The effects of fragmentation per se on biodiversity

Biodiversity is very relevant for maintaining ecosystem services, however, it is under increasing pressure. One of the main anthropogenic pressures on biodiversity is land use change. Nevertheless, the exact effects of land use change on biodiversity are still poorly understood. While it is known that habitat loss is a major driver of extinction in fragmented landscapes, the effect of fragmentation per se, meaning the breaking apart of a landscape while keeping the habitat amount constant, on biodiversity is still discussed. Several explanations have been furnished possibly explaining the seemingly contradictive findings of the effect of fragmentation per se on biodiversity in the past. Among these are spatial and temporal scale-dependencies of biodiversity measures as well as species-specific responses to fragmentation per se. In order to resolve the confusions regarding the effects of fragmentation per se on biodiversity for these factors, I established an agent-based model of species communities in landscapes subject to fragmentation including specific demographic effects. I found clear scale-dependencies of responses in biodiversity for fragmentation per se for temporal and spatial scales. For instance, the model showed positive geometric fragmentation effects on landscape-scale on biodiversity with increasing levels of fragmentation per se right after fragmentation took place. However, at the end of the model simulations, after demographic fragmentation effects were able to establish, positive, neutral, and also negative responses to fragmentation per se were found, showing that responses to fragmentation per se can vary over time. While at the end of model simulations on landscape-scale positive, neutral, and also negative effects of fragmentation per se on biodiversity depending on the included demographic fragmentation effects were found, on patch-scale only weakly negative responses in biodiversity to fragmentation per se were detected. Thus, these results show the spatial scale-dependencies of fragmentation per se on biodiversity. Lastly, responses to fragmentation per se varied pronouncedly for species with different foraging strategies and movement distances. Hence, this study helps to understand and disentangle seemingly contradictive findings of the effects of fragmentation per se on biodiversity. Additionally, I outline how to resolve further confounding findings of the past regarding fragmentation per se and discuss adequate approaches for future research on fragmentation per se. Finally, the present results can help to create suitable conservation schemes in the future.