Variation in the Adaptive Capacity of Plankton Alters Marine Ecosystem Responses to Climate Change.

Ecosystem responses to climate change depend on the collective reactions of many species, which individually can evolve, migrate, or decline. Evolutionary responses will be particularly important in areas that experience extreme or novel conditions, such as the tropics. Ecosystem function in these regions will depend on the pace of climate change, the rate at which species can adapt, and the consequences of maladaptation. Marine ecosystem models are powerful tools for exploring climate change scenarios. They can describe the physical effects of climate change and the transport (dispersal) of plankton in detail, but rarely account for evolutionary responses. We studied the response of marine ecosystems to changing ocean temperatures given different evolutionary scenarios, using an intermediate complexity global ecosystem model (COBALT) embedded within GFDL's Earth System Model. We characterized the limits of present-day plankton species to tolerate high temperatures using empirical data. Informed by this, we explored four evolutionary scenarios: (1) phytoplankton and zooplankton are limited in their response to climate change by standing variation and cannot evolve higher temperature tolerances, (2) phytoplankton can evolve, but not zooplankton, (3) phytoplankton and smaller zooplankton can evolve, but not large zooplankton, and (4) all groups evolve rapidly. Differing rates of evolutionary response between groups are likely, driven by variation in body size, generation time, reproductive mode, and population size. We will describe the results of these bounding simulations, focusing on equatorial regions. Our results highlight the importance of incorporating evolution in climate change and ecosystem studies, while providing an example of how to do so. Finally, our results illustrate how interactions between evolution, ecology, and climate variability can lead to markedly different future ecosystems.