Research

Rebecca E. Irwin

My research is currently focused on four questions.

(1) What is the relative importance of direct and indirect effects of antagonists on the ecology and evolution of plant-pollinator mutualisms?

The aim of this work is to understand the simultaneous importance of interactions among several antagonists with their host plants and mutualist pollinators, and how resource availability and community composition affect the outcome of such interactions. This work is novel in integrating the effects of multiple anatagonists on the outcome of plant-pollinator mutualisms under different environmental conditions. Understanding the complexity of plant-pollinator-antagonist interactions will provide a deeper knowledge of how species are ecologically and evolutionarily linked in biological communities.

(2) Do plant interactions with mutualists and antagonists simultaneously shape and constrain selection on nectar traits?

Determining which factors regulate and drive variation in the form and abundance of organisms in natural systems is a central goal in ecological and evolutionary research. In collaboration with Lynn Adler from UMass-Amherst, we are integrating the costs and benefits of resistance and tolerance associated with a ubiquitous but poorly understood floral trait, toxic nectar, in the context of joint forces of selection exerted by both mutualistic and antagonistic floral visitors using the perennial vine, Gelsemium simpervirens, native to the southeastern US and its native pollinators and nectar robber.  We are also working in urban systems, studying the ecological and evolutionary consequences of urbanization for plant-insect interactions.

(3) To what degree does an invasive plant alter the web of interactions between native plants and pollinators?

Species invasions are one of the leading components of global environmental change and are the second leading cause of biodiversity loss worldwide. Despite the recognition that invaders affect competitive and antagonistic interactions among natives, we know relatively little about how invaders affect mutualistic interactions, such as those between native plants and pollinators. I am currently using an experimental approach to measure the degree to which an invasive plant in the western US (Linaria vulgaris) impacts the strength of native plant-pollinator linkages in pollination webs, native plant fitness, and offspring recruitment. This work builds on the existing conceptual framework of quantitative food webs to include mutualistic interactions and provides empirical and predictive insight into the impacts of an invasive plant on native plant-pollinator mutualisms.

(4) Do patterns of host-use by one mutualist alter subsequent host-mutualist interactions?

My work up to this point has focused on how interactions among antagonists and mutualists influence the ecology and evolution of flowering plants.  However, just as herbivore feeding can influence plant interactions with other herbivores and mutualists, patterns of host-use by one mutualist may alter subsequent plant-mutualist interactions.  Yet, surprisingly little is known about the ecological and evolutionary consequences of multispecies mutualisms.  This is astonishing considering that almost 90% of flowering species require animal vectors for pollination, and many of these same plant species also require animal vectors to mediate subsequent seed dispersal.  Using the spring ephemeral plant Trillium erectum (Liliaceae), I am assessing how pollination mutualisms at the flowering stage alter the likelihood and intensity of ant-plant seed-dispersal mutualisms and how shifts in these ecological interactions translate into changes in plant demography and altered selective landscapes.