Effects of habitat loss and fragmentation on population dynamics

We used a spatially explicit population model that was generalized to produce nine ecological profiles of long-lived species with stable home ranges and natal dispersal to investigate the effects of habitat loss and fragmentation on population dynamics. We simulated population dynamics in landscapes composed of three habitat types (good-quality habitat ranging from 10-25%, poor-quality habitat ranging from 10-70%, and matrix). Landscape structures varied from highly fragmented to completely contiguous. The specific aims of our model were (1) to investigate under which biological circumstances the traditional approach of using two types only (habitat and matrix) failed and assess the potential impact of restoring matrix to poor-quality habitat, (2) to investigate how much of the variation in population size was explained by landscape composition alone and which key attributes of landscape structure can serve as predictors of population response, and (3) to estimate the maximum fragmentation effects expressed in equivalent pure loss of good-quality habitat. Poor-quality habitat mattered most in situations when it was generally not considered (i.e., for metapopulations or spatially structured populations when it provides dispersal habitat). Population size increased up to 3 times after restoring matrix to poor-quality habitat. Overall, habitat amount accounted for 68% of the variation in population size, whereas ecological profile and fragmentation accounted for approximately 13% each. The maximal effect of (good-quality) habitat fragmentation was equivalent to a pure loss of up to 15% of good-quality habitat, and the maximal loss of individuals resulting from maximal fragmentation reached 80%. Abundant dispersal habitat and sufficiently large dispersal potential, however, resulted in functionally connected landscapes, and maximal fragmentation had no effect at all. Our findings suggest that predicting fragmentation effects requires a good understanding of the biology and habitat use of the species in question and that the uniqueness of species and the landscapes in which they live confound simple analysis.