Low impact of fragmentation on genetic variation within and between remnant populations of the typical renosterveld species Nemesia barbata in South Africa
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Renosterveld is a Mediterranean-type shrubland in the south-western Cape of South Africa. It is an exceptionally species-rich habitat and a local biodiversity hotspot. However, it has been strongly fragmented due to land use intensification during the last centuries. We analysed the impact of fragmentation on the genetic variation of a typical renosterveld species, the annual herb Nemesia barbata. For our investigation we selected populations of the species in 20 renosterveld fragments of different sizes in the Cape lowlands and determined genetic variation within and between populations using amplified fragment polymorphsims (AFLPs). We expected genetic pauperisation within small and isolated fragments and a lack of gene flow between these fragments. We observed considerable genetic variation within but only a low level of variation between populations. Genetic variation within populations was not correlated with the size of the fragment or the distance to the nearest adjacent fragment. However, genetic variation between populations was positively correlated with geographic distance between fragments, indicating historical and/or actual gene flow. Based upon our results, we conclude that habitat fragmentation does not yet influence the genetic variation of N. barbata. Historical and possibly actual gene flow, combined with buffering effects of the soil seed bank, appear to have minimized the negative impacts of habitat fragmentation on genetic variation of this renosterveld species.
- RESEARCH: Esler K