The African savannas that many early hominins occupied likely experienced stark seasonality and contained mosaic habitats (i.e., combinations of woodlands, wetlands, grasslands, etc.). Most would agree that the bulk of dietary calories obtained by taxa such as Australopithecus and Paranthropus came from the consumption of vegetation growing across these landscapes. It is also likely that many early hominins were selective feeders that consumed particular plants/plant parts (e.g., leaves, fruit, storage organs) depending on the habitat and season within which they were foraging. Thus, improving our understanding of how the nutritional properties of potential hominin plant foods growing in modern African savanna ecosystems respond to season and vary by habitat will improve our ability to model early hominin dietary behavior. Here, we present nutritional analyses (crude protein and acid detergent fiber) of plants growing in eastern and southern African savanna habitats across both wet and dry seasons. We find that many assumptions about savanna vegetation are warranted. For instance, plants growing in our woodland habitats have higher average protein/fiber ratios than those growing in our wetland and grassland transects. However, we find that the effects of season and habitat are complex, an example being the unexpectedly higher protein levels we observe in the grasses and sedges growing in our Amboseli wetlands during the dry season. Also, we find significant differences between the vegetation growing in our eastern and southern African field sites, particularly among plants using the C4 photosynthetic pathway. This may have implications for the differences we see between the stable carbon isotope compositions and dental microwear patterns of eastern and southern African Paranthropus species, despite their shared, highly derived craniodental anatomy.

Apex predators can have considerable impacts on meso-carnivore diets, through competition or facilitation. Facilitation occurs when smaller predators consume carrion created by larger predators, especially large-bodied prey species normally inaccessible to meso-carnivores. In contrast, apex predators can also negatively affect meso-carnivore consumption of important resources through competitive interactions. Thus, predicting meso-carnivore responses to trophic structure changes (i.e. apex predator extirpation or reintroduction) is often difficult. We investigated stable carbon and nitrogen isotope niche breadths of black-backed jackal (Canis mesomelas) in response to the reintroduction of an apex predator, the African lion (Panthera leo), to the Karoo National Park, South Africa. Jackal faecal isotopic niche widths were larger in post-lion than pre-lion samples, indicating a niche expansion to include pure C-3- and C-4-based food sources when lions were present. Most prey items of this nature in the study area are large-bodied ungulates. Our results agree with results of traditional scat analysis, which showed that prey species >92 kg were consumed more often after the lion reintroduction. Stable isotope data from carnivore faeces are effective for tracking responses of wildlife to changing ecological conditions, providing an alternative source of information about changes in community structure brought about by management interventions.

Predator-prey size relationships are among the most important patterns underlying the structure and function of ecological communities. Indeed, these relationships have already been shown to be important for understanding patterns of macroevolution and differential extinction in the terrestrial vertebrate fossil record. Stable isotope analysis (SIA) is a powerful remote approach to examining animal diets and paleodiets. The approach is based on the principle that isotope compositions of consumer tissues reflect those of their prey. In systems where resource isotope compositions are distributed along a body size gradient, SIA could be used to reconstruct predator-prey size relationships. We analyzed stable carbon isotope distributions amongst mammalian herbivores in extant and Plio-Pleistocene African savanna assemblages, and show that the range of δ13 C values among mammalian prey species (herbivores and rodents) increases with body mass (BM), because C4 plant feeding (essentially grazing) is more common among larger taxa. Consequently, δ13 C values of mammalian carnivores in these systems are related to species' BM, reflecting a higher average C4 prey component in the diets of larger-bodied carnivores. This pattern likely emerges because only the largest carnivores in these systems have regular access to the C4 prey base, whereas smaller carnivores do not. The δ13 C-BM relationship observed in mammalian carnivores is a potentially powerful approach for reconstructing and parameterizing predator-prey size relationships in contemporary and fossil savanna assemblages, and for interpreting how various behavioral, ecological and environmental factors influence prey size selection.

Discussions about early hominin diets have generally excluded grass leaves as a staple food resource, despite their ubiquity in most early hominin habitats. In particular, stable carbon isotope studies have shown a prevalent C4 component in the diets of most taxa, and grass leaves are the single most abundant C4 resource in African savannas. Grass leaves are typically portrayed as having little nutritional value (e.g., low in protein and high in fiber) for hominins lacking specialized digestive systems. It has also been argued that they present mechanical challenges (i.e., high toughness) for hominins with bunodont dentition. Here, we compare the nutritional and mechanical properties of grass leaves with the plants growing alongside them in African savanna habitats. We also compare grass leaves to the leaves consumed by other hominoids and demonstrate that many, though by no means all, compare favorably with the nutritional and mechanical properties of known primate foods. Our data reveal that grass leaves exhibit tremendous variation and suggest that future reconstructions of hominin dietary ecology take a more nuanced approach when considering grass leaves as a potential hominin dietary resource.

AbstractStable 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 δ13Ccollagen and δ13Ccarbonate among free‐ranging southern African mammals to test predictions about the influences of dietary and physiological differences between species. Whereas the slopes of δ13Ccollagen–δ13Ccarbonate relationships among carnivores are ≤1, herbivore δ13Ccollagen increases with increasing dietary δ13C at a slower rate than does δ13Ccarbonate, resulting in regression slopes >1. This outcome is consistent with predictions that herbivore δ13Ccollagen is biased against low protein diet components (13C‐enriched C4 grasses in these environments), and δ13Ccarbonate 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 δ13Ccarbonate are also larger in ruminants than nonruminants. Accordingly, we show that Δ13Ccollagen‐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.

Carbon isotope analyses of tooth enamel have been widely employed by paleoecologists to understand past habitats. Most such studies use large-to medium-bodied mammals and exclude small taxa. However, analysis of fossil small mammals holds promise for resolving questions about past environments because these animals are often present in the fossil record (especially in South African cave sites), are diverse in dietary and habitat preference, yet have limited lifespans and home range sizes. Thus, the carbon isotope compositions of small mammal communities and/or species might reflect the composition of vegetation in local environments at fine scales. In this study, we assessed the degree to which carbon isotope compositions of small mammal tooth enamel record spatial changes in habitat in a southern African savanna environment. Modern small mammal specimens were collected from the pellet accumulations of three barn owl (Tyto alba africanus) roosts located within micro habitats varying from open grassland to mixed woodland. We examined rodent carbon isotope compositions within taxa, between taxa, and between tooth types in an effort to characterize variation within this group. We also compared rodent community delta C-13(enamel) composition between microhabitat types to evaluate how well small mammal isotope data reflect vegetation composition local to the roosts. Our analyses suggest that the relationship between small mammal community carbon isotopic means and vegetation composition is complex, but that with appropriate taxonomic control and consideration of relative abundance, small mammals have potential as a proxy for reconstructing past habitats. To complement this modern study, we performed isotopic analysis of the enamel of small mammals from three hominin-bearing sites in the Cradle of Humankind World Heritage Site, South Africa. Our results suggest a greater contribution of C4 resources to the diets of small mammals and likely more C4 grass in the past than occurs today. (C) 2017 Elsevier B.V. All rights reserved.

Unlike modern mammalian communities, terrestrial Paleozoic and Mesozoic vertebrate systems were characterized by carnivore faunas that were as diverse as their herbivore faunas. The comparatively narrow food base available to carnivores in these paleosystems raises the possibility that predator-prey interactions contributed to unstable ecosystems by driving populations to extinction. Here, we develop a model of predator-prey interactions based on diversity, abundance and body size patterns observed in the Permo-Triassic vertebrate fossil record of the Karoo Basin, South Africa. Our simulations reflect empirical evidence that despite relatively high carnivore: herbivore species ratios, herbivore abundances were sufficient for carnivores to maintain required intake levels through most of the Karoo sequence. However, high mortality rates amongst herbivore populations, even accounting for birth rates of different-sized species, are predicted for assemblages immediately preceding the end-Guadalupian and end-Permian mass extinctions, as well as in the Middle Triassic when archosaurs replaced therapsids as the dominant terrestrial fauna. These results suggest that high rates of herbivore mortality could have played an important role in biodiversity declines leading up to each of these turnover events. Such declines would have made the systems especially vulnerable to subsequent stochastic events and environmental perturbations, culminating in large-scale extinctions.

Large mammal ecosystems have relatively simple food webs, usually comprising three – and sometimes only two – trophic links. Since many syntopic species from the same trophic level therefore share resources, dietary niche partitioning features prominently within these systems. In African and other subtropical savannas, stable carbon isotopes readily distinguish between herbivore species for which foliage and other parts of dicot plants (13C-depleted C3 vegetation) are the primary resource (browsers) and those for which grasses (13C-enriched C4 vegetation) are staples (grazers). Similarly, carbon isotopes distinguish between carnivore diets that may be richer in either browser, grazer, or intermediate-feeding prey. Here, we investigate levels of carbon and nitrogen isotopic niche variation and niche partitioning within populations (or species) of carnivores and herbivores from South African savannas. We emphasize predictable differences in within-population trends across trophic levels: we expect that herbivore populations, which require more foraging effort due to higher intake requirements, are far less likely to display within-population resource partitioning than carnivore populations. Our results reveal generally narrower isotopic niche breadths in herbivore than carnivore populations, but more importantly we find lower levels of isotopic differentiation across individuals within herbivore species. While these results offer some support for our general hypothesis, the current paucity of isotopic data for African carnivores limits our ability to test the complete set of predictions arising from our hypothesis. Nevertheless, given the different ecological and ecophysiological constraints to foraging behaviour within each trophic level, comparisons across carnivores and herbivores, which are possible within such simplified foodwebs, make these systems ideal for developing a process-based understanding of conditions underlying the evolution of intra-specific, individual-level separation of ecological niches.

Carbon isotope analysis of fossil micromammalian insectivores holds promise for resolving questions about past environments because these animals have restricted home ranges and are generalist feeders. Thus, their diets likely integrate ecological information about local habitats. In this study, we assessed the degree to which carbon isotope compositions of three sympatric shrew species record spatial changes in habitat in a mosaic southern African savanna environment. Sampling sites were located within 2 km of one another, and microhabitat conditions ranged from very open (<5% canopy cover) to wooded (similar to 60% canopy cover). We compared shrew hair delta C-13 values between microhabitat types, and across taxa, in order to test whether these data follow predictable patterns based on local vegetation.Shrew carbon isotope compositions varied with habitat in a predictable manner within our study area. While taxonomy also influenced d13C values, this was largely due to differences in habitat preferences of individual taxa and the resultant variation in their relative abundance within each environment. Isotopic differences between habitat types were preserved within taxa where taxa occurred in multiple habitats. To complement this modern study, we performed isotopic analysis of the enamel of insect-eating fossil micromammals from the hominin sites Gladysvale and Sterkfontein in the Cradle of Humankind, South Africa. This subset of fossil micromammals consumed primarily C-4-derived carbon. (C) 2016 Elsevier Ltd. All rights reserved.

Species’ partitioning of resources remains one of the most integral components for understanding community assembly. Analysis of stable carbon and nitrogen isotopes in animal tissues has the potential to help resolve patterns of partitioning because these proxies represent the individual’s diet and trophic niche, respectively. Using free-ranging rodents in a southern African savanna as a model community, we find that syntopic species within habitats occupy distinct isotope niches. Moreover, species with strongly overlapping isotope niches did not overlap in their spatial distribution patterns, suggesting an underlying effect of competitive exclusion. Niche conservatism appears to characterize the behaviour of most species in our sample - with little or no observed changes across habitats - with the exception of one species, Mastomys coucha. This species displayed a generalist distribution, being found in similar abundances across a variety of habitats. This spatial pattern was coupled with a generalist isotope niche that shifted across habitats, likely in response to changes in species composition over the same spatial gradient. The case for M. coucha supports contentions that past competition effects played a significant evolutionary role in shaping community structures of today, including the absence of strong interspecific niche overlaps within particular habitats. Our study highlights the value of stable isotope approaches to help resolve key questions in community ecology, and moreover introduces novel analytical approaches to quantifying isotope niche breadths and niche overlaps that are easily comparable with traditional metrices.

Many herbivore species expand their dietary niche breadths by switching from browse-rich diets in dry seasons to grass-rich diets in rainy seasons, in response to phenological changes in plant avai...

Many herbivore species expand their dietary niche breadths by switching from browse-rich diets in dry seasons to grass-rich diets in rainy seasons, in response to phenological changes in plant availability and quality. We analyzed stable isotope series along tail hairs of captive and free-ranging African elephant (Loxodonta africana (Blumenbach, 1797)) to compare patterns of seasonal dietary variability across individuals. Results from elephants translocated from the wild into captivity, where their diets are semicontrolled, revealed tail hair growth rates of ∼0.34 mm/day, on average, and relatively rapid isotope turnover through the transition from wild into captivity. Sampling hairs at 10 mm increments thus archives dietary chronologies at a resolution suitable for tracking diet switches at seasonal, and even subseasonal, scales. Hairs of free-ranging elephants showed extensive carbon isotopic variability within individuals, consistent with seasonal switches between C3-browsing and C4-grazing. Similarly extensive, but asynchronous, shifts in nitrogen isotope ratios were also observed, suggesting an influence of factors other than seasonality. Across individuals, switching patterns differed across habitats, and across age classes, with older, larger animals including increasing amounts of C3browse into their diets. These results demonstrate how stable isotope approaches characterize complex patterns of resource use in wildlife populations.

ABSTRACTField studies of plant stable carbon and nitrogen isotope composition have revealed relationships with temperature and precipitation. These relationships conform to theoretical predictions of how extrinsic factors impact on ecophysiological processes such as photosynthesis and nitrogen cycling. However, examination of many datasets reveals high levels of variation, especially across environments with moderate precipitation (<1000 mm a−1). To test for extrinsic effects on plant isotope composition in such environments, we studied data from plants collected over three years from multiple habitats and seasons in Kruger National Park, South Africa. Our sample is sufficiently large to evaluate not only effects of environmental variables (rainfall up to ∼800 mm a−1, temperature, physical habitat structure) but also taxonomic effects. Species composition of habitats accounted for most of the variation in our data, followed by physical habitat structure (e.g. wooded or riverine compared with open, grassy habitats), while rainfall and temperature had only indirect or negligible effects. The latter finding concurs with subsections of existing datasets and we suggest therefore that such effects usually become visible in datasets that span environmental extremes, implying environmental ranges within which plant isotope variations cannot readily be ascribed to climate. Copyright © 2013 John Wiley & Sons, Ltd.

Longitudinal studies have revealed how variation in resource use within consumer populations can impact their dynamics and functional significance in communities. Here, we investigate multi-decadal diet variations within individuals of a keystone megaherbivore species, the African elephant ( Loxodonta africana ), using serial stable isotope analysis of tusks from the Kruger National Park, South Africa. These records, representing the longest continuous diet histories documented for any extant species, reveal extensive seasonal and annual variations in isotopic—and hence dietary—niches of individuals, but little variation between them. Lack of niche distinction across individuals contrasts several recent studies, which found relatively high levels of individual niche specialization in various taxa. Our result is consistent with theory that individual mammal herbivores are nutritionally constrained to maintain broad diet niches. Individual diet specialization would also be a costly strategy for large-bodied taxa foraging over wide areas in spatio-temporally heterogeneous environments. High levels of within-individual diet variability occurred within and across seasons, and persisted despite an overall increase in inferred C 4 grass consumption through the twentieth century. We suggest that switching between C 3 browsing and C 4 grazing over extended time scales facilitates elephant survival through environmental change, and could even allow recovery of overused resources.

The African elephant ( Loxodonta africana ) is a large-bodied, generalist herbivore that eats both browse and grass. The proportions of browse and grass consumed are largely expected to reflect the relative availability of these resources. We investigated variations in browse (C 3 biomass) and grass (C 4 ) intake of the African elephant across seasons and habitats by stable carbon isotope analysis of elephant feces collected from Kruger National Park, South Africa. The results reflect a shift in diet from higher C 4 grass intake during wet season months to more C 3 browse-dominated diets in the dry season. Seasonal trends were correlated with changes in rainfall and with nitrogen (%N) content of available grasses, supporting predictions that grass is favored when its availability and nutritional value increase. However, switches to dry season browsing were significantly smaller in woodland and grassland habitats where tree communities are dominated by mopane ( Colophospermum mopane ), suggesting that grasses were favored here even in the dry season. Regional differences in diet did not reflect differences in grass biomass, tree density, or canopy cover. There was a consistent relationship between %C 4 intake and tree species diversity, implying that extensive browsing is avoided in habitats characterized by low tree species diversity and strong dominance patterns, i.e., mopane-dominated habitats. Although mopane is known to be a preferred species, maintaining dietary diversity appears to be a constraint to elephants, which they can overcome by supplementing their diets with less abundant resources (dry season grass). Such variations in feeding behavior likely influence the degree of impact on plant communities and can therefore provide key information for managing elephants over large, spatially diverse, areas.

A major focus in population ecology is understanding factors that limit rare species. We used stable isotope approaches to diet to determine whether remaining rare antelope populations in Kruger National Park (KNP), South Africa experience i) nutritional stress; ii) competition with sympatric bulk grazers; iii) reduced habitat heterogeneity. Rare species consumed near-pure C4 grass-based diets throughout the seasonal cycle, in contrast to field observations that reported significant levels of C3 consumption (browse) by these taxa. This finding, coupled with low faecal %N at the height of the dry season, may indicate nutritional stress, but recent isotopic studies of the same species elsewhere in Africa suggest that field observations overestimated levels of browse consumption. We find little evidence for diet niche overlap between rare antelope with bulk grazing species. This partitioning of resources (interpreted mainly as tall- versus short-grass grazing, respectively), is consistent with reported differences in observed diet, and comparative oral morphology. Last, we find less seasonal diet variations amongst bulk grazers feeding in rare antelope habitats compared with other landscapes. We propose that loss of functional heterogeneity, apparently brought about by high densities of artificial waterholes, limits recovery of diet- and habitat-selective rare antelope populations in KNP.