HOW DOES HABITAT PATCH SIZE AFFECT ANIMAL MOVEMENT? AN EXPERIMENT WITH DARKLING BEETLES

Abstract

We used an experimental model system consisting of darkling beetles (Coleoptera: Tenebrionidae, Eleodes obsoleta Say) in a microlandscape to assess the effects of habitat patch size on the movement patterns of animals. The ratio of habitat area to nonhabitat in a 25-m2 “microlandscape” was held constant while the grain of patchiness (patch size) was varied in four treatments. Beetle movement pathways were electronically surveyed, and seven pathway metrics were used to quantify movement characteristics. ANOVA and Fisher’s Protected Least Significant Difference post hoc comparisons revealed that both the presence and the grain of spatial heterogeneity influenced how animals moved through landscapes. Intermediate patch sizes elicited the strongest behavioral responses, whereas movements were similar between finely patchy landscapes with small habitat patches and coarsely patchy landscapes with larger habitat patches. These results indicate that organisms may use landscapes that possess different configurations of habitat in similar ways. Predicting how organisms respond to spatial heterogeneity therefore requires an assessment of how organisms use landscapes, in addition to an assessment of the structural characteristics of landscapes, such as grain size.