Jacqui Codron

ELEPHANT (LOXODONTA AFRICANA) DIETS IN KRUGER NATIONAL PARK, SOUTH AFRICA: SPATIAL AND LANDSCAPE DIFFERENCES

Abstract African elephants (Loxodonta africana) are mixed feeders, incorporating varying proportions of grass and browse into their diets. Disagreement persists as to whether elephants preferentially graze or browse, and the degree to which the consumption of these foods is a reflection of their local availability. We used stable carbon isotope analysis of feces to investigate seasonal and spatial variation in the diets of elephants from Kruger National Park (KNP), South Africa. Elephant diets (overall average ∼35% grass) are shown to be distinct from those of grazers (>90% grass), browsers (<5% grass), and another mixed-feeder, the impala (Aepyceros melampus; ∼50% grass). Fecal δ13C values suggest that elephant populations from northern KNP eat more grass (∼40%) during the dry season than do their southern counterparts (∼10%). The wet-season diets of elephants from northern and southern KNP include similar amounts of grass (∼50%), because elephants in the south, but not in the north, ate significantly more grass during this time. Although habitat differences in KNP appear to account partially for variations in elephant diets, the specific influence of each habitat type on diet selectivity is not clear. The homogeneity of woody vegetation in the north (dominated by Colophospermum mopane “shrubveld”) may deter browsing and force elephants in this area to opt for alternative food sources (grass) throughout the seasonal cycle.

Nutritional content of savanna plant foods: implications for browser/grazer models of ungulate diversification

Models of herbivore diversification rely heavily on adaptations that reflect the nutritional quality of foods consumed. In particular, browsers and grazers are expected to show dichotomous adaptations to deal with high quality (concentrate) browse-based and poor quality grass-based diets, respectively. In this study, we test the widespread assumption that browse represents a higher quality food source than grass. We analyzed plants from a South African savanna, collected over one dry and one wet season across several habitat types, for percent nitrogen (%N), neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) to compare variations in nutritional value of different food types. Results show consistently higher %N and lower NDF and ADF of tree foliage and forbs compared to monocots, but the former have consistently higher ADL, implying a higher fiber digestibility in grass compared with browse. Some fruit species have a high NDF and ADL content, implying poorer nutritional value than is commonly assumed. Our findings are in agreement with several other studies depicting relatively poor digestibility of browse (tree foliage and fruit) compared to grass. Reference to browse as high quality foods is therefore misleading, and models of herbivory that rest on this assumption require revision. The more efficient fiber digestibility recorded in grazers compared to browsers cannot be treated as an adaptation to poor quality diets, but rather to maximize benefits of higher fiber digestibility of grass. Spatio-seasonal variations in plant nutritional seem to reflect seasonal and spatial diet changes expected for grazers and intermediate (mixed) feeders. We propose that future studies require further detail on variations in diet, diet quality, and digestive efficiency to properly understand mechanisms of adaptation.

What Insights Can Baboon Feeding Ecology Provide for Early Hominin Niche Differentiation

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 C4 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 C4 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 C4 resources. Thus, though the data demonstrate that the radiation of both primate groups was closely linked with the spread of C4 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.

The confounding effects of source isotopic heterogeneity on consumer–diet and tissue–tissue stable isotope relationships

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 (ΔTS) and the level of isotopic heterogeneity in the source(s). We present a set of simple hypotheses that distinguish between the effects of ΔTS 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 ΔTS 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 ΔTS 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 ΔTS. 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.

When animals are not quite what they eat: diet digestibility influences 13C-incorporation rates and apparent discrimination in a mixed-feeding herbivore

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 C3 lucerne (Medicago sativa L.) and C4 grass (Themeda triandra Forssk.). Although blood and faecal d13C 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 C4 in blood is consistent with low protein content of the grass hay. A diet switch experiment revealed an important difference in 13C-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.

Stable carbon isotope reconstruction of ungulate diet changes through the seasonal cycle

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.

Stable isotope characterization of mammalian predator–prey relationships in a South African savanna

This paper characterizes predator–prey interactions amongst African mammals from C4 savanna environments using stable carbon and nitrogen isotope proxies for diet. Stable carbon (δ13C) and nitrogen (δ15N) isotope data from hair and faeces of large African mammal carnivores, and herbivores as potential prey, are presented for a diverse range of taxa. Carbon-isotope data imply that most carnivores from the “lowveld” savanna of South Africa form part of C4 grass-based food webs. Nitrogen isotope data show clear differences between trophic levels, although it appears that the magnitude of these differences varies between predators feeding on invertebrates and vertebrates, respectively. Whilst the number of carnivore samples for which data are available is relatively few, and data for prey are restricted mainly to large ungulate herbivores, results clearly demonstrate the potential for future applications of this technique to predator–prey food webs in African savannas. In tandem with traditional approaches, stable isotopes can help elucidate patterns of predator impacts on prey populations, domestic livestock, and resolving similar food webs in palaeoenvironmental contexts.

Exploring C-4 plant foods: The nutritional properties of South African savanna vegetation

Leprosy is one of the few specific infectious diseases that can be studied in bioarchaeology due to its characteristic debilitating and disfiguring skeletal changes. Leprosy has been, and continues to be, one of the most socially stigmatising diseases in history, over-riding all other aspects of social identity for the sufferers and frequently resulting in social exclusion. This study examines the stable isotopic evidence of mobility patterns of children, adolescents, and young adult individuals with the lepromatous form of leprosy in Medieval England (10 th –12 th centuries AD) to assess whether the individuals buried with the disease were non-locals, possibly from further afield. Enamel samples from 19 individuals from the St. Mary Magdalen Leprosy Hospital, Winchester (UK) were selected for strontium ( 87 Sr/ 86 6U DQG R[\JHQ į 18 O) stable isotope analysis based on age at death (<30 years), the presence of bone changes associated with lepromatous leprosy, and the underlying geology of their burial locations. The results from these data indicate that the St. Mary Magdalen Leprosy Hospital received an almost equal mixture of local and non-local individuals from further afield, including early pilgrims. At present, the St. Mary Magdalen Leprosy Hospital is the earliest dedicated leprosaria found within Britain and mobility studies such as these can help elucidate and test some of the broader historical notions and identities associated with the movements of those infected with the disease in Medieval England.