Global Patterns and Drivers of Climatic Niche Originality and Overlap: Disentangling Ecological From Methodological Signals.

Niche overlap is widely used to study species coexistence and biodiversity patterns. However, because macroclimatic niches are typically estimated from species distributions, relationships between niche overlap and geographic range overlap may partly reflect the shared structure of environmental and geographic space rather than ecological processes. Here, we address this challenge by constructing the BioOverlap database combining IUCN range maps and bioclimatic variables to quantify macroclimatic niche properties, niche overlap, and geographic range overlap among ~16,000 terrestrial and marine species, yielding ~90 million pairwise comparisons. Using a taxonomically structured subset encompassing eight taxonomic groups with consistently available variables, we addressed two objectives. First, we quantified niche originality (i.e., the distinctiveness of a species' niche relative to other species), and identified its ecological and evolutionary determinants. Second, we used structural equation modeling integrating niche and range attributes to test whether relationships between niche and range overlap among sympatric species deviate from null expectations. Niche originality showed consistent associations with ecological variables including niche breadth, climatic heterogeneity, species richness and productivity, whereas phylogenetic isolation had limited influence. In contrast, across most sympatric taxa, the positive association between niche and range overlap was indistinguishable from null expectations, with deviations observed only in birds, Chondrichthyes, and marine fishes. This suggests that relationships between niche and range overlap estimated from distribution data may arise largely from the shared structure of species distributions and environmental space rather than from ecological structuring. Explicit null model comparisons are therefore essential when interpreting niche-range relationships and suggest that independently estimated niches (e.g., from experimental data) may be necessary to distinguish genuine ecological signal. Together, these results establish BioOverlap as a valuable global resource for investigating large-scale biodiversity patterns and niche structure across taxa, while providing a framework for benchmarking niche-based relationships against appropriate null expectations.