Departures from the Energy-Biodiversity Relationship in South African Passerines: Are the Legacies of Past Climates Mediated by Behavioral Constraints on Dispersal?

TL;DR

This study explores how past climate conditions affect bird diversity in South Africa, suggesting that behavioral limits on bird movement influence current patterns.

Contribution

The study shows that historical climate legacies affect bird distributions through behavioral dispersal constraints in regional biomes.

Findings

A northeast to southwest gradient in passerine richness aligns with Quaternary mesic refugia locations.

Phylogenetic dispersion decreases with distance from refugia in mesic biomes.

Weaker but similar patterns were found in the arid Karoo Biomes.

Abstract

Legacies of paleoclimates in contemporary biodiversity patterns have mostly been investigated with global datasets, or with weakly dispersive organisms, and as a consequence been interpreted in terms of geographical or physical constraints. If paleoclimatic legacies also occurred at the regional scale in the distributions of vagile organisms within biomes, they would rather suggest behavioral constraints on dispersal, i.e., philopatric syndromes. We examined 1) the residuals of the regression between contemporary energy and passerine species richness in South African biomes and 2) phylogenetic dispersion of passerine assemblages, using occupancy models and quarter-degree resolution citizen science data. We found a northeast to southwest gradient within mesic biomes congruent with the location of Quaternary mesic refugia, overall suggesting that as distance from refugia increased, more clades were lacking from local assemblages. A similar but weaker pattern was detected in the arid Karoo Biomes. In mobile organisms such as birds, behavioral constraints on dispersal appear strong enough to influence species distributions thousands of years after historical range contractions.

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