Dietary overlap and potential competition in a dynamic ungulate community in Northwestern Canada

Snow depth influences harvest of a boreal ungulate more than socio-economic factors: Implications for food security in a changing climate

Climate change may affect the ability of hunters to harvest wildlife and, hence, threaten food security of local people. However, few studies have investigated the relative influence of environmental conditions on wildlife harvest rates. We harnessed a 24-year dataset of harvest dates for a boreal ungulate in a region where climate change is having pronounced impacts on snow depth, precipitation, and temperatures to investigate the effect of weather on harvest rates. We used generalized linear models and a model selection framework to examine the influence of weather covariates (snow depth, mean daily temperature, precipitation) and socio-economic factors (gasoline and red meat prices, employment rates, and moose [Alces americanus] harvest) on harvest rates of bison (Bison bison) in Yukon, Canada, at two temporal scales: annual and daily. At an annual scale, snow depth was the only covariate that was important in explaining bison harvest. No socioeconomic variables improved our model beyond the null. At the daily scale, snow depth and mean daily temperature influenced bison harvest rates, with a 1 SD increase resulting in a 14 % and 9 % increase in daily harvest rates, respectively. Increased snow depth facilitates ease of travel in remote, roadless areas by snowmobile to locate bison and truncates movements of bison, resulting in increased harvest rates. Decreased snow depth due to climate change will impact hunter access to boreal ungulates and food security for northern people. More broadly, our data suggests that in some socioecological systems, environmental covariates have a greater influence on wildlife harvest rates than socioeconomic factors and need to be considered in future studies to better understand and predict harvest rates.

Seasonal Diet Composition of Goitered Gazelle (Gazella subgutturosa) in an Arid and Semi-Arid Region of Western China

Global climate change, habitat fragmentation, and human interference have resulted in a significant, ongoing decline in the population of goitered gazelles. Effective conservation strategies require an understanding of resource requirements of threatened species, such as dietary needs. Therefore, we aimed to elucidate the food composition and seasonal dietary changes of goitered gazelles through microhistological analyses of fresh feces. Fabaceae (11.5%), Gramineae (9.4%), Chenopodiaceae (20.2%), Asteraceae (10.1%), and Rosaceae (19.5%) formed the primary dietary components of goitered gazelle. Additionally, Krascheninnikovia arborescens (13.4%) and Prunus sibirica (16.3%) were identified as the key forage plants. Forbs (50.4%) were the predominant plants for grazing throughout the year, particularly in the spring (72.9%). The proportion of trees in the diet was highest in the autumn (36.7%) and comparatively lower in other seasons. Furthermore, the proportions of shrubs (22.0%) and graminoids (14.8%) both reached their peaks in the winter. Our findings indicate that goitered gazelles strategically forage seasonally to cope with resource bottlenecks, enhancing their adaptability to arid and semi-arid habitats. Our study provides essential ecological information for the conservation of goitered gazelles and emphasizes the importance of dietary studies of species of ecological significance in environmentally sensitive areas.

Bison and bighorns: Assessing the potential impacts of reintroducing a large herbivore to a mountainous landscape

The reintroduction of wildlife can have significant ecological impacts by altering the flow of energy in food webs. Recently, plains bison were reintroduced to part of Banff National Park after a 150-year absence. The large herbivore's reintroduction was expected to have far-reaching effects on the ecosystem due to its significant energy requirements and interactions with habitat and other sympatric species. This study explores the impacts of bison reintroduction on the movement and resource use of another large-bodied grazer, the Rocky Mountain bighorn sheep. Between 2018 and 2021, we collected data from GPS collars fit on 39 bighorn sheep and 11 bison. We analyzed home range patterns, resource selection, and interactions to investigate the potential for interspecific competition, facilitation, and resource complementarity. At the population level, bison and bighorn sheep exhibited low levels of spatial overlap and there was strong evidence of resource separation in all seasons. Interactions between species did not appear to affect sheep movement rates; however, we did see differences in forage selection patterns for sheep with overlapping home ranges with bison. Collectively, results did not support the potential for competition or facilitation between bison and bighorn sheep and instead provided the strongest evidence of complementarity.

Trophic niche partitioning between two prey and their incidental predators revealed various threats for an endangered species

Documenting trophic niche partitioning and resource use within a community is critical to evaluate underlying mechanisms of coexistence, competition, or predation. Detailed knowledge about foraging is essential as it may influence the vital rates, which, in turn, can affect trophic relationships between species, and population dynamics. The aims of this study were to evaluate resource and trophic niche partitioning in summer/autumn between the endangered Atlantic‐Gaspésie caribou (Rangifer tarandus caribou) population, moose (Alces americanus) and their incidental predators, the black bear (Ursus americanus) and coyote (Canis latrans), and to quantify the extent to which these predators consumed caribou. Bayesian isotopic analysis showed a small overlap in trophic niche for the two sympatric ungulates suggesting a low potential for resource competition. Our results also revealed that caribou occupied a larger isotopic niche area than moose, suggesting a greater diversity of resources used by caribou. Not surprisingly, coyotes consumed mainly deer (Odocoileus virginianus), moose, snowshoe hare (Lepus americanus), and occasionally caribou, while bears consumed mainly vegetation and, to a lesser extent, moose and caribou. As coyotes and bears also feed on plant species, we documented trophic niche overlap between caribou and their predators, as searching for similar resources can force them to use the same habitats and thus increase the encounter rate and, ultimately, mortality risk for caribou. Although the decline in the Gaspésie caribou population is mostly driven by habitat‐mediated predation, we found evidence that the low level of resource competition with moose, added to the shared resources with incidental predators, mainly bears, may contribute to jeopardize the recovery of this endangered caribou population. Highlighting the trophic interaction between species is needed to establish efficient conservation and management strategies to insure the persistence of endangered populations. The comparison of trophic niches of species sharing the same habitat or resources is fundamental to evaluate the mechanisms of coexistence or competition and eventually predict the consequences of ecosystem changes in the community.

What do caribou eat? A review of the literature on caribou diet

Historically the study of diet caribou and reindeer (Rangifer tarandus (Gmelin, 1788)) has been specific to herds and few comprehensive circumpolar analyses of Rangifer diet exist. As a result, the importance of certain diet items may play an outsized role in the caribou diet zeitgeist, e.g., lichen. It is incumbent to challenge this notion and test the relevant importance of various diet items within the context of prevailing hypotheses. We provide a systematic overview of 30 caribou studies reporting caribou diet and test biologically relevant hypotheses about spatial and temporal dietary variation. Our results indicate that in the winter caribou primarily consume lichen, but in warmer seasons, and primary productivity is lower, caribou primarily consume graminoids and other vascular plants. In more productive environments, where caribou have more competitors and predators, consumption of lichen increased. Overall, our description of caribou diet reveals that caribou diet is highly variable, but in circumstances where they can consume vascular plants, they will. As climate change affects Boreal and Arctic ecosystems, the type and volume of food consumed by caribou has become an increasingly important focus for conservation and management of caribou.

Assessing the nutritional consequences of switching foraging behavior in wood bison

Diet is one of the most common traits used to organize species of animals into niches. For ruminant herbivores, the breadth and uniqueness of their dietary niche are placed on a spectrum from browsers that consume woody (i.e., browse) and herbaceous (i.e., forbs) plants, to grazers with graminoid-rich diets. However, seasonal changes in plant availability and quality can lead to switching of their dietary niche, even within species. In this study, we examined whether a population of wood bison (Bison bison athabascae) in northeast Alberta, Canada, seasonally switched their foraging behavior, and if so, whether this was associated with changes in nutrient acquisition. We hypothesized that bison should switch foraging behaviors from grazing in the winter when standing, dead graminoids are the only foliar plants readily available to browsing during spring and summer as nutritious and digestible foliar parts of browse and forbs become available. If bison are switching foraging strategy to maximize protein consumption, then there should be a corresponding shift in the nutritional niche. Alternatively, if bison are eating different plants, but consuming similar amounts of nutrients, then bison are switching their dietary niche to maintain a particular nutrient composition. We found wood bison were grazers in the winter and spring, but switch to a browsing during summer. However, only winter nutrient consumption of consumed plants differed significantly among seasons. Between spring and summer, bison maintained a specific nutritional composition in their diet despite compositional differences in the consumed plants. Our evidence suggests that bison are selecting plants to maintain a target macronutrient composition. We posit that herbivore's can and will switch their dietary niche to maintain a target nutrient composition.

Diet selection of white-tailed deer supports the nutrient balance hypothesis

Herbivores must navigate a heterogeneous matrix of nutrients in plant communities to meet physiological requirements. Given that the only difference between an essential nutrient and a toxin is the concentration in the herbivores diet, heterogeneity of nutrient concentrations in plant communities likely force wild herbivores to balance intake of abundant nutrients that may reach toxic levels with the need to meet nutritional demands of rare nutrients (i.e., nutrient balance hypothesis). While this hypothesis has been demonstrated in controlled studies with captive herbivores, experiments testing the nutrient balance hypothesis with wild herbivores are rare. We designed a cafeteria-style experiment to measure use of forages with differing nutritional compositions by wild white-tailed deer (Odocoileus virginianus) to test the nutrient balance hypothesis. We predicted deer diet selection would be explained by attraction to some nutrients and avoidance of others. Deer selected forages with low sulfur concentrations, a nutrient that commonly reaches toxic levels in herbivores. However, deer secondarily selected forages with greater digestibility and crude protein. Thus, our data indicate that the nutrient balance hypothesis may explain diet selection in wild herbivores where they avoid reaching toxicity of abundant nutrients while secondarily maximizing intake of limiting nutrients.

Can ancestry and morphology be used as surrogates for species niche relationships?

Species interactions are difficult to quantify, and, consequently, many studies have used species traits and phylogeny as proxies under an assumption of niche conservatism (i.e., closely related and morphologically similar species should have similar niches). However, few studies have investigated whether niches actually are conserved within and across diverse communities. Here, we tested the degree to which phylogenetic relatedness and morphological similarity predict diets and stable isotopic ratios (δ 15N and δ 13C), two common descriptors of the trophic niche, in fish assemblages of two small streams in the Neotropics. We also tested the strength of the association between isotopic ratios and diet composition and found significant correlations implying that isotopic signals reveal trophic structure despite error associated with estimates of trophic enrichment and variation associated with tissue preservation, metabolism, and other factors affecting isotopic ratios. Morphological traits yielded a significant phylogenetic signal, and both morphological traits and phylogeny were correlated with diet composition, with morphological traits being a stronger predictor. We infer that functionally relevant morphological traits of fish can be used to infer trophic niches for certain kinds of questions and analyses when trophic data are lacking. However, we highlight that using phylogenetic and morphological data in combination with dietary and/or isotopic data can improve resolution of assemblage trophic structure and niche diversification.

Effects of linear features on resource selection and movement rates of wood bison (Bison bison athabascae)

Human-mediated disturbances can lead to novel environmental features that can affect native biota beyond simple habitat loss. In boreal forests of western Canada, linear features (LFs; e.g., pipelines, seismic lines, and roads) are known to alter behaviour, movements, and interactions among species. Understanding LF impacts on native species has therefore been a management priority. Here, we investigate how LFs affect the spatial behaviour of wood bison (Bison bison athabascae Rhoads, 1898), which are designated as “threatened” in Canada. Using data collected from the Ronald Lake population in northeastern Alberta, we assessed how LFs influenced habitat selection and movement of bison by testing support among three hypotheses explaining whether LFs (i) increased forage availability, (ii) enhanced movement efficiency, or (iii) increased predation risk. Results supported the movement efficiency hypothesis as bison were generally ambivalent toward LFs, showing weak selection or avoidance depending on land-cover type, but moved slightly faster when on them. These findings contrast with avoidance behaviours reported for sympatric woodland caribou (Rangifer tarandus caribou (Gmelin, 1788)), which are also “threatened.” Our results should inform critical habitat decisions for wood bison, but we caution that further research is needed to understand the effects of LFs on bison demography.

Diet and isotopic niche of eastern sand darter (Ammocrypta pellucida) near the northern edge of its range: a test of niche specificity

Niche specificity can predispose species to population declines during periods of resource limitation, yet trophic niche specificity is poorly known for many small-bodied freshwater fishes. Applying a two-tiered approach involving stomach content and stable isotope analyses, we examined the diet and trophic niche of the threatened eastern sand darter (Ammocrypta pellucida (Putnam, 1863)) and co-occurring fishes in the Thames River, Ontario, Canada. As with previous studies, stomach content analysis revealed that eastern sand darter consumed a variety of benthic organisms including Chironomidae, Cladocera, Ostracoda, Oligochaeta, and Ephemeroptera; however, proportional contributions of prey groups differed based on stable isotope analysis, highlighting the potential for seasonal variation in prey consumption. Despite evidence of a generalist strategy, stable isotope analysis indicated eastern sand darter exhibited a relatively narrow trophic niche relative to co-occurring fishes. Trophic niche overlap was relatively minor between eastern sand darter and drift-feeding fishes (spotfin shiner (Cyprinella spiloptera (Cope, 1867)), emerald shiner (Notropis atherinoides Rafinesque, 1818), and buffalo sp. (genus Ictiobus Rafinesque, 1820)), but was more evident between eastern sand darter and benthic and benthopelagic fishes (johnny darter (Etheostoma nigrum Rafinesque, 1820) and blackside darter (Percina maculata (Girard, 1859))), indicating that competition with these species may be more likely during periods of prey scarcity.

HEALTH STATUS OF REINTRODUCED WOOD BISON ( BISON BISON ATHABASCAE): ASSESSING THE CONSERVATION VALUE OF AN ISOLATED POPULATION IN NORTHWESTERN CANADA

A central goal for reintroduced populations of threatened wood bison ( Bison bison athabascae) is to maintain them free of diseases of concern, particularly bovine tuberculosis (caused by Mycobacterium bovis) and brucellosis (caused by Brucella abortus). A wood bison population in southwestern Yukon, Canada was reintroduced into the wild in 1988, but no health assessment has been done since then. To provide an initial assessment of the health status and, hence, the conservation value of this population, we serologically tested 31 wood bison (approximately 3% of the population) for pathogens of interest and obtained histopathology results for select tissues. We found no evidence of exposure to M. bovis or Brucella spp., but antibodies were present to bovine parainfluenza virus 3, bovine coronavirus, Leptospira interrogans, and Neospora caninum, with seroprevalences of 87, 7, 61, and 7% of the tested animals, respectively. Reintroduced wood bison in southwestern Yukon may be of high value for wood bison recovery because it is a large and geographically isolated population with no bacteriologic, histopathologic, or serologic evidence of exposure to Brucella spp. or M. bovis.

Dry season diet composition of four-horned antelope Tetracerus quadricornis in tropical dry deciduous forests, Nepal

It is essential to assess the feeding strategies of threatened species during resource-scarce seasons to understand their dietary niche breadth and inform appropriate habitat management measures. In this study, we examined the diet composition of four-horned antelope (FHA) Tetracerus and quadricornis, one of the least studied ungulate species, in Banke National Park, Nepal. A total of 53 fresh pellet groups were collected between December 2015 and January 2016 and analyzed using micro-histological fecal analysis technique. First, we prepared 133 micro-histological photographs of different parts of 64 reference plant species. Then we compared 1,590 fragments of 53 fecal samples with photographs of reference plants to assess the percentage of occurrence of different plant species in FHA diet. A total of 30 plant species belonging to 18 different families were identified in fecal samples. Chi-square goodness of fit tests showed that FHA appeared not to feed all plant uniformly. Out of 1,520 identified fragments in fecal samples, 1,300 were browse species and 220 were grass species. Browse represented 85.5% of the identified plant fragments, suggesting that FHA might be adopting a browser strategy at least during winter when grasses are low in abundance and their nutritive quality is poor. Tree species had the highest contribution in the diet (46.55%) followed by shrubs (24.52%). The family Gramineae was consumed in the highest proportion (27.68%) followed by Euphorbiaceae (11.95%). Overall, our results suggest that FHA has the feeding plasticity to adapt to resource fluctuation. Based on the findings of this study, we recommend that dicot plant species-particularly fruit trees and shrubs, which are the major source of nutrients for FHA during resource-lean, dry season-be conserved and natural regeneration of these taxa be promoted.

Dietary resource use and competition between white-tailed deer and introduced sika deer

Content Native communities of herbivores have evolved fundamental dietary niches that avoid or minimise competition; the introduction of exotic species can change dietary niches, cause overlap in resource use, and result in competition for resources. Aims We compared niche breadth, overlap in diet, and quality of diet between introduced sika deer and native white-tailed deer in Maryland, USA. We investigated these changes in free-ranging populations where both species are allopatric as well as when they are sympatric. Methods We used microhistological analysis of faecal samples to determine the percentage of resources used by sika deer and white-tailed deer, as measured between geographical areas of similar habitat quality. We compared resource use specifically by controlling for harvest pressure and resource availability, which are known to alter resource use other than the presence of an additional deer species. Key results We observed a significant resource overlap (range 63–88%) between species. In the presence of sika deer, white-tailed deer displayed an increased niche breadth (108%) and a lower diet quality (17%). Sika deer consumed the same resources that comprised 78% of white-tailed deer diet. Unlike other native ungulates that have dietary overlap with white-tailed deer, sika deer is neither temporally nor geographically segregated in habitat use. Conclusions Resource overlap and changes in niche breadth and diet quality during sympatry strongly denote dietary competition between sika deer and white-tailed deer. This competition results in white-tailed deer altering the dietary selection, thereby consuming lower-quality forage. Implications White-tailed deer are concentrate selectors and require higher diet quality than do sika deer, which can tolerate diets higher in fibre, consistent with their classification as intermediate feeders. A decrease in the nutritional quality of resources used by white-tailed deer could contribute to the decline of white-tailed deer over time and allow the continued spread of sika deer.

Impact of rewilding, species introductions and climate change on the structure and function of the Yukon boreal forest ecosystem

Community and ecosystem changes are happening in the pristine boreal forest ecosystem of the Yukon for 2 reasons. First, climate change is affecting the abiotic environment (temperature, rainfall and growing season) and driving changes in plant productivity and predator–prey interactions. Second, simultaneously change is occurring because of mammal species reintroductions and rewilding. The key ecological question is the impact these faunal changes will have on trophic dynamics. Primary productivity in the boreal forest is increasing because of climatic warming, but plant species composition is unlikely to change significantly during the next 50–100 years. The 9–10‐year population cycle of snowshoe hares will persist but could be reduced in amplitude if winter weather increases predator hunting efficiency. Small rodents have increased in abundance because of increased vegetation growth. Arctic ground squirrels have disappeared from the forest because of increased predator hunting efficiency associated with shrub growth. Reintroductions have occurred for 2 reasons: human reintroductions of large ungulates and natural recolonization of mammals and birds extending their geographic ranges. The deliberate rewilding of wood bison (Bison bison) and elk (Cervus canadensis) has changed the trophic structure of this boreal ecosystem very little. The natural range expansion of mountain lions (Puma concolor), mule deer (Odocoileus hemionus) and American marten (Martes americana) should have few ecosystem effects. Understanding potential changes will require long‐term monitoring studies and experiments on a scale we rarely deem possible. Ecosystems affected by climate change, species reintroductions and human alteration of habitats cannot remain stable and changes will be critically dependent on food web interactions.

Do indirect bite count surveys accurately represent diet selection of white-tailed deer in a forested environment?

Context Diet selection is studied in herbivores using three predominant methods: (1) microhistological surveys (identification of plants cell walls remaining in gut contents or faecal excretions); (2) direct bite counts (of tame animals); and (3) indirect bite counts (identifying herbivory on damaged plant tissues). Microhistological surveys and direct bite counts are accurate and provide the potential advantage of linking diet selection to particular individuals. Also, they allow diet selection to be measured in systems with sympatric herbivores more easily than indirect bite counts. However, they require expertise in cell wall structure identification or access to tame animals, and generally require greater expense than indirect bite counts. Conversely, indirect bite counts have the advantages of relatively low cost and time commitment for gathering data and do not require animal observation, but may not be accurate. Aims We tested for similarity between diet-selection estimates calculated by indirect bite counts and microhistological surveys. Methods We performed concurrent indirect bite count and faecal microhistological surveys on white-tailed deer (Odocoileus virginianus) at Fort Bragg Military Installation, NC. Key results The indirect bite count survey assignment of selection was 48% similar to assignments derived from the microhistological survey, based on Jaccard’s similarity index. Out of 23 plant species determined to be selected by indirect bite counts, 15 of those species were selected according to microhistological surveys. According to the microhistological survey, eight of the selected plants made up 51% of the overall diet, and seven of those eight were selected according to the indirect bite counts. Conclusions Our data indicate that indirect bite counts may provide a relatively accurate index of the deer-selected plants most important in the white-tailed deer diet, but may be less appropriate to determine selection of plants that infrequently occur in their diet, plants that are typically consumed in entirety, or plants where herbivory damage is poorly identified. Implications Indirect bite counts are a relatively inexpensive and time-efficient tool that may be useful to determine plant species most important to white-tailed deer within a forested landscape, particularly if additional research can improve on associated inaccuracies.

Performance of GPS collars on free-ranging bison (Bison bison) in north-western Canada

Context Global positioning system (GPS) collars are increasingly used to study animal ecology. However, understanding their real-world performance is important so that biases in data collection can be addressed. These biases may be species specific. Few studies have examined the influence of sex or temporal variation on locational fix success rates (FSR), and none has assessed GPS-collar performance on bison (Bison bison). Aims To test for sex- and temporal-based biases on the performance of GPS collars on free-ranging bison. Methods Data from 59 deployments of 37 GPS collars on 27 female and seven male bison was used to test for temporal variation and differences between sexes on collar-deployment success rates and four fix acquisition metrics. Key results Most (72.9%) of the 55 GPS collars retrieved malfunctioned before reaching their expected deployment schedule (2 years). We observed a significant difference in the performance of GPS collars deployed on male and females, with those on females functioning almost three times longer. All four fix metrics differed between sexes, with males having significantly better metrics. For females, nightly fix metrics were better than the daytime ones, whereas for males, there was no difference. We observed a significant difference in fix metrics between seasons for females, but not males. Conclusions Although the data from GPS collars may be useful in understanding animal ecology, understanding associated biases can aid in the design of field studies using, and the interpretation of results stemming from, GPS collars. Temporal variation in our study was apparent for females, but not males, and likely related to differences in habitat use and movements. Overall, sex had a significant influence on the success of GPS-collar deployments on bison, and should be examined for other species as well. Implications Bison damage to the collars was the main reason for collar failures. Researchers should plan for catastrophic failures and malfunctions when deploying GPS collars on bison, particularly adult males. Significant differences observed between daily and seasonal FSR for females were small (≤4.9%), and do not warrant post hoc treatment before analyses.