Small mammal communities in the transformed landscapes of the Western Cape lowlands and their role in alien invasion into fynbos remnants

[摘要] The fynbos eco-region in the Western Cape lowlands has been extensively transformed byanthropogenic activities such as agriculture and urban development, as well as invasive alienplants. Elandsberg Private Nature Reserve and Farms lies on Swartland Alluvium Fynbos andhas been largely fragmented by agricultural crop production, whilst Riverlands NatureReserve together with the Pella Research Site, which lie on Atlantis Sand Fynbos, are undersevere threat from the invasive woody alien Port Jackson Willow (Acacia saligna) whichforms dense stands in the lands adjacent the nature reserve. Habitat transformation hasresulted in subsequent loss of habitat and a reduction in habitat value for small mammalcommunities by creating a mosaic of optimal and sub-optimal habitats. The success of A.saligna is, in part, attributed to its production of copious amounts of small hard-shelled seedsand well established soil seed banks. In the first part of this study we investigated the effectof habitat transformation on resident small mammal communities by comparing smallmammal species richness, diversity and abundance between natural and transformed habitatsas well as between the two vegetation types. We also investigated the populationdemographics of the striped mouse (Rhabdomys pumilio) in the different habitats. Our studyshows that whilst fragments of natural habitats, especially at Riverlands and Pella, may beplaying an important role in harbouring rare and possibly endangered species, transformedhabitats are also important as secondary habitats providing both cover as well as seasonalfood resources. Reproduction and body condition in R. pumilio were dependent on seasonalchanges such as availability of water and food resources in the habitats. The second part ofthis study was carried out to investigate the effect of alien plant invasion on the resident smallmammal communities at Riverlands Nature Reserve and to determine the role of smallmammals in the removal and predation of A. saligna seeds. Rodent species richness, diversityand abundance were very low in the A. saligna stands compared to the adjacent fynbosvegetation. The interaction of rodents with seeds (removal or predation) was dependent uponseed size and seed abundance in the habitats. Whilst rodents may play an important role inpredator limitation in the acacias, it is also possible that they may be playing a significant rolein dispersing the seeds of acacias into the fynbos. More work is required to fully understandthe role small mammals play in seed predation, dispersal and limitation in alien invadedfynbos systems.

[发布机构] Stellenbosch University