Data from: Contrasting effects of specialist and generalist herbivores on resistance evolution in invasive plants

Invasive alien plants are likely to be released from specialist herbivores
and at the same time encounter biotic resistance from resident generalist
herbivores in their new ranges. The Shifting Defense Hypothesis predicts
that this will result in evolution of decreased defense against specialist
herbivores and increased defense against generalist herbivores. To test
this, we performed a comprehensive meta-analysis of 61 common garden
studies that provide data on resistance and/or tolerance for both
introduced and native populations of 32 invasive plant species. We
demonstrate that introduced populations, relative to native populations,
decreased their resistance against specialists, and increased their
resistance against generalists. These differences were significant when
resistance was measured in terms of damage caused by the herbivore, but
not in terms of performance of the herbivore. Furthermore, we found the
first evidence that the magnitude of resistance differences between
introduced and native populations depended significantly on herbivore
origin (i.e. whether the test herbivore was collected from the native or
non-native range of the invasive plant). Finally, tolerance to generalists
was found to be higher in introduced populations, while neither tolerance
to specialists nor that to simulated herbivory differed between introduced
and native plant populations. We conclude that enemy release from
specialist herbivores and biotic resistance from generalist herbivores
have contrasting effects on resistance evolution in invasive plants. Our
results thus provide strong support for the Shifting Defense Hypothesis.