Patterns of landscape disturbance may alter the strength of interactions among species, and in turn these interactions may lead to rapid evolution of one or more of the interacting species. We investigated this chain of effects using large-scale harvesting manipulations in alfalfa fields. Pea aphids, a common pest in alfalfa, may contain facultative bacterial symbionts that confer resistance to parasitoid wasps. We populated large cages (7 x 30 m) with resistant aphids and with aphids that did not contain resistance-conferring symbionts. In one set of cages we harvested all the alfalfa synchronously over the summer, while is the other set we harvested asynchronously in strips, so that alfalfa was always available for aphids. We predicted that asynchronous harvesting would lead to higher parasitism, which in turn would increase selection for the resistant aphid clone.
As predicted, parasitism was higher in cages with asynchronous harvesting, and this led to rapid resistance evolution in the aphids. In cages with asynchronous harvesting, 56% of pea aphids had symbionts that confer resistance to parasitism, whereas only 7% of aphids were resistant clones in the synchronously harvested cages. Using remote sensing to assess broad-scale patterns of alfalfa harvesting, and mathematical models parameterized by fitting them to experimental data, we extrapolated our experimental results to explore the possible ecological-evolutionary dynamics of pea aphid-parasitoid interactions. Overall, our results show that patterns of landscape disturbance can alter species interactions and consequently drive rapid evolution, thereby leading to eco-evo dynamics in this tightly coupled predator-prey system.