Why are there so many species, and what are we going to do about it?
I am interested in the forces allowing many similar species to coexist in diverse communities – and in cases in which those forces break down. Why does one super-organism not dominate the surface of the Earth or its oceans? What maintains such a diversity of plants, animals, and microbes? And when an organism is introduced from a far-off land, why does it sometimes dominate and spread to become “invasive?” Many factors contribute to diverse biological communities by creating physiological trade-offs, including abiotic variation such as temperature, moisture, and soil chemistry, as well as biotic factors such as predators, competitors, and diseases. Accelerating rates exotic introductions and biodiversity loss due to human activity make understanding these factors and their effects on diversity all the more critical.
I am interested in developing and testing theories about the factors that maintain species diversity at multiple scales. I am particularly interested in studying the biological communities in cryoconite holes. These are small holes that form in glacial ice when dust lands on it and the dark material absorbs sunlight, melting the ice beneath it. Entire ecosystems assemble in these holes, from photosynthesizing algae and bacteria to microscopic animals such as rotifers and tardigrades (“water bears”). Learn more about the project and follow updates during our field seasons (Nov-Feb) at cryoholes.wordpress.com.
In my doctoral research, I asked how predation and resource competition interact to determine species diversity, especially in the case of species invasions. I studied how buffel grass (Pennisetum ciliare), which had been introduced from Africa to North America, suppresses the regeneration of long-lived native plants where it spread. I looked at whether the adult grass prevented native seeds from germinating and seedlings from establishing, and whether it did so through resource competition or through increasing the abundance of rodents that eat native seeds. The rodents eating native seeds in areas that buffel grass invades, however, act not only as consumers, but as seed-dispersers by burying them in shallow caches outside their burrow. To find out whether the rodents were burying seeds more often under buffel grass because its dense canopy provided better hiding places from owls, I used fluorescent powder to locate caches. Finally, I asked how the cover-seeking behavior to avoid predators might affect the diversity of the rodents themselves, especially if grass cover increased their effectiveness at hiding. Since there were no robust theoretical predictions for this, I used simple consumer-resource models to determine when predator avoidance behavior would increase or decrease the ability of the avoiders, who also compete for resources, to coexist.