Modeling the decline and potential recovery of a native butterfly following serial invasions by exotic species

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Population sizes and range of the native butterfly Pieris oleracea declined after habitat loss and parasitism by an exotic braconid wasp (Cotesia glomerata) introduced to control the exotic invasive butterfly Pieris rapae. Further declines are attributed to the invasive exotic weed garlic mustard (Alliaria petiolata), an oviposition sensory trap on which P. oleracea larval survival and growth are very poor. But a population of P. oleracea has adapted to garlic mustard over the past several decades, coincident with the introduction of a second parasitoid, C. rubecula, a specialist on P. rapae that is competitively dominant to C. glomerata. We used stochastic simulation models to assess the plausibility of a hypothesis that reduced parasitoid pressure over this time period enabled P. oleracea to adapt to A. petiolata. We simulated scenarios of trait proliferation via spontaneous mutation or immigration of the trait, and residual variation in the trait following the butterfly’s isolation in North America. Results indicate that the most likely scenario for the population that has adapted to garlic mustard includes (1) a change in selection following garlic mustard invasion to favor previously neutral residual variation in the population, (2) release from parasitism, and (3) evolution of improved larval survival on garlic mustard, which allowed an increased host range, and potentially, population size.

Publication Title, e.g., Journal

Biological Invasions