OOS 11-7
Changing climate and evolving ecosystems: Trophic interactions and evolution alter the fate of marine systems
Climate change is affecting ecosystems worldwide. Changing conditions exert strong selective pressures on species, which can respond by evolving, migrating, or declining. Rapid evolution can occur in many taxa, and many studies explore the capacity of individual species to respond to climate change. It remains challenging to understand how community- and ecosystem-level responses to climate change emerge from the eco-evolutionary responses of individual species. Interspecific interactions, such as predation, between species with different evolutionary rates further complicate matters.
We study the response of marine ecosystems to changing ocean temperatures, driven by evolving phytoplankton and zooplankton. Temperature is an important determinant of biological rates, with species and entire trophic groups only able to tolerate a limited temperature range. Projected high temperatures will affect even tropical species, adapted to the hottest contemporary conditions. Evolution will determine the response of tropical communities to warming. However, the time-scale of evolutionary responses and consequences of maladaptation are unclear. Additionally, phytoplankton may evolve faster than zooplankton, leading to eco-evolutionary miss-matches. Shifts in community composition, and rates determining the processing of energy and nutrients, yield large ecosystem responses. We extended the ecological component of a global ocean circulation model to explore the consequences of evolving thermal tolerance.
Results/Conclusions
We explored how rising temperatures over the next century will affect marine ecosystems, given different rates of evolution. Our model results can be grouped into three cases; for brevity, our descriptions focus on the nutrient-limited subtropics where the largest effects occurred.
(1) Rapid evolution. Warming temperatures favored communities with smaller phytoplankton and reduced net primary productivity (NPP), with regional differences. NPP was further reduced by declines in zooplankton growth efficiency and a restructuring of the food web.
(2) Slow evolution. More dramatic declines in NPP occurred (but not extinctions); without an evolutionary response, growth and predation rates decline regionally due to rising temperatures.
(3) Rapid evolution of phytoplankton only. Phytoplankton biomass increased significantly relative to the previous cases (as predation from thermally maladapted zooplankton declined), but NPP responses were modest.
These results suggest that the importance of rapid evolution to communities and ecosystems depends on the time scale of environmental perturbations (like climate change), and can be moderated by differences in evolutionary rates between interacting species. While our results pertain to marine systems and climate change, our modeling approach and the concepts we will discuss are relevant to larger conversations regarding the consequences of eco-evolutionary dynamics for communities and ecosystems.