PREDICTING THE IMPACTS OF EDGE EFFECTS IN FRAGMENTED HABITATS

We proposed a protocol for assessing the ecological impacts of edge effects in fragments of natural habitat surrounded by induced (artificial) edges. The protocol involves three steps: (1) identification of focal taxa of particular conservation or management interest, (2) measurement of an 'edge function' that describes the response of these taxa to induced edges, and (3) use of a 'Core-Area Model' to extrapolate edge function parameters to existing or novel situations. The Core-Area Model accurately estimates the total area of pristine habitat contained within fragments. Moreover, it can be used to predict the amount of unaltered habitat preserved within any hypothetical fragment, such as a planned park or nature reserve, regardless of its size or shape. The model is simple, requiring two edge function parameters and the area and perimeter length of the fragment. Model simulations revealed that for any edge-sensitive species and habitat type there exists a critical range of fragment sizes in which the impacts of edge effects increase almost exponentially. This critical size range cannot be predicted without empirical measurement of the edge function.