How the relationship between vegetation cover and land-cover variance constrains biodiversity in a human dominated world

Alteration of natural vegetation cover across the landscape drives biodiversity changes. Although several studies have explored the relationships between vegetation cover and species richness, as well as between land-cover variance and species richness, few have considered the non-independence of these two biodiversity drivers. The goal of this perspective paper is to present theoretical and empirical relationships linking vegetation cover to land-cover variance at the landscape scale, and the implication of these relationships for species richness change along a gradient of increasing anthropization. We used simulated and empirical Normalized Difference Vegetation Index data to examine the generality of the relationship between vegetation cover and land-cover variance. Using the province of Quebec (Canada) as a case study, our results show that decreasing vegetation cover captures the transition from landscapes with low land-cover variance (non-anthropized landscapes), to intermediate variance (agricultural landscapes), to high variance (urban landscapes). Based on this relationship between vegetation cover and land-cover variance, and assuming independent positive monotonic relationships between biodiversity and both of these drivers, we predict a unimodal relationship between species richness and anthropization. This suggests a threshold of anthropization beyond which the positive effects of land-cover variance no longer compensate for the negative effects of vegetation cover loss. Identifying these thresholds could be key to setting conservation targets at a landscape scale.