Abstract
Invasive predatory species are frequently observed to cause evolutionary
responses in prey phenotypes, which in turn may translate into evolution
of the prey’s population dynamics. Research has provided a link between
rates of predation and the evolution of prey population growth in the
lab, but studies from natural populations are rare. Here we tested for
evolutionary changes in population dynamics parameters of zooplankton
Daphnia pulicaria following invasion by the predator Bythotrephes
longimanus into Lake Kegonsa, Wisconsin, US. We used a resurrection
ecological approach, whereby clones from pre- and post-invasive periods
were hatched from eggs obtained in sediment cores and were used in a
3-month growth experiment. Based on these data we estimated intrinsic
population growth rates (r) and carrying capacities (K) using
theta-logistic models. We found that post-invasion Daphnia maintained a
higher r and K under these controlled, predation-free laboratory
conditions. Thus, whereas previous experimental evolution studies of
predator-prey interactions have demonstrated that genotypes that have
evolved under predation have inferior competitive ability when the
predator is absent, this was not the case for the Daphnia. Given that
our study was conducted in a laboratory environment and the possibility
for genotype-by-environment interactions, extrapolating these apparent
counterintuitive results to the wild should be done with caution.
However, barring such complications, we discuss how selection for
reduced predator exposure, either temporally or spatially, may have led
to the observed changes. This scenario suggests that complexities in
ecological interactions represents a challenge when predicting the
evolutionary responses of population dynamics to changes in predation
pressure in natural systems.