Application of Fragmentation and Variegation Models to Epigaeic Invertebrates in South Africa

Abstract

Landscape fragmentation restricts certain species to remnant patches of vegetation within a matrix of less favorable habitat conditions. The concept of variegation is a modification of the fragmentation model, in which the landscape elements are seen as a fuzzy‐edged mosaic, resulting in differential filtration of species across them. Each species responds to a landscape’s pattern in its own particular way, which may not coincide with human visual perception of the landscape pattern. We tested the two extremes of the fragmentation and variegation model (totally discontinuous, fragmented distribution versus continuous, and variegated distribution) using epigaeic macroarthropods in South Africa as a model. The results suggest that the Blattodea, Hemiptera, and Diptera are the most stenotopic taxa, generally restricted to remnant patches of vegetation and highly negatively affected by fragmentation. In contrast, the Hymenoptera, Arachnida, and Orthoptera were generally more cosmopolitan and were distributed regardless of obvious landscape boundaries. All the orders contained at least some species that tended to eurytopy and others that were more stenotopic, illustrating that the landscape pattern should be viewed at the species level (and perhaps even a particular life stage) rather than at higher taxonomic levels. Although these results tend to favor the concept of variegation, some species do respond to the landscape pattern us seen through human eyes. To maximize biodiversity there should be rotational management of edges coupled with encouragement of various stages of secondary succession. Gradual rather than sharp ecotones should be established. Also, because generalized corridor management is utopian, wide corridors with biotype “stepping stones” are probably the best option.