Conclusions:
The negative effects of patch size and isolation on species may not occur until the landscape consists of less than 10% suitable habitat for birds, and 30% suitable habitat for mammals.
Thresholds/Learnings:
The negative effects of patch size and isolation on species may not occur until the landscape consists of less than 10% suitable habitat for birds, and 30% suitable habitat for mammals.
Synopsis: This study involved a review of studies on birds and mammals in habitat patches in landscapes with different proportions of suitable habitat. The findings demonstrate that there exists a threshold in proportion of suitable habitat in the landscape, above which fragmentation becomes pure habitat loss. The threshold is 10% of suitable habitat for birds and 30% suitable habitat for mammals. The negative effects of patch size and isolation on the original species may not occur until the landscape consists of less than these threshold amounts of suitable habitat. For mobile organisms, the effects of isolation may appear only in landscapes with very fragmented habitat. In landscapes with highly fragmented habitat, a further reduction in habitat results in an exponential increase in distances between patches. Thus, in landscapes with highly fragmented habitat, the spatial arrangement of habitat patches is very important. Moreover, the effect of patch size and isolation will not only depend on the proportion of original habitat in the landscape, but also on the suitability of the surrounding habitats. Beta diversity, may increase when new patches of habitat are created within a continuous habitat, because new species may be found there, even if the new patches are human-made. The beta diversity in the landscape will probably be highest when two habitats occur in about equal proportions
