Exploring the effects of habitat fragmentation on biodiversity

Debate rages as to whether, once habitat loss effects are discounted, habitat fragmentation leads to biodiversity declines or has positive effects. Studies define fragmentation in different ways, as the converse of connectivity, isolation of patches, or with habitat loss. Studies need to address “fragmentation per se”, which is, specifically, at the landscape level and not confounded by habitat loss. Different patterns have been found, suggesting that fragmentation per se does not always have a negative effect. To help bring clarity to the debate, I investigated some of the reasons for these differing results.
To investigate fragmentation per se, I developed a multi-species landscape-scale individual-based model (IBM), with species able to move around my simulated landscapes. I investigated species-level perspectives and incorporated the concepts from this analysis into IBM. I investigated, using the IBM, the effect of fragmentation per se of a focal-habitat on diversity across landscapes and if the effect differed with different species’ characteristics and modification of the land covers between patches of the focal-habitat.
I found species each have a unique unshared perspective of the multiple land covers in landscapes. It is inappropriate to lump species into being associated with one land cover. Overall gamma-diversity increases with fragmentation per se under a range of assumptions but species that are less competitive and prefer the focal-habitat decline. Specialists, generalists and species able to traverse the matrix to reach patches are unaffected or increase with fragmentation per se. Landscapes used in fragmentation studies are important in determining what result is found, with often-used landscapes tending to lead to more negative results.
These findings help resolve the fragmentation per se debate. While our study suggests general patterns of gamma-diversity increase under fragmentation, critically for conservation and policy responses, species associated with the fragmented habitat decline. But declines are not universal. Species are affected differently.