Species packing and the latitudinal gradient in beta-diversity

Abstract

The decline in species richness at higher latitudes is among the most fundamental patterns in ecology. Whether changes in species composition across space (beta-diversity) contribute to this gradient of overall species richness (gamma-diversity) remains hotly debated. Previous studies that failed to resolve the issue suffered from a well-known tendency for small samples in areas with high gamma-diversity to have inflated measures of beta-diversity. Here, we provide a novel analytical test, using beta-diversity metrics that correct the gamma-diversity and sampling biases, to compare beta-diversity and species packing across a latitudinal gradient in tree species richness of 21 large forest plots along a large environmental gradient in East Asia. We demonstrate that after accounting for topography and correcting the gamma-diversity bias, tropical forests still have higher beta-diversity than temperate analogues. This suggests that beta-diversity contributes to the latitudinal species richness gradient as a component of gamma-diversity. Moreover, both niche specialization and niche marginality (a measure of niche spacing along an environmental gradient) also increase towards the equator, after controlling for the effect of topographical heterogeneity. This supports the joint importance of tighter species packing and larger niche space in tropical forests while also demonstrating the importance of local processes in controlling beta-diversity.

Global patterns of vascular plant alpha diversity

“…This suggests that the tropics might be shaped by processes promoting species coexistence through a tighter packing in the niche space. Recent work found a latitudinal increase in niche specialization and marginality of trees towards the equators, which has been attributed to the stable climate and high productivity in the tropics 51 . Alternative explanations include rarity and priority effects related to high productivity 29 , more uniform environmental conditions and stronger dispersal limitation at fine scales 28 , or stronger mycorrhiza-mediated effects of interspecific competition and habitat adaptation 52 in the tropics compared to temperate regions.…”

Artificial grass in parks as a potential new threat for urban bird communities

“…In other words, the higher turnover component in natural grass parks indicates that these green areas harbour more occasional species. Contrarily, the higher nestedness component in the artificial grass parks points to a diversity loss, where poorest parks (in terms of species richness and abundances) are subsets of the richest ones (Socolar et al 2016, Cao et al 2021). In addition, the effect of park type on beta diversity components is also significant for the group of ground birds.…”

“…Perillo et al 2017, Howes and Reynolds 2021). However, beta diversity is a key conservation planning element because it indicates whether diversity is concentrated in a few sites or spreads across many (Socolar et al 2016, Cao et al 2021).…”

Species pool size and rainfall account for the relationship between biodiversity and biomass production in natural forests of China

“…Alternatively, biotic factors, such as species pool size and community composition, might play an essential role in the strength of biodiversity–biomass production relationships (Armitage, 2016 ; Burley et al, 2016 ; Hagan et al, 2021 ). For example, better hydrothermal conditions are often associated with a larger species pool, resulting in a more heterogeneous community composition (Cao et al, 2021 ), which can have interactive effects on the biodiversity–biomass production relationships. However, more studies are needed to disentangle these sources of variation.…”