Plant richness, turnover, and evolutionary diversity track gradients of stability and ecological opportunity in a megadiversity center

Abstract

Research on global patterns of diversity has been dominated by studies seeking explanations for the equator-to-poles decline in richness of most groups of organisms, namely the latitudinal diversity gradient. A problem with this gradient is that it conflates two key explanations, namely biome stability (age and area) and productivity (ecological opportunity). Investigating longitudinal gradients in diversity can overcome this problem. Here we investigate a longitudinal gradient in plant diversity in the megadiverse Cape Floristic Region (CFR). We test predictions of the age and area and ecological opportunity hypotheses using metrics for both taxonomic and phylogenetic diversity and turnover. Our plant dataset includes modeled occurrences for 4,813 species and dated molecular phylogenies for 21 clades endemic to the CFR. Climate and biome stability were quantified over the past 140,000 y for testing the age and area hypothesis, and measures of topographic diversity, rainfall seasonality, and productivity were used to test the ecological opportunity hypothesis. Results from our spatial regression models showed biome stability, rainfall seasonality, and topographic heterogeneity were the strongest predictors of taxonomic diversity. Biome stability alone was the strongest predictor of all diversity metrics, and productivity played only a marginal role. We argue that age and area in conjunction with non–productivity-based measures of ecological opportunity explain the CFR’s longitudinal diversity gradient. We suggest that this model may possibly be a general explanation for global diversity patterns, unconstrained as it is by the collinearities underpinning the latitudinal diversity gradient.

The influence of climate and palaeoclimate on distributions of global conifer clades depends on geographical range size

“…While the influence of Cenozoic and Quaternary climatic oscillations on biodiversity patterns has been noted in previous work (Kissling et al, 2012;Ma et al, 2016;Sandel et al, 2011Sandel et al, , 2016, our results suggest that there is a particularly strong palaeoclimatic signal (in terms of past climatic stability) in the distributions of small to mid-range clades (see also Colville et al, 2020). This palaeoclimatic signature has important implications for interpreting current conifer distributions and ecological associations, and may also be important for understanding the biodiversity of other groups of woody plants as well.…”

Disentangling the effects of latitudinal and elevational gradients on bee, wasp, and ant diversity in an ancient neotropical mountain range

“…Despite having a wide latitudinal range, we worked in a single ecosystem classified as an OCBIL—old, climate‐buffered, and infertile landscape (Silveira et al, 2016). These characteristics—old age and stability or climatic buffering of the landscape (Hopper, 2009)—can also encompass intrinsic environmental filters that can homogenize LDG effects (Colville et al, 2020). Patterns that break the LDG rule are not uncommon.…”

The composition, geography, biology and assembly of the coastal flora of the Cape Floristic Region

“…Here, we present a unified flora of these coastal calcareous habitats of the CFR and analyse the flora to assess its size, taxonomic composition, growth-form mix, biological traits, biogeographic affinities and endemism. We further sketch a brief scenario of the flora’s assembly, with a focus on the Pleistocene—a period whose dynamic sea levels and vacillating climate had a profound impact on the geography and diversification of floras in the Cape ( Cowling et al, 2017 ; Forest, Colville & Cowling, 2018 ; Colville et al, 2020 ), especially along the coast ( Grobler et al, 2020 ).…”