Rapid contemporary evolution can alter the temporal dynamics of predator-prey interactions, and the amount of genetic variance determines the rate of response to selection. How, then, does the amount of genetic variance affect predator-prey dynamics? In this talk we present theory and experimental results showing that changes in adaptive genetic variance can radically alter eco-evolutionary predator-prey dynamics. We used rotifer-algal microcosms in which we manipulated the variance of a heritable trait of the prey (Chlamydomonas) that confers defense against predation by rotifers (Brachionus).
A mathematical model for our system predicts that as prey trait variance declines so that the most and least defended genotypes become progressively more similar to each other, the dynamics change from evolutionary cycles (out-of-phase, long period cycles with prey genetic variation maintained by genotype cycling), to stable coexistence with only the more defended prey genotype present, and ultimately to typical consumer-resource cycles (short cycle periods, quarter-phase lag between predator and prey) with only the more defended genotype present. We created algal populations with different levels of defense trait (cell clumping) by culturing algae for many generations either with or without rotifers present. Chlamydomonas cultured without rotifers grew only as isolated single cells, whereas those cultured with rotifers formed palmeloid clumps of several to many (over 100) cells. We initiated predator-prey interactions in replicate chemostats using one or the other of these cultures. Consistent with our model, we observed evolutionary cycles when palatability of the more defended type was very low (high algal density required for rotifer population growth) and stable coexistence when palatability was moderate (low algal density required for rotifer population growth).