Examination of the feeding habits of mammalian species such as the African elephant ( Loxodonta africana ) that range over large seasonally dynamic areas is exceptionally challenging using field-based methods alone. Although much is known of their feeding preferences from field studies, conclusions, especially in relation to differing habits in wet and dry seasons, are often contradictory. Here, two remote approaches, stable carbon isotope analysis and remote sensing, were combined to investigate dietary changes in relation to tree and grass abundances to better understand elephant dietary choice in the Kruger National Park, South Africa. A composited pair of Landsat Enhanced Thematic Mapper satellite images characterising flushed and senescent vegetation states, typical of wet and dry seasons respectively, were used to generate land-cover maps focusing on the forest to grassland gradient. Stable carbon isotope analysis of elephant faecal samples identified the proportion of C 3 (typically browse)/C 4 (typically grass) in elephant diets in the 1–2 days prior to faecal deposition. The proportion of surrounding C 4 land-cover was extracted using concentric buffers centred on faecal sample locations, and related to the faecal %C 4 content. Results indicate that elephants consume C 4 vegetation in proportion to its availability in the surrounding area during the dry season, but during the rainy season there was less of a relationship between C 4 intake and availability, as elephants targeted grasses in these periods. This study illustrates the utility of coupling isotope and cost-free remote sensing data to conduct complementary landscape analysis at highly-detailed, biologically meaningful resolutions, offering an improved ability to monitor animal behavioural patterns at broad geographical scales. This is increasingly important due to potential impacts of climate change and woody encroachment on broad-scale landscape habitat composition, allowing the tracking of shifts in species utilisation of these changing landscapes in a way impractical using field based methods alone.

All of the data on the nutritional and antifeedant properties of plants collected in 2014 from five habitats within the Cradle of Humankind World Heritage Site. These data accompany the paper by Henry et al. in the Review of Paleobotany and Palynology.

The selection of foods in any environment depends on a variety of factors, including the nutrient availability and antifeedant loads in the component habitats. How these nutritional properties vary and covary in time and space is not well known, particularly among wild plant species. We collected plant samples from several habitats within the Cradle of Humankind World Heritage Site in South Africa, and measured their macronutrient and antifeedant properties in order to explore how season, habitat, plant type, and plant organ affected the quality of these potential plant foods. Our results have implications for early hominin use of similar habitats.

Data from Small mammal insectivore stable carbon isotope compositions as habitat proxies in a South African savanna ecosystem Leichliter et al. Journal of Archaeological Science: Reports

Faecal stable isotope compositions reflect wildlife diets, if digestive processes along the gastrointestinal tract (GIT) do not alter diet–faeces isotopic relationships in an unpredictable way. We investigated 13C and 15N compositions of digesta along the ruminant GIT, using Saanen dairy goats kept on pure grass hay or browse for >20 days. Isotopic changes occurred in the ventral rumen, and in the small intestine, where digesta had significantly higher δ13C and δ15N (associated with lower C or higher N content, respectively) values relative to other GIT sites. However, effects on isotope fractionation were small (∼1.0‰ for δ13C and ∼ 2.0‰ for δ15N), and were reversed in the hindgut such that faecal isotope compositions did not differ from the foregut. No other substantial isotopic changes occurred across GIT sites, despite the morphophysiological complexity of the ruminant GIT. We found similarly small differences across GIT components of rheem gazelles (Gazella leptoceros) fed a mixture of C3 lucerne and C4 grass, although in this case faeces were 15N-depleted relative to other GIT components. Along with differences in δ15N between goats fed browse or grass, this result implies a systematic difference in diet–faeces δ15N relationships, contingent on the botanical composition of ruminant diets. Thus, while our results support faecal δ13C as a reliable proxy for wildlife diets, further work on factors influencing faecal 15N abundance is needed. Finally, we note high levels of isotopic variability between individuals fed the same diets, even accounting for the relatively short duration of the experiments, suggesting an important influence of stochasticity on isotope fractionation.

Stable isotope analysis of consumer tissues document patterns of resource use because data are linearly related to isotope compositions of their source(s) (i.e., food, water, etc.). Deviations in parameters estimated for these relationships can arise from variations in consumer tissue–diet spacing (Δ TS ) and the level of isotopic heterogeneity in the source(s). We present a set of simple hypotheses that distinguish between the effects of Δ TS and source isotope heterogeneity. The latter may arise via mixed diets, during tissue turnover, or by isotopic routing of dietary components. We apply these concepts to stable carbon and nitrogen isotope relationships between gut contents and body tissues of large mammal herbivores from mixed C3/C4 South African savannas and test predictions based on the compound- and/or time-specific data archived within each material. Predicted effects of source isotope heterogeneity are readily detected in carbon isotope relationships between materials representing different time periods or comprising bulk versus protein-only diet components. Differences in Δ TS of carbon isotopes across mammal herbivore species with very different feeding niches (and diet isotope compositions) are likely to be small or non-existent in these habitats. Variations in Δ TS estimated for nitrogen isotopes are much greater, leading to inconsistencies that cannot be explained by diet or trophic level effects alone. The effects of source heterogeneity on isotopic relationships generate numerical artefacts that have been misinterpreted as variations in Δ TS . We caution against generalized application of hypotheses based on assumptions of source isotopic homogeneity, even for single diets commonly used in laboratory studies. More careful consideration of how heterogeneity affects consumer–diet relationships is needed for many field and laboratory systems.

The stable carbon isotope composition of animal tissues represents the weighted sum of the variety of food sources eaten. If sources differ in digestibility, tissues may overrepresent intake of more digestible items and faeces may overrepresent less digestible items. We tested this idea using whole blood and faeces of goats ( Capra hircus L., 1758) fed different food mixtures of C3lucerne ( Medicago sativa L.) and C4grass ( Themeda triandra Forssk.). Although blood and faecal δ13C values were broadly consistent with diet, results indicate mismatch between consumer and diet isotope compositions: both materials overrepresented the C3(lucerne) component of diets. Lucerne had lower fibre digestibility than T. triandra, which explains the results for faeces, whereas underrepresentation of dietary C4in blood is consistent with low protein content of the grass hay. A diet switch experiment revealed an important difference in13C-incorporation rates across diets, which were slower for grass than lucerne diets, and in fact equilibrium states were not reached for all diets. Although more research is needed to link digestive kinetics with isotope incorporation, these results provide evidence for nonlinear relationships between consumers and their diets, invoking concerns about the conceptual value of “discrimination factors” as the prime currency for contemporary isotope ecology.

Background: Theories of density-dependent habitat selection provide two solutions for co-existence of competing species. The niche compression hypothesis predicts that species reduce their respective niche breadths in response to inter-specific competition. Alternatively, if the species have similar resource preferences, the subordinate species may be forced to expand its niche to incorporate secondary resources.Aim: Determine whether grazing ungulate species partition the resource by compression or expansion of dietary niches.Organisms: Black wildebeest (Connochaetes gnou) and blue wildebeest (C. taurinus).Methods: Stable carbon and nitrogen isotope analysis of faeces. Isotopic niche breadths are compared across allopatric and sympatric wildebeest populations in South African grasslands.Results: Stable carbon and nitrogen isotope niche breadths of the two wildebeest species were virtually identical. In sympatry, however, black wildebeest had a narrower δ13C niche breadth (indicating almost exclusive use of C4 grass), whereas blue wildebeest had a wider δ13C niche breadth (indicating significant contributions from C3 sources). Blue wildebeest also had a wider δ15N niche breadth than sympatric black wildebeest. Moreover, the δ13C niche breadths of sympatric black wildebeest and blue wildebeest were narrower and wider, respectively, than those of allopatric populations of either species.Conclusions: Isotope niche dynamics across allopatric and sympatric populations arise due to the combined effects of competition and habitat heterogeneity on resource use. Although results for black wildebeest resemble niche compression, this hypothesis cannot explain patterns observed in blue wildebeest. Expansion of the blue wildebeest niche, and restricted niche breadth of black wildebeest, is consistent with predictions of a shared preference model in which black wildebeest are the dominant competitor. When competition is operating, differences in the way species use secondary resources can have an important role in structuring grazer assemblages.

We tested the reliability of herbivore faecal δ13C and δ15N values for reconstructing diet through review of an extensive database derived from a 3-year study of ungulates in South Africa’s Kruger National Park. Faeces are a useful material for stable isotope studies of diet because they record dietary turnover at very short time scales, and because sampling is non-invasive. However, the validity of faecal isotope proxies may be questioned because they represent only undigested food remains. Results from Kruger Park confirm that free-ranging browsers have faecal δ13C consistent with C3 feeding, grazer faeces are C4, and mixed-feeder faeces intermediate. Although the respective ranges do not overlap, there is significant variation in faecal δ13C of browsers and grazers (∼2.0–4.0%o) across space and through time. We demonstrate that most (∼70%) of this variation can be ascribed to corresponding patterns of variation in the δ13C of C3 and C4 plants, respectively, re-enforcing the fidelity of faecal isotope proxies for diet but highlighting a need for mixing models that control for variations in plant δ13C in order to achieve accurate diet reconstructions. Predictions for the effects of climate (rainfall) and ecophysiology on15N-abundance variations in mammals do not persist in faeces. Rather, faecal δ15N tracks changes in plant δ15N, with further fractionation occurring primarily due to variations in dietary protein (reflected by %N). Controlling for these effects, we show that a dual-isotope multiple source mixing model (Isosource) can extend diet reconstructions for African savanna herbivores beyond simplified C3/C4 distinctions, although further understanding of variations in mammal δ15N are needed for greater confidence in this approach.

We tested the reliability of herbivore faecal δ 13 C and δ 15 N values for reconstructing diet through review of an extensive database derived from a 3-year study of ungulates in South Africa’s Kruger National Park. Faeces are a useful material for stable isotope studies of diet because they record dietary turnover at very short time scales, and because sampling is non-invasive. However, the validity of faecal isotope proxies may be questioned because they represent only undigested food remains. Results from Kruger Park confirm that free-ranging browsers have faecal δ 13 C consistent with C 3 feeding, grazer faeces are C 4 , and mixed-feeder faeces intermediate. Although the respective ranges do not overlap, there is significant variation in faecal δ 13 C of browsers and grazers (∼2.0–4.0%o) across space and through time. We demonstrate that most (∼70%) of this variation can be ascribed to corresponding patterns of variation in the δ 13 C of C 3 and C 4 plants, respectively, re-enforcing the fidelity of faecal isotope proxies for diet but highlighting a need for mixing models that control for variations in plant δ 13 C in order to achieve accurate diet reconstructions. Predictions for the effects of climate (rainfall) and ecophysiology on 15 N-abundance variations in mammals do not persist in faeces. Rather, faecal δ 15 N tracks changes in plant δ 15 N, with further fractionation occurring primarily due to variations in dietary protein (reflected by %N). Controlling for these effects, we show that a dual-isotope multiple source mixing model (Isosource) can extend diet reconstructions for African savanna herbivores beyond simplified C 3 /C 4 distinctions, although further understanding of variations in mammal δ 15 N are needed for greater confidence in this approach.

We assess whether interspecific differences in craniodental morphology within a single ruminant feeding guild, the grazers, represent anatomical adaptations to subtle differences in diet. Differences in craniodental anatomy follow a distinct taxonomic pattern that is paralleled by dietary niche differentiation recorded in species' stable carbon (delta C-13) and nitrogen isotope (delta N-15) compositions, strongly supporting a hypothesis for functional divergence within the grazers. We propose that the evolutionary origin of grazers were multifold; at least two and up to four different types of grazing can be discerned within the 11 taxa studied here alone. However, correspondence between craniodental adaptations and isotopic differences across species are not found when only VC data are considered (i.e. morphological differences do not reflect varying proportions of C-3 browse to C-4 grass consumed). This implies that alternate anatomical adaptations to grazing are not related to differences between variable (part-time browsing) and obligate grazers, as previously predicted. Rather, anatomical differences correlate strongly with changes in delta N-15, which we infer to reflect functional responses to changes in diet quality associated with the degree of feeding selectivity and short-, medium-, or tall-grass grazing. (c) 2008 The Linnean Society of London.

Several authors have proposed that papionin baboons provide appropriate analogs for early hominin niche differentiation. Savanna-dwelling baboons and australopiths both radiated around the same time after Neogene expansion of C-4 grasslands, likely experiencing similar environmental changes and faced with solving similar ecological problems. We explore the insights baboons may provide into dietary ecology of savanna-occupying hominins. We compare dietary information from stable isotope data for feces, hair, and tooth dentine collagen of modern chacma baboons (Papio ursinus) with dietary data for Plio-Pleistocene papionins and hominins from South African savannas. Results confirm that, like the australopiths, baboons consume substantial amounts of C-4 food sources. However, the magnitude of inter- and intraindividual variation in baboon diets across different seasons and habitats is less than that from specimens of Australopithecus africanus and Paranthropus robustus analyzed to date. Hominins also consumed greater amounts of C-4 resources. Thus, though the data demonstrate that the radiation of both primate groups was closely linked with the spread of C-4 grasslands, hominins were even more extreme ecological generalists than baboons were. The absence of a fixed-diet in papionins implies that it was unlikely that the more ecologically flexible hominins evolved specializations for any one food type, an interpretation consistent with recent carbon isotope, dental microwear, and ecomorphological studies. We propose that researchers place less emphasis on resolving the foods that were most important for hominin differentiation; instead, future research should focus on questions related to ecological generalism.

We analysed stable carbon isotope ratios (δ13C) in faeces of 11 African ungulate species from three South African savanna environments to determine whether this approach is sufficiently sensitive to record short-term seasonal diet changes in browsers (BR), mixed-feeders (IM), and grazers (GR). At monthly intervals, faecal δ13C revealed variations in proportions of C3 (browse) to C4 (grass) biomass consumed that were not detected by broader dry versus wet season comparisons, including subtle diet shifts amongst BR and GR. However, trends in faeces were influenced by changes in C3 and C4 plant isotope composition of up to 3‰. Nonetheless, faeces and plants showed strongly similar patterns of variation through the seasonal cycle, so that small diet shifts can be reliably inferred, provided that the variations in plants are controlled for. Faecal δ13C of BR may be further influenced by consumption of isotopically different plant parts such as foliage versus fruit and flowers, and GR faeces may reflect differential utilization of grass following different photosynthetic sub-pathways. Future studies will need to incorporate data that capture isotopic variations in herbivore food sources, and if this is achieved, the approach may well become adopted as a routine addition to traditional methods for assessing diet, habitat use, and habitat condition.