Disentangling the geometric and demographic effects of habitat fragmentation on biodiversity across spatial scales

• Applicant: Dr. Felix May
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems ; Ecology of Land Use ; Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 456976465

Anthropogenic land use change causes the loss and fragmentation of natural habitat and is a major threat for biodiversity. While there is consensus that habitat loss negatively affects biodiversity, the consequences of fragmentation, i.e. the splitting up of a given total habitat amount into small patches, are still intensely debated and positive, neutral, and negative effects on biodiversity have been reported. However, understanding the effects of fragmentation on ecological communities is crucial for biodiversity conservation in modified landscapes. In this project, we aim at reconciling previous contrasting results by improved mechanistic understanding and by embracing the scale-dependence of fragmentation effects. We hypothesize that two types of fragmentation effects, namely geometric and demographic effects, have to be distinguished to reach these goals. Geometric fragmentation effects emerge from the spatial configuration of habitat modifications relative to non-random species distributions, while demographic effects refer to changes in species birth, death, or migration rates in modified landscapes.In work package (WP) 1, we will develop spatial and dynamic simulation models to demonstrate the interplay between geometric and demographic fragmentation effects. Specifically, we will investigate under which conditions negative effects on patch-scale biodiversity can be reconciled with a positive association of fragmentation to landscape-scale biodiversity. We will further show that varying relative importance of geometric vs. demographic fragmentation effects can explain positive, neutral and negative fragmentation-biodiversity relationships at the landscape scale.In WP2, we will develop analytical approaches to disentangle geometric and demographic fragmentation effects using simulated data. We will assess three approaches to control for spatial extent and thus for geometric effects: (i) spatial rarefaction, (ii) distance-decay, and (iii) “cookie-cutter” simulations. By using simulated data with known importance of geometric and demographic effects provided by WP1, we can quantify the power of the analytical approaches with respect to disentangling the two types of effects.In WP3, we will apply the methods derived in WP2 to synthesize previous fragmentation-biodiversity studies. For this purpose, we will acquire spatial biodiversity data from databases and from primary studies. We will conduct a meta-analysis to quantify the influence of habitat type, taxonomic group, and time since land use change on the relative importance of geometric vs. demographic effects.The explicit consideration of geometric and demographic fragmentation effects across scales will advance our fundamental understanding of spatial biodiversity patterns and meta-community dynamics and is key for improving predictions of biodiversity change in modified landscapes.

• DFG Programme: Research Grants