Food Webs In Space!
All organisms engage in trophic interactions, as consumers of or as resources for other organisms in a food web. And all organisms move through space, sometimes dispersing to a new location, where they still engage in trophic interactions, but in a different food web. As a result, dispersal connects not just populations of organisms across space, but also the food webs in which they exist. This dissertation comprises five studies examining how dispersal and trophic interactions combine to influence the spatial dynamics of populations and food webs. In addressing this topic, I utilize theoretical and empirical approaches, with the empirical component focused on a system of freshwater rock pools on Appledore Island, Maine, USA. In Chapter One, I use a set of mathematical models describing a simple two-patch predator-prey metapopulation to show that the inherent variation in the timing of demographic events (called demographic stochasticity) qualitatively alters the effect of dispersal on trophic interactions. Chapter Two describes the dominant food chain in the Appledore rock pools and shows how the age structure of the apex predator (Trichocorixa) population drives withinpool trophic dynamics through allometric increases in per capita consumption rates. I begin exploring dispersal in the Appledore pools in Chapter Three, where I examine the ability of Larus gulls to disperse invertebrates between pools. I combine experimental and observational studies to show that gull-mediated dispersal occurs frequently enough to homogenize the taxonomic composition of the pools and may be the main mode of dispersal for many taxa that cannot actively disperse. The apex predator Trichocorixa, however, can fly among pools, and their flight is the focus of Chapter Four, where I show that Trichocorixa's high, yet variable, dispersal rate combines with high, and variable, rates of population turnover to cause complex spatial population dynamics. And in Chapter Five, I explore how Trichocorixa's actions as a frequent disperser and a voracious predator may combine to drive the spatial dynamics of their prey Moina. In particular, because Trichocorixa emigrates frequently more when Moina are in lower densities, they are not likely to drive local Moina populations extinct, potentially promoting spatial food-web persistence.
dispersal; metapopulation; predator-prey
Hairston Jr, Nelson George
Ellner, Stephen Paul; Agrawal, Anurag; Flecker, Alexander S
Ph.D. of Ecology
Doctor of Philosophy
dissertation or thesis