When does fragmentation of breeding habitat affect population survival?

The goal of this study was to delineate the circumstances in which fragmentation of breeding habitat affects population survival. Fragmentation is defined (literally) as the breaking apart of habitat; note fragmentation does not imply loss of habitat. I developed a spatially explicit simulation model in which I varied the spatial pattern of breeding habitat in the landscape from contagious to fragmented, while also varying a disturbance regime, breeding habitat permanence, and the life history and movement attributes of organisms living in the landscape. The simulation results suggest that fragmentation of breeding habitat affects population survival only under the following relatively narrow set of conditions: (1) the average between-generation movement distance of the organism is about 1-3 times the expected nearest distance between breeding sites; (2) the breeding habitat of the organism covers less than 20% of the landscape; (3) the habitat is not ephemeral; (4) the organism has high breeding site fidelity; and (5) the mortality rate in the non-breeding habitat areas is much higher than the mortality rate in breeding habitat areas. Note that all of these conditions must hold for there to be an effect of breeding habitat fragmentation on population survival. These results suggest that spatially explicit simulation modelling of population dynamics is only necessary under a relatively narrow range of conditions. (C) 1998 Elsevier Science B.V.