No abstract

Exotic plants may act as population sinks or evolutionary traps for native herbivores. The native butterfly Pieris oleracea lays eggs on garlic mustard, Alliaria petiolata, but larvae develop very poorly on this exotic invasive plant. We examined oviposition preference of individual females and larval performance of their offspring for individuals from one area where garlic mustard is well established and one where it is absent. These data were used to assess whether garlic mustard is being incorporated into or excluded from the diet. Females from the area without garlic mustard showed a wide range of preference, families had low larval survival on garlic mustard, and larval survivorship showed no correlation with mothers' preferences. Females from the area with garlic mustard preferred it to the native host, and larval survivorship on garlic mustard was positively correlated with the mother's preference. Individuals surviving on garlic mustard took longer to pupate and weighed >30% less compared to pupae reared on normal hosts. Our results suggest that where garlic mustard is well established P. oleracea may be adapting to this plant by both improved larval performance and increased adult female oviposition preference for it.

No abstract

We evaluated the effects of landscape characteristics associated with urbanization, as well as local features, on butterfly species richness at four spatial scales (50, 150, 500, and 1,000 m from survey plots). We also evaluated these effects separately by butterfly guilds based on their region-wide rarity and on degree of specialization. The distribution of abundances of the 44 species observed showed an excess of uncommon species compared to a log-normal distribution, and the two most abundant species were exotic (Thymelicus lineola and Pieris rapae). We used an information theoretic approach to model selection to determine the most important correlates of butterfly species richness. Models of mean butterfly richness per visit explained greater variance than did models of cumulative richness across the season. Cumulative butterfly species richness was affected more at larger spatial scales, while richness per visit was affected similarly at all spatial scales. The most consistent local factor affecting butterfly diversity was the number of nectar producing plants that were flowering. The most consistent landscape-level correlates of species richness were number of people (at small spatial scales) and green space. Measures of increased urbanization were associated with decreased butterfly species richness, and rare and specialized species were most affected. Species that were regionally rare, and those that specialized both in host plants and had few broods, disappeared with declining richness across sites 2.9-4.5 times faster than did generalists and less restricted specialists.