al., 2012 ;Moeller et al., 2012 ;Hargreaves et al., 2015 ). While it is known that pollinator abundance, activity, and metabolic performance may decrease with temperature and elevation ( Hodkinson, 2005 ), our understanding of the role of pollinators in determining species' distributions is limited because it has been hard to demonstrate the link between pollen limitation and pollinator activity ( HilleRisLambers et al., 2013 ). ...
Article
Premise of the study: Many studies assume climatic factors are paramount in determining species' distributions, however, biotic interactions may also play a role. For example, pollinators may limit species' ranges if floral abundance or floral attractiveness is reduced at range margins, thus causing lower pollinator visitation and reduced reproductive output. Methods: To test if pollinators influence the altitudinal distribution of Erythronium montanum (Liliaceae) at Mount Rainier National Park, we asked whether (1) seed production in this species relies on pollinators, (2) seed production and pollen limitation is greatest at range limits, and (3) pollinator visitation rates (either overall or by individual taxonomic groups) reflect patterns of seed production and pollen limitation. Results: From this three-year study, we established that this plant does rely on pollinators for fruit set and we found that pollen limitation trended toward being higher at the upper range limit in some years, but not consistently year to year. Insect visitation rates did not mirror spatial patterns of pollen limitation, but annually variable pollinator composition suggested differential importance of some pollinator taxonomic groups (specifically, bumblebees may be better pollinators than syrphid flies). Conclusions: Overall, these results suggest that while pollinators are critical for the reproductive success of this high mountain wildflower, plant-pollinator interactions do not obviously drive the distribution of this species. Nonetheless, high spatio-temporal variability in range-wide plant-pollinator dynamics may complicate responses to climate change.
... An important risk associated with pollinator management is the introduction for crop pollination of an alien pollinator species that subsequently becomes invasive (Ghisbain et al., 2021;Russo et al., 2021). The mechanisms by which introduced (but also native) managed pollinators and their trade can affect native species and ecosystems include (a) exploitative or interference competition for flower resources and nesting sites (Hansen et al., 2002;Inoue et al., 2008;Howlett and Donovan, 2010;Morales et al., 2013;Hudewenz and Klein, 2015;Lindström et al., 2016;Torné-Noguera et al., 2016;Ropars et al., 2019), (b) inadequate pollination of native flora, leading to changes in the reproduction of native plants (Gross and MacKay, 1998;Dohzono et al., 2008;Valido et al., 2019), (c) undesirable pollination of exotic flora (Barthell et al., 2001;Stout et al., 2002;Morales et al., 2014), (d) transmission of parasites or pathogens to wild or native populations, including the co-introduction of natural enemies (Colla et al., 2006;Morales et al., 2013;Murray et al., 2013;Fürst et al., 2014;Schmid-Hempel et al., 2014), and (e) genetic introgression or reproductive disturbance of native pollinator species (Tsuchida et al., 2010;Kraus et al., 2011). Managed pollinators can even have a negative impact on wild plant reproduction and crop yields when they become superabundant (Aizen et al., 2020;Russo et al., 2021). ...
Article
Cultivation of pollinator-dependent crops has expanded globally, increasing our reliance on insect pollination. This essential ecosystem service is provided by a wide range of managed and wild pollinators whose abundance and diversity are thought to be in decline, threatening sustainable food production. The Western honey bee (Apis mellifera) is amongst the best-monitored insects but the state of other managed pollinators is less well known. Here, we review the status and trends of all managed pollinators based on publicly accessible databases and the published literature. We found that, on a global scale, the number of managed A. mellifera colonies has increased by 85% since 1961, driven mainly by Asia. This contrasts with high reported colony overwinter mortality, especially in North America (average 26% since 2007) and Europe (average 16% since 2007). Increasing agricultural dependency on pollinators as well as threats associated with managing non-native pollinators have likely spurred interest in the management of alternative species for pollination, including bumble bees, stingless bees, solitary bees, and flies that have higher efficiency in pollinating specific crops. We identify 66 insect species that have been, or are considered to have the potential to be, managed for crop pollination, including seven bumble bee species and subspecies currently commercially produced mainly for the pollination of greenhouse-grown tomatoes and two species that are trap-nested in New Zealand. Other managed pollinators currently in use include eight solitary bee species (mainly for pollination services in orchards or alfalfa fields) and three fly species (mainly used in enclosures and for seed production). Additional species in each taxonomic category are under consideration for pollinator management. Examples include 15 stingless bee species that are able to buzz-pollinate, will fly in enclosures, and some of which have a history of management for honey production; their use for pollination is not yet established. To ensure sustainable, integrated pollination management in agricultural landscapes, the risks, as well as the benefits of novel managed pollinator species must be considered. We,
... To date, few studies have addressed the issue of the introduction of honeybee hives on the dynamics of native plant communities. It has been documented that introduced colonies enhance the visitation frequency of honeybees on invasive plant species, enhancing their reproduction (e.g. the effect on the purple loosestrife, Lythrum salicaria, in America: Barthell et al., 2001;Mal et al., 1992). By contrast, other studies have demonstrated that the introduction of honeybee hives can negatively affect the reproductive success of plants through increased pollen theft (Hargreaves et al., 2009), nectar robbing , physical damage to the flowers (Dohzono et al., 2008) or through the disruptive influence of honeybee workers on the patterns of pollen transfer among compatible plants that have otherwise evolved highly specialized interactions with native pollinators (Gross and Mackay, 1998;Vaughton, 1996;Watts et al., 2012). ...
... Invasive mutualism occurs when two or more species facilitate each other in establishment and spread into a new geographic region ( Richardson et al., 2000). Bees and weeds can be invasive mutualists, such as is the case of honey bees and the yellow star-thistle (Barthell et al., 2001). Invasive mutualism may also occur between other introduced thistle species (Centaurea sp.) and M. apicalis (Barthell et al., 2003). ...
Article
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This chapter reviews currently available information on the success of introduced pollinators, their effects on native ecosystems, and examines the viability of using native pollinators to prevent unnecessary introductions of exotic species. Exotic species of bees have been introduced to different countries as crop pollinators. Well-known examples are the alfalfa leafcutting bee (Megachile rotundata) and several species of bumble bees (Bombus spp.). In most cases, these imports have been done without prior assessment of possible negative impacts of the pollinators on native ecosystems. Other species have been accidentally introduced, or introduced for purposes other than pollination of crops. The best known of such introductions is the African honey bee, imported to Brazil in the 1950s. African honey bees (Apis mellifera scutellata) have become important pollinators of crops like coffee or avocado in tropical and subtropical regions of the Americas.
... One of the more recurrent example is related to the humaninduced massive presence of the domestic honeybee and their consequences on mutualistic native plant-animal interactions on islands (e.g. Kato et al., 1999;Craig et al., 2000;Barthell et al., 2001;England, 2001;Roubik & Wolda, 2001;Hansen et al., 2002;Goulson et al., 2002;Valido et al., 2002;Goulson, 2003;Dupont et al., 2004b;Kato & Kawakita, 2004;Abe, 2006b;Kaiser-Bunbury et al., 2009;Dohzono & Yokoyama, 2010;Valido et al., in prep.). The principal conclusion obtained from these authors is that the extreme local abundance of honeybees, influenced by beekeeping activities, reduces considerably the flower-visitation rates of native pollinators (predominantly insects but also birds and lizards). ...
... Studies of some New Zealand species such as heather (Calluna vulgaris) have had conflicting results as to the importance of honeybees and weed fecundity (Mahy & Jacquemart 1998). However, a growing body of international evidence confirms that honeybees aid seed-set in plants that are regarded as serious weeds in New Zealand, including purple loosestrife (Lythrum salicaria) in North America (Goulson 2010), yellow star-thistle (Centaurea solstitialis) on Santa Cruz Island (Barthell et al. 2001) and lupin (Lupinus arboreus) in Tasmania (Stout et al. 2002). ...
Technical Report
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The honeybee (Apis mellifera) has been intentionally introduced to many parts of the world to produce honey and improve the pollination of food crops. Although honeybees are seldom viewed as harmful in environments outside their natural range, a growing body of research confirms that their presence can have negative consequences for indigenous ecosystems across the globe. In recent years, there have been an increasing number of applications for beehives on public conservation lands in New Zealand, making it important that we fully understand the impacts that honeybees may have on indigenous ecosystems. Introduced honeybees are known to disadvantage indigenous fauna by competing for floral resources. However, in New Zealand ecosystems, these interactions are generally poorly understood, largely due to a lack of knowledge about species diversity, population numbers and the ecology of the majority of flower-visiting fauna. There is also a widely held belief that there is ample nectar/pollen within New Zealand ecosystems to support both introduced bees and indigenous flower visitors, although with recent changes in land use and environmental pressures, this may not be the case. Honeybees have also been shown to alter pollination processes in indigenous plants and facilitate the reproduction of weeds, and may act as vectors for pathogens and disease, although little information is available in the New Zealand context. Despite the lack of conclusive scientific evidence for the impact of honeybees in the natural environments of New Zealand, they do pose a very real threat to indigenous biodiversity. Therefore, it is recommended that the precautionary principle is used to inform the management of honeybees on public conservation lands in the interests of both conservation and economics. Keywords: honeybee, Apis mellifera, apiculture, ecosystem, resource competition, weed pollination, pathogens and diseases, biodiversity, pollination processes
... Goulson, unpublished data). In North America, honeybees increase seed set of the yellow star thistle, Centaurea solstitialis (Barthell et al. 2001) and are the main pollinators of two important weeds, purple loosestrife, Lythrum salicaria (Mal et al. 1992) and Raphanus sativus (Stanton 1987). Donovan (1980) reports that bumblebees are major pollinators of introduced weeds in New Zealand. ...
Article
Abstract Bees are generally regarded as beneficial insects for their role in pollination, and in the case of the honeybee Apis mellifera, for production of honey. As a result several bee species have been introduced to countries far beyond their home range, including A. mellifera, bumblebees (Bombus sp.), the alfalfa leafcutter bee Megachile rotundata, and various other solitary species. Possible negative consequences of these introductions include: competition with native pollinators for floral resources; competition for nest sites; co-introduction of natural enemies, particularly pathogens that may infect native organisms; pollination of exotic weeds; and disruption of pollination of native plants. For most exotic bee species little or nothing is known of these possible effects. Research to date has focused mainly on A. mellifera, and has largely been concerned with detecting competition with native flower visitors. Considerable circumstantial evidence has accrued that competition does occur, but no experiment has clearly demonstrated long-term reductions in populations of native organisms. Most researchers agree that this probably reflects the difficulty of carrying out convincing studies of competition between such mobile organisms, rather than a genuine absence of competitive effects. Effects on seed set of exotic weeds are easier to demonstrate. Exotic bees often exhibit marked preferences for visiting flowers of exotic plants. For example, in Australia and New Zealand many weeds from Europe are now visited by European honeybees and bumblebees. Introduced bees are primary pollinators of a number of serious weeds. Negative impacts of exotic bees need to be carefully assessed before further introductions are carried out.
... Once established, the species can survive at higher population densities year after year, affecting the development and germination of other spe-cies (Callaway et al., 2003). Seed production, germination and dispersal are mayor determinants of its invasive potential (Barthell et al., 2001). Dimorphism of achenes is a reproductive characteristic; they are clear, with a small pappus in the center of the capitulum, dark and without pappus in the periphery (Lamberto et al., 1997). ...
Article
Full-text available
In Argentina, information on invasive plants is restricted to croplands, while no information is available on rangelands. Our objectives were to 1) identify and describe various characteristics of the most important non-native species that have become invasive and widespread in major rangeland territories of Argentina; 2) summarize the biological information about some naturalized, non-native species with potential to transform natural plant communities, and 3) discuss strategies for plant invasion management and biodiversity conservation in local rangeland ecosystems. The invasive species most represented at local, regional or state scale studies were Acroptilon repens, Centaurea solstitialis, Eleagnus angustifolia, Medicago minima, Chondrilla juncea, Dipsacus sativus and Sorghum halepense. Successful invasion and naturalization rates have been the result of several combined ecological traits: 1) capacity to produce allelophatic compounds, 2) deep rooting, 3) high module density, 4) rapid vegetative spread aboveground, 5) various traits that make species highly competitive, 6) tolerance to shading and water stress, 7) ability to take advantage of disturbances, 8) high seed production, germination and dispersal, and 9) high viability of residual seed banks. The determination of the abundance of invasive species at country scale, and their ecological and economical damage, are objectives of future research. This information will be a critical tool to make decisions on the need to control invasive species. Ecological studies providing understanding of the strategies which make an invader species a successful competitor are critical, and should be the first step to establish policies for control of invasive species and use of rangelands.
... It was found in a study by Hanley and Goulson (2003) that introduced bees favored foraging on introduced plant species and in some cases the bees depended entirely on these plants for sources of pollen and nectar. A study by Barthell et al. (2001) examined the relationship between honey bees and seed set in yellow star thistle (Ceutavrea solstitialis). Honey bees were the most frequent visitors to thistle and had a significant correlation between visit rates and the average number of viable seeds produced. ...
... Quality of pollination services may vary within the guild at different plot types (Brown et al., 2017). However, this may be difficult to measure, as invasive species may be most efficiently pollinated by (and provide more desirable nectar and pollen rewards for) only a subset of the species that forage at native flowering plants (Barthel et al., 2001;Morales & Aizen, 2006;Stout & Morales, 2009). ...
Conference Paper
Background/Question/Methods Disturbance events often alter community composition and structure. A goal of post-fire habitat rehabilitation often is to restore disturbed habitats and communities to conditions that approximate the pre-disturbance state. The relative success of these activities is often measured by vegetation composition and structure, without any measure of how the habitat is utilized by wildlife after a rehabilitation treatment. The sagebrush-steppe of the Intermountain West is a large ecosystem type that has been extensively altered by wildfires fueled by invasive annual grasses. We examined the influence of wildfire and post-fire seeding on insect communities within sagebrush-steppe habitats in southwest Idaho by comparing vegetation and insect assemblages among three condition classes: burned areas that were seeded after fire, burned areas that were not seeded, and nearby unburned areas that approximated conditions prior to burning. We determined vegetation composition and cover values and captured and identified >22,000 insects to family using flight and pitfall traps within 35 field plots in 2010 and 2011. Results/Conclusions Our preliminary results indicate that post-fire seeding changed the vegetation composition at burned plots by increasing the percent coverage of bunchgrass and forb species relative to that of burned-unseeded as well as unburned sagebrush-steppe habitats. Reseeding did not achieve the vegetation composition of unburned plots, especially because it lacked the pre-fire shrub component. Some insect families were strongly associated with specific vegetation components such as bunchgrasses or forbs. Despite relationships between vegetation composition and insects, there was not strong evidence that insect assemblages at burned-seeded plots were different from those at burned plots that were not seeded, though the vegetation at the seeded plots contained higher percent coverage of seeded bunchgrasses and native forbs. However, insect assemblages at plots that were burned, regardless of seeding, were different from those at plots that were not burned. Our preliminary results indicate that wildfire altered insect assemblages by removing insects that are sagebrush specialists. Additionally, post-fire seeding did not successfully restore the vegetation (especially sagebrush) or insect assemblages at our sites. However, insight into specific relationships between insect families and vegetation components from this study may inform future attempts to restore habitat for specific insect groups, such as pollinators.
... Additionally, honey bees more than other pollinators may seek out the highest per-capita nectar and pollen rewards provided by some introduced plants (Aizen et al., 2008). These mechanisms may explain why honey bees were a dominant visitor to introduced plants in previous studies (Aizen et al., 2008;Wood et al., 2018) and have been linked to the spread of an invasive plant species (Barthell, Randall, Thorp, & Wenner, 2001 (Salisbury et al., 2015). However, because honey bees and wild pollinators may differ in their use of introduced plant species, removing or maintaining introduced plants may benefit one group of pollinators more than the other. ...
Article
Full-text available
Introduced plants may be important foraging resources for honey bees and wild pollinators, but how often and why pollinators visit introduced plants across an entire plant community is not well understood. Understanding the importance of introduced plants for pollinators could help guide management of these plants and conservation of pollinator habitat. We assessed how floral abundance and pollinator preference influence pollinator visitation rate and diversity on 30 introduced versus 24 native plants in central New York. Honey bees visited introduced and native plants at similar rates regardless of floral abundance. In contrast, as floral abundance increased, wild pollinator visitation rate decreased more strongly for introduced plants than native plants. Introduced plants as a group and native plants as a group did not differ in bee diversity or preference, but honey bees and wild pollinators preferred different plant species. As a case study, we then focused on knapweed (Centaurea spp.), an introduced plant that was the most preferred plant by honey bees, and that beekeepers value as a late‐summer foraging resource. We compared the extent to which honey bees versus wild pollinators visited knapweed relative to coflowering plants, and we quantified knapweed pollen and nectar collection by honey bees across 22 New York apiaries. Honey bees visited knapweed more frequently than coflowering plants and at a similar rate as all wild pollinators combined. All apiaries contained knapweed pollen in nectar, 86% of apiaries contained knapweed pollen in bee bread, and knapweed was sometimes a main pollen or nectar source for honey bees in late summer. Our results suggest that because of diverging responses to floral abundance and preferences for different plants, honey bees and wild pollinators differ in their use of introduced plants. Depending on the plant and its abundance, removing an introduced plant may impact honey bees more than wild pollinators.
... This phenomenon, reported as invasive mutualism or alien mutualism, can strongly erode native pollination networks by modifying the strength of interactions and distributions of asymmetries to the advantage of 'super-generalist' alien species during invasion (Aizen, Morales & Morales, 2008). The invasive mutualism of non-native honeybees and the exotic yellow star thistle (Centaurea solstitialis), both introduced to the western USA in the 1800s, is a key factor that allowed the expansion of both aliens (Barthell et al., 2001). Similarly, human-driven colonization by milkweeds (Asclepias spp.) in non-native locations has aided the dramatic expansion of the highly mobile monarch butterfly across both the Pacific and Atlantic oceans in the 19th century (Vane-Wright, 1993;Pierce et al., 2014). ...
Article
Full-text available
Global changes are severely affecting pollinator insect communities worldwide, resulting in repeated patterns of species extirpations and extinctions. Whilst negative population trends within this functional group have understandably received much attention in recent decades, another facet of global changes has been overshadowed: species undergoing expansion. Here, we review the factors and traits that have allowed a fraction of the pollinating entomofauna to take advantage of global environmental change. Sufficient mobility, high resistance to acute heat stress, and inherent adaptation to warmer climates appear to be key traits that allow pollinators to persist and even expand in the face of climate change. An overall flexibility in dietary and nesting requirements is common in expanding species, although niche specialization can also drive expansion under specific contexts. The numerous consequences of wild and domesticated pollinator expansions, including competition for resources, pathogen spread, and hybridization with native wildlife, are also discussed. Overall, we show that the traits and factors involved in the success stories of expanding pollinators are mostly species specific and context dependent, rendering generalizations of ‘winning traits’ complicated. This work illustrates the increasing need to consider expansion and its numerous consequences as significant facets of global changes and encourages efforts to monitor the impacts of expanding insect pollinators, particularly exotic species, on natural ecosystems.
... To date, few studies have addressed the issue of the introduction of honeybee hives on the dynamics of native plant communities. It has been documented that introduced colonies enhance the visitation frequency of honeybees on invasive plant species, enhancing their reproduction (e.g. the effect on the purple loosestrife, Lythrum salicaria, in America: Barthell et al., 2001;Mal et al., 1992). By contrast, other studies have demonstrated that the introduction of honeybee hives can negatively affect the reproductive success of plants through increased pollen theft (Hargreaves et al., 2009), nectar robbing , physical damage to the flowers (Dohzono et al., 2008) or through the disruptive influence of honeybee workers on the patterns of pollen transfer among compatible plants that have otherwise evolved highly specialized interactions with native pollinators (Gross and Mackay, 1998;Vaughton, 1996;Watts et al., 2012). ...
... Quality of pollination services may vary within the guild at different plot types (Brown et al., 2017). However, this may be difficult to measure, as invasive species may be most efficiently pollinated by (and provide more desirable nectar and pollen rewards for) only a subset of the species that forage at native flowering plants (Barthel et al., 2001;Morales & Aizen, 2006;Stout & Morales, 2009). ...
... To date, few studies have addressed the issue of the introduction of honeybee hives on the dynamics of native plant communities. It has been documented that introduced colonies enhance the visitation frequency of honeybees on invasive plant species, enhancing their reproduction (e.g. the effect on the purple loosestrife, Lythrum salicaria, in America: Barthell et al., 2001;Mal et al., 1992). By contrast, other studies have demonstrated that the introduction of honeybee hives can negatively affect the reproductive success of plants through increased pollen theft (Hargreaves et al., 2009), nectar robbing , physical damage to the flowers (Dohzono et al., 2008) or through the disruptive influence of honeybee workers on the patterns of pollen transfer among compatible plants that have otherwise evolved highly specialized interactions with native pollinators (Gross and Mackay, 1998;Vaughton, 1996;Watts et al., 2012). ...
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Since the rise of agriculture, human populations have domesticated plant and animal species to fulfil their needs. With modern agriculture, a limited number of these species has been massively produced over large areas at high local densities. Like invasivespecies, these Massively Introduced Managed Species (MIMS) integrate local communities and can trigger cascading effects on the structure and functioning of ecosystems. Here, we focus on plant and insect MIMS in the context of plant–pollinator systems. Several crop species such as mass flowering crops (e.g. Brassica napus ) and domesticated pollinating insects (e.g. Apis mellifera , Bombus terrestris ) have been increasingly introduced worldwide and their impact on natural communities is addressed by an increasing number of scientific studies. First, we review the impacts of major insect and plant MIMS on natural communities by identifying how they affect other species through competition (direct and apparent competition) or facilitation (attraction, spillover). Second, we show how MIMS can alter the structure of plant–pollinator networks. We specifically analysed the position of A. mellifera from 63 published plant–pollinator webs to illustrate that MIMS can occupy a central position in the networks, leading to functional consequences. Finally, we present the features of MIMS in sensitive environments ranging from oceanic islands to protected areas, as a basis to discuss the impacts of MIMS in urban context and agrosystems. Through the case study of MIMS in plant–pollinator interactions, we thus provide here a first perspective of the role of MIMS in the functioning of ecosystems.
... Introduced bees are also known to reduce fitness of some native plant species (Roubik 1996;Gross and Mackay 1998). On the other hand, they may enhance pollination and, consequently, invasiveness of exotic weeds, as shown by Barthell et al. (2001) for Centaurea solstitialis L. in North America and Stout et al. (2002) for Lupinus arboreus Sims in Tasmania (Nadel et al. 1992). ...
Article
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A literature survey identified 403 primary research publications that investigated the ecological effects of invasive alien insects and/or the mechanisms underlying these effects. The majority of these studies were published in the last 8 years and nearly two-thirds were carried out in North America.These publications concerned 72 invasive insect species, of which two ant species, Solenopsis invicta and Linepithema humile, accounted for 18% and 14% of the studies, respectively.Most publications investigated effects on native biodiversity at population or community level. Genetic effects and, to a lesser extent, effects on ecosystem services and processes were rarely explored. We review the effects caused by different insect invaders according to: their ecosystem roles, i.e. herbivores, predators, parasites,parasitoids and pollinators; the level of biological organisation at which they occur; and the direct and indirect mechanisms underlying these effects. The best documented effects occur in invasive ants,Eurasian forest herbivores invasive in North America,and honeybees. Impacts may occur through simple trophic interactions such as herbivory, predation or parasitism. Alien species may also affect native species and communities through more complex mechanisms such as competition for resources,disease transmission, apparent competition, or pollination disruption, among others. Finally, some invasive insects, particularly forest herbivores and ants, are known to affect ecosystem processes through cascading effects. We identify biases and gaps in our knowledge of ecological effects of invasive insects and suggest further opportunities for research.
... Generalist pollinators like honey bees prefer plants with nectar rewards, reducing the quality of visits and seed set in native nonnectar producing plants (Traveset & Richardson 2014 p. 100) such as the rare bearpoppies (Portman et al. 2018b p. 603). This breakdown of mutualisms and pollination networks has been increasingly documented with the introduction of honey bees as they visit common, weedy plants and increase the seed set of invasive, non-native plants (Barthell et al. 2001(Barthell et al. p. 1874Aizen et al. 2014 pp. 324-325). ...
... This covered most studies focusing on mutualism as a feedback process. Feedback mechanisms involving other mutualistic relationships were excluded as we could only find two studies that examined interactions between invasive plants and invasive animals (Kourtev et al., 1998;Barthell et al., 2001). We also included studies where we felt feedbacks were implicated (based on the description, in cases where feedbacks were not explicitly mentioned; see Appendix S3). ...
Article
Aim A major challenge for invasion ecology is to identify high-impact invaders to guide prioritization of management interventions. We argue that species with the potential to cause regime shifts (altered states of ecosystem structure and function that are difficult or impossible to reverse) should be prioritized. These are species that modify ecosystems in ways that enhance their own persistence and suppress that of native species through reinforcing feedback processes. Methods Using both systems analysis and meta-analysis approaches, we synthesized changes to ecosystems caused by 173 invasive plant species. For the systems analysis, we examined published studies of impacts of invasive plants to determine which presented evidence consistent with a reinforcement of feedback processes. For the meta-analysis, we calculated the effect size ratio between standardized changes in recipient ecosystem and in the status of introduced species as an indication of a reinforcing feedback in particular species-environment combinations. The systems analysis approach allowed us to conceptualize regime shifts in invader-dominated landscapes and to estimate the likelihood of such changes occurring. The meta-analysis allowed us to quantitatively verify the conceptual model and the key invader-context feedbacks and to detect the strength and direction of feedbacks. Results Most reinforcing feedbacks involve impacts on soil-nutrient cycling by shrub and tree invaders in forests and herbaceous invaders in wetlands. Feed-backs resulting in regime shifts were most likely related to processes associated with seed banks, fire and nutrient cycling. Results were used to derive a key for identifying high-impact invaders. Main conclusions Identifying combinations of plant life-forms and ecosystems most likely to result in regime shifts is a robust approach for predicting high-impact invasions and therefore for prioritizing management interventions. The meta-analysis revealed the need for more quantitative studies, including manip-ulative experiments, on ecosystem feedbacks.
... However, the listed bee visitors are polylectic, or generalist, pollinators that collect pollen and nectar from a wide variety of plant species, reducing fidelity and efficacy. Non-native pollinators visit common, weedy plants and can increase the seed set of invasive plants that outcompete the honeycomb head (Barthell et al. 2001(Barthell et al. p. 1874Aizen et al. 2014 pp. 324-325). ...
Technical Report
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Petition to list the Gulf Coast solitary bee (Hesperapis oraria) as an endangered species under the Endangered Species Act
... Further, generalist pollinators like honey bees prefer plants with nectar rewards, reducing the quality of visits and seed set in native non-nectar producing plants (Traveset & Richardson 2014 p. 100) such as the rare bear-poppies (Portman et al. 2018b p. 603). This breakdown of mutualisms and pollination networks has been increasingly documented with the introduction of non-native pollinators as they visit common, weedy plants and increase the seed set of invasive, non-native plants (Barthell et al. 2001(Barthell et al. p. 1874Aizen et al. 2014 pp. 324-325). ...
Technical Report
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Filed petition to list the Mojave poppy bee (Perdita meconis) as an endangered species under the Endangered Species Act
... Few studies, however, have described successful 'integration' by also quantifying invasive plant reproductive success (e.g. fruit and seed production, seedling establishment) in invaded communities (Barthell et al., 2001;Stokes et al., 2006;Kaiser-Bunbury et al., 2011;Thompson & Knight, 2018;and see van Kleunen et al., 2008; Table 1). A third component of invasive 'integration' refers to the role that invasive plants play within native plant-pollinator communities. ...
Article
The disruption of mutualisms by invasive species has consequences for biodiversity loss and ecosystem function. Although invasive plant effects on the pollination of individual native species has been the subject of much study, their impacts on entire plant‐pollinator communities are less understood. Community‐level studies on plant invasion have mainly focused on two fronts: understanding the mechanisms that mediate their integration; and their effects on plant‐pollinator network structure. Here we briefly review current knowledge and propose a more unified framework for evaluating invasive species integration and their effects on plant‐pollinator communities. We further outline gaps in our understanding and propose ways to advance knowledge in this field. Specifically, modeling approaches have so far yielded important predictions regarding the outcome and drivers of invasive species effects on plant communities. However, experimental studies that test these predictions in the field are lacking. We further emphasize the need to understand the link between invasive plant effects on pollination network structure and their consequences for native plant population dynamics (population growth). Integrating demographic studies with those on pollination networks is thus key in order to achieve a more predictive understanding of pollinator‐mediated effects of invasive species on the persistence of native plant biodiversity.
... Non-native species are often one of the biggest threats to the local biodiversity, although they can have positive impacts on the new environment. In the case of bees, non-native species might compete with the native fauna for floral resources or nesting sites, transmit pathogens or parasites, affect the pollination of native plants, disrupt pollination networks, or pollinate invasive plant species (Goulson 2003, Barthell et al. 2001, Hall and Avila 2016, Mallinger et al. 2017. They might also pollinate non-native crops and become economically important, as in the case of Megachile rotundata (Fabricius, 1787), a solitary bee introduced to many parts of the world as a pollinator of alfalfa (Pitts-Singer and Cane 2011). ...
Article
Full-text available
We record for the first time for Colombia Megachile ( Pseudomegachile ) lanata (Fabricius, 1775), a bee species from Southeast Asia. This is the first record of an adventive bee species for the country besides Apis mellifera Linnaeus, 1758, the European honey bee. Megachile lanata appears to have arrived to the Caribbean coast of Colombia nearly half a century ago, reaching the Orinoquia region recently. We provide comments on diagnostic features to facilitate the recognition of this bee species and discuss its possible establishment in Colombia.
... Pyšek et al., 2008;Lowry et al., 2013;Frehse et al., 2016), the bias found for IM was mainly due to pollination studies. Indeed, pollination interactions provide strong evidence for IM because generalist species such as bees are frequently able to form new mutualisms with non-native plants that have a generalist reproductive biology (Barthell et al., 2001;Olesen et al., 2002;Beavon and Kelly, 2012). ...
Chapter
Positive interactions among species can be central for community structure and ecosystem functioning. Given the current scenario of species invasions worldwide, the question arises of how non-native species will interact in the new environment. Such reasoning has led to the invasional meltdown hypothesis (IM) which states that non-native species facilitate one another's invasion, increasing their likelihood of survival, ecological impact and possibly the magnitude of their impact. However, given the importance of antagonistic interactions in natural communities, it is not yet known to what extent these facilitative effects of non-native species occur. We used the hierarchy-of-hypotheses (HoH) approach to differentiate key aspects of IM and link empirical studies to specific sub-hypotheses of the overall hypothesis. Evidence related to IM was gathered by assessing citations of Simberloff and Von Holle (1999) who first defined it. Our HoH was categorized by the type of interaction among non-native species (e.g. facilitation, mutualism and multi-species interactions), ecological level of evidence and the outcome of the interaction for each non-native species (i.e. response variable measured in the study). We additionally looked for taxonomic and geographic variability. On the basis of the 208 relevant studies we found, the broad hypothesis and the majority of sub-hypotheses indicate that positive interactions among non-natives are happening more frequently than negative ones. Thus, IM is broadly supported by currently available studies. Evidence against IM relates to sub-hypotheses involving reciprocal interactions (e.g. competition between non-native species). We suggest that future research focuses on controlled experimental setups aiming at elucidating the
... Por ejemplo, la planta arroyuela (Lythrum salicaria, Lythraceae), nativa de Eurasia, es una de las especies exóticas invasoras más dañinas del mundo (Invasive Species Specialist Group, ISSG 2015), siendo uno de sus mayores polinizadores la abeja melífera (Mai et al. 1992). En Estados Unidos, la abeja melífera contribuye a la producción de semillas viables, lo que favorecería el establecimiento y propagación de esta especie (Barthell et al. 2001). ...
Article
The honey bee (Apis mellifera L.) has been spread all over the world by humans and is now the most widespread bee invasive species. In spite of being considered a beneficial species, there is a controversy around its impact on natural habitats caused by its high densities. Here we review the most important effects and mechanisms attributed to an increase in honey bee abundance on plants and wild bees. We found that the impacts can be negative and positive as well, playing an important role the ecological context (resource availability, wild pollinator community, etc.) and the honey bee density. Effects occur at the individual, population, and community level, affecting plant-pollinator networks, while the consequences for ecosystem functioning and crop pollination are still uncertain. It has been recently shown that the honey bee can also act as a selective force affecting plant evolution in a relative short time. The parasite and pathogen transmission from honey bees to wild pollinators has become a relevant issue in the last years. Although honey bees can benefit wild plants pollination, because impacts in other bees are primary negative, we should be careful with hives introduction at natural sites. Especially until we can determine the parasites and pathogen transmission consequences.
... One potential driver of this pattern is the native status of the plant. Differences in the species composition of bees visiting native and introduced plant species has been hypothesized for several reasons, including "invasive mutualisms" (Barthell et al. 2001) and the co-evolution of oligolectic bees and their plant hosts (Armbruster 2017). While some studies have found evidence consistent with these theories (e.g., McIver and Erickson 2012, Morandin and Kremen 2013), we found no evidence that the native status of a plant species influenced its visiting bee species composition. ...
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Native bees are declining worldwide, but conserving or restoring their habitat requires a better understanding of bee-flower associations. High quality bee habitat includes flowers that provide pollen and nectar preferred by bees. However, little data exist about which plants are commonly used by bees in the Pacific Northwest, or whether bees prefer certain plant characteristics over others. We examined bee and plant communities in an Oregon riparian ecosystem. Our purpose was to describe bee-plant associations, determine which plants are most frequently visited by bees, identify plants that may be preferred by bees, and examine how a plant's native status, flower color, and floral morphology affect the types of bees visiting it. We found that many blooming plants received a diverse set of bee visitors, but some plants had a higher number and species richness of visiting bees than others. No plant species seemed limited to visitation by a small set of specialist bees. The number and type of visiting bees were not influenced by the plant's native status. However, flower morphology (but not color) significantly affected types of bees visiting plants. Bilaterally symmetrical and medium tubular flowers, with nectar and pollen typically more difficult to reach, were associated with larger bees with longer tongues, while smaller, easily accessible flowers attracted smaller bees with shorter tongues. Our results suggest that certain plants are particularly useful for supporting abundant and diverse bee communities, and increasing diversity in the morphology of blooming plants is a key factor to consider when restoring riparian areas for bee pollinators.
... The Varroa mite (Varroa destructor), which jumped from Apis cerana to managed colonies of A. mellifera (Rosenkranz et al., 2010) leading to a dramatic decline of A. mellifera colonies worldwide, is probably a good example in this context. Apart from that, managed honey bees could also contribute to proliferation of weeds because the species was implicated in pollination of some weed species (Collevatti et al., 1998;Barthell et al., 2001). ...
... These ecosystems lie in a global hotspot of bee diversity (Moldenke and Neff 1974;Michener 1979) and harbor a rich but under-studied pollinator fauna that includes several hundred species of primarily solitary bees (Hung et al. 2015, Hung et al. in revision). Apis mellifera is abundant in this region, as it is in other parts of California (Barthell et al. 2001;Alarcón et al. 2008;Bruckman and Campbell 2014), where it has been present since the 1850s (Watkins 1969). Both European and Africanized lineages are common in San Diego County, with the majority of individuals belonging to feral rather than managed colonies (Kono and Kohn 2015). ...
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Pollination services are compromised by habitat destruction, land-use intensification, pesticides, and introduced species. How pollination services respond to such stressors depends on the capacity of pollinator assemblages to function in the face of environmental disruption. Here, we quantify how pollination services provided to a native plant change upon removal of the non-native, western honey bee (Apis mellifera)—a numerically dominant floral visitor in the native bee-rich ecosystems of southern California. We focus on services provided to clustered tarweed (Deinandra fasciculata), a native, annual forb that benefits from outcross pollination. Across five different study sites in coastal San Diego County, tarweed flowers attracted 70 insect taxa, approximately half of which were native bees, but non-native honey bees were always the most abundant floral visitor at each site. To test the ability of the native insect fauna to provide pollination services, we performed Apis removals within experimental 0.25 m² plots containing approximately 20 tarweed plants and compared visitation and seed set between plants in removal and paired control plots (n = 16 pairs). Even though 92% of observed floral visits to control plots were from honey bees, Apis removal reduced seed production by only 14% relative to plants in control plots. These results indicate that native insect assemblages can contribute important pollination services even in ecosystems numerically dominated by introduced pollinators.
... For example, pollination dependent exotic plants might have advantage in urban areas because of increased pollinator abundance and vice versa (Parker 1997). Exotic pollinators may also prefer exotic plants used in landscaping (MacIvor et al. 2015) or occurring spontaneously in cities (Barthell et al. 2001), increasing their foraging opportunities and competitive edge on native pollinators. 4. Altered environmental conditions Plant species diversity has decreased with urbanization in Harbin, China, but there has been an increase in tropical species as urban temperatures have increased (Chen et al. 2014). ...
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Urban environments are often seen as unique or degraded habitats that both present hardships for some sensitive species and provide opportunities to others. Non-indigenous species (NIS) are commonly referenced in the latter group, and are comprised of species that can tolerate the unique conditions or capitalize on the opportunities found in urban environments. Moreover, these urban beneficiaries may be those that normally cannot overcome competitive interactions in intact native communities, but find opportunity to flourish in urban habitats. We ask the question: do NIS benefit from urbanization? We answer this question using three strategies. First, we explore the problem conceptually, using community assembly theory. Second, we perform a broad literature review. Finally, we analyze studies with sufficient information using a meta-analysis. We show that the available evidence supports the proposition that NIS benefit from urbanization, with NIS obtaining higher abundances and greater diversity in more urbanized habitats. There were only 43 studies that measured NIS abundance and diversity while adequately quantifying the degree of urbanization surrounding plots, and effect sizes (measured by Hedge’s D) reveal that NIS obtain higher abundances in more urbanized habitats, and especially for invertebrates. Despite the intense interest in NIS dynamics and impacts, we note a general dearth of robust studies that adequately quantify ‘urbanization’, and we end with a general call for more detailed research.
Technical Report
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Santa Cruz Island (SCI) is the largest, most topographically diverse, most speciose, least disturbed, and most intensively researched of the eight California Channel Islands. However, this natural laboratory has itself changed significantly in the recent past, and determining where limited research and management funds should be allocated is a significant issue that will determine the course of research and conservation on all of the Channel Islands. Santa Cruz Island has undergone a significant transformation in the past two decades. Large introduced herbivores such as cattle, sheep and pigs that roamed the island for over a century have been completely removed. As such, the island is in a transition phase from one where vegetation communities and their associated fauna are controlled and limited by ungulate impacts to one where the vegetation is largely controlled by bottom- up processes such as edaphic controls, weather events, and interspecific competition. The fauna is likewise adapting to the removal of a significant terrestrial predator in feral pigs. The response of amphibians, reptiles, ground-nesting birds, and small mammals to the removal of pigs is likely to be significant, and in many cases surprising. While many decades of research have been conducted, the island is now significantly changed, and new questions and management issues will need to be addressed. A wide diversity of literature has been produced from studies of the island over the past fifty years, including island biogeography (Diamond 1971, Jones and Diamond 1976), vegetation community evolution (Axelrod 1965), and even the biocontrol of native species (Goeden et al. 1967, Goeden and Ricker 1980). Klinger and Van Vuren (2000) reviewed and analyzed the articles published in the four symposia on California Islands that had been held. They provided a series of recommendations including 1) place research and management projects in an appropriate theoretical framework; 2) link genetic, demographic, and evolutionary studies across all of the islands; 3) continue basic life history studies of both plant and animal species; and 4) conduct ecosystem studies that integrate community and single species studies at multiple scales. The need for the fourth recommendation was recently demonstrated by the finding that restoration methods suitable at small scales had different results at larger scales (Ogden and Rejmanek 2005). In our analysis and recommendations below, we are mindful of the importance of long-term research, and of the value of studies that provide datasets that have lasting utility. Therefore, while it is important to recognize the latest conceptual paradigms in a given field, we feel that scarce conservation-oriented funding for island projects are best spent answering specific questions that have practical conservation and management utility. We also feel that management dollars are best spent conducting long-term monitoring of species and communities, rather than short-term small-scale studies. One method for extending out the time frame of a study is by using historical papers and other data sets as comparisons for recently collected data. For instance, Yeaton (1974) provides abundance estimates for bird species in pine forest and chaparral habitats that could be compared with more recent values, and Bjorndalen (1978) provides vegetation community data that could be compared to more recent, post-ungulate samples. A significant finding of this research effort was that a substantial amount of data exists in various institutions, but has yet to be analyzed due to lack of funding. For instance, many thousands of Channel Island plant specimens exist in some collections that have yet to be catalogued due to insufficient funding and staff time. Likewise, entomological collections at several institutions contain untold numbers of Santa Cruz Island specimens, yet these institutions have not electronically databased their collections. These collections are organized systematically, and retrieving the data for a given geographic area such as Santa Cruz Island entails examining all the specimens for each systematic group of organisms that may occur on the island. Providing financial support for efforts to make these data available to researchers—data that have already been collected during past field work—would provide a substantial contribution to our understanding of the ecology of the island, at relatively low cost.
Article
The objective of this work is to evaluate plant species origin importance for biological invasion consequences, through the analysis of the influence of native and exotic dominant plant species for ecosystem functioning. Five pairs of native dominant species (Agrostis stolonifera, Rubus caesius, Populus nigra, Urtica dioica et Salix alba) and exotic invasive species (Paspalum distichum, Fallopia japonica, Buddleja davidii, Impatiens glandulifera et Acer negundo) were compared for litter breakdown process and primary production. A more detailed analysis evaluates the consequences of A. negundo invasion for riparian forests. Our results indicate that the lack of coevolution between exotic species and the organisms of recipient areas has little implications for ecosystem functioning, even if exotic invasive species can be more efficient in some ecological processes. No general pattern can be drawn for functional consequences of native dominant species replacement by exotic invasive ones.
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A biodiversity conservation strategy for Catalina Island, California
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Recent global declines of pollinator populations have highlighted the importance of pollinators, which are undervalued despite essential contributions to ecosystem services. To identify critical knowledge gaps about pollinators, we describe the state of knowledge about responses of pollinators and their foraging and nesting resources to historical natural disturbances and new stressors in Great Plains grasslands and riparian ecosystems. In addition, we also provide information about pollinator management and research needs to guide effort s to sustain pollinators and by extension, flowering vegetation, and other ecosystem services of grasslands. Although pollinator responses varied, pollinator specialists of disturbance-sensitive plants tended to decline in response to disturbance. Management with grazing and fire overall may benefit pollinators of grasslands, depending on many factors; however, we recommend habitat and population monitoring to assess outcomes of these disturbances on small, isolated pollinator populations. The influences and interactions of drought and increasingly variable weather patterns, pesticides, and domesticated bees on pollinators are complex and understudied. Nonetheless, habitat management and restoration can reduce effects of stressors and augment floral and nesting resources for pollinators. Research needs include expanding information about 1) the distribution, abundance, trends, and intrare-gional variability of most pollinator species; 2) floral and nesting resources critical to support pollinators; 3) implications of different rangeland management approaches; 4) effects of missing and reestablished resources in altered and restored vegetation; and 5) disentangling the relative influence of interacting disturbances and stressors on pollinator declines. Despite limited research in the Great Plains on many of these topics, consideration of pollinator populations and their habitat needs in management plans is critical now to reduce future pollinator declines and promote recovery. Published by Elsevier Inc. on behalf of The Society for Range Management. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
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Plant invasions are a threat to biodiversity, as changes in plant community characteristics resulting from invasion can affect other organisms, such as arthropods. The effects of invasions may interact with other disturbances and alter the efficacy of restoration strategies. We sought to understand the effects of Old World bluestem grasses (OWBs, Bothriochloa, Dichanthium spp.), which have become dominant in prairie ecosystems and reduce the quality of habitat for wildlife. In an attempt to reduce OWBs, we applied treatments to modify soil conditions to a state which favors native plants and arthropods. We conducted our research in 2011, which coincided with extreme drought and provided us with the opportunity to test the efficacy of soil modification under varying conditions. First, we explored the effects of plant invasion and drought on native plant and arthropod communities by comparing characteristics of plots dominated by native plants to plots dominated by OWBs. As drought subsided, we observed a shift from an arthropod community driven by detritivores to one driven by herbivores associated with plant invasion. Arthropod communities were dominated by invasive species. Second, we explored the efficacy of soil modification and seeding treatments to reduce OWBs in the presence and absence of drought based on a field experiment and a more controlled microcosm experiment. Although changes in soil chemistry from soil treatments were short-lived, we observed reduced dominance of OWBs in areas treated with soil disturbance and seeding in both experiments and we observed no differences between experiments when we alleviated the effects of drought. Finally, we examined the concomitant effects of our soil modification and seeding treatments on arthropod communities in the field experiment. We observed fewer arthropods in treated plots than undisturbed OWB monocultures, but soil and seeding treatments increased arthropod diversity and reduced dominance of invasive arthropods relative to undisturbed OWB monocultures. Based on our findings, simple soil disturbance in combination with seeding of native plants may increase diversity of native plants and arthropods where invasive plants are dominant in the short term, but monitoring over longer time frames may reveal additional benefits from soil modification.
Conference Paper
It is common in nature for an animal of the same or different species to work together if the two share a common goal. Most commonly, working together can help ensure the survival of both animals. Applying to drone technology, it would be advantageous to give drones the capability to assist other drones, combining in swarming formations. It would increase flight efficiency and allow for a wider range of missions. Drones that could assist one another mid-flight, or if one drone suffered a failure, another could recover or help prevent damage would be beneficial. The purpose of designing adaptive formation to fixed-wing drones is to allow them to take advantage of phenomena that occur in nature. In this paper, the drag reduction of echelon-shaped swarming drones while transitioning to attached drones is investigated in order to achieve a specific task.
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In experimental plots, E. asimillima showed: increased adult emigration, increased brood rearing success, and/or relatively later colony founding, compared to controls. The possibility of resource competition with Apis mellifera causing the observed changes is discussed. -Authors
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Experimental studies of food competition were performed in lowland forest of French Guiana by controlled introduction and removal of a small number of African honey bee colonies. Trends in brood production and food storage by observation colonies of native social bees, Melipona favosa and M. fulva, were described with linear stochastic statistical models. During a 1-mo introduction of honey bees in the wet season, when floral resources were at low abundance, African Apis had no significant effect on native bee colonies. All colonies foraged during experiments, yet no competition was recorded. Since the 3 species are diet generalists and share many of the same resources, competition at flowers was not disproved, although any cumulative effects were negligible.-from Author
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The evolutionary ecology of plant defenses against herbivores is generally understood ill a cost-benefit framework. We studied the ecological consequences of the spines of Ccn taurea solstitialis L. (yellow star thistle) which are typically thought of as defenses against mammalian herbivores. By experimentally removing spines, which consist of dead tissue, we show that "nectar robbing" lepidopteran all visitors are deterred by naturally occurring spines (a benefit). Unlike the lepidoptera, legitimate pollinators (bees and flies) were not more likely to visit spineless flower heads, although bees and flies did spend 20% more time per visit on spineless flower heads. One potential cost of having spines is the lower time per visit of the bees. The net result of spine removal from flower heads was a 22% reduction in the percentage of Riled seeds of spineless flower heads compared to, spined controls. Thus, spines of yellow star thistle mall not only deter mammalian herbivory, but also deter lepidoptera which are illegitimate flower visitors. Although the spines may be energetically costly (not measured in this experiment), or costly because of other ecological trade-offs, it appears that these costs are outweighed by the benefits of spines as a plant defense.
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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.
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The Africanized honey bee, a hybrid of European and African honey bees, is thought to displace native pollinators. After experimental introduction of Africanized honey bee hives near flowers, stingless bees became less abundant or harvested-less resource as visitation by Africanized honey bees increased. Shifts in resource use caused by colonizing Africanized honey bees may lead to population decline of Neotropical pollinators.
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Rangeland infestations of yellow starthistle, a facultative winter annual from the Mediterranean region, increased >60-fold in SE Washington between 1954-1964. Some 92% of achenes fell within 0.6 m and 48% fell within 0.3 m of the source. A combination of gusty wind and dry conditions maximized achene dispersal. Total achene dispersal was highly correlated with the daily maximum saturation deficit multiplied by the maximum wind gust per day. Predation by seed-eating birds reduced achene numbers and may have increased dispersal distances. Although wind normally does not move achenes long distances, it serves to fill intervening space between occasional plants and increase populations by persistently advancing the perimeter. -from Author
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Cirsium vinaceum (Asteraceae), an endemic thistle of the Sacramento Mountains, New Mexico, is federally listed as threatened. It occurs in spring and streamside habitats; individual patches of plants vary widely in size and in distance from one another. We used floating seed traps to determine if seed movement by water contributes to gene flow and migration between patches. Seeds move in substantial numbers for considerable distances along these streams, indicating that a biological definition of population for this species must encompass more than single patches. We discuss implications for management, including the potential for restoration or recovery via aquatic dispersal.
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Recent concern that honey bees may threaten natural areas by increasing weed abundances through increased pollination was investigated by reviewing the literature to determine which weed taxa surveyed from New Zealand Protected Natural Areas (PNAs) are visited by honey bees. The contribution made by honey bees to weed reproduction was assessed by checking reproductive strategies and pollination mechanisms of a subset of problem weeds. A substantial proportion of surveyed weeds in PNAs are probably visited by honey bees (43%) including half of the problem weeds. However, reproduction of the majority of problem weeds is characterised by plastic reproductive mechanisms and/or simple pollination mechanisms where honey bee influence is low or unimportant. Although honey bees may be important pollinators of some weeds, they probably do not contribute substantially to weed problems.
Article
Temporal and spatial characteristics of a community of cavity nesting megachilid bee species and their introduced competitors were examined at a site in the Central Valley of California. Two of the introduced bee species, Megachile apicalis Spinola and Megachile rotundata (F.), were frequent nest site occupants and accounted for 19.6 and 3.4% of all artificial nesting cavities (trap-nests) monitored during the 1st and 2nd yr of this study, respectively. These species were most active before and after the peak in native bee nesting activity and tended to occupy xeric habitats, despite significantly higher larval mortality associated with such environments. The ability to occupy a wide array of habitats may account for the invasion success of M. apicalis in California. Another invader, the European earwig, Forficula auricularia L., was a frequent occupant of nesting cavities in mesic habitats, accounting for 59 and 85% occupancy of trap-nests during the 1st and 2nd yr of the study, respectively. Exclusion experiments indicate earwig densities were sufficient to displace female bees at nest sites with 113 as much nesting activity occurring in sampling units that allowed entry by earwigs as those made inaccessible to them with sticky barriers. In comparison, all native species (including bees and wasps) never accounted for >25% of all occupied nesting cavities of either monitoring period of the study.
Article
Yellow starthistle (Centaurea solstitialis Linnaeus) (Compositae), native to Eurasia and the Mediterranean Basin, is a spiny and poisonous, naturalized, invasive weed of grasslands and other environments in the western USA. Chaetorellia australis Hering is a trivoltine natural enemy of yellow starthistle whose larvae feed on developing seeds within capitula. Following host-specificity studies in Greece and the USA, C. australis was first introduced from Greece into the USA in 1988 for the biological control of yellow starthistle. Field samples of yellow starthistle capitula revealed that 10.3% (four years after initial release) and 18.0% (three years after initial release) of capitula at Colfax, Washington, and Merlin, Oregon, respectively, were infested by ≥ 1 C. australis (mature larvae or empty puparia). Both sites also contained naturalized, weedy populations of, Centaurea cyanus, a second host-plant of Chaetorellia australis. The fly was also recovered from Centaurea cyanus capitula two years after its release at Kendrick, Idaho. The potential importance of the presence of C. cyanus for Chaetorellia australis and biological control of yellow starthistle is discussed. At the Colfax site, all infested yellow starthistle capitula contained 1 C. australis, while at the Merlin site 28.8% of infested capitula contained > 1 C. australis, with a mean of 1.36 C. australis per infested capitulum. A preliminary seed destruction impact study at the Merlin site showed that there was a 83.4% reduction in seeds per capitulum infested by ≥ 1 C. australis, and the presence of > 1 C. australis resulted in a 95.4% reduction in seeds per infested capitulum.
Article
The Bonin (Ogasawara) Islands are oceanic islands located in the northwest Pacific, and have ten native (nine endemic) bee species, all of which are nonsocial. The European honeybee (Apis mellifera), which was introduced to the islands for apiculture in the 1880s, became naturalized in a few islands shortly after introduction. To detect the impact of the honeybees upon native bee diversity, we analyzed pollen harvest by honeybees and surveyed the relative abundance of honeybees and native bees on flowers on several islands. Both hived and feral honeybee colonies were active throughout the year, harvesting pollen of both native and alien flowers and from both entomophilous and anemophilous flowers. Honeybees strongly depended on the alien plants, especially during winter to spring when native melittophilous flowers were rare. From June to November, honeybees exhaustively utilized native flowers, which had originally been utilized and pollinated by native bees. On Chichi and Haha Islands, where human disturbance of forests has been severe, both native and alien flowers were dominated by honeybees, and native bees were rare or extinct even in well-conserved forests. In contrast, on Ani Island and Haha's satellite islands where primary forests were well conserved and honeybees were still uncommon or absent, native bees remained dominant. These results suggest that competition for nectar and pollen of the native flowers between honeybees and native bees favors honeybees on the disturbed islands, which are thoroughly invaded by alien nectariferous, sometimes aggressive, weedy plants.
Article
Seed dispersal is important both to plant fitness and to plant population structure. We suggest that the tail of the seed dispersal curve is at least as important biologically as the modal portion of the curve, and we present a relatively simple, four-parameter model, based on diffusion principles, for the tail of the seed distribution. This model includes two types of qualitative behavior: algebraic tails (which tend to be longer and have greater reach) and exponential tails (which are shorter and have less reach). We have selected 68 data sets from the literature, each giving a seed shadow that could be categorized statistically as (1) exponential, (2) algebraic, (3) neither, or (4) both models fit adequately. Algebraic shapes for seed-shadow tails were common in this sample, and tail behavior was not generally specific to a particular dispersal mode. This result may suggest that algebraic tails are generally favored by selection and can be achieved by several means, but limitations of existing data sets and of statistical methodology preclude final judgement. Smaller complete samples of seed distances would provide a better basis for the analysis of tails than do the present form of data sets (consisting of counts of seeds in discrete distance categories).
Article
Populations of exotic earthworms responded positively to the presence of the nitrogen-fixing tree, Myrica faya, which is currently invading early succesional habitats in Hawaii Volcanoes National Park. Earthworm biomass in one high-density stand of Myrica was over three times the levels in nearby submontane forest and rainforest. Comparisons of earthworm populations under pairs of Myrica and the dominant native tree, Metrosideros polymorpha, showed biomass levels to be elevated from over two- to almost eightfold under the exotic tree. The increased rate of burial of nitrogenrich litter by earthworms can alter the rate of nitrogen accretion and cycling in these ecosystems.
Article
Study of interactions between pairs or larger groups of nonindigenous species has been subordinated in the literature to study of interactions between nonindigenous and native species. To the extent that interactions among introduced species are depicted at all, the emphasis has been on negative interactions, primarily resource competition and interference. However, a literature search reveals that introduced species frequently interact with one another and that facilitative interactions are at least as common as detrimental ones. The population significance of these interactions has rarely been determined, but a great variety of types of direct and indirect interactions among individuals of different nonindigenous species is observed, and many are plausibly believed to have consequences at the population level. In particular, mutualisms between plants and the animals that disperse and/or pollinate them and modification of habitat by both animals and plants seem common and often important in facilitating invasions. There is little evidence that interference among introduced species at levels currently observed significantly impedes further invasions, and synergistic interactions among invaders may well lead to accelerated impacts on native ecosystems – an invasional meltdown process.
Article
Along the Pacific coast of North America, four introduced cordgrass species (Spartina alterniflora, S. anglica, S. patens and S. densiflora) have thus far invaded five isolated estuaries. Dense growth of introduced Spartina spp. reduces open mud feeding habitats of shorebirds, while in the upper intertidal, introduced Spartina spp. compete with native salt marsh vegetation. Prediction of Spartina invasions is facilitated by the remarkable restriction of these species to distinct estuarine habitats which generally lack interspecific competitors and herbivores. We used physical characteristics to identify 31 specific sites along the US Pacific coast that are vulnerable to future Spartina invasions and then used species characteristics, like native latitudinal range and past invasion success, to predict which Spartina species will be likely to invade these sites in the future. All 31 sites were predicted to be vulnerable to S. alterniflora, while the other invasive Spartina spp. may be restricted to a subset of the vulnerable sites. At a finer scale, within a vulnerable site, the mean tidal range can be used to predict the extent of spatial spread of a Spartina sp. after colonization. These prediction techniques might be used to identify and prioritize sites for protection against future invasions. We suggest that a cost-effective way to prevent the transformation of unique North American Pacific mudflat and saltmarsh communities into introduced Spartina-dominated marshes is to survey the vulnerable sites frequently and eliminate introduced Spartina spp. propagules before they spread.
Article
Bromus tectorum L., the most ubiquitous alien in steppe vegetation in the intermountain West of North America, entered British Columbia, Washington, and Utah ca. 1889–1894. By ca. 1928 the grass had reached its present distribution occupying much of the perennial grasslands in Washington, Idaho, Oregon, Nevada, Utah and British Columbia as native grasses dwindled with overgrazing and cultivation. In the process this cleistogamous winter annual may have competitively displaced both native colonizers (including cleistogamous us annual grasses) as well as the dominants of climax stands. The spread of B. tectorum demonstrates the degree of success an alien may achieve when preadaption, habitat alteration simultaneous with entry, unwitting conformation of agricultural practices to the plant's ecology and apparent susceptibility of the native flora to invasion, are all in phase.
Article
Myrica faya, an introduced actinorhizal nitrogen fixer, in invading young volcanic sites in Hawaii Volcanoes National Park. We examined the population biology of the invader and ecosystem-level consequences of its invasion in open-canopied forests resulting from volcanic cinder-fall. Although Myrica faya is nominally dioecious, both males and females produce large amounts of fruit that are utilized by a number of exotic and native birds, particularly the exotic Zosterops japonica. In areas of active colonization, Myrica seed rain under perch trees of the dominant native Metrosideros polymorpha ranged from 6 to 60 seeds m⁻² yr⁻¹; no seeds were captured in the open. Planted seeds of Myrica also germinated an established better under isolated individuals of Metrosideros than in the open. Diameter growth of Myrica is > 15-fold greater than that of Metrosideros, and the Myrica population is increasing rapidly. Rates of nitrogen fixation were measured using the acetylene reduction assay calibrated with ¹⁵N. Myrica nodules reduced acetylene at between 5 and 20 μmol g⁻¹ h⁻¹, a rate that extrapolated to nitrogen fixation of 18 kg ha⁻¹ in a densely colonized site. By comparison, all native sources of nitrogen fixation summed to 0.2 kg ha⁻¹ yr⁻¹, and precipitation added < 4 kg ha⁻¹ yr⁻¹. Measurements of litter decomposition and nitrogen release, soil nitrogen mineralization, and plant growth in bioassays all demonstrated that nitrogen fixed by Myrica becomes available to other organisms as well. We conclude that biological invasion by Myrica faya alters ecosystem-level properties in this young volcanic area; at least in this case, the demography and physiology of one species controls characteristics of a whole ecosystem.
Article
It is widely believed that mutualisms, interspecific interactions that benefit both species, have been grossly neglected relative to their true importance in nature. I have reviewed the recent primary literature in order to assess quantitatively the frequency of studies of mutualism, the types of questions they address, and their general scientific approach. All articles appearing from 1986 to 1990 in nine major journals that publish ecological and evolutionary research were examined. It is clear that mutualism research is not in fact rare. Studies of interspecific interactions made up about 22% of the over 4500 articles published during this period; of these, about one-quarter investigated some form of mutualism. Over 90% of them investigated plant-animal interactions, primarily pollination (52 %) and seed dispersal (31 %), a bias probably related in part to the particular journals examined. The diversity of questions addressed in these articles was surprisingly low. The majority (63 %) focused simply on identifying the mutualists of some species of interest. Furthermore, almost all studies were unilateral, that is, they focused on only one of the interacting species, plants being studied much more frequently than their animal partners. Mutualism studies do not appear to have focused on mutualism as a form of interaction in the same way as studies of competition and predation. Rather, researchers have treated mutualism primarily as a life history attribute of one of the two partners. Consequently, although an impressive amount of information has accumulated about these interactions, we are still far from achieving an overall picture that transcends the boundaries of particular taxa or combinations of taxa. Three other obstacles have prevented data on mutualisms from being brought together: the historical isolation of studies of different kinds of mutualism, a nearly total disconnection between mutualism theories and empirical studies, and the unilateral approach almost always used to study these bilateral interactions. I identify eight research questions whose answers have the potential to reveal broad-based generalizations about the evolution and ecology of mutualism.