Tortuosity of habitat edges affects animal movement

Abstract

Animal travel between habitat patches affects populations, communities, and ecosystems. I used computer simulations to test whether animals form an emergent response to edges—i.e., whether simply responding to an edge causes an animal to behave as if it can recognize edge tortuosity. Animals were simulated inside a habitat patch that contained a tortuous edge and three straight edges. I varied the following parameters: scale of edge tortuosity, edge crossing probability, and avoidance/attraction to edges. Permeability estimates were standardized to remove the effects of edge length, path shape, path size, and distance to animals. Results showed that when animals are attracted to edges, or are neutral to edges and have a high edge-crossing probability, edge tortuosity does not affect permeability. However, when animals avoid edges, or are neutral to edges and have a low edge-crossing probability, then permeability is higher at smaller scales. Linking this to body size suggests that larger animals who avoid edges have increased edge permeability compared to smaller animals. Edge tortuosity also affects where animals cross edges and what direction they travel after crossing them. Thus, edge tortuosity can affect metapopulation dynamics in more ways than simply due to an increase in edge length.