Assessing habitat fragmentation’s hierarchical effects on species diversity at multiple scales: the case of Thousand Island Lake, China

Context: The study of habitat fragmentation is fraught with definitional and conceptual challenges. Specifically, a multi-scale perspective is needed to address apparent disagreements between landscape- and patch-based studies that have caused significant uncertainty concerning fragmentation’s effects. Objectives: Here we test the hypothesis that habitat fragmentation alters biological communities by creating hierarchically nested selective pressures across plot-, patch-, and landscape-scales in the Thousand Island Lake, China. We assess the variation in fragmentation-diversity relationships contextualize the interplay of scale-dependent relationships. Methods: This work utilized two datasets. At the island scale, islands were sampled to adequately capture the vast majority of species on each island using 5 × 5 m sampling cells. To capture intra-island variation, we sampled 400 m² plots set up along an edge gradient on each island. The variation in species richness at each scale was then compared using Wilcoxon tests, Spearman rank correlations, generalized linear models, and single-large-or-several-small (SLOSS) simulations. Results: We find that edges have little impact on plot α-diversity and between-plot β-diversity, but increase the amount of β-diversity that can be attributed to nestedness at the plot-scale. We also find that the percent habitat in the surrounding landscape has a positive effect on species richness at the patch-scale and that small islands accumulate species faster than large islands of equal total size at the landscape-scale. Conclusions: By observing interdependent effects at each scale, we find support for the hypothesis that habitat fragmentation’s effects are hierarchically structured. Therefore, multi-scale approaches are needed to understand the patterns, processes, and consequences of fragmentation.