Niche breadth and species richness: Correlation strength, scale and mechanisms

Abstract

Aim It is often assumed that species in richer sites are more specialized, but empirical studies show conflicting results. In the present study, we quantify the correlation between community‐level niche breadth and richness. We contrast three mechanisms for gradients in niche breadth: climate, community assembly and nested interactions. First, the climatic stability within the tropics enables species to specialize, resulting in high richness. Under this scenario, we predict stronger richness–niche breadth correlations over larger latitudinal extents and when using environmental niche breadth measures (e.g., habitat). Second, in species‐rich areas, biotic interactions drive species to specialize. This may yield richness–niche breadth correlations regardless of the latitudinal extent and the type of niche breadth measure examined, whether environmental or functional (e.g., diet). Third, increased richness intensifies interactions between extreme specialists and generalists. Here, we predict stronger richness–niche breadth correlations when using functional niche breadth measures. Location Global. Time period 1973–2018. Major taxa studied Many taxa. Methods We conducted a meta‐analysis, with the effect size estimated as the correlation between richness and community‐averaged niche breadth extracted from each study. We also examined how these correlations depend on the niche breadth measure used (environmental or functional), scale (grain and latitudinal extent), ecosystem and taxa. Results We found a strong negative correlation between richness and niche breadth, and overall, a non‐significant correlation between latitude and niche breadth. The richness–niche breadth correlation was independent of the niche breadth measure used (environmental or functional). Scale, ecosystem and taxa had little effect on the strength of the correlation. Main conclusions We confirm that species in richer sites, but not necessarily in the tropics, are more specialized. This finding is not dependent on scale or on the type of niche breadth measure used. These results suggest that high richness drives community‐level specialization, and thus community assembly is likely to be the major driver of niche breadth rather than climatic gradients shaping both niche breadth and richness.

The role of ecological specialization in shaping patterns of insular communities

“…Similar effects of other ‘key’ habitats and habitat features can be expected to affect other taxa, such as the occurrence of tree stands, a more rugged topography, or a more variable vegetation. Furthermore, our findings corroborate the results of the meta‐analysis performed by Granot and Belmaker (2020) on various communities that showed species in richer sites to be more specialized.…”

“…Habitat specialization, in addition to its extensive use in population and conservation genetics, has received considerable attention in community ecology and metacommunity dynamics frameworks (e.g., Granot & Belmaker, 2020; Levins, 1968; Pandit et al., 2009), but less so in island biogeography. Gravel et al.…”

Niche Breadth: Causes and Consequences for Ecology, Evolution, and Conservation

“…Under the first scenario, the theory of limiting similarity implies that extensive niche overlap among species precludes coexistence (MacArthur and Levins 1967;Chesson 2008), and thus more narrow NB species can coexist in a community ("niche packing"). This idea is supported by a strong negative relationship between species richness and NB (whether based on habitat, climate, diet, or other species interactions) reported in a recent meta-analysis (Granot and Belmaker 2020). This is consistent with "stabilizing" niche differences, which reduce resource competition, allowing more species to coexist (Chesson 2000).…”

The spatial frequency of climatic conditions affects niche composition and functional diversity of species assemblages: the case of Angiosperms

“…Understanding the mechanisms underlying the spatial coexistence of specialists and generalists has been a central focus in ecology (Wilson & Yoshimura ; Brown ; McPeek ; Büchi & Vuilleumier ) because species varying in their niche breadths commonly co‐occur locally and regionally (see Granot & Belmaker for a meta‐analysis). Our results provide evidence that climate generalists are more likely to coexist with specialists in rare climates (i.e., negative slope of standard deviation of niche breadth on climate frequency).…”