Modelling plant population size and extinction thresholds from habitat loss and habitat fragmentation: Effects of neighbouring competition and dispersal strategy

Habitat destruction is a key determinant of species extinction. Its principle components, habitat fragmentation and habitat loss, affect species persistence in landscapes, but few models have investigated how dispersal type and intraspecific competition (crowding effect) modulate this. If dispersal type or crowding changes extinction thresholds, then fragmentation and habitat loss might act differently on different species. Here we generate fragmented landscapes by varying the orthogonal neighbouring correlation between suitable and unsuitable habitat. We show that local dispersers undergo a strong negative impact of habitat fragmentation (lower occupancy of suitable sites), but only under severe habitat loss. In contrast, global dispersal eliminated fragmentation effects through random establishment. Both fragmentation and crowding effects enhanced the extinction risk of species that spread their seeds at close range, while long-range dispersers were not influenced. However, fragmentation improved the persistence of global dispersers that are highly sensitive to crowding, probably through reduced intraspecific competition. With respect to species conservation, our results suggest that random habitat destruction is a more serious threat to species persistence than clustered habitat destruction. Moreover, as species responses to habitat fragmentation depend on dispersal type and sensitivity to crowding, fragmented landscapes with different properties may accommodate different species.