L. Mucina

Strontium isotope analyses of large herbivore habitat use in the Cape Fynbos region of South Africa

The Cape Fynbos region of South Africa, a global biodiversity hotspot, hosted a diverse large mammal fauna till shortly after permanent European settlement (1652). How these animals survived in this exceptionally nutrient-poor environment is puzzling and it is generally believed that they restricted their movements to the more fertile shale areas. We tested the hypothesis that large herbivores avoid nutrient-poor limestone and sandstone fynbos shrublands in favour of shale-derived renosterveld vegetation using strontium (Sr) isotope analysis. If this technique could reconstruct the preferred feeding habitats of the contemporary fauna, it might also be useful for reconstructing the preferred feeding grounds of an extinct fauna. Using the assumption that small rodents have spatially restricted foraging activities, we determined the 87Sr/86Sr isotope ratios of rodent teeth to establish the isotopic signal characteristic of the different geological substrates in the area. We then analysed 87Sr/86Sr isotope ratios in the bones of a number of different large herbivores found in De Hoop Nature Reserve using laser ablation multi-collector inductively coupled plasma mass spectrometry. These values were compared to the bioavailable (rodent) values on the respective geological substrates. The technique identified differences in feeding substrate selection between different species and groups of the same species. The results also showed that shale renosterveld shrubland is not the exclusive source of nutrition for the large herbivores. Strikingly different isotope ratios among individuals in some populations pointed to significant dispersal events from distant sources. However, we were unable to pinpoint the exact feeding areas using Sr isotope analysis probably because some animals use a combination of substrates for feeding and because the geology of the study area is complex with graded isotope signals. We suggest that this technique is a valuable additional tool for exploring large mammal foraging behaviour on habitats associated with contrasting and less complex geology.

Vegetation of mesas and surrounding plains in the southeastern Nama Karoo, South Africa

Plant community composition and distribution on and off isolated mesas were investigated across Nama Karoo communities in the Eastern Cape, South Africa. Species composition and cover were measured in plots along a transect extending from the SE plains and slopes, across the plateaux, onto the NW slopes and plains of three mesas (Tafelberg, Folminkskop and Buffelskop). Data were then classified using the floristic-sociological approach, assisted by the computer package TWINSPAN. Canonical Correlation Analysis was used to analyse the relationship between vegetation and environmental patterns. Mesa communities were found to be distinctly different from plains communities, with no shared communities between the two habitats. The distribution of communities across the landscape is attributed to a soil-moisture gradient. Differences in habitat probably existed before the impact of domestic livestock, but overgrazing has likely exacerbated the differences. The potential to use mesas as sources of seeds and propagules for the surrounding degraded plains is low, since few species are shared between the two habitats. However, generalist, palatable species such as Felicia muricata, Eragrostis obtusa, Pentzia incana etc. could have some potential for future restoration. Dolerite-capped mesas such as Tafelberg and Folminkskop had a general slope community shared between the two mesas. Aspect and the expected cooler, more moist conditions on SE slopes as factors determining community composition for the dolerite mesas were overridden by soil type and associated nutrient status. In xeric sandstone mesas such as Buffelskop, soil type and associated nutrient status were overridden by aspect and slope as determinants of community composition. Mesa habitats are generally not grazed heavily by livestock due to their inaccessible nature, and are not threatened by current land use practices. Plains habitats are often degraded, a consequence of 200 years of selective grazing.