Extinction-Debt Trajectories and Spatial Patterns of Habitat Destruction
Extinction-debt theory holds that following habitat destruction, some extant species in remnants of habitat are doomed to eventual extinction. The extinction debt will affect the interpretation of ongoing impacts and extinctions, because little is understood about the changes in species abundance through time in remnants following surrounding habitat destruction. In some models, thresholds in mean time to extinction are sensitive to the spatial configuration of the remnants, but changes in abundance through time could also be affected. A simulation that includes hierarchical competition, reproduction, dispersal, and mortality was run on two-phase landscapes varying in spatial pattern and extent of habitat destruction. In this article, the courses of temporal change in species abundance, or trajectories, are examined. Thresholds are not evident among different amounts of extant habitat or across a range of spatial patterns. Instead, trends exist in the amount of impact per unit reduction in habitat. Better competitors are more sensitive to the initial stage of destruction and to destruction leaving a more dispersed pattern of habitat; better colonizers have the opposite trends. Assessment of cumulative impacts will vary with species in the initial and penultimate stages of habitat destruction.