Fast-growing species shape the evolution of reef corals

Authors: Alexandre C. Siqueira, Wolfgang Kiessling & David R. Bellwood.

Abstract:

Interspecific competition is an axiom of ecological theory and is epitomized on coral reefs, where sessile organisms compete for limited space. Within these high-diversity systems, scleractinian corals represent a major component of the benthos and can compete through overgrowth, or by limiting substrate availability. The role of competition among reef corals is well established on ecological timescales. However, its effect on broad macroevolutionary patterns remains unclear. By analysing the rich fossil record of Scleractinia, here we show that reef coral biodiversity experienced marked evolutionary rate shifts in the last 3 million years, likely driven by diversity-dependent mechanisms. We found an overwhelming effect of staghorn corals (family Acroporidae) on the fossil diversity trajectories of other coral groups. Staghorn corals showed an unparalleled spike in diversification during the Pleistocene. But surprisingly, their expansion was linked with increases in both extinction and speciation rates in other coral families, driving an eight-fold increase in lineage turnover. These results reveal a double-edged effect of diversity dependency on reef evolution. Given their fast growth, staghorn corals likely increased extinction rates via competitive interactions, but they also promoted speciation, probably through their fundamental role as ecosystem engineers. This suggests that recent widespread human-mediated reductions in staghorn coral cover, may be disrupting the key macroevolutionary processes that established modern coral reef ecosystems.