Intraspecific functional diversity of common species enhances community stability

Common species are fundamental to the structure and function of their communities and may enhance community stability through intraspecific functional diversity (iFD). We measured among‐habitat and within‐habitat iFD (i.e., among‐ and within‐plant community types) of two common small mammal species using stable isotopes and functional trait dendrograms, determined whether iFD was related to short‐term population stability and small mammal community stability, and tested whether spatially explicit trait filters helped explain observed patterns of iFD. Southern red‐backed voles (Myodes gapperi) had greater iFD than deer mice (Peromyscus maniculatus), both among habitats, and within the plant community in which they were most abundant (their “primary habitat”). Peromyscus maniculatus populations across habitats differed significantly between years and declined 78% in deciduous forests, their primary habitat, as did the overall deciduous forest small mammal community. Myodes gapperi populations were stable across habitats and within coniferous forest, their primary habitat, as was the coniferous forest small mammal community. Generalized linear models representing internal trait filters (e.g., competition), which increase within‐habitat type iFD, best explained variation in M. gapperi diet, while models representing internal filters and external filters (e.g., climate), which suppress within‐habitat iFD, best explained P. maniculatus diet. This supports the finding that M. gapperi had higher iFD than P. maniculatus and is consistent with the theory that internal trait filters are associated with higher iFD than external filters. Common species with high iFD can impart a stabilizing influence on their communities, information that can be important for conserving biodiversity under environmental change.     

The influence of spring floods on small mammal communities in the Nemunas River Delta, Lithuania

The influence of the annual spring floods on small mammal communities was studied in the Nemunas River Delta, SW Lithuania. The aim of the investigation was to compare the diversity of small mammals inhabiting spring-flooded meadows, meadows not subjected to flooding and spring-flooded forest in years characterized by differing heights and durations of spring flood. In the years of the high flood, the number of species and diversity index were higher, while index of dominance was less than in the years of low flood. Significantly, the highest proportions of Apodemus agrarius were recorded in spring-flooded meadows in years of high flood (41.7%), while Microtus oeconomus occurred in the highest proportions in spring-flooded meadows in years of low flood (66.8%) and in meadows not subjected to flooding (47.1%). In non-flooded areas, M. Oeconomus is not expelled by the floods and outcompetes other species. After high levels of flooding, during the process of re-population, the voles may be outcompeted by A. agrarius. In the absence of dominant species, greater opportunities existed for the establishment of more species (13 species in flooded meadows). Micromys minutus accounted for up to 19.5–30.1% in the years of high flood. We concluded that the annual spring floods in the Nemunas Delta had no long-term negative effects, the number of small mammal species and their abundance had been restored in just a few months. The worst consequences of the high flood were recorded in forest habitat. Spring floods, and especially the higher floods, are natural environmental agents, maintaining the high diversity of small mammals in meadows and reed-beds.     

Spatio‐temporal covariation in abundance between the cyclic common vole Microtus arvalis and other small mammal prey species

Populations of the common vole Microtus arvalis in mid‐western France show cyclic dynamics with a three‐year period. Studies of cyclic vole populations in Fennoscandia have often found inter‐specific synchrony between the voles and other small mammals which share the voles' predators. Although predators are central to the favoured mechanism to explain Fennoscandian vole cycles and the spatial variation of small mammal populations, their role in vole cycles elsewhere, including France, is less clear. Establishing whether alternative prey species in France cycle in parallel with voles as they do in Fennoscandia is thus an important step towards understanding the generality of predators' influence on cyclic vole populations. We applied spatial and temporal autocorrelation and cross‐correlation methods to French populations of M. arvalis and two sympatric non‐cyclic small mammal species, Apodemus sylvaticus and Crocidura russula. Patterns of time‐lagged cross‐correlation between the abundance of M. arvalis and the other two species suggested synchrony in their dynamics beyond that expected of stochastic environmental variation, and indicated a weak three‐year cycle in A. sylvaticus and C. russula that was in phase with that of M. arvalis. We interpret the synchrony between these species as the effect of shared predators and environmental stochasticity. Abundance within species showed weak spatial autocorrelation in June at scales consistent with dispersal being the mechanism responsible, but a more general lack of spatial structure within and between species was consistent with the strong spatial synchrony at regional scales often found in fluctuations of small mammal abundance.     

Trophic niche similarities of sympatric Turdus thrushes determined by fecal contents,stable isotopes,and bipartite network approaches

An ecological niche has been defined as an n‐dimensional hypervolume formed by conditions and resources that species need to survive, grow, and reproduce. In practice, such niche dimensions are measurable and describe how species share resources, which has been thought to be a crucial mechanism for coexistence and a major driver of broad biodiversity patterns. Here, we investigate resource partitioning and trophic interactions of three sympatric, phylogenetically related and morphologically similar species of thrushes (Turdus spp.). Based on one year of data collected in southern Brazil, we investigated niche partitioning using three approaches: diet and trophic niche assessed by fecal analysis, diet and niche estimated by stable isotopes in blood and mixing models, and bipartite network analysis derived from direct diet and mixing model outputs. Approaches revealed that the three sympatric thrushes are generalists that feed on similar diets, demonstrating high niche overlap. Fruits from C3 plants were one of the most important food items in their networks, with wide links connecting the three thrush species. Turdus amaurochalinus and T. albicollis had the greatest trophic and isotopic niche overlap, with 90% and 20% overlap, respectively. There was partitioning of key resources between these two species, with a shared preference for fig tree fruits—Ficus cestrifolia (T. amaurochalinus PSIRI% = 11.3 and T. albicollis = 11.5), which was not present in the diet of T. rufiventris. Results added a new approach to the network analysis based on values from the stable isotope mixing models, allowing comparisons between traditional dietary analysis and diet inferred by isotopic mixing models, which reflects food items effectively assimilated in consumer tissues. Both are visualized in bipartite networks and show food‐consumers link strengths. This approach could be useful to other studies using stable isotopes coupled to network analysis, particularly useful in sympatric species with similar niches.     

Resource partitioning of sympatric small mammals in an African forest‐grassland vegetation mosaic

It is often hypothesized that two species competing for the same resource cannot stably coexist unless they partition their resources in space and time. More recently stable isotope analyses have complemented traditional, observation‐based niche research by conceptualizing many of the characteristics of communities, for example, trophic niche width and the partitioning of resources. Here we quantify resource partitioning of sympatric small mammal species in an African ecosystem by analysing stable isotope ratios of hair collected from a South African forest‐grassland vegetation mosaic, and combine this with known spatial and temporal behavioural data to interpret community competition and resource partitioning. We observe niche separation to different degrees across the entire community, with different species displaying either unique isotopic dietary preferences, or partitioning resources in space and/or time. δ¹³C values were more enriched in species that inhabited afromontane grassland compared with those that inhabited afromontane forest, a reflection of the dominant vegetation in each habitat. Contrary to expectations, arboreal rodents occupied higher trophic positions than terrestrial rodents and approaching δ¹⁵N values similar to insectivorous shrews, suggesting that arboreal rodents feed on items such as arthropods enriched in ¹⁵N. While grassland species display phenotypic plasticity in terms of dietary preferences, small mammals that occurred in forests display narrow niche preferences, suggesting these species may be particularly sensitive to habitat modifications. Our results illustrate that the use of stable isotopes can be used in conjunction with spatial and temporal behavioural knowledge to elucidate resource partitioning in small African mammal communities.     

Habitat patch and matrix effects on small-mammal persistence in Amazonian forest fragments

Tropical forest mammal assemblages are widely affected by the twin effects of habitat loss and habitat fragmentation. We evaluated the effects of forest patch metrics, habitat structure, age of patch isolation, and landscape metrics on the species richness, abundance and composition of small mammals at 23 forest fragments (ranging in size from 43 to 7,035 ha) in a highly deforested 3,609-km² landscape of southwestern Brazilian Amazonia. Using pitfall traps and both terrestrial and arboreal traplines of Sherman, Tomahawk and snap traps, we captured a total of 844 individuals over 34,900 trap-nights representing 26 species and 20 genera of small-mammals, including 13 rodent and 13 marsupial species. We also consider the effects of distance from forest edges on species occupancy and abundance. Overall small mammal abundance, species richness and species composition were primarily affected by the quality of the open-habitat matrix of cattle pastures, rather than by patch metrics such as fragment size. Ultimately, small mammal community structure was determined by a combination of both landscape- and patch-scale variables. Knowledge of the anthropogenic factors that govern small mammal community structure is of critical importance for managing the persistence of forest vertebrates in increasingly fragmented neotropical forest landscapes.     

Similarity in occupancy of different-sized forest patches by small mammals on clearcuts: conservation implications for red-backed voles and small mustelids

Many mammalian species decline on forest sites that are harvested by clearcutting because of a loss of food, cover, and other components of stand structure. Small mustelids are impacted negatively as is the southern red-backed vole (Myodes gapperi), a principal prey species, that disappears from clearcuts within a year of harvest. These effects may be potentially ameliorated by aggregated retention harvests that leave unlogged patches on clearcuts. We tested three hypotheses (H) that (H₁) abundance, reproduction, and survival of M. gapperi populations, (H₂) total abundance, species richness, and diversity of the forest-floor small mammal community, and (H₃) the presence of small mustelids would be greater in large than small patches of retention forest on new clearcuts. We measured demographic responses of M. gapperi, total small mammals, and the presence of small mustelids (American marten, Martes americana, and small weasels (Mustela spp.)) from 2014 to 2016 in replicated treatments of four sizes (ha) of retention patches (means of 0.53, 1.50, 4.13, and 18.73) near Elkhart in south-central British Columbia, Canada. Mean abundance, reproduction, and survival attributes of M. gapperi were similar among treatment sites over the 3-year study. Overall mean abundance ranged from 3.5 to 5.3 voles per line in patches while this microtine was extirpated on clearcut sites (i.e., no forest patches). The similarity in population dynamics among the various forest patches across a gradient of increasing patch size of 4.5 to 35.3 times did not support H₁. Mean abundance, species richness, and diversity of total forest-floor small mammals were similar among treatment sites, and hence did not support H₂. Although not formally significant, mean species diversity did show a consistent increase from the largest (0.82) to the smallest (1.11) patch size, owing primarily to the presence of several generalist species such as Neotamias amoenus, Microtus, and Sorex in nearby early successional habitat. Small mustelids were present at similar levels among patch sizes, presumably in response to abundance of small mammal prey, and hence did not support H₃. Although our results were relatively short-term, the detailed assessment of population dynamics of M. gapperi indicated that habitat quality was sufficient to maintain this species regardless of patch sizes, ranging from 0.3 to 20.0 ha. Similarly, the total forest-floor small mammal community and presence of small mustelids also followed this pattern. All sizes of forest patches have conservation value and will help to maintain abundance and diversity of forest mammals, both predator and prey species, on clearcuts. Longer-term studies (e.g., at 5- to 10-year intervals) are essential to determine if our results are sustainable in augmenting forest restoration.

     

Predicting small‐mammal responses to climatic warming: autecology,geographic range,and the Holocene fossil record

Forecasting how species will respond to climatic change requires knowledge of past community dynamics. Here we use time‐series data from the small‐mammal fossil records of two caves in the Great Basin of the American West to evaluate how contrasting and variable local paleoclimates have shaped small‐mammal abundance dynamics over the last ～7500 years of climatic change. We then predict how species and communities will respond to future scenarios of increased warming and aridity coupled with continued spread of an invasive annual grass (Bromus tectorum). We find that most community‐level responses to climatic change occur in the mammalian abundance structure at both sites; the dominance of the community by individuals from species with a southern geographic affinity increases with climatic warming. This suggests that responses occurred in situ rather than by the immigration of new taxa over this time interval. Despite predictability at the community‐scale, species‐level relationships between abundance and climate are variable and are not necessarily explained by a species' geographic affinity. Species present at both sites, however, exhibit remarkably similar responses to climate at each site, indicating that species autecology (specifically dietary functional group) is important in determining response to climatic warming. Regression‐tree analyses show remarkable concordance between the two cave faunas and highlight the importance of a granivorous dietary strategy in this desert ecosystem. Under projections of increased temperature and decreased precipitation over the next 50 years, our results indicate that granivores should thrive as communities become more dominated by individuals with a southern geographic affinity. Granivores, however, are negatively impacted by the invasion of cheatgrass. The last century of anthropogenic impacts has thus placed granivores at a greater risk of extinction than predicted under climate‐only scenarios.     

Niche dynamics of sympatric non-breeding shearwaters under varying prey availability

Variation in prey availability can cause changes in species interactions among marine predators. Foraging theory predicts that niche breadth will expand when resources become limited, possibly leading to higher niche overlap among sympatric species; however, a species’ niche can become constrained by interactions with other similar species, resulting in an inability to shift niche breadth or position. In coastal Newfoundland, Capelin Mallotus villosus is the main forage fish species and its availability (i.e. biomass) during the summer has varied considerably following a population collapse in the 1990s. During the summer, non-breeding Great and Sooty Shearwaters Ardenna gravis and A. grisea migrate and aggregate at annually persistent Capelin spawning sites. We used stable isotope ratios (δ¹³C, δ¹⁵N) of blood components (plasma, red blood cells) to investigate variation in isotopic niche breadth (95% prediction ellipse areas) and overlap of the two shearwater species during 2014, 2015 and 2016. Capelin availability varied among years, illustrated by lower peak biomass in 2015 (0.126 g/m²) and 2016 (0.027 g/m²) relative to 2014 (0.254 g/m²). The isotopic niche breadth (plasma) of both shearwater species expanded similarly from 2014 (0.65–0.66‰²) to 2015 (2.22–2.57‰²) and 2016 (1.15–1.42‰²), suggesting the incorporation of alternative prey types into their diet during years of lower prey availability. Isotopic niche overlap between Great and Sooty Shearwaters remained high across years (44–63%), however, providing little evidence for dietary niche partitioning during years of lower prey availability. Findings suggest that both shearwater species are flexible foragers and can modify their diet during the non-breeding season to accommodate fluctuations in prey availability.     

Niche partitioning between close relatives suggests trade‐offs between adaptation to local environments and competition

Niche partitioning among close relatives may reflect trade‐offs underlying species divergence and coexistence (e.g., between stress tolerance and competitive ability). We quantified the effects of habitat and congeneric species interactions on fitness for two closely related herbaceous plant species, Mimulus guttatus and Mimulus laciniatus, in three common habitat types within their sympatric range. Drought stress strongly reduced survival of M. guttatus in fast‐drying seeps occupied by M. laciniatus, suggesting that divergent habitat adaptation maintains this niche boundary. However, neither seedling performance nor congeneric competition explained the absence of M. laciniatus from shady streams where M. guttatus thrives. M. laciniatus may be excluded from this habitat by competition with other species in the community or mature M. guttatus. Species performance and competitive ability were similar in sympatric meadows where plant community stature and the growing season length are intermediate between seeps and streams. Stochastic effects (e.g., dispersal among habitats or temporal variation) may contribute to coexistence in this habitat. Habitat adaptation, species interactions, and stochastic mechanisms influence sympatric distributions for these recently diverged species.     

Mammalian Diet and Broad Hunting Strategy of the Dingo (Canis familiaris dingo) in the Wet Tropical Rain Forests of Northeastern Australia1

The diet of dingoes (Canis familiaris dingo) in the Australian Wet Tropics was examined by analyzing 383 dingo scats collected throughout the region for the presence of mammal prey remains. The scats yielded 29 native and 4 introduced mammal prey species from 14 families. The most important species in terms of percentage occurrence in the scats were Melomys cervinipes (22.2%), hoodon macrourus (17.0%), Perameles nasuta (12.5%), and Thylogale stigmatica (12.5%). The most important families were Muridae (37.1%), Peramelidae (29.5%), and Macropodidae (25.8%). Examination of small‐scale habitat preferences revealed species that preferentially use the forest edge ranked significantly higher in the diet than those that do not, and species that are terrestrial ranked higher in the diet than those that are arboreal. Relative abundance was also a significant factor in the ranked dietary occurrence of each species, with abundant species ranked significantly higher than those that are less abundant. These results suggest that dingoes in the Australian Wet Tropics are opportunistic predators of a wide variety of mammal species, with abundant terrestrial and forest edge‐dwelling taxa the most susceptible to predation.     

Using scats of a generalist carnivore as a tool to monitor small mammal communities in Mediterranean habitats

Owl pellets have long been used to analyze communities of small mammals, while analogous analyses of faeces of mammal carnivores are not available. We demonstrate that common genet (Genetta genetta) scats can be used as a reliable method to sample small mammal communities and to monitor their variations. We have compiled data on 6350 small mammal remains of 18 species found in scats from 51 different latrines in a 1200 km² area of northeastern Spain. Genet scats sampled effectively 95.6% of the small mammal species ranging in size from 2.7 to 385 g. Spatial patterns of diet composition along environmental gradients of elevation, climate and land-use matched expected changes in small mammal communities along these gradients according to ecological requirements of prey species. Frequencies of occurrence of prey in genet scats were strongly correlated with frequencies of occurrence in barn owl (Tyto alba) pellets. Genet scats included two forest species not preyed upon by owls, whereas only one species was not preyed upon by genets. Forests species were more frequent in genet than in barn owl diets after correcting for environmental effects, whereas the opposite was true for open-habitat and synanthropic species. Scats of generalist carnivores can be used to estimate the spatial patterns of distribution and abundance of small mammal communities. Genet scats in fact overcome some of the limitations of more traditional sampling methods (live-trapping and owl diets), as genets were less selective and their diets reflect more accurately changes in community composition.     

Trophic levels of small mammals: Multi-elemental composition and toxic load

The chemical compositions (25 elements) of the diet and carcass of two sympatric small mammal species (Clethrionomys glareolus and Sorex caecutiens) inhabiting near a large copper smelter and in unpolluted area (Middle Ural, Russia) have been analyzed and compared. The group of phytophages is shown to play a special role in the translocation of chemical elements over the trophic levels of mammals. Specific features of the diet and a barrier at the gastrointestinal level limit accumulation of chemical elements in the animal body. Under the same conditions, carnivores act in the mammal community as concentrators of several elements (Pb, Cd, Cr, and As), displaying increased their concentrations in the body as compared with the diet. On the other hand, the toxic load on the animal organism is independent of trophic specialization.     

Species‐specific ontogenetic diet shifts among Neotropical Crenicichla: using stable isotopes and tissue stoichiometry

Ontogenetic diet shifts were compared among five sympatric pike cichlids Crenicichla in a subtropical South American stream using stable C and N isotopes and tissue stoichiometry (C:N). Within species, stable N isotopes were positively related to body size while C:N showed negative relationships. Stable C isotopes, however, were not related to body size in any species. By modelling the switch to piscivory using gut content‐isotope‐body size relationships, diet shifts were shown to be species‐specific with regard to both rate and degree of piscivory. Compared to other piscivorous lineages, Crenicichla appear to be unusually small‐bodied (based on maximum body size). Because of their diversity, abundance and dynamic size‐structured functional roles, Crenicichla may exert broad and complex predation pressures on the aquatic community.     

Diet and prey selection of sympatric tropical skinks

Most skinks are opportunistic predators, taking available prey from the environment as it is encountered. Variation in their diet composition is thought to reflect differences in prey abundance in the environment. We studied diet composition and prey selection in a community of three sympatric skink species (genus Carlia) in northern Australia by comparing contents of skink stomachs with arthropod prey available in their habitat. Carlia were entirely carnivorous and fed on a range of arthropod prey. We found high overlap in diet and prey size among the three species and between the wet and dry seasons, but found that skinks generally focused their foraging efforts on prey types and prey sizes that were not abundant in the habitat. Spiders (Aranea), orthopterans, blattarians, isopods and termites (Isoptera) were important prey of skinks, but these arthropods were rarely trapped in the environment. Skinks also frequently consumed large‐bodied prey, despite the higher relative abundance of small prey in the environment. Skinks were more selective in their foraging and diet than previously assumed. Selection of prey by consumers is a fundamental ecological process, important to consumers for maintaining energy requirements to grow and reproduce, but equally important to the community dynamics of the prey consumed.     

Prey choice by marten during a decline in prey abundance

Summary We examined variation in diet choice by marten (Martes americana) among seasons and between sexes and ages from 1980–1985. During this period prey populations crashed simultaneously, except for ruffed grouse (Bonasa umbellus) which was common at the beginning and end of the study, and masked shrews (Sorex cinereus) which were abundant in 1983. Marten were catholic in selection of prey and made use of most available mammalian prey, ruffed grouse, passerine birds, berries, and insects. Diet niche was widest during the latter three years when prey was scare, particularly in late winter. Diet niche breadth was negatively correlated with abundance of all common prey species. Proportion of small prey species in the diet was correlated with absolute abundance of those species, but proportion of some large prey was related to their relative abundance. Diet choice varied among years and among seasons. Berries and insects were common in summer diets while large prey, particularly varying hare (Lepus americanus), were more frequent in winter diet than in summer diet. We found little evidence that any small mammal species was a preferred prey. Sexual size dimorphism between the sexes did not affect prey choice, nor did age. Reduced foraging effort in winter resulted in a wider diet niche only when prey was scarce. The only prediction of optimal foraging models fully supported by our data was a wider diet niche with reduced prey abundance. However, among the three most profitable prey species choice was dependent on the absolute abundance of the most profitable type (varying hare). We suggest that marten primarily forage for large prey but employ a strategy which results in encounters with small prey as well. These small prey are eaten as they provide energy at minimal cost, between captures of large prey.     

Temporal variation in trophic relationships among three congeneric penguin species breeding in sympatry

Penguins are a monophyletic group in which many species are found breeding sympatrically, raising questions regarding how these species coexist successfully. Here, the isotopic niche of three sympatric pygoscelid penguin species was investigated at Powell Island, South Orkney Islands, during two breeding seasons (austral summers 2013–2014 and 2015–2016). Measurements of carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope ratios were obtained from blood (adults) or feather (chicks) samples collected from Adélie Pygoscelis adeliae, chinstrap P. antarctica, and gentoo P. papua penguins. Isotopic niche regions (a proxy for the realized trophic niches) were computed to provide estimates of the trophic niche width of the studied species during the breeding season. The isotopic niche regions of adults of all three species were similar, but gentoo chicks had noticeably wider isotopic niches than the chicks of the other two species. Moderate to strong overlap in isotopic niche among species was found during each breeding season and for both age groups, suggesting that the potential for competition for shared food sources was similar during the two study years, although the actual level of competition could not be determined owing to the lack of data on resource abundance. Clear interannual shifts in isotopic niche were seen in all three species, though of lower amplitude for adult chinstrap penguins. These shifts were due to variation in carbon, but not nitrogen, isotopic ratios, which could indicate either a change in isotopic signature of their prey or a switch to an alternative food web. The main conclusions of this study are that (1) there is a partial overlap in the isotopic niches of these three congeneric species and that (2) they responded similarly to changes that likely occurred at the base of their food chain between the 2 years of the study.     

Indiscriminate Feeding by a Predatory Stonefly (Plecoptera: Perlidae) in a Tropical Asian Stream

The diet of an undescribed species of Kamimuria was investigated in Tai Po Kau Forest Stream, Hong Kong, by comparing larval gut contents with the array of available prey living on and among cobble substrates. Diets were dominated by chironomids and philopotamid caddisflies, with Baetidae, Heptageniidae, Hydropsychidae and Simuliidae comprising secondary dietary items. These six taxa made up 94% of the prey individuals eaten by Kamimuria. Data analysis using a selectivity index revealed that these stoneflies fed indiscriminately, eating individual prey taxa in proportion to their availability in the environment. Large and small Kamimuria exploited essentially the same prey. A comparison of the diet of Kamimuria with the diets of four sympatric Odonata indicated that the degree of interspecific similarity was determined by the extent of overlap in microhabitat use. Diets of Euphaea decorata (Zygoptera) larvae, which live under cobbles, were most similar to Kamimuria. This is the first – albeit limited – study of the gut contents of a tropical Asian stonefly. The results suggest that these predators have the potential to limit benthic invertebrate abundance but, because Kamimuria larvae feed unselectively, community structure may not be affected by their activities.     

Sympatric Chimpanzees (<Emphasis Type="Italic">Pan troglodytes troglodytes</Emphasis>) and Gorillas (<Emphasis Type="Italic">Gorilla gorilla gorilla</Emphasis>) in Loango National Park,Gabon: Dietary Composition,Seasonality, and Intersite Comparisons

Dietary overlap of sympatric apes is complex and understudied, but its examination is essential to further our understanding of species distribution, abundance, and community ecology. Over 3 yr we studied food availability and dietary composition of central chimpanzees (Pan troglodytes troglodytes) and western gorillas (Gorilla gorilla gorilla) in Loango National Park, Gabon. We predicted that living in a habitat dominated by mature forest with sparse terrestrial herbaceous vegetation would lead to an increase in frugivory by gorillas, resulting in increased dietary overlap between the 2 ape species vs. other sites, but that chimpanzees would remain more frugivorous than gorillas. Through fecal analysis we measured overlap in fruit consumption between the 2 species on a bimonthly basis using the Renkonens method. Mean overlap was 27.5% but varied greatly seasonally, ranging between 0.3% and 69%, indicating that when examined on a finer scale, the degree of overlap appears much lower than at other study sites. In contrast to studies elsewhere, there was not a positive correlation between rainfall and fruit availability in Loango, and the long dry season was a period of high fruit production. As observed elsewhere, we found a positive correlation between fruit consumption and fruit availability for both chimpanzees and gorillas and we found that chimpanzees were more frugivorous than gorillas. A very low availability of herbs did not lead to increased frugivory by gorillas nor increased overlap between the 2 ape species vs. other field sites. We conclude that forest composition, fruit availability, and dietary variability of sympatric species can vary greatly between locations, and that chimpanzees and gorillas can adapt to primary forest with little undergrowth, where they concentrate their diet on fruit and leaves.     

Habitat use by singing voles and tundra voles in the southern Yukon

Summary We investigated how far competitive interactions influence the use of habitats and relative abundance of two species of Microtus in the southwestern Yukon. We worked in the ecotone between alpine tundra and subalpine shrub tundra where populations of singing voles (Microtus miurus) and tundra voles (M. oeconomus) overlap little.We removed tundra voles from shrub tundra on one live-trapping area to look at the effect on the contiguous population of singing voles in alpine tundra. The removal of tundra voles did not affect the distribution or relative abundance of singing voles. The spatial distribution of these species and their movements within habitats suggest that they have a strong habitat preference.Populations of small mammals in the area are extremely dynamic and the relative importance of competitive interactions may change as density varies. At present we have no evidence that competition affects habitat use in M. miurus.