HABITAT FRAGMENTATION AND EXTINCTION THRESHOLDS IN SPATIALLY EXPLICITMODELS

1. The incidence of habitat destruction on the survivorship of a singl e metapopulation is studied by means of a spatially explicit model. 2. As the proportion of destroyed sites increases, the structural proper ties of the resulting landscape change in a non-linear way, showing th e existence of critical thresholds and phase transitions. 3. Such crit ical thresholds are identified by means of an order parameter, which d iscriminates a quantitative process, i.e. habitat loss, from a qualita tive one, i.e. habitat fragmentation, This difference is only well und erstood using a spatially explicit framework. 4. We introduce on such a fragmented landscape the dynamics of a metapopulation balanced by lo cal colonization and extinction by means of the cellular automaton for malism. 5. The existence of extinction thresholds when a given fractio n of habitat is destroyed is reported. These thresholds are determined both by the critical behaviour of the landscape structural properties , and by the demographic properties of the metapopulation. 6. Some dif ferences between these results and those derived from the study of spa tially implicit models are described and explained. In particular, the percentage of patch occupancy is lower for a given value of habitat d estruction in the spatially explicit formulation. Extinction threshold also take place for a lower destruction value. Some implications for the management of natural landscapes are discussed.