Evidence for environmental conditions during the last 20 000 years in Southern Africa from C-13 in fossil hyrax dung

Abstract

C-13/C-12 ratios in plants depend on factors like temperature, evaporation or seasonal moisture distribution. Fluctuations of C-13/C-12 in Procavia capensis (hyrax) dung samples from different vegetation zones and various ages over the last 20 000 years indicate variations in the amounts of C4 and CAM, or C3 plants consumed by these herbivores. Potentially they also indicate vegetation changes that may have occurred. C-13/C-12 values for a series of hyrax middens of Late Pleistocene/Holocene age, from a variety of biomes across Southern Africa, show that hyraxes favour mainly C3 plants in their diets but they do incorporate CAM or C4 plants under certain circumstances. In the eastern mountainous summer-rain area around Clarens with C3 woodland and unpalatable "sour" grassland consisting mainly of C4 grasses and fewer of the C3 type, hyraxes seem to avoid at least the C4 component of grass and rely mainly on leaves of the woody plants. Isotopic data for hyrax dung in the western Cape Cederberg region indicate diets composed almost exclusively of C3 plants during the last 20 000 years. Slight shifts towards more enriched values occur, e.g., around 420 and 2100 years ago, which may indicate slight increase in CAM or C4 plants. Interestingly no enrichment occurs during the Last Glacial Maximum when a shortage of atmospheric CO, may have favoured C4 plants. During the late Holocene some CAM and/or C4-plant ingestion by hyraxes is suggested in the dry western and southern areas which receive more summer rains, probably reflecting the availability of some palatable (or "sweet") summer grasses. Although slight, a comparable pattern of isotope change is observed in three areas viz., the Cederberg, the Karoo and the Namib Desert, suggesting that plant cover is responding to regional climate mechanism ca. 2100 years BP. This does not necessarily imply similar seasonal rainfall shifts over the whole of this wide area