WHEN DOES FRAGMENTATION OF BREEDING HABITAT AFFECT POPULATION SURVIVAL

The goal of this study was to delineate the circumstances in which fra gmentation of breeding habitat affects population survival. Fragmentat ion is defined (literally) as the breaking apart of habitat; note frag mentation does not imply loss of habitat. I developed a spatially expl icit simulation model in which I varied the spatial pattern of breedin g habitat in the landscape from contagious to fragmented, while also v arying 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 narro w set of conditions: (1) the average between-generation movement dista nce of the organism is about 1-3 times the expected nearest distance b etween 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 r ate in the non-breeding habitat areas is much higher than the mortalit y rate in breeding habitat areas. Note that all of these conditions mu st hold for there to be an effect of breeding habitat fragmentation on population survival. These results suggest that spatially explicit si mulation modelling of population dynamics is only necessary under a re latively narrow range of conditions. (C) 1998 Elsevier Science B.V.