Summary data from experimental invasions of Callosobruchus maculatus. Click for more information.

Summary data from experimental invasions of Callosobruchus maculatus. Click for more information.

Rapid evolution during biological invasions

Invasion dynamics are notoriously difficult to predict. In addition to being highly stochastic, invading populations are subject to a slew of unique ecological and evolutionary forces that aren't present in stationary populations. Interestingly, many of these forces arise as a simple consequence of populations expanding across space.

For example, if there are differences among individuals in dispersal ability (the ability to run, walk, fly, swim, hop, etc.), populations can become spatially-structured by dispersal ability, with good dispersers being overrepresented at the edge of the invasion. This can lead to non-random mating among good dispersers, which can result in the evolution of enhanced dispersal ability at the edge. This process, known as 'spatial sorting', can cause invasions to spread faster and faster over time, and may affect how we make predictions about invading species.

I use laboratory experiments and simulation models to study spatial sorting and other processes unique to invading populations. One experiment, using the bean beetle Callosobruchus maculatus, was among the first to show that spatial sorting could accelerate biological invasions. Some of the simulation models I've built explore how demographic processes and genetic constraints can affect the outcome of these spatial evolutionary processes.

A male Callosobruchus maculatus dispersing across a tabletop. The beetle in this photo is much larger than life; in reality they're only about 3 mm long. Photo by Jeff Fitlow.

A male Callosobruchus maculatus dispersing across a tabletop. The beetle in this photo is much larger than life; in reality they're only about 3 mm long. Photo by Jeff Fitlow.

Demographic modeling and population dynamics

Demography is the study of populations that takes into account the age, sex, body size, reproductive stage, and other characteristics of individuals in a population. Understanding what drives demographic changes can help us make predictions about how populations will respond to environmental pressures, such as increases in population density, loss of habitat, or change in climate. I use observational data, often coupled with computer simulations, to model demography and population dynamics.