Networks of species are changing at an unprecedented rate due to a range of human-related
factors. Often species are lost, leading to simpler communities. Like most organisms, plants have to
cope with multiple enemies. Most plant species are attacked by a multitude of herbivores and
pathogens. If certain enemies are lost, it seems intuitive that plants should invest less in defense.
This has often been cited as an explanation for the success of invasive plant species, as they typically
escape from their specialist enemies. However, this is not always the case, as plants with fewer
enemy species sometimes even develop higher defense levels. We propose that this apparent
paradox can be explained by different enemies exerting different, often opposing evolutionary
pressures on the plant’s defense traits. We hypothesize that escape from a complex enemy
community may enable the plant to evolve stronger defenses against the remaining enemies. I will
test this hypothesis across three different plant species: woodland strawberry (Fragaria vesca), wild
cabbage (Brassica oleracea), and Dalmatian toadflax (Linaria dalmatica). Common garden
experiments will be performed in the field using clonal plant genotypes or a sib design, with
experimentally imposed or natural variation in enemy community complexity. By investigating three
widely different systems of plants and their natural enemies, we will be able to assess the
robustness and generality of our hypothesized explanation.