Patterns and processes of rodent and shrew assemblages in the Savanna Biome of KwaZulu-Natal, South Africa.

Abstract

The identification of non-random species composition patterns predicted by assembly rules is a central theme in community ecology. Based on life history characteristics, species composition patterns of rodents and shrews should be consistent with predictions from nestedness rather than competition hypotheses. This study investigated the seasonal changes in rodent and shrew assemblages in eleven savanna vegetation types in a protected reserve in South Africa. Rodents and shrews were sampled between 2009 and 2010 at Phinda Private Game Reserve (PPGR), KwaZulu-Natal. Sample-based rarefaction curves showed that rodent and shrew abundance and richness varied among seasons and vegetation types. Species richness estimators indicated that inventories for rodents (80%) and shrews (100%) were fairly complete. Null-model analyses found no evidence that species co-occurrence patterns in the reserve were non-random with respect to predictions from Diamond’s Assembly rules, niche limitation hypothesis and nestedness hypothesis. I also investigated seasonal changes in species richness and abundance of rodent and shrew assemblages on cattle, pineapple and former cattle farms surrounding PPGR, and used cluster analyses to compare the species composition of rodents and shrews at farm and PPGR study sites. Small mammal assemblages exhibited a heterogeneous distribution and species composition patterns changed between seasons. Sample-based rarefaction curves showed that rodent and shrew abundance and richness varied among seasons and study sites. Species richness estimators indicated that inventories for the rodents (91%) and shrews (100%) on the farms were essentially complete. Rodent and shrew species composition patterns did not group study sites according to land use, nor could species composition patterns be explained by vegetation characteristics. My results suggest that complex biotic and abiotic processes other than competition, nestedness, land use and vegetation characteristics operate at different spatial and temporal scales to structure rodent and shrew assemblages.