Post-extinction recovery of the Phanerozoic oceans and biodiversity hotspots

Abstract

The fossil record of marine invertebrates has long fuelled the debate as to whether or not there are limits to global diversity in the sea1–5. Ecological theory states that, as diversity grows and ecological niches are filled, the strengthening of biological interactions imposes limits on diversity6,7. However, the extent to which biological interactions have constrained the growth of diversity over evolutionary time remains an open question1–5,8–11. Here we present a regional diversification model that reproduces the main Phanerozoic eon trends in the global diversity of marine invertebrates after imposing mass extinctions. We find that the dynamics of global diversity are best described by a diversification model that operates widely within the exponential growth regime of a logistic function. A spatially resolved analysis of the ratio of diversity to carrying capacity reveals that less than 2% of the global flooded continental area throughout the Phanerozoic exhibits diversity levels approaching ecological saturation. We attribute the overall increase in global diversity during the Late Mesozoic and Cenozoic eras to the development of diversity hotspots under prolonged conditions of Earth system stability and maximum continental fragmentation. We call this the ‘diversity hotspots hypothesis’, which we propose as a non-mutually exclusive alternative to the hypothesis that the Mesozoic marine revolution led this macroevolutionary trend12,13.

Diversity dependence is a ubiquitous phenomenon across Phanerozoic oceans

“…This finding is robust enough across our datasets, so that it is unlikely to be generated by statistical artifacts. At the same time, it complements previous studies showing that bounded models may represent appropriate characterization of diversity dynamics even when diversity fluctuates and, for most of the history, is out of equilibrium (4,6). The evidence of diversity dependence of extinction and origination rates in most explored taxa (Table 1) is congruent with the hypothesis of a carrying capacity of the environment for diversity (20).…”

“…This has potentially important implications for analytical tests of diversity regulation. Because the environment has not been constant during the Phanerozoic and the functional form of diversity dependence is not known, the use of simple logistic models (or any models based on a priori–chosen functional forms of causal links) ( 1 , 4 ) may not be appropriate. The reason is that these models are able to reveal only a specific form of diversity regulation, constrained by the model structure.…”

“…There has been a longstanding debate whether biological diversity on Earth during the Phanerozoic has steadily increased or whether it is bounded and regulated by biotic interactions ( 1 – 3 ). Biodiversity dynamics might have been influenced by abiotic factors such as environmental changes ( 4 ) or tectonics ( 5 ); by biotic interactions such as competition, leading to diversity dependence (higher diversity levels lead to decreasing origination or increasing extinction rates and vice versa) ( 6 ); or by a mixture of both abiotic and biotic effects ( 7 ). The entanglement of biotic and abiotic factors makes it essential to study these components together ( 8 ).…”

Increases in reef size, habitat and metacommunity complexity associated with Cambrian radiation oxygenation pulses

“…Available habitat and environmental stability, i.e. habitat age, are established to promote rapid species diversification in reefs 45 , 47 , 50 , 51 , so such habitat expansion may have been a major driver in promoting ecosystem complexity perhaps via niche differentiation (Fig. 3f, h, i ).…”

“…Similarly, nutrient input, which controls primary productivity and food availability, can also exert a profound control on the net diversification rate of taxa with higher nutrient availability leading to higher rates 51 . It has been hypothesised that during the lower Cambrian, the long-term burial of reductants that permitted gradual atmospheric (and eventual oceanic) oxygenation, was directly associated with enhanced marine primary productivity 7 .…”