How does the pace of life evolve when familiar fluctuations in the environment change? All environments fluctuate in nature, many in a cyclical fashion. A prime example is seasons. Climate change is warping seasonal fluctuations in the physical environment around the world, most prominently in the form of expanding the length of the warm growing season. In response, phenologies in such seasonal environments are shifting. Here I address the general linkage between physical environmental fluctuations and biological evolution of life-histories. I present three approaches: 1) a species-agnostic fitness landscape model, 2) a life-history evolution experiment with the tidepool copepod Tigriopus californicus, and 3) an agent-based simulation to bridge the first two.
Results/Conclusions
Previously I showed that linear algebraic demographic analyses allow us to predict optimal life-histories in fluctuating environments. When I conducted an evolutionary experiment to test these optimal life-history predictions in artificial fluctuating environments, the intrapopulation variance of traits rose conspicuously when fluctuation was slowed down. This result was true for all cases in the experiment. Remarkably, intrapopulation variance in these slowly fluctuating environments was even higher than in purely stochastic environments. This is surprising because it seems to be at odds with a simple tenet in ecology: that turbulent environments, as opposed to slowly fluctuating environments, should increase trait variance in a population. Here I show that fast and slow environmental fluctuations produce different amounts of trait variation within populations, and that there is a whole calculatable spectrum in between. I discuss how my previous theoretical framework (fitness landscapes) can be used to intuit why this may happen. Finally, I corroborate this conceptual intuition, and the experimental results, with dynamics seen in an agent-based simulation. I show a new, simple mechanism by which life-history diversity can be increased by the dynamics in the environment. This mechanism also speaks to the discordant phenological shifts often seen among individuals in populations living in changing seasonal environments.