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 spider species diversity, alpha, beta, and gamma, variation 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, Israel. Methods: The Measurements of Biodiversity (MoB) framework analyzes changes in species rarefaction curves by decomposing into three components: (a) species abundance distribution, (b) individual density, and (c) spatial arrangement. Comparing spatial and non-spatial species rarefaction curves enables the capture of the relative importance of each component in influencing species richness change. Results: Spider abundance peaked at moderate precipitation levels. A patch-scale analysis revealed a positive association between rarefied α-scale species richness and annual precipitation. Landscape analysis indicated that spatial aggregation and species evenness decreased with annual precipitation. These opposing effects (species richness being negatively correlated with spatial aggregation and positively correlated with species evenness) intensified with spatial scale, leading to similar rarefied species richness 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: Community organization is affected by spatial aggregation and species abundance distribution 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.