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Habitat use by large and small herbivores in a fluctuating Mediterranean ecosystem: Implications of seasonal changes
Abstract
Different-sized herbivores differ in several aspects from their relationship with food to predation risk whilst foraging. Consequently, the spatial distribution of food, food quality and refuge availability can determine differences in habitat selection by large and small herbivores. In regions under Mediterranean climate, food and water availability are subjected to spatial and temporal variations and habitat selection needs to be interpreted within a seasonal context. To assess the influence of seasonality on foraging habitat use by large and small herbivores, we developed a priori models taking into account direct factors influencing habitat use (food, refuge and water), and indirect soil factors (moisture, fertility and stoniness). Models were tested for free-ranging sheep and wild rabbits in spring, summer and winter using structural equation modelling. The importance of direct factors varied with body size and season. Sheep were highly influenced by food abundance throughout the seasons. Rabbits were mainly influenced by refuge availability in spring and winter, when food was not a limiting resource. However, in summer, the relevance of refuge disappeared and food quality became an important factor. Seasonality can modify the relative importance of known predictors for habitat use by large and small herbivores inhabiting Mediterranean environments.
... Several factors may influence the occurrence of facilitation by the creation of grazing lawns and its balance with competition in mammalian grazer assemblages. There might be a temporal (seasonal) trade-off between facilitation and competition , RUEDA et al., 2008 as forage maturation especially occurs during the growing season (FRYXELL, 1991). Whether facilitation does occur or not also depends on the density of the large grazers and of the facilitated grazers . ...
... Second, facilitation may show strong seasonality, e.g. only occur during the plant growing seasons(FRYXELL, 1991; or when food resources become limited(RUEDA et al., 2008). Third, feeding facilitation can be expected to be function of the difference in body mass among coexisting herbivores (PRINS & OLFF, 1998); i.e. when differences are either very small or very large, smaller species may not (or to a lesser extent) benefit from the presence of larger ones. ...
This thesis focuses on the positive interaction ‘feeding facilitation’ which is predicted to occur in assemblages of large and small(er) herbivore species. The main hypothesis of the research is that introduced large herbivores facilitate rabbits (medium-sized herbivores) by modification of the vegetation. This modification involves creating short swards, creating denser (more productive) swards, creating swards that have a high food quality for rabbits and influencing vegetation composition. By conducting field observation, semi-controlled field experiments up to entirely controlled feeding experiments, we tried to test several aspects of the main hypothesis. From our results, we conclude that the main hypothesis could not be affirmed, although some causal mechanisms of feeding facilitation have been affirmed. We suggest that feeding facilitation is not necessarily absent, but is hard to detect or is not present under particular conditions. Experimental research is needed for further unravelling causal mechanisms about feeding facilitation and alternative approaches, while field observations remain necessary to gain insight into other variables (e.g. habitat productivity, predators, food accessibility, seasonality) that may shift the balance between the occurrence and absence of feeding facilitation.
... On the Iberian Peninsula, the rabbit has a wide distribution and it has been observed in diverse ecosystems, from Mediterranean scrublands to dehesa agroecosystems, mountainous areas, and coastal sand dunes (e.g. Rueda et al., 2008aRueda et al., , 2008bBarrio et al., 2009;Dellafiore et al., 2009;Tapia et al., 2010Tapia et al., , 2014. The coastal sand dune ecosystem represents 40% of the 7,880 km of the Iberian coast (Ley et al., 2011) and rabbit populations have been observed in almost all such sand dune areas (Villafuerte, 2002), but they have been poorly studied to date. ...
... Other authors found seasonal differences in habitat use by rabbits in grassland environments (Rueda García, 2006;Rueda et al., 2008aRueda et al., , 2008b. In our study area, although we did not test for differences in habitat use between seasons, we found no change in habitat use in each season. ...
We studied habitat use by the wild European rabbit (Oryctolagus cuniculus) in a coastal sand dune system in the south western Iberian peninsula. Our goals were to define the use of this habitat by rabbits in relation to food and shelter availability between seasons. Rabbit density, food availability and refuge abundance were analysed using multiple regression analyses. We found that, independently of season, habitat selection was principally related to cover by the woody shrub Retama monosperma which rabbits use both as a food resource and as protection against predators. Although it is an invasive native plant, the benefits that R. monosperma provides to the wild rabbit population should be taken into account when deciding wild rabbit management strategies.
... Likewise, vegetative growth in the OBHF also likely provided suffi cient cover and forage to be used in proportion to its availability. The importance of habitat selection in rabbits is most often related to cover and avoiding predation (Iason et al. 2002), but the importance of cover for rabbits may be seasonal (Rueda et al. 2008). Rabbits will make use of areas with more vegetation, especially during the growth season, when vegetation provides for both forage and cover (Rueda et al. 2008). ...
... The importance of habitat selection in rabbits is most often related to cover and avoiding predation (Iason et al. 2002), but the importance of cover for rabbits may be seasonal (Rueda et al. 2008). Rabbits will make use of areas with more vegetation, especially during the growth season, when vegetation provides for both forage and cover (Rueda et al. 2008). The senescent season was the driest and hottest season, and the OF was cut during this time. ...
Sylvilagus aquaticus (Swamp Rabbit) is of conservation concern throughout portions of its range, primarily due to habitat loss and alteration. Understanding habitat selection is requisite for natural resource managers providing suitable habitat to support populations of Swamp Rabbits. Swamp Rabbits are thought to be territorial and, as such, emphasis should be placed on males when studying habitat selection. Seasonal (dormant, growth, and senescent) habitat selection by male Swamp Rabbits was assessed at landscape, home-range, and plot scales. In each season, young (<20 yr) bottomland hardwood forests were selected in greater proportion, open field was selected intermediately, and old (>35 yr) bottomland hardwood forests were selected least relative to availability at the landscape scale. Male Swamp Rabbits selected home ranges from the landscape to include access to higher-elevation habitats, perhaps important during flood events. At the home-range scale, young bottomland hardwood forests and open fields were selected most during the dormant and senescent seasons, respectively, and old bottomland hardwood forests were selected least during the senescent season; the remaining cover types in each season were selected in proportion to their availability. At the home-range scale, locations with suitable cover were selected suggesting predation-risk was important at this scale. At the plot scale, predictor variables indicated Swamp Rabbits selected sites conducive to daytime resting, nighttime foraging, or latrine use. We present the first work that examines habitat selection of male Swamp Rabbits at multiple scales. Our results emphasize the importance of interspersion of cover types and stand age selected by male Swamp Rabbits.
... Because European rabbits physiologically are not well adapted to dry conditions (Correa-Cuadros et al. 2022 and references therein), their occurrence in arid ecosystems could be restricted to areas close to water resources. The association of rabbits to wetlands or places with rivers, streams, or high humidity has been previously reported (Fernández 2005;Rueda et al. 2008;Bonino and Soriguer 2009;Cuevas et al. 2011). Indeed, Bonino and Soriguer (2004) highlighted the importance of watercourses as dispersal routes for this invasive species, especially in arid environments. ...
The European rabbit Oryctolagus cuniculus is an exotic herbivorous mammal undergoing an active phase of geographical expansion in the arid ecosystems of Argentina. The Adaptive Flexibility Hypothesis states that populations at the range edge (new populations) will exhibit greater flexibility in the use of resources compared with populations located in the range core (older populations). The objective of this work was to compare the rabbit’s use of spatial and trophic resources in relation to the establishment time of their populations. The sampling was carried out for 2 years (2017 and 2018) in sites with different establishment times for rabbit populations. Random sampling stratified by type of habitat was applied using 115 fixed strip transects of 1,000 m2 laid out across the study areas. Fresh rabbit signs were recorded in each transect, and environmental and anthropic variables were measured. Our results show that the individuals from the range edge are more selective in the use of habitat than those from the range core. At the microhabitat level, we observed a pattern in the particular components of habitat use by rabbits mainly linked to food availability and proximity to water. From a trophic perspective, rabbits could show flexible adjustment to novel conditions and environments in the range edge. The variability in resource use by the European rabbit confirms its ecological flexibility, pivotal for their advance toward new environments in Argentina.
... This study, which explored blackbuck habitat use in a human-dominated landscape in India, also reported an interaction between resource and risk, as in our study. As another example, in rabbits Oryctolagus cuniculus, refuge abundance played a major role in habitat-selection in spring and winter when resources were comparatively abundant, whereas when summer arrived, quality of food available became the sole important factor and the importance of refuge was minimal (Rueda et al., 2008). ...
The only means of conserving a species or a habitat in a human-dominated landscape is through promoting coexistence while minimizing conflict. To achieve this, it is vital to understand how wildlife are impacted by direct and indirect human activities. Such information is relatively rare from areas with high human densities. To investigate how animals respond to altered ecological conditions in human-dominated landscapes, we focussed on a wild herbivore of conservation concern in Krishnasaar Conservation Area (KrCA) in Nepal. Here, blackbuck Anticope cervicapra, a generalist grazer, lives in refugia located in a growing human population. We studied the impacts of humans on habitat-use and behaviour of blackbuck. We laid 250 x 250 m grid cells in the entire KrCA and carried out indirect sign surveys with three replications for habitat-use assessment. We observed herds of blackbuck for 89 hours in different possible habitat types, location and time of the day using scan sampling methods. Our habitat-use survey showed that habitats under intensive human use were hardly used by blackbuck, even when high-quality forage was available. In areas with low levels of human activity, natural risk factors, primarily habitat openness, was the major predictor of habitat-use. Interestingly, livestock presence positively influenced habitat-use by blackbuck. Blackbuck were substantially more vigilant when they were in forest than in grassland, again indicating an influence of risk. Overall, blackbuck appear to be sensitive to risk associated with both natural and anthropogenic factors. Our findings have direct implications for managing human-wildlife interactions in this landscape, specifically regarding strategies for livestock grazing in habitats highly used by blackbuck and concerning predictions of how changing land-use will impact long-term persistence of blackbuck. Our work suggests that wild herbivores may be able to persist in landscapes with high human densities so long as there are refuges where levels of human activity are relatively low.
... The impacts of human activity produce changes in the composition of mammal assemblages over large regions, for example through the extinction of sensitive species or the invasion of exotic species, unbalancing ecological interactions, homogenising species composition, or prompting the loss of ecosystem services [3,4]. Medium to large wild terrestrial mammals, hereafter referred to as mammals, are involved in important ecosystem functions as predators [5], herbivores [6], and seed dispersers [7]. As the extent and intensity of human activity increase at an exponential rate, regional changes in the composition of mammal assemblages are expected to accelerate. ...
Detecting rapid changes in mammal composition at large spatial scales requires efficient detection methods. Many studies estimate species composition with a single survey method without asking whether that particular method optimises detection for all occurring species and yields reliable community-level indices. We explore the implications of between-method differences in efficiency, consistency, and sampling effort for the basic characterisation of assemblages of medium to large mammals in a region with three contrasted Mediterranean landscapes. We assessed differences between camera traps, scent stations, scat surveys, and track surveys. Using track surveys, we detected all species present in the regional pool (13) and obtained the most accurate description of local species richness and composition with the lowest sampling effort (16 sampling units and 2 survey sessions at most). Had we chosen camera traps, scent stations, or scat surveys as the only survey method, we would have underestimated species richness (9, 11, and 12 species, respectively) and misrepresented species composition in varying degrees. Preliminary studies of method performance inform whether single or multiple survey methods are needed and eventually which single method might be most appropriate. Without such a formal assessment current practices may produce unreliable and incomplete species inventories, ultimately leading to incorrect conclusions about the impact of human activity on mammal communities.
... Because water is a crucial limiting factor in arid and semiarid environments (Gereta, Mwangomo, & Wolanski, 2009;Redfern, Grant, Biggs, & Getz, 2003;Western, 1975), its availability strongly contributes to explaining animal distribution, density and behaviour (Redfern, Grant, Gaylard, & Getz, 2005;Rozen-Rechels et al., 2015;Rueda, Rebollo, G alvez-Bravo, & Escudero, 2008;Thrash, Theron, Bothma, & Du, 1995). In particular, access to water constrains daily activity patterns and spatial use of the landscape in most herbivore species (Smit, Grant, & Devereux, 2007) and waterholes, as gathering places, concentrate predatoreprey interactions (Valeix et al., 2009) and competition among herbivores (Valeix, Fritz, Matsika, Matsvimbo, & Madzikanda, 2007). ...
Access to surface water is crucial for herbivores in arid ecosystems. Here, we build a game-theoretical model, based on an evolutionary algorithm, to study the influence of ecological factors on the temporal patterns of presence at waterholes in the herbivore community. In this model, we incorporate the specific features of arid environments, namely, the important hydric losses endured by individuals exposed during the warmest hours of the day, and competition for access to water, both within and between species. We also consider the presence of ambushing predators around waterholes, particularly during dark hours. In response to this predation regime, our model predicts a strong aggregative tendency in herbivores. The number of groups, however, is variable, as well as the time these groups choose to attend the waterhole, even if the total number of individuals is fixed. The reason is a multiplicity of possible evolutionarily stable strategies, corresponding to different responses to the trade-off between the advantages of grouping, in terms of risk dilution, and its costs, in terms of increased competition. This variety of possible behavioural responses affects, in turn, the moments when the waterhole is occupied, and the moments when the different species meet each other. In general, herbivores also respond to predation threat by avoiding coming to waterholes after dusk. However, the cumulative effects of a relatively high level of predation during the day and a high level of interspecific competition for access to water may induce an important presence of herbivores at the waterhole at night. Our predictions are discussed in the light of existing empirical studies.
... As a result, the distribution of high quality plant tissues is spatially and temporally heterogeneous, so herbivores have evolved physiological and behavioural strategies to optimise energetic gain and reduce processing time. Allometric scaling of body volume with surface area impacts on thermoregulation, and results in larger mammals having lower basal metabolic rates (BMR) than small mammals, despite having higher absolute energetic requirements (Bell, 1971;du Toit and Yetman, 2005;Jarman, 1974;Rueda et al., 2008). This has important implications for foraging behaviour due to gut capacity and digestive efficiency in relation to the quantity of energy required (McNaughton and Georgiadis, 1986): the Jarman-Bell principle states that larger animals can therefore tolerate lower quality diets than small animals (Bell, 1971;Geist, 1974;Jarman, 1974). ...
The 28-month study assessed the impacts of five syntopic medium-sized mammalian browsers and one fire event in a woodland savanna in the Matobo Hills, Zimbabwe. Aspects of herbivory, mechanical pressures, seed dispersal and nutrient cycling were investigated for three species of small antelope (common duiker [Sylvicapra grimmia]1, klipspringer [Oreotragus oreotragus] and steenbok [Raphicerus campestris]) and two medium-sized species (bushbuck [Tragelaphus scriptus] and greater kudu [T. strepsiceros]). Focusing on Burkea africana2 woodland, in a system that does not include elephant (Loxodonta africana), effects of browsing antelope on woody and herbaceous vegetation development were investigated using exclusion plots. Browsers regulated woody plant cover (measured as basal stem area), with smaller antelope having a greater impact than larger species. This was linked to feeding height, feeding selectivity and mechanical pressures (e.g. twig breakage and trampling). Fire caused an initial reduction in above-ground standing biomass, but in the presence of fauna, pre-fire equilibria were attained within 15 months. In antelope exclosures, herbaceous biomass increased and woody biomass decreased following fire. Responses by woody vegetation to browsing varied among species, with highly palatable species typically exhibiting compensatory regrowth. Woody species richness and abundance (especially of palatable species) increased in the absence of browsers, but species richness of the herbaceous layer was promoted by moderate disturbance (trampling or fire). Faecal deposition behaviour, primarily the use of latrines by small antelope, resulted in localised soil enrichment within defended territories. Decomposition rates (and therefore return of nutrients to the soil) varied among species and seasons, due to defecation site selection, accessibility to decomposers and desiccation rates of faecal pellets. Controlled seed germination experiments indicated that ingestion by small antelope enhances germination rates of large, hard-seeded fruits such as Sclerocarya birrea. However, germination of savanna seeds may require multiple cues. This study demonstrated the critical roles of small antelope in ecosystem functioning, and highlights the importance of the less visible impacts of frequently overlooked smaller mammalian herbivores. Perturbations to the faunal community, especially small antelope, are predicted to have substantial impacts on woody plant cover.
... One key-stone species in the Mediterranean Basin is the wild rabbit (Oryctolagus cuniculus, hereafter rabbit), (Delibes-Mateos et al., 2008). Although rabbits can endure extended periods of drought (Hayward, 1961;Cooke, 1982) and distance to drinking water does not seem to affect their abundance in any season in Central Spain (Rueda et al., 2008), their reproduction has been correlated with environmental temperature and water content of the vegetation (Gonçalves et al., 2002). Furthermore, many gamekeepers and wildlife managers claim that rabbits frequently use water troughs when water is scarce. ...
Installation of water troughs is a common approach to increase densities of small game species in the Iberian peninsula but little is known about the watering patterns of target species, such as the wild rabbit (Oryctolagus cuniculus). Using camera trapping, we monitored the use of water troughs by wild rabbits over 228 weeks in three consecutive periods, from June to October in 2008, 2009 and 2010, on farmland in north–west Spain. Wild rabbits used 43% of the water troughs. A significantly higher number of rabbits were observed drinking at troughs surrounded by shrub cover than at those in open fields. Most drinking events were recorded from July to September (98%), though the use of water troughs was not clearly related to weather. Wild rabbits drank mainly during the morning (52% of rabbits), less so in the evening and at night, and rarely in the afternoon. Wild rabbits were photographed together with red–legged partridges (Alectoris rufa) in 6% of photographs. These findings suggest water troughs are useful for species such as wild rabbits and should be allocated close to shrub areas.
... The main characteristics of Mediterranean ecosystems that are important for wildlife are the prolonged dry, hot period and high biodiversity (Blondel et al. 2010;Sokos et al. 2012). Flexibility in foraging is a typical response of herbivores to cope with seasonal differences in food availability and quality in the Mediterranean (Rueda et al. 2008). Mammals such as the brown hare (hereafter hare) have higher genetic diversity (Antoniou et al. 2013), a longer reproductive period (Antoniou et al. 2008), and a more diverse diet (Kontsiotis et al. 2011) in the Mediterranean than in more northern ecosystems of its distribution. ...
Background
Brown hares (Lepus europaeus) were collected before and after autumn rains from a mixed
farmland and scrubland area. The age and sex of each specimen were determined, and
microhistological technique was applied to analyze the stomach contents.
Results
Hares consumed a higher number of plant species in comparison with other studies in
continental European farmlands. A different pattern in diet of hare was found, where from a
partial herbivory, frugivory, and granivory during the dry period, hares turn to primarily
herbivory during the wet period. An expansion of diet breadth and an increase in food
consumption was found in the dry season. Farming contributes to the enrichment of diet
especially during the dry season. Diet composition was differed between ages, but no
significant difference was found between the two sexes.
Conclusions
Hare is a facultative generalist herbivore that adapts its diet to the seasonal vegetation
changes. In Mediterranean ecosystems, the seeds, fruits, and grapes are important additions to
the diet. Results suggest that during the dry period juveniles cannot exploit all the available
food resources, such as fruits and seeds, as effectively as adults.
... In free and natural conditions, sheep prefer open environment than goats and these open and without stress environments play an important role in the milk composition richness and protein. Rueda and colleagues (2008) studied sheep grazing behavior in central Spain rangelands. They concluded that spatial pattern of sheep grazing during different seasons is affected by the forage availability. ...
For proper grazing management and improvement of husbandry system efficiency, it is necessary to
have enough knowledge of sheep diet and plant species cover variations in long-term period. This
investigation was carried out in order to draw a clear concept of the sheep diet and plant species cover
variations during April to December in Mountainous rangelands of Baladeh, Mazandaran province,
Iran. Using an initial study, the region husbandry situations were determined that lead to identification
of three pastoralists with suitable pastoral units. Based on initial study and plants growth season,
sampling was conducted in 15-day time point to end of the grazing year in December. The chronic
technique was used to determine the percentage of plant species in sheep daily diet. The result of
Pearson correlation test showed that the species cover and the species contribution to the sheep diet are
related (r= 0.828, P<0.01(. Bromus tomentellus, Astragalus sp and Artemisia aucheri have the highest
covers and contribution to the sheep diet in each area. From April to September, Bromus tomentellus
had more than 30% the sheep diet but it reduced to less than 12% in the September to December
period. Astragalus sp almost had constant proportion of the sheep diet (25- 35%). Artemisia aucheri
had little contribution to the sheep diet in April to September period even decreased to zero in July, but
had more than 30% of the sheep diet in the September to December period. Finally the results showed
that during April to September period, sheep had higher interest to grasses but in the September to
December period, Sheep had higher interest to shrubs. Also the forbs had constituted little proportion
of the sheep diet (5-10%) during April to December.
Keywords: Husbandry system; sheep feed; plant species; Mountainous rangelands;
Iran.
... (1) plant heterogeneity and local landscape structure (Bertolino et al. 2011;Fernandez 2005;Hamilton et al. 2006;Lombardi et al. 2007; Monzon et al. 2004;Tash and Litvaitis 2007;Wilson et al. 2002), (2) location and use of warrens (Barrio et al. 2010;Gea-Izquierdo et al. 2005;Rueda et al. 2008;Sanchez and Rachlow 2008), and (3) abundance and density (Cabezas and Moreno 2007;Wilson et al. 2010). These studies emphasised maintaining local habitat heterogeneity at fine scales to maintain populations. ...
Extensive resources are allocated to managing vertebrate pests, yet spatial understanding of pest threats, and how they respond to management, is limited at the regional scale where much decision-making is undertaken. We provide regional-scale spatial models and management guidance for European rabbits (Oryctolagus cuniculus) in a 260,791 km2region in Australia by determining habitat suitability, habitat susceptibility and the effects of the primary rabbit management options (barrier fence, shooting and baiting and warren ripping) or changing predation or disease control levels. A participatory modelling approach was used to develop a Bayesian network which captured the main drivers of suitability and spread, which in turn was linked spatially to develop high resolution risk maps. Policy-makers, rabbit managers and technical experts were responsible for defining the questions the model needed to address, and for subsequently developing and parameterising the model. Habitat suitability was determined by conditions required for warren-building and by above-ground requirements, such as food and harbour, and habitat susceptibility by the distance from current distributions, habitat suitability, and the costs of traversing habitats of different quality. At least one-third of the region had a high probability of being highly suitable (support high rabbit densities), with the model supported by validation. Habitat susceptibility was largely restricted by the current known rabbit distribution. Warren ripping was the most effective control option as warrens were considered essential for rabbit persistence. The anticipated increase in disease resistance was predicted to increase the probability of moderately suitable habitat becoming highly suitable, but not increase the at-risk area. We demonstrate that it is possible to build spatial models to guide regional-level management of vertebrate pests which use the best available knowledge and capture fine spatial-scale processes.
... Large herbivores that inhabit semi-arid savannas face the challenge of acquiring adequate nutrition in highly seasonal environments emphasized by periods of food scarcity (Owen-Smith and Cooper, 1989;Rueda et al., 2008;Wilmshurst et al., 1999b). Driven by metabolic requirements, mammalian herbivores often become more selective in order to obtain high-quality forage during dry seasons (Belovsky, 1991;Demment and Van Soest, 1985;Wilmshurst et al., 2000), and as a result animals sometimes exhibit great behavioural changes in foraging coinciding with seasonal changes (Birkett et al., 2012). ...
... This harsh period is thus regarded as a pivotal stage for mammals in their life history and compels them to adapt to new habitat use for survival (Homan et al. 2000). The habitat selection by this animal also takes into consideration the predation risks, abundance and quality of food resources which changed seasonally (Rueda et al. 2008). Across all habitat types, the macaques subspecies on which this study was conducted, in winter and early spring, invested much of its time on the activities of foraging and resting, in addition to other characteristic behaviours of grooming, playing, moving around etc. (Seth & Seth 1986). ...
The chosen habitat of any animal species comprises a range of environmental features that provide adequate resources for its continuous survival. Consequently, the criteria of habitat selection by animals, combines a wider spectrum of both environmental and extrinsic factors, with major prerequisites based on food resources, availability of shelter and suitable ethics for procreation. From this study, conducted in winter and early spring, at Mt. Wangwushan area, located on 35°05′–35°15′ N, 112°12′–112°22′ E, in Taihangshan Macaque National Nature Reserve (TMNNR), Jiyuan, Henan Province, we show by elaborative results that Macaca mulatta tcheliensis was specifically associated with the following habitat characteristics: (1) the average tree DBH (diameter at breast height) with over 15 cm; (2) the distance from human disturbance of less than 2000 m; (3) the distance to water with less than 1000 m; (4) the gradient of mountain slope of 15°∼40°; (5) which was markedly tarrying with the altitude ranges from 1000 m to 1300 m; and (6) where the canopy coverage was less than 60%. In addition, during this study, rhesus macaque mostly inhabited the sunny slopes of mountains than the shady areas. Results of the first five principal components analysis (PCA) accounted for the total variance of 68.88%, while the other factors showed insignificant effects on habitat selection by rhesus macaque in the temperate forest. In conclusion, these new results increase our understanding on the living status, under the harshest condition, in winter and early spring of Macaca mulatta tcheliensis, the subspecies of rhesus macaques as may be linked to its habitat selection and utilization, in the temperate forest.
... The first set are studies that use SEMs to describe how climate affects ecological systems. Perhaps the field where this is most developed is population ecology (e.g., [48][49][50][51]), but similar models are also starting to be developed in community ecology [52][53][54] and disturbance ecology [55]. We propose that these studies could benefit by incorporating more sophisticated descriptors of seasonality into their SEMs. ...
Seasonality drives ecological processes through networks of forcings, and the resultant complexity requires creative approaches for modeling to be successful. Recently ecologists and climatologists have developed sophisticated methods for fully describing seasons. However, to date the relationships among the variables produced by these methods have not been analyzed as networks, but rather with simple univariate statistics. In this manuscript we used structural equation modeling (SEM) to analyze a proposed causal network describing seasonality of rainfall for a site in south-central Florida. We also described how this network was influenced by the El Niño-Southern Oscillation (ENSO), and how the network in turn affected the site's wildfire regime. Our models indicated that wet and dry seasons starting later in the year (or ending earlier) were shorter and had less rainfall. El Niño conditions increased dry season rainfall, and via this effect decreased the consistency of that season's drying trend. El Niño conditions also negatively influenced how consistent the moistening trend was during the wet season, but in this case the effect was direct and did not route through rainfall. In modeling wildfires, our models showed that area burned was indirectly influenced by ENSO via its effect on dry season rainfall. Area burned was also indirectly reduced when the wet season had consistent rainfall, as such wet seasons allowed fewer wildfires in subsequent fire seasons. Overall area burned at the study site was estimated with high accuracy (R (2) score = 0.63). In summary, we found that by using SEMs, we were able to clearly describe causal patterns involving seasonal climate, ENSO and wildfire. We propose that similar approaches could be effectively applied to other sites where seasonality exerts strong and complex forcings on ecological processes.
... These results suggest that changes in NPP alone are unlikely to explain the patterns observed. Woody vegetation has positive effects on rabbit (Oryctolagus cunniculus L.) abundance during summer in semi-arid Mediterranean grasslands (Rueda et al., 2008). Rabbits are common in all of our study sites (Maestre et al., 2009), and we suggest that the increase in the activity of urease found in SH plots, which cannot be linked to their overall higher soil fertility (Appendix 3), could have been caused by changes in rabbit abundance in these plots. ...
Shrub encroachment is a worldwide phenomenon with implications for desertification and global change. We evaluated its effects on the activities of urease, phosphatase and β-glucosidase in Mediterranean semiarid grasslands dominated by Stipa tenacissima by sampling 12 sites with and without resprouting shrubs along a climatic gradient. The presence of shrubs affected the evaluated enzymes at different spatial scales. Soils under S. tenacissima tussocks and in bare ground areas devoid of vascular plants had higher values of phosphatase and urease when the shrubs were present. For the β-glucosidase, this effect was site-specific. At the scale of whole plots (30 m × 30 m), shrubs increased soil enzyme activities between 2% (β-glucosidase) and 22% (urease), albeit these differences were significant only in the later case. Our results indicate that shrub encroachment does not reduce the activity of extracellular soil enzymes in S. tenacissima grasslands.
... Sites were all located within scenic reserves managed by Christchurch City Council and, while subject to extensive sheep grazing, were free from human settlement. Across sites, grazing intensity was quantified using fresh pellet counts (Rueda et al. 2008) and grazing intensity at a site was independent of its elevation (See Methods S1; Fig. S1, in Supporting information). ...
1. Although observed functional differences between alien and native plant species support the idea that invasions are favoured by niche differentiation (ND), when considering invasions along large ecological gradients, habitat filtering (HF) has been proposed to constrain alien species such that they exhibit similar trait values to natives. 2. To reconcile these contrasting observations, we used a multiscale approach using plant functional traits to evaluate how biotic interactions with native species and grazing might determine the functional structure of highly invaded grasslands along an elevation gradient in New Zealand. 3. At a regional scale, functional differences between alien and native plant species translated into nonrandom community assembly and high ND. Alien and native species showed contrast-ing responses to elevation and the degree of ND between them decreased as elevation increased, suggesting a role for HF. At the plant-neighbourhood scale, species with contrasting traits were generally spatially segregated, highlighting the impact of biotic interactions in struc-turing local plant communities. A confirmatory multilevel path analysis showed that the effect of elevation and grazing was moderated by the presence of native species, which in turn influ-enced the local abundance of alien species. 4. Our study showed that functional differences between aliens and natives are fundamental to understand the interplay between multiple mechanisms driving alien species success and their coexistence with natives. In particular, the success of alien species is driven by the pres-ence of native species which can have a negative (biotic resistance) or a positive (facilitation) effect depending on the functional identity of alien species.
... At the same time, H. squamatum growing in this habitat avoid being trampled owing to deterrence caused by perennial shrubs (Baraza et al. 2006). It is also known that grazing mammals vary considerably in their use of habitat at relatively large scales (Rueda et al. 2008), which could explain why the incidence of sheep grazing on these two blocks which are close spatially is so different. At smaller scales, this effect is exacerbated by the feeding behavior of the two main grazers in the community , sheep and rabbits, which results in clustered herbivory-induced deaths (De la Cruz et al. 2008). ...
Habitat heterogeneity may influence plant demography because conditions for survival, growth, and reproduction vary within a species' range. We assessed the role of microhabitat spatial structure on the demography of Helianthemum squamatum, a shrubby gypsum specialist endemic to the Iberian Peninsula. We evaluated the demographic effect of microhabitat spatial variation using an approach that combined cellular automata with matrix population models, and included environmental and demographic stochasticty. We collected data on seed bank (2003-2005), seedling emergence (2003-2006), and adult survivorship (2004-2007) for H. squamatum in two independent blocks with different grazing intensity in BelinchA(3)n (Cuenca, Spain). We built spatial scenarios for each block based on field data of cover and spatial pattern of four microhabitats: lichenic crust, litter, H. squamatum, and shrub. Seedling survivorship was affected by year, block, and microhabitat, with individuals emerging under conspecifics having the highest survival rate and on litter the lowest in both blocks, whereas the effect of crust and other shrubs differed across blocks. Our models indicated population increase in the block with low grazing, but population decline in the block with intense grazing. We hypothesize that higher pressure of livestock grazing and trampling leads to a shift in relative microhabitat suitability for crust and shrub. This potential effect of grazing on spatial demographic variation opens interesting questions for future research. We emphasize the importance of considering microhabitat spatial structure when evaluating management and conservation strategies.
... In each surveying time, we collected five soil samples from each linear transect, located at distances of approximately 500 m. The soil samples were collected at least one week after a rainfall event and not during a dry period (Rueda et al. 2008). The soil moisture was determined as the difference of the weight of dried samples at 100 °C for 24-h by the net weight of soil. ...
Recently, the European rabbit (Oryctolagus cuniculus) has received contrasting considerations due to its multidimensional role in the Mediterranean ecosystems. Within this framework, knowledge of factors determining its population size may have important consequences for designing an effective management plan. In this paper, we quantified the combined influence of the major demographic and mechanistic factors on seasonal population fluctuation of European rabbits on Lemnos Island (Greece), during 2007–2009. We developed a hypothetical model taking into account direct (productivity, predation, hunting pressure, food shortage, habitat treatment) and indirect factors (soil moisture, adverse weather conditions) using structural equation modeling. We tested for their influence on the seasonal population growth rate (spgr) as determined by line transects to estimate rabbit abundance. The productivity induced higher pgr. Food shortage, which is affected by low soil moisture during the late summer and early autumn, is demonstrated to be the most important negative factor followed by the hunting pressure and predation. Demographic and mechanistic factors highlighted in this analysis could be used either for conservation or for controlling populations of the species.
... Villafuerte et al. (1996) related the increase of rabbit numbers observed in Doñana National Park with the availability of high-quality food. Our pasturelands, dominated by wheat (Secale cereale), Festuca spp., young shrubs (Baccharis trimera, Halimium alyssoides) and other herbaceous plants, provide a large spectrum of food items that can be used by rabbits (Ferreira and Alves 2009), particularly during summer when food resources become scarcer (Rueda et al. 2008). Additionally, the implementation of these measures seems to be particularly relevant in lower-quality habitats (Moreno and Villafuerte 1995). ...
In Mediterranean ecosystems, rabbits are a key prey species for many predators, such as the Iberian lynx, which is threatened with extinction and has gone extinct locally in several regions of its historical distribution range. One of these regions is Serra da Malcata Nature Reserve, Portugal, which is also currently proposed as a potential site for reintroduction. We intended to investigate annual varia-tion, potential time trends and the effects of management practices on the rabbit population in Serra da Malcata as a model for future potential reintroduction areas. The rabbit population was monitored over 12 years (from 1997 to 2009) by counting latrines along linear transects. These data were used to estimate rabbit occupancy, colonization and extinction patterns using a likelihood-based method including habitat, population and topographic covariate effects. Our results suggest that initial occupancy, when management practices were absent, was driven by the presence of Erica spp. and Cistus ladanifer shrubs and by distance to summits. Site colonization was positively influenced by the presence of edges between shrubs and pastureland and by patterns of rabbit distribution in the previous sampling season. On the other hand, local extinction was negatively influenced by edges. We conclude that the increase in rabbit occupancy and local colonization patterns was clearly associated with management actions (particularly, the creation of pasture-lands), although the recovery of the species was noticeably limited by previous patterns of spatial distribution.
... 4-6 may allow managers to monitor the sustainability of intense browsing and grazing systems over time (Du Toit et al., 1990), as well as the distribution of herbivores, by understanding variations in the grazing resource. Herbivore habitat is multifaceted, but a key factor is the grazing resource, which may well be a limiting resource, especially at particular times of the year, or in drought periods (Coulson et al., 2001;Rueda et al., 2008). This approach has particular potential for smaller areas of African savanna where animals are bound by fences and where densities are generally much higher than in larger conservation areas (Owen-Smith et al., 2006). ...
Savanna covers about two-thirds of Africa, with forage quantity and quality being important factors determining the distribution and density of wildlife and domestic stock. Testing hypotheses about the distribution of herbivores is hampered by the absence of reliable methods for measuring the variability of vegetation quality (e.g. biochemical composition) across the landscape. It is demonstrated that hyperspectral remote sensing fills this gap by revealing simultaneously the spatial variation of foliar nitrogen (crude protein) as well as the total amount of polyphenols, in grasses and trees. For the first time, the pattern of resources important for feeding preferences in herbivores (polyphenols and nitrogen) is mapped across an extensive landscape and the modeled foliar concentrations are shown to fit with ecological knowledge of the area. We explain how estimates of nitrogen (crude protein) and polyphenols may be scaled up from point-based observations to reveal their spatial pattern, and how the variation in forage quality can influence the management of savannas, including farms, communal grazing areas, and conservation areas. It provides a glimpse of the choices herbivores must face in selecting food resources of different qualities.
... We do not attempt to illustrate them all here, but shrub encroachment impacts are varied and numerous, and their valuation depends upon the human culture which perceives it. In the Mediterranean, the primary current use of Stipa grasslands is either hunting of small game, which tends to be enhanced by shrub cover (Rueda et al. 2008), or livestock production. The palatability of Stipa is similar to that of sprouting shrubs (Ben Salem et al. 1994), and thus shrub encroachment does not greatly decrease the foraging value of Stipa grasslands. ...
The worldwide phenomenon of shrub encroachment in grass-dominated dryland ecosystems is commonly associated with desertification. Studies of the purported desertification effects associated with shrub encroachment are often restricted to relatively few study areas, and document a narrow range of possible impacts upon biota and ecosystem processes. We conducted a study in degraded Mediterranean grasslands dominated by Stipa tenacissima to simultaneously evaluate the effects of shrub encroachment on the structure and composition of multiple biotic community components, and on various indicators of ecosystem function. Shrub encroachment enhanced vascular plant richness, biomass of fungi, actinomycetes and other bacteria, and was linked with greater soil fertility and N mineralization rates. While shrub encroachment may be a widespread phenomenon in drylands, an interpretation that this is an expression of desertification is not universal. Our results suggest that shrub establishment may be an important step in the reversal of desertification processes in the Mediterranean region.
Time and location factors have different effects on livestock grazing behaviors, so that different parameters of the time why grazing and trapped livestock in rangeland are effective factors that studying them can be an important tool for management. Why and Range is Effective. For this purpose, this study was carried out in Kalat Naderi district of Khorasan Razavi province in 2017. In this study, the length of the journey per day, the time taken for the reason, the rest and the time spent on milking during the five different working hours (BARREH DONBAL, DAMODOOSH, GHOOCH ANDAZI, GALLEDASHT, and ZEHGAH) were measured. To determine the indices used to evaluate the behavior of grazing livestock from the GPS device (geographical positioning device) was used. The results of the research showed that: four work periods in the study area are carried out in the field of rangeland and the period of drainage in the embankment. There have been many changes in the time and type of livestock activities during the herding of the herd in the rangeland. The start and end hour why it changes due to the warming up of the day and the warming up of the air, so that daytime raining begins early in the warmer seasons and ends later in the night. The most daily livestock activity was in the first half of June with 1015 minutes in the rangeland. In all periods except for GALLEDASHT period, the largest share of livestock's daily activity is related to steady grazing, as the longevity of the day and the increase in temperature increase the livestock march in the region. Also, the study of financial returns and expenditures showed that the value of meat produced had the highest amount of financial value for the livestock, and the cost of forage, shepherd's wages, and the cost of maintaining the stock had the highest share in the current costs of livestock. Finally, the financial efficiency for all three areas was evaluated positive.
Rangelands and animal husbandry have a substantial role in providing daily and with regard to the importance of energy as one of the pillars of sustainable development and efficiency of husbandry activities, this study was done to investigate herder and livestock activities typology, animal husbandry regime, animal diet and vegetation conditions; to estimate the energy consumed in animal husbandry, energy balance; and to evaluate the financial profitability and rangeland ecosystem value based on annual field sampling (April 2012 - April 2013) in Baladeh-Nour rangelands, Mazandaran province. First, three herders with certain rangelands were selected. Next, livestock and husbandry activities and animal diet and vegetation conditions were monitored during a year. Daily consumptive energy was then measured with MAFF equation and Nicol coefficients. Total amount of consumptive energy was determined by considering the composition of flock and the husbandry work periods. Energy efficiency of traditional husbandry was finally determined by calculating livestock productions and their energy. The results showed that five different work periods with various number and duration of animal activities can be determined. In the grazing season, the constant grazing was the dominant daily activity between April to September and the walking grazing was the common daily activity between September to December. Bromus tomentellus, Astragalus cf gossypinus and Artemisia aucheri had the maximum contributions in livestock feed from April to December. The grasses had the most shares on animal diet between April to September. The contribution of bushes in livestock feed had substantially increased from September to December, so that bushes share on animal diet reached to 70% of animal feed diet. The energy efficiency results revealed that energy balance was negative in these regions so that the performance of traditional husbandry was estimated to be 38% at the best region. Financial profit was calculated by assessing incomes and costs. The net value of animal products per hectare on traditional rangeland based system was determined to be 750000 RLS (25$).
The possible consequences of top predators for the success of restoration actions for animals is still poorly understood. Our main objective was to analyze whether there could be a risk of creating habitats with an excess of predation by top predators when carrying out actions to improve cliff habitats for cliff-nesting birds at mining sites. We surveyed 28 mining sites in Spain to obtain information regarding the Eagle Owl (Bubo bubo) presence and diet, and analyzed its relationship with the density of cliff-nesting birds and rabbits (Oryctolagus cuniculus, its main prey) at the mining sites. We detected Eagle Owls in 18 mining sites (64%) and collected enough prey remains in 11 mining sites. A total of 732 minimum number of prey were identified. The diet of the Eagle Owl consisted mainly of mammals (83%) and the proportion of birds in the diet was low (13%). There was no relationship between the presence of Eagle Owls and the density of rabbits in the mining sites, but there was a positive relationship with the density of cliff-nesting birds. We conclude that the Eagle Owl does not seem to exert a significant pressure on the cliff-nesting birds, even on wild pigeons, the most abundant cliff-nesting birds in its diet. Restoration projects which promote cliff-nesting birds would not entail a significant risk of generating ecological traps by excess of predation by the Eagle Owl. Furthermore, this species could be favored in restoration plans, as it is a threatened species in some areas in Europe.
Time and location factors have different effects on livestock grazing behaviors, so that different parameters of the time why grazing and trapped livestock in rangeland are effective factors that studying them can be an important tool for management. Why and Range is Effective. For this purpose, this study was carried out in Kalat Naderi district of Khorasan Razavi province in 2017. In this study, the length of the journey per day, the time taken for the reason, the rest and the time spent on milking during the five different working hours (BARREH DONBAL, DAMODOOSH, GHOOCH ANDAZI, GALLEDASHT, and ZEHGAH) were measured. To determine the indices used to evaluate the behavior of grazing livestock from the GPS device (geographical positioning device) was used. The results of the research showed that: four work periods in the study area are carried out in the field of rangeland and the period of drainage in the embankment. There have been many changes in the time and type of livestock activities during the herding of the herd in the rangeland. The start and end hour why it changes due to the warming up of the day and the warming up of the air, so that daytime raining begins early in the warmer seasons and ends later in the night. The most daily livestock activity was in the first half of June with 1015 minutes in the rangeland. In all periods except for GALLEDASHT period, the largest share of livestock's daily activity is related to steady grazing, as the longevity of the day and the increase in temperature increase the livestock march in the region. Also, the study of financial returns and expenditures showed that the value of meat produced had the highest amount of financial value for the livestock, and the cost of forage, shepherd's wages, and the cost of maintaining the stock had the highest share in the current costs of livestock. Finally, the financial efficiency for all three areas was evaluated positive.
For proper grazing management and improvement of husbandry system efficiency, it is necessary to have enough knowledge of sheep diet and plant species cover variations in long-term period. This investigation was carried out in order to draw a clear concept of the sheep diet and plant species cover variations during April to December in Mountainous rangelands of Baladeh, Mazandaran province, Iran. Using an initial study, the region husbandry situations were determined that lead to identification of three pastoralists with suitable pastoral units. Based on initial study and plants growth season, sampling was conducted in 15-day time point to end of the grazing year in December. The chronic technique was used to determine the percentage of plant species in sheep daily diet. The result of Pearson correlation test showed that the species cover and the species contribution to the sheep diet are related (r= 0.828, P<0.01(. Bromus tomentellus, Astragalus sp and Artemisia aucheri have the highest covers and contribution to the sheep diet in each area. From April to September, Bromus tomentellus had more than 30% the sheep diet but it reduced to less than 12% in the September to December period. Astragalus sp almost had constant proportion of the sheep diet (25-35%). Artemisia aucheri had little contribution to the sheep diet in April to September period even decreased to zero in July, but had more than 30% of the sheep diet in the September to December period. Finally the results showed that during April to September period, sheep had higher interest to grasses but in the September to December period, Sheep had higher interest to shrubs. Also the forbs had constituted little proportion of the sheep diet (5-10%) during April to December.
ABSTRACT The nature reserve Serra da Malcata, Portugal, was recently considered a site for Iberian lynx (Lynx pardinus) reintroduction. Because of potential disease risk posed by red foxes (Vulpes vulpes) in the area, a reliable estimate of fox abundance was critical for a dependable reintroduction program. We adapted camera-trapping techniques for estimating red fox abundance in the reserve. From July 2005 to August 2007, we conducted 7 camera-trapping sessions, allowing for individual identification of foxes by physical characteristics. We estimated abundance using the heterogeneity (Mh) model of the software program CAPTURE. Estimated density ranged from 0.91 ± 0.12 foxes/km2to 0.74 ± 0.02 foxes/km2. By estimating red fox density, it is possible to define the number of foxes that must be sampled to assess the presence of potential fox-transmitted diseases that may affect lynx reintroduction.
The study of plant–plant interactions along grazing and abiotic stress gradients is a major research topic in plant ecology, but the joint effects of both stressors on the outcome of plant–plant interactions remains poorly understood. We used two different factorial experiments conducted in a semi-arid Mediterranean steppe to assess: 1) the role of the perennial grass Stipa tenacissima, a low-palatability species, providing protection from rabbit herbivory to the shrub Retama sphaerocarpa (experiment 1), and 2) the effects of environmental amelioration provided by Stipa on the recovery of Retama after rabbit damage under two contrasted levels of water availability (experiment 2). In the experiment 1, water stress worked as an indirect modulator of herbivore protection by Stipa. This species protected Retama seedlings from rabbit herbivory during the wetter conditions of spring and winter, but this effect dissapeared when rabbit pressure on Retama increased during summer drought due to the decrease in alternative food resources. In the experiment 2, Stipa exerted a negative effect on the survival of Retama seedlings during the three years of the experiment, regardless of inter-annual differences in rainfall or the watering level applied. This negative effect was mainly due to excessive shading. However, Stipa increased Retama recovery after initial rabbit impact, overriding in part this negative shade effect. Conversely, Stipa impact on the Fv/Fm of Retama seedlings depended on the intra-annual water dynamics and its experimental manipulation, overall contradicting predictions from the stress–gradient hypothesis. The complex interactions found between herbivory, microclimatic amelioration from Stipa, and water availability as drivers of Retama performance illustrate the importance of considering the temporal dynamics of both biotic and abiotic stressors to fully understand the outcome of plant–plant interactions.
The factors determining habitat utilization among a large grazing herbivore community on Malilangwe Estate, southeastern Zimbabwe, were investigated. Gross vegetative structure, herbaceous composition and topographic features thought likely to determine herbivore distribution were measured and analysed using a single multivariate technique. Seasonal variation in resource distribution was considered and research extended over an entire year. Herbivore distribution and niche separation were explained by several environmental variables, and potential interspecific competition inferred. Ungulates showed a large degree of niche overlap in both the hot-wet season and the cool-dry season. Ecological separation between grazers was pronounced in the hot-dry season. Herbivore distribution was associated most closely with distance from water, grass sward height, time since last burn, woody plant density and by the presence of the predominant grasses Urochloa mossambicensis, Panicum maximum, Heteropogon contortus and Digitaria eriantha. Management options are considered. The findings of the study provide a better understanding of ecological separation, and possible competitive interactions, among members of the large grazing herbivore community on Malilangwe Estate.
To establish a successful strategy for managing wild rabbit (Oryctolagus cuniculus algirus) populations it is essential to have a clear understanding of reproductive biology. In Portugal, previous work suggested a seasonal pattern of reproductive activity for this species. In this study we present additional information on the seasonal reproductive activity of the wild rabbit as well as data on the influence that environmental factors have on the onset and length of the breeding season.
The study was carried out in Pancas, southern Portugal, from October 1997 to September 1998. Rabbits were collected every two months and post mortem analyses were performed. In the males, circulating concentration of testosterone, gonadal weight, daily sperm production, diameter of the seminiferous tubules and the thickness of epithelial cells were measured. The numbers of corpora lutea, embryos and placental scars were recorded in the females. To assess abundance and quality of food, samples of herbaceous vegetation were collected and analysed for water, fibre and crude protein content.
The reproductive season extended from November to June with a peak in March/April, with both sexes showing an annual cycle of gonadal development and subsequent regression. All analysed females were pregnant and/or lactating between March and June. The mean litter size estimated by counting the embryos in the uteri was 3.90 ± 0.50. Daily sperm production was highest between November and April. Testicular function was strongly correlated with environmental temperature and the water content of the vegetation, and both testicular and ovarian development were correlated with vegetation biomass.
Models that integrate plant growth, ungulate movement, and foraging are suggested as a way to improve analyses of spatial plant-herbivore systems. Models must give due attention to non-forage constraints on herbivore distribution, such as topography. Models should assess the significance of movement as a means of coping with local climatic variation (patchy rainfall). Models that distribute an aggregate population over a landscape in relation to the distribution of habitat features de-emphasize aspects of ungulate movements and population responses that inevitably cause nonideal distributions, particularly in natural ecosystems. It is important to account for small scale phenomena such as tiller defoliation patterns, patch grazing, and grazing lawns as well as large scale patterns such as rotation and migration. -from Author
Disappearance speed of two signs of presence (isolated pellet groups and dunghills) of the wild rabbit Oryctolagus cuniculus was measured between May 1990 and July 1991 on two sites in Provence, southern France, to validate the use of the pellet group counts technique for this species in the French Mediterranean region. Four ecological factors were tested to explain the disappearance speed of isolated pellet groups and dung-hills : season, site, vegetation type and climatic parameters. Even if the results are more pertinent for dung-hills than for isolated pellet groups, the two signs of presence have the same general plan of disappearance. Our results show that season is the most important factor to be considered to sample the habitat-use of the wild rabbit. Using the pellet group counts technique, if any comparison is to be made, spring is the most favourable time of year because pellets disappear faster during this season. Whatever the season, if a comparison between several sites and biotopes is to be made, only fresh signs should be used. The influence of climatic parameters and the limits of pellet group counts technique are discussed.
Seasonal changes in the diet of rabbits from three temperate (Mediterranean) areas in south-western Australia were identified using microscopic determination of the percentage occurrence of various food groups in sampled stomachs. The sites differed in soil type and in the availability of summer perennials, native vegetation bush remnants (size of, and number of plant species), improved pastures, and summer rainfall, and hence, enabled a comparison of the diet of rabbits from the different vegetation communities. Although the diet of these rabbits was quite flexible, with some switching in food items occurring between seasons, there were marked differences in the proportion of monocotyledonous and dicotyledonous species eaten in each habitat. There was a strong reliance on seeds (1-5 species) during late spring and summer in all three habitats. Guildford grass (Romulea rosea) leaf and corms were a major component of the diet in the two habitats where this species was common. Further, as a result of the summer die-off of pasture species, there was a shift in where rabbits sourced food items during winter and summer. Pasture species were eaten during winter, but rabbits fed mainly on those dicotyledons found only in the surrounding scrub during summer. This suggests that rabbits may impact negatively upon such remnant vegetation at this time. Rabbits in all three habitats consumed several plant species with high water content (>54%) during summer, presumably to help maintain their water balance. Rabbits also consumed the seeds and foliage of several weed/nuisance species in each habitat, but any role of rabbits in weed dispersal was not determined.
Iberian wild rabbit numbers have decreased in the last decades. The management implemented to recover rabbit populations includes several techniques, one of the most common being the construction of artificial rabbit warrens. To optimally distribute the artificial warrens in the field it is essential to understand natural warren microhabitat. Few studies have investigated the relationship between rabbits and grassland communities. In this work we study the spatial distribution and characteristics of rabbit warrens as well as their relation to grasslands in Mediterranean woodlands of central Spain. During the summer of 2001, three 12.5-ha study plots, including the most representative grassland communities of the area, were selected. All rabbit warrens were surveyed and the active and total entrances, shrub cover, grassland community and warren cover type were characterised. A grassland community selection index was calculated and the warren spatial distribution analysed. Ploughed lands and shallow soils were unsuitable for warren establishment. The mean number of burrow entrances per warren was 5.8 (4.4 active), and warren clustering occurred only in ploughed plots. However, pasture communities composed of annual and perennial species growing on unploughed deep sandy soils were preferentially selected. Most warrens (81.4%) were dug under some kind of protection such as shrub roots and rocks. According to our results, when designing rabbit restocking programs that include the provision of artificial warrens, unploughed deep soils with plenty of shrubs and rocks should be preferentially selected to locate the artificial warrens, which should be spaced so there are ∼10 warrens per hectare and ∼5-6 burrow entrances per warren.
(1) A simulation model of grazing mechanics in ruminants shows that, due to the allometric relations of bite size and metabolic requirements to body size, small animals are able to subsist on shorter swards than large animals.
(2) The density of nutrients in the grazed horizon of the modelled swards markedly affected the ability of animals of a given body size to satisfy their energy requirements.
(3) By extension, the allometric relationships would be expected to apply in selective grazing and browsing species in their choice of food items of different size and nutrient content.
(4) The results support the argument that sexual segregation and habitat choice of dimorphic species is an effect of scramble competition for limited resources, the males thus being excluded from mutually preferred swards.
(5) The model provides an explanation for two interspecific phenomena amongst grazers: grazing succession and grazing facilitation.
The Wild rabbit (Oryctolaguscuniculus) is an endemic species of the Iberian Peninsula and is essential for the conservation of endangered predators. Rabbits are
also of high importance as a hunting species. From 1988, rabbits suffered the severe effects of rabbit hemorrhagic disease,
which caused large declines in most populations. Despite this fact, the National Red Data Lists continued to classify rabbits
as a “Least Concern” species. We used available hunting bag data from 1973 to 2002 to model national trends of rabbit abundance
and to evaluate the conservation status according to the criteria of the National Red Data List and the World Conservation
Union (IUCN). Generalized Additive Models were used as the statistical framework. The rabbit population of Spain suffered
a large decline of about 71% between 1973 and 1993. This decline was 49% in the period 1980–1990. Based on both Spanish and
World Conservation Union criteria, rabbits should be listed as ‘Vulnerable’, which demands a Conservation Plan Program. We
suggest that the lack of concordance between the best available evidence and the conservation status of the species is a consequence
of sociological constraints in conservation decisions. Rabbit conservation could face strong opposition from important socio-economic
lobby groups (hunters and farmers). As such, governments and researchers may prefer to exclude rabbits from any status category
requiring conservation action, despite the evidence of decline. We call for the urgent development of a nation-wide conservation
program for rabbits which includes both socioeconomic constraints and the available biological data on population trends.
KeywordsDecline-GAM-Haemorrhagic disease-Hunters-Population trends-Rabbit-Spain-Threatened species
Foraging herbivores respond to the spatial pattern of resources at a variety of scales. At small scales of space and time, existing models capture the essence of the feeding process and successfully predict intake rates. Models that operate over larger scales have not exhibited a similar success, in part because we have a limited understanding of the rules used by animals to make decisions in spatially complex environments, or of the consequences of departing from these rules. To evaluate the rules that large herbivores use when navigating between forages, we examined movements of bighorn sheep foraging on apparent prey (alfalfa plants) in hand-constructed patches of plants. Observations of movements and path lengths were compared to simulations that used a variety of different rules-of-thumb to determine a search path. Rules used in simulations ranged from a random walk with various detection distances, to more complicated rules that solved a variant of the travelling salesman problem. Simulations of a random walk yielded movement lengths that exceeded observations by a factor of 3 for long detection distances, and by 30-fold for short detection distances. Observed move distances were most closely approximated by simulations based on a nearest-neighbor ruleover 75 % of all moves by bighorn sheep were to the closest available plant. Movement rules based on random walks are clearly inappropriate for many herbivores that typically consume visually apparent plants, and we suggest the use of a nearest-neighbor rule for modelling foraging by large herbivores.
Structural equation modelling (SEM) is a powerful tool to explore and contrast hypotheses on causal relationships among variables using observational data. It constitutes an alternative to experimental approaches that is especially useful in the conservation of small populations where the implementation of treatments may have a negative effect on population viability. We are presently applying SEM to study the factors that condition reproductive success, seed emergence and plantlet survival in several plant species. We are also using model comparisons through multi-sample analysis to assess the implications of different microhabitats on the viability of a population. The most outstanding advantages of this tool are the global perspective used in the study of complex problems, the ability to discern the essential from the accessory, and the possibility of evaluating one's own hypotheses. The basic procedure, the limitations of this method and further applications in conservation and management are also discussed.
The role of herbivores in controlling plant species richness is a critical issue in the conservation and management of grassland biodiversity. Numerous field experiments in grassland plant communities show that herbivores often, but not always, increase plant diversity. Recent work suggests that the mechanisms of these effects involve alteration of local colonization of species from regional species pools or local extinction of species, and recent syntheses and models suggest that herbivore effects on plant diversity should vary across environmental gradients of soil fertility and precipitation.
The dehesas of the southwestern Iberian Peninsula are 'man-made' ecosystems characterised by a savannah like physiognomy. The trees are viewed as an integrated part of the system, and as a result are planted, managed , and regularly pruned. Palynological and historical evidence of the manipulation of initial ecosystems by man to obtain a savannah-like ecosystem is presented. The ecological functions of the tree are detailed using results obtained at two complementary scales. At a local scale, strong soil structural differences and functional differences in water budget and patterns of water use are observed under and outside the tree canopy. Using the concept of ecosystem mimicry, the two coexistent components of dehesas can be compared to two distant stages of a secondary succession characterised by very different behaviours. At the regional scale, evidence of relationships between tree density and mean annual precipitation over more than 5000km2 suggests that the structure of these man-made agroecosystems have adjusted over the long-term and correspond to an optimal functional based on the hydrological equilibrium hypothesis. Finally, the future of the dehesas in the face of contemporary exogenous threats of economic and global environmental origin is discussed.
The purpose of this book is to provide a readable account of the biological basis of the behaviour of sheep and of the relevance of this to the current practice of sheep production throughout the world. The focus is on issues central to animal production: feeding; social behaviour and organization; reproductive behaviour; maternal behaviour; and behaviour of the lamb.
(1) Faecal pellets of rabbits were collected from the Holkham sand dunes, Norfolk. The proportion of leaf epidermis of various plant species in the faecal pellets was compared with the proportions of the species in the surrounding vegetation. (2) Festuca rubra was the major contributor to the diet and was apparently preferred, since the proportion was greater in the faeces than in the vegetation. Ammophila arenaria, Carex arenaria, Poa pratensis and Dicranum scoparium were apparently disliked. (3) Monocotyledonous species formed the major part of the diet of rabbits throughout the year, but the contribution of dicotyledonous species and mosses increased slightly during spring and summer.
Illustrates the capabilities of structural equation modelling (SEM) for path analyses, using data from a study of hummingbird pollination of Ipomopsis aggregata. The main drawback to conventional path analysis is that the overall agreement between the path diagram (or "model') and the data is not quantified; this also means that there is no clear way to directly compare competing models of the same system. One of the major advantages of SEM is that it can test the descriptive ability of different models, allowing comparison. When unmeasured latent variables are required (eg to circumvent problems with multi-collinearity, to include estimates of measurement error, or to represent general "factors' such as size), SEM can directly incorporate them as well. SEM provides "modification indices' that indicate areas where the fit of a given model is especially poor, and therefore point to further observations or models that might adequately describe the data. Beyond these advantages, SEM also provides all the information provided by standard path analysis, including path coefficients, measures of explained variance, and total effects. -from Author
(1) Using the results of diet selection studies and two wild and two domestic species, we compare some aspects of ecology in relation to body size, the recent evolutionary history of the species and current forage conditions. (2) Food niche breadth and mter-species diet overlap seemed dependent upon recent evolutionary history as well as upon body size, but values were strongly influenced by forage quantity and quality. (3) Dietary selectivity appears especially sensitive to seasonal changes in forage quality, e.g. large as well as small animals pursued relatively selective strategies when forage conditions permitted, but body size and related nutritional-energetic demands appeared to set the limits where switches from selective to non-selective tactics took place. (4) Sensitivity to diet composition and quality increased with decreasing size except in the domestic sheep. It is likely that anatomical-physiological adaptations, including a relatively large rumeno-reticulum allow domestic sheep to utilize more forage plant species and mhabit a wider variety of niches and ecosystems than most ungulates. Human selection has made the sheep food and habitat generalists despite their relatively small size.
We experimented on how illumination, habitat structure, and three different species of owls affected the foraging behavior of Gerbillus allenbyi and G. pyramidum, two gerbil species that coexist on sand dune habitats in the Negev Desert, Israel. We also tested how illumination and habitat structure affected rates of predation by owls on the two gerbil species. In a large aviary, we manipulated presence and absence of owls, owl species, presence and absence of illumination, and shrub cover. In response to the presence of owls or to increased illumination, gerbils foraged less, shifted foraging activity to the bush microhabitat, and quit patches at a higher giving-up density of resources. In accord with moonlight avoidance, both gerbil species suffered higher predation rates under illumination than in the absence of illumination. In addition, G. pyramidum distinguished among owl species, as indicated by changes in patch use and habitat selection. Habitat structure also affected foraging behavior and rates of predation. Gerbils foraged less in the open than in the bush microhabitat, foraged less when there was no cover present, and foraged less in the bush microhabitat when patches were encumbered by entangling branches. In accord with avoidance of open areas, both gerbil species suffered higher rates of predation when shrub cover was 0% than when shrub cover was 10%. With 0% cover, G. allenbyi suffered higher predation rates than G. pyramidum, but with 10% cover, rates of owl predation did not differ between gerbil species. Rates of owl predation on the two species corresponded to their natural patterns of macro- and microhabitat partitioning; relative to G. allenbyi, G. pyramidum predominates on open sand dunes and biases its behavior toward the open microhabitat. The results suggest that predation interacts with resource competition to determine the distribution and habitat separation of G. allenbyi and G. pyramidum.
The potential of measurements of faecal accumulation in estimating absolute numbers of ungulate populations was tested in a study of enclosed Fallow deer populations (Dama dama L.). Faecal accumulation plots were established in two sites with known populations of deer. Weekly pellet group counts were related to the number of deer known to be in the area to produce a conversion factor for number of animal minutes per plot represented by a single pellet group. Conversion factors derived from the two separate sites were compared and used to estimate the unknown population of a third area. Defaecation rate of the deer was recorded and used with pellet group counts to derive an independent estimate of population size in all three areas. Conversion factors were consistent between areas (127.3; 126.0) and over time. Estimates of the size of the unknown population, based on the conversion factor, did not differ significantly from the true population size as assessed by direct count. Estimates derived from calculations involving defaecation rate were less reliable than those from the conversion factor method. Possible sources of maccuracy are reviewed, but it is concluded that faecal accumulation techniques have real value in estimating large ungulate populations.
(1) Radio-collared rabbits were followed throughout the year on an area of upland grazing and forestry plantations in the Scottish Borders to study their use of burrows and cover for refuge during the day. (2) Observations on the distribution of radio-collared rabbits, faecal pellets and burrows suggested an isolated, discrete population, using an area of approximately 37 ha. Trapping out at the end of the study gave a breeding density of approximately two rabbits ha-1. (3) A few rabbits were permanently in burrows in the middle of a field in the centre of the area. The remainder, 86% of the population, were to be found during the winter on the surface in surrounding forestry plantations. (4) Young rabbits at the end of the summer were initially to be found in burrows, but most of these left during November and went to live in the plantations. The youngest rabbits were the last to leave. (5) Ferreting the warrens in the middle of November suggested that all burrows within 70 m of Sitka spruce plantations were empty. (6) The movements of radio-collared rabbits in the plantations were not affected by the removal of those in burrows in the field in November and rabbits were not seen again in the field until the following February. (7) Surface-living rabbits were found further into the trees and away from the field edge as the winter progressed (up to 250 m) but started to move back to the field during the spring. (8) The results are discussed in relation to the causes of surface living in rabbits from the viewpoints of social behaviour and avoidance of predation, and in relation to the effectiveness of gassing burrows as a method of rabbit control in afforested areas.
We report on the responses of wild European rabbits (Oryctolagus cuniculus) to a reduction in predation risk from red foxes (Vulpes vulpes) in a predator removal experiment in montane Australia. Specifically we tested whether rabbits in two sites with reduced fox numbers moved further from refuge than rabbits in two sites with abundant foxes. We then compared diet quality by analysing stomach contents, gut morphology and age-specific body mass to determine if release from predation risk enables rabbits to access higher quality food and hence attain higher body mass and condition. During spotlighting on three quarterly surveys in 1994-1995, rabbits in fox removal sites were observed, on average, three times further from refuge compared to rabbits at sites with foxes. However, this freedom to forage far from cover did not translate into a higher quality diet. Analysis of the nitrogen and neutral-detergent fibre content of stomach samples taken from a shot sample of rabbits at their peak densities after fox removal showed no differences in short-term diet quality of male or female rabbits due to fox removal. In contrast, analyses of gut morphologies, which reflect long-term fibre intake, suggested that rabbits in removal sites fed on a diet higher in fibre and hence of lower quality. This was possibly due to the large increases in rabbit density associated with fox removal. Despite this, male rabbits in fox removal sites were heavier for their age, had longer intestines, and heavier stomach and gut contents. We suggest that rabbits in fox removal sites compensated for the lower quality diet by increasing intake which enabled them to maintain higher age-specific body mass but only because predation risk was reduced. This result highlights the untenable link between resource limitation and predation risk.
Evidence is presented showing that the wild rabbit, Oryctolagus cuniculus (L.),
is able to conserve body water and live through relatively long periods of environmental
heat and dryness.
Rabbits were kept in a 2-acre enclosure without access to water. After the
onset of extremely dry summer conditions, the rabbits lost weight slowly over a
period of 2 months, when most died after losing nearly 50% of their original weight.
The long survival of the rabbits under the experimental conditions is a result of the
efficiency of their mechanisms of water economy. Two such mechanisms were
studied; one was the ability to concentrate the urine. The data show that urine
concentrations vary in response to availability of water within the range 0.35 to
1.5M urea. The maximum value recorded was 2.OM urea. During severe restriction,
urine volume was greatly reduced. The other mechanism of water economy studied
was reduction of evaporative water loss. Measurements of burrow temperatures
and humidities emphasized the importance of this insular climate as an aid to
temperature regulation and water conservation. The burrow was shown to present
an environment of moderate, stable temperature and high humidity, which is
determined by the temperature and moisture content of the surrounding soil.
Shortage of water in natural pastures led to a sharp decline in a large rabbit population in arid, northeastern
South Australia. The pastures were dry and some rabbits drank at springs and water troughs.
Further from water, rabbits climbed trees and shrubs to obtain succulent leaves and twigs. Rabbits
provided with water maintained their weight and apparently survived better than those which did not
drink. It seems unlikely that the rabbits lost weight because the water shortage reduced the amount of dry
food they could eat. In caged rabbits, water shortage limits food intake but also results in low gut fill;
whereas the wild rabbits had the normal amount of digesta in their guts. It is more likely that, as the
pastures became dry, rabbits ate woody twigs and bark which were moist enough to meet their water
requirements but contained too little digestible energy for maintenance. The water shortage apparently
arose because rabbits were numerous and had eaten out the succulent pasture plants. Normally, it takes a
long drought to reduce arid-zone plants to dry straw, and overgrazing is probably the usual cause of a
lack of adequate water for rabbits.
European rabbits (Oryctolagus cuniculus) are of special concern, for different reasons. They are prey of many predators in Mediterranean ecosystems, an important game species, and even a pest that causes economic losses. Hence, estimate of population abundance is a major interest for conservation management and control programs. I estimated abundance of European rabbits in 6 different habitats by line transect sampling, pellet count, and warren count. Rabbits were most abundant in Mediterranean scrubland, closely followed by ash stands. Pastureland, lentiscus in plantations, and pine plantations had 3, 7, and 27 times fewer rabbits than the Mediterranean scrubland, respectively. Abundance determined by pellet counts corroborated results obtained by line transect sampling, except in the Mediterranean scrubland habitat, where number of pellets was less than expected. There was a significant correlation between number of pellets and rabbit density when data from the Mediterranean scrubland were replaced by data from pellet counts performed at the edge of the Mediterranean scrubland. Number (mean±SE) of warrens/100 m of transect was greatest for Mediterranean scrubland (3.5±0.5) and least for pastureland (0.6±0.2). Number of entrances/warren also differed among habitats; warrens in the pastureland had more entrances (11±1.2) than warrens in other habitats (between 5.5±0.6 and 9.0±1.2). Entrances were used more during spring (54.8%±4.3-74.6%±2.4) than during summer; the only habitat where entrances were used regularly in summer was the pastureland (54.6%±4.2 of entrances). Counting pellets and warrens can provide reliable estimates of rabbit abundance.
The effect of the growing season and topographic zone on biomass production, protein content, cell content (CC), lignin, cellulose, hemicellulose, digestibility (DMD), and mineral element concentrations (P, K, Ca, Mg, Na, Mn, Fe, Cu, Zn) were studied in herbage samples collected from semiarid grasslands in Central-Western Spain. Protein and mineral contents decreased as the growing season progressed whereas fibre properties tended to increase. Topographic gradient significantly affected peak biomass production, fibre properties, protein and mineral contents. Stepwise multiple regression showed that the prediction of biomass production on these areas was related to cellulose, Na, Fe, and Mg contents in the grassland community whereas fibre properties were mainly predicted by Ca, Na, and Cu. Principal component analysis indicated that the temporal evolution (component ID of the organic variables determined pasture quality whereas most of the variation in mineral content was related to the topographical gradient (component I). Some organic and inorganic parameters may cause deficiencies in cattle grazing on the upper and middle zones, mostly at the end of the growing season. The data suggest that information about the temporal and spatial variations of the production and nutritional quality of semiarid grassland is necessary for making correct management.
From 1987 to 1996, the nutritional quality of the main botanical components (grasses, legumes and forbs) in semi-arid grasslands in the dehesa ecosystem in western Spain was analysed. Herbage samples were collected at the end of spring, in 30 locations, at two different topographic positions (upper and lower slope zones). Herbage mass over 2 cm and proportion of botanical components were estimated and samples were analysed for crude protein, neutral-detergent fibre (NDF), hemicellulose, cellulose, lignin and in vitro dry matter digestibility (DMD). Analysis of variance revealed a significant effect of sampling year on the herbage mass, proportion of botanical components and their nutritional quality. The three botanical groups, grasses, legumes and forbs, followed similar year-to-year trends in their crude protein, cellulose and lignin contents and in vitro DMD. Herbage mass was not significantly related to any meteorological variables, suggesting that interannual variation in biomass production of botanically complex pastures cannot be explained by a single factor. However, annual precipitation was significantly related to the proportion of the botanical group that was dominant at each slope zone: grasses in the lower zone and forbs in the upper zone. In the upper zone, spring precipitation explained part of the interannual variation in the NDF, cellulose, lignin contents and in vitro DMD of the botanical components.
Rabbit warrens in a semiarid environment of New South Wales were concentrated in those areas where impact
penetrometer readings indicated friable soil to a depth of at least 75 cm. Isolated warrens in areas with few
warrens were found in restricted patches of favourable soil. The absence of warrens from areas with shallow
soil was considered to be due to high soil temperatures. The distribution of the rabbit in Australia was examined
in relation to deep soil temperatures. It was suggested that the application of bituminous coating on ripped
warrens may be a useful technique for the control of rabbits in the arid zone.
'Rabbits equipped with miniature radio transmitters were located when at rest during the day at Cape Naturaliste, W.A. The study site was open pasture with numerous warrens, surrounded by and containing patches of native vegetation in which there were few warrens. Rabbits for instrumentation were live-trapped on the pasture and were located by radio once per day during each of four tracking periods in February, March-April (non-breeding season), May, and June (breeding season). A total of 31 individuals provided 284 locations, 263 (93%) of which were in the scrub. Of 216 locations in the scrub where the position of the rabbit (above or below ground) was known, 164 (765%) were above ground. Individual rabbits were found at several places within their resting areas, some of which were over 100 m into the scrub. The relevance of these results to current methods of rabbit control is discussed.
The study determined the species components of the diets of small ruminants grazing mountain ranges of the Montseny Biosphere Reserve (Catalunya, NE Spain). Three mixed flocks of sheep and goats, led by shepherds, were monitored for a year. Animals grazed a mountain rangeland composed of Qeurcus ilex woodland and Calluna-Erica heathland during the day and were returned to their corrals every night. Diet selection was estimated using fecal analysis. Of the 111 species that were identified, 71 were common to both sheep and goat. Of these, 23 were represented in proportions of more than 1% of the annual diet. Even though goats and sheep grazed together, their diets were significantly different (p < 0.0001), the animal factor accounting for 18% to 60% of the total variation among the main diet components. Variation between seasons was also a major (5% to 56%) highly significant factor, while differences between flocks accounted for a significant, but relatively small part (3% to 10%) of the total variation in diet. The outstanding difference was the avoidance of the tree, Quercus ilex, by the sheep while the goats selected it throughout the year. Sheep selected graminoids throughout the year while goats tended to avoid them. For the rest there.was substantial overlap in species composition between the diet of sheep and goats, especially when analysed over an entire cycle.
Changes over 14 yr were investigated in the composition of a species-rich grassland in SW Spain. The vegetation was dominated by winter annuals, which germinated after the autumn rains and fruited in late spring or early summer; they comprised 86 of the 99 species recorded. Most of these species displayed considerable variations in abundance over the period of study. The abundance of many species was highly correlated with rainfall, which accounted for up to 83% of year-to-year variance (in Juncus capitatus). Rainfall over the whole growing season was a good predictor of abundance for more species than any of its component periods (25 species with significant associations out of 99). Cluster analysis resolved five groups of species with similar year-to-year variations in abundance: two groups contained most of the species showing significant positive correlations with rainfall, and another group contained a small number of generally infrequent species that showed significant negative correlations. The species in the remaining two groups had few significant correlations with rainfall. Only three moderately abundant species were significantly correlated with time. -from Authors
SUMMARY1By adopting the Habitats Directive (Directive 92/43 of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora) in 1992, the governments of the European Community committed themselves to the creation of the Natura 2000 ecological network, with the aim of conserving an extensive range of European habitat types and wildlife species. In doing so, they set in motion the most significant initiative for nature conservation in the history of Europe.2In Spain, Natura 2000 will have a considerable impact on the conservation of habitats and species, potentially increasing the percentage of national territory within protected areas from 6% to as much as 20%.3This paper aims to illustrate the importance of extensive farming systems to the maintenance of habitats within Natura 2000, and vice versa.
The seasonal and spatial pattern of diet composition of a population of wild rabbits Oryctolagus cuniculus L. occupying a southern Portuguese montado was estimated using the n-alkane technique. The diet was analysed in terms of components that are relevant to habitat management. The dietary categories considered were gum cistus leaves and flowers, cork oak and holm oak seedlings and acorns, cereals, olive tree regrowth and grass-forb species. The objectives were to assess the changes in diet across seasons in relation to the reproductive cycle of the rabbits, and to relate these changes to herbaceous biomass availability and to habitat structure, in terms of density of scrub cover and accessibility to arable crops. The results demonstrated that the diet was dominated by grass-forbs, and cereals when they were available. Browse was an important component of the diet and became more important in a year of low herbaceous biomass availability and in areas dominated by dense scrub. A similar phenomenon was observed in relation to consumption of acorns in winter. Seasonal and spatial variation in diet composition suggested a strategy aimed at maintaining a high quality diet. This was supported by the observed high dry matter digestibility of the diet during most of the year. The relevance of growing arable crops and providing fodder, as a means of increasing the carrying capacity of montados for rabbits and protecting the natural regeneration of trees, is discussed.
Leporids have long been known to reingest soft faeces. However, it was recently found that they regularly reingest hard faeces, too. During the daytime, both soft and hard faeces are defecated and all of the faeces are reingested. Excreted at night are the hard faeces, which are normally discarded but reingested in starvation. The separation mechanism in the proximal colon, which diverts fine particles into the caecum and thus only passes large food particles, produces hard faeces. When the mechanism ceases acting, fermented caecal materials are excreted as soft faeces. The reingestion of soft faeces, rich in vitamins and microbial proteins, is physiologically imperative. Hard faeces are basically a refuse, but their thorough mastication at reingestion reduces poorly digestible large particles to fine ones good for fermentation. The regular reingestion of daytime hard faeces thus promotes food digestibility. The temporary use of night-time hard faeces allows leporids to do without food for some time. It thus gives leporids behavioural flexibility and thereby an ecological advantage. Reingestion is also known in other small- to medium-sized herbivores, which are all caecal fermenters. Morphological differentiation between faeces is reported only in larger species, but all ingested faeces are found to be richer in nutrients than discarded ones. Thus a separation mechanism is probably present in all reingesting species. Reingestion activity is deeply related to other behavioural and physiological traits of small mammalian herbivores, hence its study is important to understanding of their ecology and biology. Leporids are the largest of the reingesting species except for the semi-aquatic Coypu, and reingestion by leporids is certainly the most sophisticated. This development of a reingestion-involved digestive system has probably brought them to their present niche, as terrestrial medium-sized generalist mammalian herbivores, and consequently made their characteristic hide-and-run lifeforms by exposing them to a strong predation pressure.
1. A dense understorey of annual and perennial herbs grow under the canopy of Retama sphaerocarpa shrubs in semiarid environments of south-east Spain, influencing plant productivity and diversity at a regional scale. We investigated the facilitation by the shrub on its understorey in field and laboratory experiments with Barley designed to explore the mechanisms of interaction between both vegetation layers and their spatial variation.
2. There was a gradient of spatial heterogeneity in soil chemical fertility under the shrub canopy, with organic matter and soil nitrogen contents higher at the centre than at the edge of the canopy. Dry mass production of Barley was also higher in soils from intermediate positions, and lower in soils from both the centre and edge of the canopy.
3. In the field, pots sown with Barley placed near the centre, at an intermediate position and at the edge of the canopy of Retama shrubs showed significant differences in productivity, suggesting a mulching effect of the canopy that also affects seedling establishment.
4. Micro-climatic measurements showed significant differences in total radiation reaching the soil, mean air and soil temperatures and maximum temperature among different positions in the understorey, increasing radially from the centre to the edge of the canopy.
5. These results and field observations suggest that the optimal association of climatic factors under the canopy would combine with a high soil fertility mediated by litter decomposition to increase biomass production mid-way between the centre and the edge of the canopy. Overstorey and understorey thus interact to increase nutrient retention locally, which benefits both the shrub and the herb layer.
1. The relationship between available biomass and short-term rate of intake (functional response) of herbivores is expected to provide a link between their food supply, and their distribution.
2. The functional response of captive wild rabbits (Oryctolagus cuniculus L.) on artificially produced broad-leaved (Lolium perenne L.) and narrow-leaved (Festuca ovina L.) grass swards was quantified.
3. The general prediction that habitat selection varied with biomass, and reflected the potential rate of intake defined by the functional response, was also tested. The main alternative predictions, that both intake rate and habitat selection increased asymptotically with biomass, or were biased towards intermediate habitat standing crop biomasses, were distinguished.
4. There was no relationship between biomass and short-term rate of intake on the narrow-leaved Festuca swards, but on the broad-leaved Lolium sward the short-term rate of intake increased asymptotically with biomass.
5. In a field experiment on Lolium swards, a population of free-living wild rabbits selected the shortest swards with the lowest biomasses, and which provided the lowest potential rates of intake.
6. Results demonstrate that free-living wild rabbits do not select habitats that provide the maximum potential rate of intake, nor did they select foraging habitat with intermediate standing crops. It is suggested that their selection of foraging areas in these grasslands which typify rabbit foraging habitat, is dominated by antipredator considerations rather than purely by rate of intake.
I address the selection of plants with different characteristics by herbivores of different body sizes by incorporating allometric relationships for herbivore foraging into optimal foraging models developed for herbivores. Herbivores may use two criteria in maximizing their nutritional intake when confronted with a range of food resources: a minimum digestibility and a minimum cropping rate. Minimum digestibility should depend on plant chemical characteristics and minimum cropping rate should depend on the density of plant items and their size (mass). If herbivores do select for these plant characteristics, then herbivores of different body sizes should select different ranges of these characteristics due to allometric relationships in digestive physiology, cropping ability and nutritional demands. This selectivity follows a regular pattern such that a herbivore of each body size can exclusively utilize some plants, while it must share other plants with herbivores of other body sizes. I empirically test this hypothesis of herbivore diet selectivity and the pattern of resource use that it produces in the field and experimentally. The findings have important implications for competition among herbivores and their population and community ecology. Furthermore, the results may have general applicability to other types of foragers, with general implications for how biodiversity is influenced.
Summary 1. A central concept in ruminant foraging ecology is that even slight changes in plant quality affect body growth substantially, because ruminants not only gain more protein and energy but also use less time for rumination when eating high-quality forage. Increased access to highly nutritious forage is thus regarded as an important driving force in the evolution of migration in large herbivores, because the temporal and spatial variation in plant quality is huge. Body weight is in turn a major determinant of repro- ductive performance and survival in ungulates, and therefore important for population dynamics.
SummaryEuropean rabbits, Oryctolagus cuniculus, are the basic prey of several endangered predators and an important hunting bag in the area of its origin in southwestern Europe. Conversely, they are considered an undesirable species in other areas where they were introduced. Therefore, there is great interest in understanding the factors that influence population dynamics and abundance of this species. I studied the effects of relatively common heavy rains on inter-annual variations in rabbit density in four habitats of Doñana National Park and surrounding areas (southwestern Spain) during several years when rainfall was either lower or higher than average. I estimated spring and autumn rabbit densities by line transect sampling between autumn 1993 and autumn 1998, and counted rabbit warrens and entrances in two of the habitats (one with and the other without scrubland vegetation) in 1995, 1996 and 1997. Rabbit density significantly decreased in all habitats during the rainy years, densities being on average 5.3 and 4.6 times lower for spring and autumn censuses, respectively. Both number of warrens and entrances significantly decreased after two consecutive years of heavy rain in both habitat types, although in the scrubland habitats some recovery was observed during the second consecutive year of heavy rains. The area where warrens were apparently free of the effects of rains was only between 2.7 and 3.8% in the open habitat and 21.5% in the scrubland. At least for the open habitat, no clear relationship was observed between the height above sea level and whether warrens were affected by rain or not. The results indicate that heavy rains may be an important factor decreasing rabbit density, at least in flat areas, by negatively acting on warrens during the breeding period.
Field observations were made on collared pikas, Ochotona collaris, in Alaska to determine whether the risk of predation affected foraging behaviour in this small, herbivorous lagomorph. Four lines of evidence suggest that pika foraging is risk sensitive. First, pikas concentrated their foraging near talus (rock piles) rather than away from it despite the increase in vegetation biomass with increasing distance from the talus. Second, juveniles increased their foraging distance from the talus to match adults after juveniles had been above ground for 2 weeks, and lactating females foraged further from the talus than when they were pregnant, exposing themselves to a greater risk, but also availing themselves of more food. Third, after an ermine, Mustela erminea, appeared, pika latency to resume foraging depended on how close the ermine had come to capturing the pika. Finally, foraging distance was altered experimentally by constructing talus ‘fingers’, which reduced predator risk, and by fertilizing different meadow areas, which enhanced forage value. In addtion to energy and nutrients, the risk of predation plays an important role in pika foraging behaviour.
It is generally recognized that larger animals eat more, live longer, have larger offspring, and so on; but it is unusual to see these commonplace observations as a basis for scientific biology. A large number of empirically based relationships describe biological rates as simple functions of body size; and other such relations predict the intrinsic rate of population growth, animal speed, animal density, territory size, prey size, physiology, and morphology. Such equations almost always exist for mammals and birds, often for other vertebrates and invertebrates, sometimes for protozoa, algae, and bacteria, and occasionally even for plants. There are too many organisms to measure all aspects of the biology of every species of population, so scientists must depend on generalizations. Body size relations represent our most extensive and powerful assemblage of generalizations, but they have never been organized for use in ecology. This book represents the largest single compilation of interspecific size relations, and instructs the reader on the use of these relationships; their comparison, combination, and criticism. Both strengths and weaknesses of our current knowledge are discussed in order to indicate the many possible directions for further research. This important volume will therefore provide a point of departure toward a new applied ecology, giving quantitative solutions to real questions. It will interest advanced students of ecology and comparative physiology as well as professional biologists.
(1) Three tropical grassland systems were examined in the Serengeti region of Tanzania with respect to changes in grass off-take by ungulates, small mammals and grasshoppers, within the annual cycle. These groups comprised most of the herbivore trophic level. (2) Within all three grassland systems there was, on average, a short period of one to four months during the dry season when available food was lower than the requirements of the herbivore trophic level. Such a shortage would be sufficient to limit the herbivore populations. (3) The limiting resource was the green component of the primary production during the dry season. At this time it was sufficiently low in abundance to be affected by the density of grazing herbivores. (4) Because grasses are dormant when grazing is greatest, and can recover quickly from the impact of grazing, this vegetation-herbivore system was potentially stable. (5) The temporary shortage of the food component of the primary production limiting the herbivores could be a feature common to all terrestrial vegetation-herbivore systems. (6) Since both primary and tertiary trophic levels must also be resource limited, this work suggests that all trophic levels may be limited by their resources.