AUTHORS: Kimberly A. With*, Kansas State University
ABSTRACT: Although habitat loss and fragmentation occur at a landscape scale, their effects are typically studied at a patch scale (patch area and isolation effects), thereby agitating debate over whether it is the amount or configuration of habitat that has the greater ecological effect. This patch-based view is reflected in the design of most fragmentation experiments, where the size and relative isolation of patches are manipulated to create landscape patterns (a “bottom-up” approach). Conversely, one can adopt a landscape perspective, in which the total habitat amount and overall fragmentation of the entire landscape are the focus of study (a “top-down” approach). Using fractal neutral landscape models, in which both the amount and fragmentation of habitat are adjusted independently, I created an experimental model landscape system (EMLS) in the field to investigate the relative effects of habitat amount versus fragmentation on arthropod diversity and species interactions. The EMLS comprised a replicated series of plots (16 m x 16 m) that consisted of different amounts of red clover (10-80%) arrayed as either a clumped or fragmented distribution. Although habitat amount generally had a greater effect on patterns of species diversity in this system, the effect of fragmentation was more nuanced and complex, involving both direct and indirect effects. Contrary to conventional wisdom, the effect of fragmentation was not always greatest when habitat was limiting. Furthermore, the scaling of diversity in this system demonstrates why it is not always possible to scale-up from patches to make inferences about fragmentation effects at the landscape scale. This results of this EMLS thus underscore the need for more landscape-based studies—at traditionally defined scales—that investigate the relative effects of habitat loss and fragmentation.
