Ecologists and evolutionary biologists are fundamentally interested in how interactions among organisms influence their distribution, abundance, and evolution. Substantial variation in natural selection has been documented across habitats. The goal of this study is to understand how a ubiquitous form of spatial habitat variation, urbanization, alters patterns of natural selection on a native plant through changes in species interactions. Some of the most rapidly increasing habitats are those dominated by humans. The ecological consequences of land-use change associated with housing development (urbanization) include lower native species diversity, increased density of the remaining species, shifts in community composition, and changes in hydrology and ecosystem function. These ecological changes likely have implications for contemporary selection pressures experienced by native species.

Plants interact simultaneously with myriad visitors, including mutualists (such as pollinators) as well as antagonists (such as herbivores, florivores, and nectar robbers). Both mutualists and antagonists have been implicated in the evolutionary diversification of host plants via selection on attractive and defensive traits. Urbanization may alter plant-animal interactions important to selection on plants traits through a variety of mechanisms, including increased nest site or food availability, that alter the abundance or behavior of insects acting as selective agents.

University of Massachusetts Assistant professors Lynn Adler, Plant, Soil and Insect Sciences and Paige Warren, Natural Resources Conservation, along with Dr. Rebecca Irwin of the Department of Biological Sciences at Dartmouth College will evaluate how urbanization alters selection on floral and defensive traits in the native plant Gelsemium sempervirens through changes in interactions with pollinators, nectar robbers and florivores.

Pilot data suggest that plants growing in suburban (developed) sites experience higher rates of nectar robbing and florivory compared to forested (less developed) sites; however, the evolutionary implications of such changes in interactions are unknown. This study will compare the direction and magnitude of phenotypic selection on floral and defensive traits in suburban versus forested sites, assess the generality of these patterns by measuring species interactions in four additional native plant species, isolate the pathways by which species interactions impact selection on floral and defensive traits, and identify potential mechanisms driving variation in species interactions and selection in suburban versus forested sites. Pilot data suggests that traits associated with defense against florivores and robbers will be under stronger selection in suburban sites, and traits associated with pollinator attraction in forested sites. The proposed research represents a comprehensive examination of how species interactions and selection change with urbanization, and provides empirical and predictive insight into the potential mechanisms linked to such changes. This research represents one of the most detailed studies of the mechanisms by which habitat variation alters selection via plant-insect interactions.

 Urban growth increasingly involves interspersion of suburban development with remnant wildlands, making this research broadly relevant to society. This study provides a powerful approach to document changes in the patterns of species interactions due to urbanization. It will isolate interactions responsible for changes in selection, and predict and test mechanisms responsible for such changes.