RESEARCH

My research program aims to identify the causes and consequences of species diversity in natural communities. While theoretical development in ecology has proceeded rapidly, rigorous tests of theory are often lacking. Because of this disconnect, much of my current work utilizes existing theory to tackle applied ecological problems in a rigorous, experimental context. I have also undertaken specific modeling efforts to expand existing theory as needed. As I further develop my research program, integration of alternative theories into a single, cohesive framework will be central to my efforts to identify the causes and consequences of diversity.

Active research areas include:

1) Application of competition theory to invasions and biocontrol

While many researchers have assumed that species successfully invade because escape from natural enemies has made them better resource competitors than the natives they displace, this assumption has rarely been rigorously tested in the field. Community ecology offers several models of plant competition that may predict invasions and biocontrol success, including the resource competition model (Tilman 1982), the response to resource availability model (Goldberg 1996), and the plant size model (Gaudet and Keddy 1988, Miller and Werner 1987). All three offer specific measures of competitive ability that, in theory, predict competitive ability and thus the invasive potential of an exotic species. For instance, according to the plant size hypothesis, an exotic will successfully invade if it is “larger” than the native species with which it is likely to compete. In addition, all three models predict that a biocontrol agent (e.g., an insect herbivore) will succeed, short of killing its host outright, only by reducing the competitive ability of its host, for instance by making the invader “smaller” than its native competitors.

We have been experimentally testing these theories with the widespread invasive, Purple Loosestrife, its native competitor, Broad-leaved Cattail, and Galerucela calmariensis, a leaf-feeding beetle widely released in an effort to biologically control purple loosestrife. My experimental design consists of cattle tank mesocosms (2 m2) containing both monocultures of each species and competition treatments between the two species, at both high and low fertility, and across a gradient of insect herbivore density (216 mesocosms in all). Theory predicts that traits measured in monoculture will predict the outcome of competition, as well as identify the level of insect damage required to reverse the outcome of competition and allow biocontrol to succeed. To identify the specific mechanisms of competition I have used highly controlled mesocosms, and also implemented a similar design in natural marshes.

2) Modeling plant competition for light

Resource competition theory was originally modeled with the assumption that resources, such as soil nitrogen, are distributed homogenously. However, in many productive environments, plants compete primarily for light. Because competition for light is asymmetric, one cannot simply measure light availability at the soil surface and conclude that the species that casts more shade is the better competitor: a shorter species simply cannot fully shade a taller species. To address this limitation, we have modeled competition for light between species that differ in height and foliage distribution. The model predicts coexistence between two species, one of which must be sufficiently taller yet have less foliage than the other - basically a gleaner-opportunist tradeoff for light. Importantly, the model also provides a simple empirical approach for measuring light competitive ability in species monocultures and thus predicting the outcome of competition for light, as I am doing in the experiments outlined above.

3) Biodiversity and ecosystem function: Integrating multiple mechanisms into a single predictive framework

A common goal of community ecology is to explain the causes and consequences of species abundance, distribution and diversity. Although many ecologists lament our limited predictive ability, I believe this is largely because ecology is a young science studying very complex systems. As a result, ecology is just now developing to the point where major syntheses are possible. For instance, while many alternative but not mutually exclusive mechanisms have been proposed to explain the well documented positive relationship between biodiversity and ecosystem functioning (BEF), these alternative mechanisms have not been fully integrated into a single predictive framework, nor have they been tested simultaneously. Indeed, plant-soil feedbacks, associational resistance to insect herbivory, niche complementarity and the sampling effect, among many others, are all plausible mechanisms for BEF, yet the relative contributions of these mechanisms to BEF are poorly known. My current research program is increasingly focused on integrating these mechanisms through theoretical, observational and experimental methods.