The effect of spatial configuration of habitat capacity on β diversity

Patterns of b diversity are commonly used to infer underlying ecological processes. In this study we examined the effect of spatial configuration of habitat capacity on different metrics of b diversity i.e., b diversity measured as turnover and as variation. For b diversity as turnover, a monotonic species spatial turnover pattern is typically considered as a benchmark for species distributions driven only by dispersal process. Deviations from a monotonic curve are attributed to local environmental filtering (i.e., the same environmental factors affecting different species differently). However, we found non-monotonicity in species spatial turnover in models without environmental filtering effect. This non-monotonicity was caused by variation in a diversity, introduced by spatial configuration of habitat capacity. After applying a recent null-model approach-designed to tease out the effect of variation in a diversity-species spatial turnover remained non-monotonic. This non-monotonicity makes it problematic to use species spatial turnover to infer the underlying processes for species distribution, i.e., whether it is driven by environmental filtering or dispersal processes. Spatial configuration of habitat capacity also influences landscape connectivity. Small-habitat capacity sites may constrain movements of organisms (i.e., dispersal) between sites supporting high capacity habitats. We showed that in a landscape where small-habitat capacity sites were located in positions important for dispersal (e.g., in the center as opposed to on the edge of a landscape) has a higher spatial variation of species composition, hence, higher b diversity. Ecologists who use different measures of b diversity should be aware of these effects introduced by spatial configuration of habitat capacity.