Diversity in neotropical wet forests during the Cenozoic is linked more to atmospheric CO ₂ than temperature

Abstract

Department of Biology, Wesleyan University, Middletown, CT 06459, USA Models generally predict a response in species richness to climate, but strong climate-diversity associations are seldom observed in long-term (more than 10 6 years) fossil records. Moreover, fossil studies rarely distinguish between the effects of atmospheric CO 2 and temperature, which limits their ability to identify the causal controls on biodiversity. Plants are excellent organisms for testing climate-diversity hypotheses owing to their strong sensitivity to CO 2 , temperature and moisture. We find that pollen morphospecies richness in an angiosperm-dominated record from the Palaeogene and early Neogene (65 -20 Ma) of Colombia and Venezuela correlates positively to CO 2 much more strongly than to temperature (both tropical sea surface temperatures and estimates of global mean surface temperature). The weaker sensitivity to temperature may be due to reduced variance in long-term climate relative to in higher latitudes, or to the occurrence of lethal or sub-lethal temperatures during the warmest times of the Eocene. Physiological models predict that productivity should be the most sensitive to CO 2 within the angiosperms, a prediction supported by our analyses if productivity is linked to species richness; however, evaluations of non-angiosperm assemblages are needed to more completely test this idea.

A Novel Hypothesis for the Role of Photosynthetic Physiology in Shaping Macroevolutionary Patterns

“…This appears to contradict the concept of an explosive radiation of angiosperms in a declining [CO 2 ], cooling world (Supplemental Fig. S1, A and B; Royer and Chernoff, 2013). Royer and Chernoff (2013) suggested that, although within-group species richness should positively correlate with [CO 2 ] levels, large physiological differences across groups could result in a group outcompeting others under declining [CO 2 ].…”

“…Royer and Chernoff (2013) suggested that, although within-group species richness should positively correlate with [CO 2 ] levels, large physiological differences across groups could result in a group outcompeting others under declining [CO 2 ]. Our results lend support to the hypothesis of Royer and Chernoff (2013), as they hint at a mechanistic basis for the previously reported photosynthetic advantages of angiosperms in a low-[CO 2 ] world and the photosynthetic toll on gymnosperms under the same conditions Nackley et al, 2018). However, further species sampling within and between evolutionary groups is required to test the robustness of our idealized paleosimulations.…”

Evolution of a unique anatomical precision in angiosperm leaf venation lifts constraints on vascular plant ecology

“…The vegetative biology of angiosperms is often treated as end members on a physiological continuum shared by other vascular plants and as if angiosperm advantages can be neutralized under the right environmental conditions, such as greatly elevated levels of atmospheric CO 2 , with other plants being elevated to comparably high levels of productivity [3,9,[17][18][19]. Alternatively, the angiosperms can be viewed as presenting fundamentally new ecological strategies founded upon novel physiological innovations enabling uniquely high growth rates [2,6,13,20,21]. The results presented here support the view that angiosperm physiology-at least among more derived angiosperms-is fundamentally distinct.…”

Paleobotany and Global Change: Important Lessons for Species to Biomes from Vegetation Responses to Past Global Change

“…There is no clear consensus on the deep-time evolution of photosynthesis in vascular plants from studies using proxy estimates from fossil leaves (26, 96,102) or model estimates derived from fossil leaf traits (54). Similarly, there remains a wide range of opinions on the evolution of the productivity of terrestrial ecosystems through time and whether modern systems are the most productive (24, 25) or less so than those of the geological past (such as the Eocene), assuming a positive correlation between diversity and productivity (77,130). What is clear, however, is that the total area of forested ecosystems expands dramatically poleward during greenhouse intervals (Figures 1 and 2), which on evolutionary timescales enabled a greater speciation rate during the Cenophytic era and likely higher productivity in many biomes because of a species-area effect (77).…”