Significance of diet type and diet quality for ecological diversity of African ungulates

1. We test two nutritional hypotheses for the ecological diversity of ungulates, the browser/grazer (diet type) and diet quality models, among free-ranging herbivores in a South African savanna, the Kruger National Park. Tests are based on assessment of relationships between diet type and diet quality with body mass and hypsodonty, two morphological features that have been associated with both elements. 2. We use stable carbon isotope ratios of faeces to reconstruct diet in terms of proportions of C(3) plants (browse) and C(4) plants (grass) consumed by different species in different seasons. These data are combined with proxies for diet quality (per cent nitrogen, neutral detergent fibre, acid detergent fibre, and acid detergent lignin) from faeces to track changes in diet quality. 3. Two statistical approaches are used in model selection, i.e. tests of significant correlations based on linear regression analyses, and an information-theory approach (Akaike's Information Criterion) providing insight into strength of evidence for models. 4. Results of both methods show that, contrary to many predictions, body mass and diet type are not related, but these data confirm predictions that diet quality decreases with increasing body size, especially during the dry season. Hypsodonty, as expected, varies with diet type, increasing with increased grass intake. 5. These findings support both a diet type and diet quality model, implying some degree of exclusivity. We propose that congruence between models may be achieved through addition of diet quality proxies not included here, because hypsodonty is more likely a reflection of the abrasive properties of consumed foods, i.e. related to food quality, rather than food type. This implies that adaptation to diets of varying quality, through changes in body size and dental features, has been the primary mechanism for diversification in ungulates. 6. Our interpretation contrasts with several recent studies advocating diet type as the primary factor, exemplifying that further reconciliation between the two models is needed. We discuss the implications of this study for future approaches to achieve a more cohesive understanding of the evolutionary outcomes of herbivore nutrition.     

Processing of prehistoric bones for isotopic analysis and the meaning of collagen C/N ratios in the assessment of diagenetic effects

Diagenetic shifts in the isotopic composition of collagen in prehistoric bones still remain a big problem in the reconstruction of ancient diets by stable carbon and nitrogen isotope analysis. Recently,DeNiro (1985) suggested the measurement of bone collagen C/N ratios as a means of estimating substantial alterations of stable isotope ratios. Bones with collagen C/N ratios lying within a range between 2.9 and 3.6 should have isotopic properties quite close to thein vivo conditions. It can be demonstrated that the C/N ratios are varying considerably with the duration of acid hydrolyzation of the bone samples. Even small changes of the hydrolyzation time cause shifts in the C/N ratios large enought to produce values far outside the range worked out byDeNiro. Besides, our experiments led us to recommend a hydrolyzation at reducing conditions.     

A late Holocene climate record from a stalagmite, Cold Air Cave, Northern Province, South Africa

Stable isotope analyses of a uranium-series-dated stalagmite from South Africa provide a record of climate changes for the periods 4400–4000 years and 800 years ago to recent, interrupted by a prolonged growth hiatus. Generally enriched stable oxygen isotope values, interpreted here to indicate more humid conditions, occurred around 800 years ago. Subsequently a marked depletion in oxygen and carbon isotope values occurred about 600 years ago, reflecting, we believe, shifts toward drier, cooler conditions as the regional indication of the Little Ice Age. This period with depleted, yet oscillating isotope values, is replaced by a period with enriched isotopes until recent times. The record is notable for sharp shifts in isotopic values, on the scale of decades, which reflect rapid oscillations in local climate conditions.     

Florisbad and human population succession in Southern Africa.

The human cranium recovered at Florisbad in 1932 is compared with other Sub-Saharan African hominid remains from Broken Hill, the Omo and Klasies River Mouth. The Florisbad frontal is very broad, but despite this breadth and differences in zygomatic form, there is a definite resemblance to archaic Homo sapiens from Broken Hill. There is also some similarity to both Omo I and Omo II, while fragmentary remains from Klasies River are more lightly built and hence more modern in appearance. These impressions are strengthened by measurement and statistical analysis, which demonstrates that Florisbad and Broken Hill are distant from recent African populations. Even if Florisbad is less archaic than the earlier (Middle Pleistocene?) hominid, it is not noticeably Bushman-like. New dates suggestive of early Upper Pleistocene antiquity also place Florisbad securely in a lineage containing Broken Hill, and there is no evidence to support special ties with any one group of living Africans.     

DIETARY STUDIES OF MARINE MAMMALS USING STABLE CARBON AND NITROGEN ISOTOPIC RATIOS OF TEETH

This study used naturally occurring carbon and nitrogen stable isotopes of teeth to study the diets of marine mammals. The isotopic ratios of nonchemically preserved teeth from eight species of marine mammals, representing 87 individuals that spanned the trophic continuum, were found to reflect nutritional sources. The δ¹³C signals distinguished animals that lived in waters dominated by different primary producers (e. g., seagrass, kelp, and phytoplankton), and δ¹⁵N values indicated the diet and trophic level of the species. This research suggests that isotopic signatures of teeth can be used in dietary studies to show differences and similarities among age classes, genders, geographic locations, and time periods.