Geometric and demographic effects explain contrasting fragmentation-biodiversity relationships across scales
There is consensus that habitat loss is a major driver of biodiversity loss, while the effects of fragmentation, given a constant total habitat amount, are still debated. Here, we use a process-based metacommunity model to show how strongly scale- and context-dependent fragmentation-biodiversity relationships can emerge from the interplay of two types of fragmentation effects - geometric and demographic. Geometric effects arise from the spatial distribution of species and landscape modification, whereas demographic effects reflect long-term changes in species demographic rates following landscape modification. We introduce a novel approach to partitioning these two types of effects and assess how key ecological processes and factors, such as dispersal, habitat heterogeneity, and edge effects, influence geometric, demographic, and net fragmentation effects across spatial scales. We conclude that the framework of geometric and demographic effects can reconcile previous apparently conflicting results and hopefully unlock and advance the debate on biodiversity change in modified landscapes.