Dispersal and diversity in patchy landscapes. Many species live in patchy habitats (metacommunities) like as ponds, islands or plants with clumped distributions. Dispersal between these habitat patches can strongly influence the coexistence and diversity of the species that inhabit them. I’m interested in how dispersal shapes diversity, the methods that we use to test this question, and the role that local species interactions play in mediating the effects of dispersal. I’ve explored these ideas through several projects, including a synthesis paper (Grainger and Gilbert (2016) Oikos) and empirical work in milkweed patches (Grainger et al. (2017) Ecology), aspen stands (Jones et al. (2015) Journal of Ecology) and serpentine grasslands (paper in review). These projects are in collaboration with Ben Gilbert (U of T), Rachel Germain (UBC) and Natalie Jones (UC San Diego).
Local and regional impacts of climate change. Although there is strong evidence that warming can alter both local species interactions within habitat patches and dispersal rates between habitat patches, the combined impacts of warming on these two processes remains unknown. I’m using the small suite of specialist insects that live in milkweed patches as a metacommunity system to test this question. I conducted a field experiment with warmed and unwarmed milkweed metacommunities to determine how warming-induced changes in both local competitive interactions and dispersal scale up to affect metacommunity diversity (Grainger and Gilbert (2017) Global Change Biology). In a related experiment conducted in growth chambers, I warmed and manipulated the arrival time of competing milkweed specialist aphid species and found that warming strengthens plant-herbivore interactions, which simultaneously increases the importance of arrival order at local patches and alters relative dispersal rates (Grainger et al. (2018) The American Naturalist). These projects are in collaboration with Ben Gilbert (U of T).
Coexistence across environmental gradients. Contemporary coexistence theory describes the balance between niche differences that promote coexistence by causing species to be more limited by conspecifics than heterospecifics, and fitness differences that preclude coexistence by favoring the dominance of one species (Chesson 2000). It is the relative strength of these differences that determines whether competing species experience coexistence (both species can invade), exclusion (only one species can invade), or priority effects (neither species can invade). Although this framework includes these three possible outcomes, empirical work to date has focused on only two of these: coexistence and exclusion. In addition, most empirical tests of this theory occur in a single environment, so it remains unclear if and when environmental gradients change coexistence outcomes by systematically altering niche and fitness differences. I’m using nectar yeast that inhabit Mimulus flowers to test the role that abiotic conditions play in mediating coexistence outcomes, and in particular mutual non-invasibility (priority effects) (paper in review). This project is in collaboration with Tad Fukami (Stanford), Andrew Letten (Stanford) and Ben Gilbert (U of T).