Scale-dependent diversity patterns in spider communities along climate and fragmentation gradients

Context: Understanding the mechanisms driving biodiversity changes along environmental gradients and across scales is a key challenge in community ecology. Objectives: We investigated how spider species diversity—alpha, beta, and gamma—varies with annual precipitation, ranging from 450 mm in the north to 250 mm in the south, across 34 habitat patches in the Southern Judea Lowlands of Israel. Methods: We employed the Measurements of Biodiversity (MoB) framework to assess scale-dependent changes in biodiversity patterns, focusing on how species abundance distribution, individual density, and spatial aggregation contribute to this spatial variation. Results: Spider abundance peaked at moderate precipitation levels. A patch-scale analysis revealed a positive association between the rarefied α-scale species richness and annual precipitation. Landscape analysis indicated that spatial aggregation and species evenness decreased with annual precipitation. These opposing effects on biodiversity (i.e., species richness being negatively correlated with spatial aggregation and positively correlated with species evenness) intensified with spatial scale to the extent that no differences in the rarefied species richness were observed at the γ scale. Along the fragmentation gradient, abundance and richness decreased with patch connectivity at the α and γ-scales, though these patterns turned non-significant after controlling for individual density. Conclusions: Our results show that community organization is affected by spatial aggregation and species abundance distribution, which change along climate and fragmentation gradients. Our findings can enhance our understanding of the processes shaping spider communities in fragmented agroecosystems. Future studies should explore functional traits that change along gradients, including body size and hunting strategies.