Diets of savanna ungulates from stable carbon isotope composition of faeces

Environmental context shapes the relationship between grass consumption and body size in African herbivore communities

Though herbivore grass dependence has been shown to increase with body size across herbivore species, it is unclear whether this relationship holds at the community level. Here we evaluate whether grass consumption scales positively with body size within African large mammalian herbivore communities and how this relationship varies with environmental context. We used stable carbon isotope and community occurrence data to investigate how grass dependence scales with body size within 23 savanna herbivore communities throughout eastern and central Africa. We found that dietary grass fraction increased with body size for the majority of herbivore communities considered, especially when complete community data were available. However, the slope of this relationship varied, and rainfall seasonality and elephant presence were key drivers of the variation-grass dependence increased less strongly with body size where rainfall was more seasonal and where elephants were present. We found also that the dependence of the herbivore community as a whole on grass peaked at intermediate woody cover. Intraspecific diet variation contributed to these community-level patterns: common hippopotamus (Hippopotamus amphibius) and giraffe (Giraffa camelopardalis) ate less grass where rainfall was more seasonal, whereas Cape buffalo (Syncerus caffer) and savanna elephant (Loxodonta africana) grass consumption were parabolically related to woody cover. Our results indicate that general rules appear to govern herbivore community assembly, though some aspects of herbivore foraging behavior depend upon local environmental context.

Faecal nutrient deposition of domestic and wild herbivores in an alpine grassland

The contribution of herbivores to ecosystem nutrient fluxes through dung deposition has the potential to, directly and indirectly, influence ecosystem functioning. This process can be particularly important in nutrient-limited ecosystems such as alpine systems. However, herbivore dung content (carbon, C; nitrogen, N; phosphorus, P; potassium, K) and stoichiometry (C/N) may differ among species due to differences in diet, seasonality, body type, feeding strategy, and/or digestive system with consequences for soil biogeochemistry. Here we explore how species, body size, and seasonality may result in differences in dung stoichiometry for four alpine herbivores (chamois, sheep, horse, and cattle). We found that herbivore dung nutrient content often varies among species as well as with body size, with the dung of small herbivores having larger C, N, and P faecal content. Seasonality also showed marked effects on faecal nutrient content, with a general pattern of decreasing levels of faecal P, N and an increase of C/N as the summer progresses following the loss of nutrient value of the vegetation. Moreover, we showed how herbivores play an important role as natural fertilizers of C, N, and P in our study area, especially cattle. Our study highlights the importance of considering the relative contribution of different herbivores to ecosystem nutrient fluxes in management practices, especially with ongoing changes in wild and domestic herbivore populations in alpine ecosystems.

Fatty acid isotopic composition in Atlantic pollock is not influenced by environmentally relevant dietary fat concentrations

The application of fatty acid (FA) isotopic analysis has great potential in elucidating food web structure, but it has not experienced the same wide-spread use as amino acid isotopic analyses. The failure to adopt FA isotopic methods is almost certainly linked to a lack of reliable information on trophic fractionation of FA, particularly in higher predators. In this work, we attempt to address this shortfall, through comparison of FA δ¹³C values in captive Atlantic pollock (Pollachius virens) liver and their known diets. Since catabolism is likely the main cause of fractionation and it may vary with dietary fat content, we investigated the impact of dietary fat concentration on isotopic discrimination in FA. We fed Atlantic pollock three formulated diets with similar FA isotopic compositions but different fat concentrations (5-9% of diet), representative of the range found in natural prey, for 20 weeks. At the conclusion of the study, δ¹³C values of liver FA were very similar to the FA within the corresponding diets, with most discrimination factors < 1. For all FA except 22:6n-3, dietary fat had no effect on discrimination factors. Only for 22:6n-3 did fish fed the highest fat diet have lower δ¹³C values than the diet consumed. Thus, these FA-specific discrimination factors can be applied to evaluate diets in marine fish consuming natural diets and will serve as additional and valuable biomarkers in fish feeding ecology.

Livestock displace European mouflon from optimal foraging sites

The conflict between free-ranging livestock and wildlife is a serious conservation concern across rural communities worldwide. Livestock may affect wild herbivores via direct competition for resources due to spatial and diet overlap or via behavioural interference. It is imperative that we disentangle the effects of livestock on wildlife behaviour to obtain an empirical basis able to stir management and conservation decisions. Here, we studied the effect of livestock presence on the habitat selection in a free-ranging European mouflon (Ovis aries musimon) population in Sardinia, where the species is under strict protection. We collected spatial data on mouflon and livestock during two consecutive years to investigate whether the mouflon selection of key feeding grassland sites was negatively impacted by the livestock presence. We found that mouflon preferably selected grassland, and its selection significantly increased when grass was of better quality (greener). We showed that livestock presence led to the displacement of mouflon from such preferred feeding sites, an effect clearly exacerbated by livestock proximity. We indeed found that the selection of grassland by mouflon dropped significantly when the distance between livestock and mouflon was below ~ 650 m, providing a useful management threshold indication. Livestock presence in close proximity displaced mouflon to sub-optimal habitat, and its effects may have negative impact on the population dynamic of this species which is already characterized by low female productivity within harsh Mediterranean environment. Our results give clear management indications aimed at better managing livestock grazing within natural areas to ultimately improve wildlife conservation.

A non-invasive assessment of essential trace element utilization at different trophic levels in African wildlife

The complex relationships that exist between terrestrial mammals and their habitats make African ecosystems highly interactive environments. Anthropogenic activities including climate change have altered geochemical cycles, which influence nutrient availability and deficiency at local, regional and global scales. As synergistic and antagonistic interactions occur between essential elements at both deficiency and excess concentrations, the differences in feeding strategy between trophically distinct groups of terrestrial vertebrates are likely to influence the degree to which overall nutrient needs are met or may be deficient. The overall aim of this study was to investigate and compare quantitative differences of nine essential elements in terrestrial vertebrates occupying different trophic levels within two protected areas; Tswalu Kalahari Reserve (TKR) and Manyeleti Nature Reserve (MNR) South Africa, using faeces as an analytical matrix. Results from linear mixed effects models highlight that concentrations varied widely between individuals. Overall, measured concentrations above their respective means were evident for B and Mn in herbivores, Fe in omnivores and Cu, Co, Fe, Se and Zn in carnivores. Measured concentrations of Mo and Ni did not differ significantly between trophic groups. Although site-specific differences were evident for specific elements, measured mean concentrations of B, Co, Cu, Fe, Mo, Ni, Se and Zn were significantly higher overall at the MNR study site compared to the TKR site. This is the first study to non-invasively assess essential element concentrations across trophic levels in free ranging African wildlife species within protected areas of the savannah biome. Combined with the assessment of environmental matrices, this approach can be used as an effective diagnostic tool for the assessment of animal welfare and the management of protected areas globally.

How spatial and dietary overlap with domestic livestock affect African wild ass nutrition on the Messir Plateau (Eritrea)

Competition with livestock over forage resources has been identified as a potential threat to the survival of the African wild ass (Equus africanus) in the Danakil ecosystem (Eritrea). The Messir Plateau is an important breeding area for the African wild ass but also hosts cattle, sheep, goats, donkeys, and camels. Locations and fecal samples of African wild ass and livestock were collected in dry and rainfall months. Stable carbon isotopes [δ 13C ‰] in fecal samples were used to assess diet composition and overlaps with domestic herbivores. Fecal samples also were used to assess the nutritional quality of African wild ass and domestic donkey diets. During the dry months, African wild ass were concentrated in the northern section of the Messir Plateau, approximately 9 km from the permanent water source, and overlapped spatially with local livestock. During the rainfall months, African wild ass dispersed throughout the Messir Plateau (124 km2) when a high number of livestock, particularly cattle from the highlands with herders, were concentrated in the northern section. During the rainfall months, the northern section had relatively better vegetation cover and access to seasonal water. The grass contribution to the diet of the African wild ass in both dry and rainfall months overlapped significantly with that of domestic donkeys and cattle. In rainfall months, the percent fecal nitrogen and phosphorus contents of African wild ass were significantly lower than those of domestic donkey samples. The lower nutrient levels in fecal samples of African wild ass during rainfall months may be due to their displacement from the northern sector by the high number of immigrant highland cattle with people. Our work provides evidence as to how the presence of domestic herbivores, particularly cattle, may negatively impact the nutrient level of wild equids and threaten the survival of the critically endangered African wild ass.

An analysis of threats, strategies, and opportunities for African rhinoceros conservation

The complexity and magnitude of threats to black (Diceros bicornis) and white (Ceratotherium simum) rhinoceros conservation in Africa have triggered global concerns and actions. In this study, we analyzed (i) threats to rhinoceros conservation including external shocks, (ii) historical rhinoceros conservation strategies in Zimbabwe and Africa, more broadly, and (iii) opportunities for enhanced rhinoceros conservation in Zimbabwe and Africa. A literature search from 1975 to 2020 was carried out using a predefined search protocol, involving a number of filters based on a set of keywords to balance search sensitivity with specificity. A total of 193 articles, which were most relevant to key themes on rhinoceros conservation, were used in this study. The common threats to rhinoceros conservation identified in this paper include poaching, habitat fragmentation and loss, international trade in illegal rhino products, and external shocks such as global financial recessions and pandemics. Cascading effects emanating from these threats include small and isolated populations, which are prone to genetic, demographic, and environmental uncertainties. Rhinoceros conservation strategies being implemented include education and awareness campaigns, better equipped and more antipoaching efforts, use of innovative systems and technologies, dehorning, and enhancing safety nets, and livelihoods of local communities. Opportunities for rhinoceros conservation vary across the spatial scale, and these include (a) a well-coordinated stakeholder and community involvement, (b) strategic meta-population management, (c) enhancing law enforcement initiatives through incorporating real-time surveillance technologies and intruder detection sensor networks for crime detection, (d) scaling up demand reduction awareness campaigns, and (e) developing more certified wildlife crime and forensic laboratories, and information repository for international corporation.

Host phylogeny and host ecology structure the mammalian gut microbiota at different taxonomic scales

The gut microbiota is critical for host function. Among mammals, host phylogenetic relatedness and diet are strong drivers of gut microbiota structure, but one factor may be more influential than the other. Here, we used 16S rRNA gene sequencing to determine the relative contributions of host phylogeny and host diet in structuring the gut microbiotas of 11 herbivore species from 5 families living sympatrically in southwest Kenya. Herbivore species were classified as grazers, browsers, or mixed-feeders and dietary data (% C4 grasses in diet) were compiled from previously published sources. We found that herbivore gut microbiotas were highly species-specific, and that host taxonomy accounted for more variation in the gut microbiota (30%) than did host dietary guild (10%) or sample month (8%). Overall, similarity in the gut microbiota increased with host phylogenetic relatedness (r = 0.74) across the 11 species of herbivores, but among 7 closely related Bovid species, dietary %C4 grass values more strongly predicted gut microbiota structure (r = 0.64). Additionally, within bovids, host dietary guild explained more of the variation in the gut microbiota (17%) than did host species (12%). Lastly, while we found that the gut microbiotas of herbivores residing in southwest Kenya converge with those of distinct populations of conspecifics from central Kenya, fine-scale differences in the abundances of bacterial amplicon sequence variants (ASVs) between individuals from the two regions were also observed. Overall, our findings suggest that host phylogeny and taxonomy strongly structure the gut microbiota across broad host taxonomic scales, but these gut microbiotas can be further modified by host ecology (i.e., diet, geography), especially among closely related host species.

Seasonal dietary changes increase the abundances of savanna herbivore species

African savannas are home to the world's last great megafaunal communities, but despite ongoing population declines, we only poorly understand the constraints on savanna herbivore abundances. Seasonal diet shifts (except migration) have received little attention, despite a diversity of possible dietary strategies. Here, we first formulate two theoretical models that predict that both mixed feeding and migratory grazing increase population sizes. These predictions are borne out in comprehensive data across African savanna parks: Mixed feeders are the most abundant herbivores in Africa, alongside a few migratory grazer populations. Overall, clear mixed-feeder dominance may reflect a historical pattern or may instead mirror a general global decline in specialists. Regardless, mixed feeders dominate the savannas of the present and future.

Digesta passage in common eland (Taurotragus oryx) on a monocot or a dicot diet

The way that fluids and particles move through the forestomach of a ruminant is species-specific, and can be used to classify ruminants according to their digestive physiology into 'moose-types' (with little difference in fluid and small particle passage) and 'cattle-types' (where fluids move through the forestomach much faster than small particles). So far, 'moose-types' appear limited to a dietary niche of browsing, whereas 'cattle-types' are particularly prominent in the intermediate and grazing diet niches. However, some species, including members of the spiral-horned antelopes (the Tragelaphini), have a 'cattle-type' physiology but a browse-dominated diet niche. Eland (Taurotragus oryx), the largest member of the Tragelaphini, are strict browsers in the wild but have been considered intermediate feeders in the past, and can seemingly be maintained on grass diets. We quantified food intake, mean retention time (MRT) in the gastrointestinal tract and the reticulorumen (RR) of a solute, a small and a large particle marker, and diet digestibility in six eland each fed a monocot (grass hay) and a dicot (lucerne silage) forage. Food intake and digestibility was lower on the diet with higher fibre content (grass hay), with corresponding longer MRT. At the higher intakes on lucerne, the difference in MRT between small and large particles was larger, indicating a greater reliance on particle sorting and clearance under this condition of potentially limiting gut capacity. Regardless of diet or intake, the ratio of small particle and solute MRT in the RR was constant and small, at a quotient of 1.54, classifying the eland as a typical 'moose-type' ruminant. This finding is consistent with previous literature reports on low faecal metabolic nitrogen and high apparent protein digestibility in eland. Given the relative ease at which eland can be maintained under farm husbandry conditions, they appear ideal model ruminants to study the effects of differences in rumen physiology compared to cattle.

Large herbivore conservation in a changing world: Surface water provision and adaptability allow wildebeest to persist after collapse of long-range movements

Large herbivores, particularly wide-ranging species, are extensively impacted by land use transformation and other anthropogenic barriers to movement. The adaptability of a species is, therefore, crucial to determining whether populations can persist in ever smaller subsets of their historical home ranges. Access to water, by drinking or from forage moisture, is an essential requirement, and surface water provision is thus a long-established, although controversial, conservation practice. In the arid Kgalagadi Transfrontier Park (KTP), South Africa, surface water provision in the 1930s facilitated the establishment of a sedentary wildebeest (Connochaetes taurinus) population in a region historically accessed only in the wet season, via now collapsed long-distance movements. Here, we investigate the behaviour and diet of this wildebeest population, and how these relate to water in the landscape, to better understand the process of transitioning from a mobile to sedentary population. Data from 26 monthly surveys reveal that wildebeest distributions are shaped by water availability and salinity, shade, forage, season and possibly predator detectability. Areas with saline or no water are used predominantly in the wet season when forage moisture is high. Wet season movements beyond the study area mean the timing of wildebeest grazing in these regions matches historical timing. Grass utilization field data suggest that the KTP grazer population experiences forage deficits during the dry season, when ~80% of grass tufts are grazed and C:N and crude protein levels decline. Nonetheless, dung isotope data show that wildebeest meet their crude protein intake requirements during the dry season, likely by consuming unprecedentedly high levels of browse (>33%). While restoring the full historical range and movements of most large herbivore populations is not possible, these findings highlight that understanding the behavioural and dietary adaptability of a species can augment 'next best' efforts to conserve viable populations while home ranges contract.

Multiple dimensions of dietary diversity in large mammalian herbivores

Theory predicts that trophic specialization (i.e. low dietary diversity) should make consumer populations sensitive to environmental disturbances. Yet diagnosing specialization is complicated both by the difficulty of precisely quantifying diet composition and by definitional ambiguity: what makes a diet 'diverse'? We sought to characterize the relationship between taxonomic dietary diversity (TDD) and phylogenetic dietary diversity (PDD) in a species-rich community of large mammalian herbivores in a semi-arid East African savanna. We hypothesized that TDD and PDD would be positively correlated within and among species, because taxonomically diverse diets are likely to include plants from many lineages. By using DNA metabarcoding to analyse 1,281 faecal samples collected across multiple seasons, we compiled high-resolution diet profiles for 25 sympatric large-herbivore species. For each of these populations, we calculated TDD and PDD with reference to a DNA reference library for local plants. Contrary to our hypothesis, measures of TDD and PDD were either uncorrelated or negatively correlated with each other. Thus, these metrics reflect distinct dimensions of dietary specialization both within and among species. In general, grazers and ruminants exhibited greater TDD, but lower PDD, than did browsers and non-ruminants. We found significant seasonal variation in TDD and/or PDD for all but four species (Grevy's zebra, buffalo, elephant, Grant's gazelle); however, the relationship between TDD and PDD was consistent across seasons for all but one of the 12 best-sampled species (plains zebra). Our results show that taxonomic generalists can be phylogenetic specialists, and vice versa. These two dimensions of dietary diversity suggest contrasting implications for efforts to predict how consumers will respond to climate change and other environmental perturbations. For example, populations with low TDD may be sensitive to phylogenetically 'random' losses of food species, whereas populations with low PDD may be comparatively more sensitive to environmental changes that disadvantage entire plant lineages-and populations with low dietary diversity in both taxonomic and phylogenetic dimensions may be most vulnerable of all.

Trophic rewilding revives biotic resistance to shrub invasion

Trophic rewilding seeks to rehabilitate degraded ecosystems by repopulating them with large animals, thereby re-establishing strong top-down interactions. Yet there are very few tests of whether such initiatives can restore ecosystem structure and functions, and on what timescales. Here we show that war-induced collapse of large-mammal populations in Mozambique's Gorongosa National Park exacerbated woody encroachment by the invasive shrub Mimosa pigra-considered one of the world's 100 worst invasive species-and that one decade of concerted trophic rewilding restored this invasion to pre-war baseline levels. Mimosa occurrence increased between 1972 and 2015, a period encompassing the near extirpation of large herbivores during the Mozambican Civil War. From 2015 to 2019, mimosa abundance declined as ungulate biomass recovered. DNA metabarcoding revealed that ruminant herbivores fed heavily on mimosa, and experimental exclosures confirmed the causal role of mammalian herbivory in containing shrub encroachment. Our results provide mechanistic evidence that trophic rewilding has rapidly revived a key ecosystem function (biotic resistance to a notorious woody invader), underscoring the potential for restoring ecological health in degraded protected areas.

Large herbivore assemblages in a changing climate: incorporating water dependence and thermoregulation

The coexistence of different species of large herbivores (ungulates) in grasslands and savannas has fascinated ecologists for decades. However, changes in climate, land‐use and trophic structure of ecosystems increasingly jeopardise the persistence of such diverse assemblages. Body size has been used successfully to explain ungulate niche differentiation with regard to food requirements and predation sensitivity. But this single trait axis insufficiently captures interspecific differences in water requirements and thermoregulatory capacity and thus sensitivity to climate change. Here, we develop a two‐dimensional trait space of body size and minimum dung moisture content that characterises the combined food and water requirements of large herbivores. From this, we predict that increased spatial homogeneity in water availability in drylands reduces the number of ungulate species that will coexist. But we also predict that extreme droughts will cause the larger, water‐dependent grazers as wildebeest, zebra and buffalo–dominant species in savanna ecosystems – to be replaced by smaller, less water‐dependent species. Subsequently, we explore how other constraints such as predation risk and thermoregulation are connected to this two‐dimensional framework. Our novel framework integrates multiple simultaneous stressors for herbivores and yields an extensive set of testable hypotheses about the expected changes in large herbivore community composition following climate change.

Contrasting Winter Moose Nutritional Carrying Capacity Models on a Dynamic Landscape

Many models used to estimate nutritional carrying capacity (NCC) for ungulates differ structurally, but the implications of those differences are frequently unclear. We present a comparative analysis of NCC estimates for a large herbivore in a dynamic landscape, using models that differ in structure and scope. We compared three model structures across three estimates of winter ranges under three winter-severity scenarios for an isolated, introduced moose Alces alces population on the Copper River Delta of south-central Alaska. Model estimates of NCC ranged from 205 to 4,592 moose, demonstrating the critical influences of model structure and assumptions when applying NCC. Furthermore, population estimates during recent severe winters suggest that past models underestimated NCC on the Copper River Delta. We conducted a sensitivity analysis of a preferred model and determined that model components with the highest and lowest sensitivity were snow depth and lignin- and tannin-caused reductions in forage nutritional quality, respectively. Our low sensitivity values for lignin and tannin influences on NCC contrast with results in other NCC estimates. Overall, our results reinforce the need for, and will hopefully assist, adaptive management in response to landscape, population, behavioral, and climatic changes on the Copper River Delta, and demonstrate the importance of understanding model assumptions and structure in application of NCC estimates in the management of large herbivores in variable ecosystems.

Drought-response strategies of savanna herbivores

Climate models predict increases in drought frequency and severity worldwide, with potential impacts on diverse systems, including African savannas. These droughts pose a concern for the conservation of savanna mammal communities, such that understanding how different species respond to drought is vital.Because grass decreases so consistently during droughts, we predict that grass-dependent species (grazers and mixed feeders) will respond strongly to drought, whether by changing diets, seeking drought refugia, or suffering mortality.A recent severe but heterogeneous drought in Kruger National Park, South Africa, afforded a rare opportunity to test these hypotheses in situ-crucial, given the central role of landscape-scale movement as a potential herbivore strategy. We used herbivore dung as a proxy, integrating spatial distributions (dung counts) with diet composition (carbon isotope analysis of dung).As predicted, browsers showed little response to drought. However, mixed feeders switched their diets to incorporate more C3 trees/forbs, but did not move. Meanwhile, grazers and megaherbivores instead moved toward drought refugia. Synthesis and applications: The responses we observed by savanna herbivores are largely amplifications of typical dry season strategies and reflect constraints imposed by body size and feeding ecology. Grazers may be at particular risk from increased drought frequency and spatial extent if drought refugia become decreasingly available. Conservation strategies should recognize these constraints and work to facilitate the diverse responses of herbivores to drought.

Herbivore dung quality affects plant community diversity

Nutrient availability is important for plant community composition and diversity, but most studies focus on inorganic nutrients. Far less is known about the impact of nutrients in organic forms such as herbivore dung. Here we show that dung of 11 European herbivore species varies widely in nitrogen (N) and phosphorus (P) concentrations, as well as in C:N:P ratios. We demonstrate that variation in dung quality of five herbivore species influences the diversity and composition of a mesocosm plant community. The impact of dung quality was at least as strong as, or stronger than, the effect of manipulating the quantity of dung by a factor six. Our study supports the hypothesis that both nutrient quantity and nutrient imbalances are important controlling factors for plant species diversity, and stresses the important role of herbivores on plant communities, not only via selective foraging, but also via stoichiometric variation of nutrients in their dung.

Complexity in African savannas: Direct, indirect, and cascading effects of animal densities, rainfall and vegetation availability

Savanna ecosystems are popular subjects for interaction studies. Multiple studies have been done on the impact of elephants on vegetation, the impact of grass and browse availability on animal densities or on competition between herbivore species. Previous studies showed that elephant densities are frequently negatively correlated with densities of tall trees, and that browse and grass availability are correlated with browser and grazer density respectively. Additionally, a competition effect between browse and grass availability has been reported. These relationships are usually analysed by testing direct relationships between e.g., herbivore densities and food availability, without addressing competition effects or other indirect effects. In this study, multiple interactions in a savanna system have been analysed simultaneously using Partial Least Square-Path Modelling (PLS-PM) using mammal and vegetation data from three different wildlife reserves in southern KwaZulu-Natal. The results showed that the processes that three separate models for the three areas provided the best understanding of the importance of the different interactions. These models suggest that elephants had a negative impact on trees, but also on grass availability. The impact is stronger when elephants are not able to migrate during the dry season. Browsers and grazers were correlated with browse and grass availability, but competition between browse and grass was not detected. This study shows that due to the complexity of the interactions in an ecosystem and differences in environmental factors, these interactions are best studied per area. PLS-PM can be a useful tool for estimating direct, indirect, and cascading effects of changing animal densities in conservation areas.

Within trophic level shifts in collagen-carbonate stable carbon isotope spacing are propagated by diet and digestive physiology in large mammal herbivores

Stable carbon isotope analyses of vertebrate hard tissues such as bones, teeth, and tusks provide information about animal diets in ecological, archeological, and paleontological contexts. There is debate about how carbon isotope compositions of collagen and apatite carbonate differ in terms of their relationship to diet, and to each other. We evaluated relationships between δ¹³C_collagen and δ¹³C_carbonate among free‐ranging southern African mammals to test predictions about the influences of dietary and physiological differences between species. Whereas the slopes of δ¹³C_collagen–δ¹³C_carbonate relationships among carnivores are ≤1, herbivore δ¹³C_collagen increases with increasing dietary δ¹³C at a slower rate than does δ¹³C_carbonate, resulting in regression slopes >1. This outcome is consistent with predictions that herbivore δ¹³C_collagen is biased against low protein diet components (¹³C‐enriched C₄ grasses in these environments), and δ¹³C_carbonate is ¹³C‐enriched due to release of ¹³C‐depleted methane as a by‐product of microbial fermentation in the digestive tract. As methane emission is constrained by plant secondary metabolites in browse, the latter effect becomes more pronounced with higher levels of C₄ grass in the diet. Increases in δ¹³C_carbonate are also larger in ruminants than nonruminants. Accordingly, we show that Δ¹³C_collagen‐_carbonate spacing is not constant within herbivores, but increases by up to 5 ‰ across species with different diets and physiologies. Such large variation, often assumed to be negligible within trophic levels, clearly cannot be ignored in carbon isotope‐based diet reconstructions.

Settling the browser–grazer debate for African buffalo in grass-limited Eastern Cape thicket, South Africa

Despite extensive evidence that African buffalo Syncerus caffer are grazers, De Graaff et al. using rumen content analysis of animals that had starved to death proposed that buffalo in grass-limited Eastern Cape thicket should be considered browsers. Although these anomalous findings were initially accepted, but later challenged, the browse-dominated diet continues to be used as a foundation for hypotheses on the diet of healthy animals. Consequently, the debate around buffalo as browsers or grazers in thicket has not yet been settled. We describe the diet of buffalo in the Addo Elephant National Park and include data from other published work from the region to test the importance of grass in buffalo diet. We show that the diet is dominated by grasses, even in grass-limited thicket, and that browse species are seldom dominant foods. Thus, there is no empirical evidence to corroborate the notion that buffalo switch their diet to browse when grass availability is low. In an attempt to advance our understanding of buffalo foraging in thicket, we reiterate that De Graaff’s work is not a valid measure of buffalo diet in succulent thicket and that additional testing of the browser–grazer hypothesis is not needed.Conservation implications: Our results confirm that buffalo are grazers, rather than browsers, in grass-limited Eastern Cape thicket. Thus, additional testing of the browser–grazer hypothesis for buffalo in the region is not needed.

A stoichiometric perspective of the effect of herbivore dung on ecosystem functioning

Ungulate herbivores play a prominent role in maintaining the tree-grass balance in African savannas. Their top-down role through selective feeding on either trees or grasses is well studied, but their bottom-up role through deposition of nutrients in dung and urine has been overlooked. Here, we propose a novel concept of savanna ecosystem functioning in which the balance between trees and grasses is maintained through stoichiometric differences in dung of herbivores that feed on them. We describe a framework in which N₂-fixing trees and grasses, as well as ungulate browsing and grazing herbivores, occupy opposite positions in an interconnected cycle of processes. The framework makes the testable assumption that the differences in dung N:P ratio among browsers and grazers are large enough to influence competitive interactions between N₂-fixing trees and grasses. Other key elements of our concept are supported with field data from a Kenyan savanna.

Stable isotope signatures of large herbivore foraging habitats across Europe

We investigated how do environmental and climatic factors, but also management, affect the carbon (δ¹³C) and nitrogen (δ¹⁵N) stable isotope composition in bone collagen of the two largest contemporary herbivores: European bison (Bison bonasus) and moose (Alces alces) across Europe. We also analysed how different scenarios of population recovery- reintroduction in bison and natural recovery in moose influenced feeding habitats and diet of these two species and compared isotopic signatures of modern populations of bison and moose (living in human-altered landscapes) with those occurring in early Holocene. We found that δ¹³C of modern bison and moose decreased with increasing forest cover. Decreasing forest cover, increasing mean annual temperature and feeding on farm crops caused an increase in δ¹⁵N in bison, while no factor significantly affected δ¹⁵N in moose. We showed significant differences in δ¹³C and δ¹⁵N among modern bison populations, in contrast to moose populations. Variation in both isotopes in bison resulted from inter-population differences, while in moose it was mainly an effect of intra-population variation. Almost all modern bison populations differed in δ¹³C and δ¹⁵N from early Holocene bison. Such differences were not observed in moose. It indicates refugee status of European bison. Our results yielded evidence that habitat structure, management and a different history of population recovery have a strong influence on foraging behaviour of large herbivores reflected in stable isotope signatures. Influence of forest structure on carbon isotope signatures of studied herbivores supports the “canopy effect” hypothesis.

Feeding choices and impacts of extralimital giraffe on two keystone tree species in the Kgalagadi National Park

In this article we determine the effect of an extralimital megaherbivore on the reproductive potential and vegetation structure of two keystone tree species in the Auob River in the south western Kalahari Desert of southern Africa. Using spoor and dung counts we establish the presence of giraffe in three predetermined density zones by walking 50 transects across the river in each zone. We also photographed six trees from each species in each zone and use these photographs to determine browse impact on reproductive potential, canopy volume as well as the percentage dieback on the extremities of the canopy. We then perform stable carbon and nitrogen isotope analysis on the leaves of the trees and compare these relative to the isotope ratios of giraffe dung to ascertain dietary preference. Crude protein was determined as a guide to nutritive value. Finally, we determine both chemical and physical defences for the two species. Our results show a significant negative impact of giraffe browse on tree canopies, no significant differences in recruitment and a noticeable decrease in flowers and pods at the giraffe browse height of 2 m – 5 m. No significant differences in crude protein or condensed tannins were found but significant differences in spinescence. Giraffe are not endemic to the Auob River and our study shows that the introduction of these animals is having a negative impact on the canopies of Vachellia haematoxylon. While there are, as yet, no significant impacts on reproductive potential we speculate that this will happen with time.Conservation implications: Our study shows that giraffe are significantly impacting the canopies of two common tree species in the Auob River in the arid Kgalagadi Transfrontier Park. Without management intervention an increasing population of giraffe will result in substantial changes to the plant community vegetation structure of the river.

Isotopic ecology of coyotes from scat and road kill carcasses: A complementary approach to feeding experiments

Scat is frequently used to study animal diets because it is easy to find and collect, but one concern is that gross fecal analysis (GFA) techniques exaggerate the importance of small-bodied prey to mammalian mesopredator diets. To capitalize on the benefits of scat, we suggest the analysis of scat carbon and nitrogen isotope values (δ¹³C and δ¹⁵N). This technique offers researchers a non-invasive method to gather short-term dietary information. We conducted three interrelated studies to validate the use of isotopic values from coyote scat: 1) we determined tissue-to-tissue apparent C and N isotope enrichment factors (ε¹³* and ε¹⁵*) for coyotes from road kill animals (n = 4); 2) we derived diet-to-scat isotope discrimination factors for coyotes; and 3) we used field collected coyote scats (n = 12) to compare estimates of coyote dietary proportions from stable isotope mixing models with estimates from two GFA techniques. Scat consistently had the lowest δ¹³C and δ¹⁵N values among the tissues sampled. We derived a diet-to-scat Δ¹³C value of -1.5‰ ± 1.6‰ and Δ¹⁵N value of 2.3‰ ± 1.3‰ for coyotes. Coyote scat δ¹³C and δ¹⁵N values adjusted for discrimination consistently plot within the isotopic mixing space created by known dietary items. In comparison with GFA results, we found that mixing model estimates of coyote dietary proportions de-emphasize the importance of small-bodied prey. Coyote scat δ¹³C and δ¹⁵N values therefore offer a relatively quick and non-invasive way to gain accurate dietary information.

Isotopic evidence for dietary niche overlap between barking deer and four-horned antelope in Nepal

BACKGROUND

Morphologically similar sympatric species may have a high degree of niche overlap. Barking deer Muntiacus vaginalis and four-horned antelope Tetracerus quadricornis are solitary ungulates of the Indian sub-continent. Limited information is available regarding their trophic ecology, particularly of the endemic four-horned antelope. We present stable carbon (δ(13)C), nitrogen (δ(15)N), and sulphur (δ(34)S) isotopic values, and nitrogen content (%N) of faeces from barking deer and four-horned antelope living in lowland Nepal to assess trophic niche differentiation of these herbivores along the browser-grazer continuum. We also describe trophic differences between those two species in ecological niches and seasonal effects on their diets.

RESULTS

We found that the barking deer and four-horned antelope consumed C3 plant sources exclusively. The niche partitioning in their diet was reflected by δ(34)S values. Some seasonal effects observed were: δ(13)C and δ(15)N were significantly lower in the dry season diet of four-horned antelope than that of barking deer, while δ(34)S values were significantly higher in the winter diet; monsoon diet was similar for both species. Faecal N levels for barking deer and four-horned antelope were similar throughout all the seasons, indicating that both species adapted their feeding behaviour so as to maximize protein intake, in accordance with season and environment.

CONCLUSIONS

Barking deer and four-horned antelope both are browsers; their dietary sources overlapped during monsoon but differed during the dry season. Conservation actions focused on resource management during the dry season to reduce food scarcity and competition over limited resources is likely to be the most effective.

Combining paleo-data and modern exclosure experiments to assess the impact of megafauna extinctions on woody vegetation

Until recently in Earth history, very large herbivores (mammoths, ground sloths, diprotodons, and many others) occurred in most of the World's terrestrial ecosystems, but the majority have gone extinct as part of the late-Quaternary extinctions. How has this large-scale removal of large herbivores affected landscape structure and ecosystem functioning? In this review, we combine paleo-data with information from modern exclosure experiments to assess the impact of large herbivores (and their disappearance) on woody species, landscape structure, and ecosystem functions. In modern landscapes characterized by intense herbivory, woody plants can persist by defending themselves or by association with defended species, can persist by growing in places that are physically inaccessible to herbivores, or can persist where high predator activity limits foraging by herbivores. At the landscape scale, different herbivore densities and assemblages may result in dynamic gradients in woody cover. The late-Quaternary extinctions were natural experiments in large-herbivore removal; the paleoecological record shows evidence of widespread changes in community composition and ecosystem structure and function, consistent with modern exclosure experiments. We propose a conceptual framework that describes the impact of large herbivores on woody plant abundance mediated by herbivore diversity and density, predicting that herbivore suppression of woody plants is strongest where herbivore diversity is high. We conclude that the decline of large herbivores induces major alterations in landscape structure and ecosystem functions.

DNA metabarcoding illuminates dietary niche partitioning by African large herbivores

Niche partitioning facilitates species coexistence in a world of limited resources, thereby enriching biodiversity. For decades, biologists have sought to understand how diverse assemblages of large mammalian herbivores (LMH) partition food resources. Several complementary mechanisms have been identified, including differential consumption of grasses versus nongrasses and spatiotemporal stratification in use of different parts of the same plant. However, the extent to which LMH partition food-plant species is largely unknown because comprehensive species-level identification is prohibitively difficult with traditional methods. We used DNA metabarcoding to quantify diet breadth, composition, and overlap for seven abundant LMH species (six wild, one domestic) in semiarid African savanna. These species ranged from almost-exclusive grazers to almost-exclusive browsers: Grass consumption inferred from mean sequence relative read abundance (RRA) ranged from >99% (plains zebra) to <1% (dik-dik). Grass RRA was highly correlated with isotopic estimates of % grass consumption, indicating that RRA conveys reliable quantitative information about consumption. Dietary overlap was greatest between species that were similar in body size and proportional grass consumption. Nonetheless, diet composition differed between all species-even pairs of grazers matched in size, digestive physiology, and location-and dietary similarity was sometimes greater across grazing and browsing guilds than within them. Such taxonomically fine-grained diet partitioning suggests that coarse trophic categorizations may generate misleading conclusions about competition and coexistence in LMH assemblages, and that LMH diversity may be more tightly linked to plant diversity than is currently recognized.