Impacts of terrestrial habitat transformation on temporary wetland invertebrates in a sclerophyllous Sand fynbos landscape

There has been recent debate about the extent to which human disturbance of the landscape affects wetland invertebrates given that the organisms are already adapted to high levels of natural disturbance. Using repeated sampling of a set of 12 temporary wetlands occurring in a differentially transformed Sand fynbos landscape in Cape Town (South Africa), we investigated patterns of macroinvertebrate and microcrustacean assemblage composition, richness and diversity in relation to a physico-chemical gradient resulting from variable habitat loss in the adjacent landscape. Both macroinvertebrates and microcrustaceans showed clear gradational changes in assemblage composition in relation to the surrounding cover of indigenous vegetation (as a proxy for habitat loss). Although the composition of assemblages appeared to be affected by this gradient of habitat transformation, no relationships were detected using various measures of taxon richness and diversity. At the small spatial scale for which patterns are analysed, the influence of natural variation on invertebrate assemblages appears to have been overridden by that resulting from habitat transformation in the adjacent landscape. Depression wetlands embedded in Sand fynbos habitat appear to be unique in terms of their physico-chemistry (acidic and rich in humic substances) and the invertebrate assemblages they support.