Landscape ecology and genetics
Habitat fragmentation is widely considered to be the key factor leading to species extinction worldwide. It is therefore important to understand the biological mechanisms that contribute to extinction during and after habitat loss. Many studies have documented that species losses or shifts due to fragmentation can vary based on trophic position, but examinations of specific interactions are almost always restricted to two-species models. The few studies that have examined multi-trophic interactions focused on isolation and/or area effects. To date, however, the impacts of edge effects on multi-trophic interactions have been ignored. This has happened despite the fact that habitat edges have been a topic of research for nearly a century, as they are key to understanding fragmentation, and are also ubiquitous features of both natural and managed landscapes. Previously, we found declines in the densities of both specialist herbivores and predators near edges, but, contrary to expectation, this was not driven by a decline in plant resources, but rather was due to an increase in generalist predators (Wimp et al. 2011). We are now examining the role of food web composition and altered species interactions on species and community responses to habitat edges.
Although we have long recognized the importance of preserving larger habitat areas in order to maintain biodiversity, only recently have studies begun to merge the fields of landscape ecology and population genetics in order to explore the effects of habitat fragmentation on gene flow. Species surviving in fragmented habitats may be impacted not only by the size of habitat fragments, but also by increasing isolation among patches and altered species interactions along habitat edges. These factors may in turn affect micro-evolutionary processes in habitat fragments, leading to changes in genetic diversity within and among subpopulations. Changes in population genetic diversity within habitat fragments may in turn affect the persistence of subpopulations, and the loss of such diversity may decrease the genetic resources that could be utilized under changing environmental conditions, ultimately leading to extinction. In collaboration with Prof. Matt Hamilton, I am working on an interdisciplinary landscape genetics project that examines the specific landscape patterns (habitat area, isolation, and edge effects) that lead to changes in animal population genetic diversity in a salt marsh, where an increase in mean tidal height over the past 70 years has led to the fragmentation of one of the dominant species of salt marsh grasses (Spartina patens). We hypothesize that such changes in landscape structure could affect the population genetic diversity of the dominant, specialist herbivores that feed on this grass. Additionally, because predaceous hunting spiders accumulate along habitat edges, altered predator-prey interactions could further impact gene flow in specialist herbivores. We have developed 12 novel variable microsatellite loci for two S. patens specialist herbivores (Aggarwal et al. 2011) to understand how effective population size and gene flow are influenced by habitat fragmentation, which could ultimately help us better understand how fragmentation and edge effects influence genetic diversity.
Although we have long recognized the importance of preserving larger habitat areas in order to maintain biodiversity, only recently have studies begun to merge the fields of landscape ecology and population genetics in order to explore the effects of habitat fragmentation on gene flow. Species surviving in fragmented habitats may be impacted not only by the size of habitat fragments, but also by increasing isolation among patches and altered species interactions along habitat edges. These factors may in turn affect micro-evolutionary processes in habitat fragments, leading to changes in genetic diversity within and among subpopulations. Changes in population genetic diversity within habitat fragments may in turn affect the persistence of subpopulations, and the loss of such diversity may decrease the genetic resources that could be utilized under changing environmental conditions, ultimately leading to extinction. In collaboration with Prof. Matt Hamilton, I am working on an interdisciplinary landscape genetics project that examines the specific landscape patterns (habitat area, isolation, and edge effects) that lead to changes in animal population genetic diversity in a salt marsh, where an increase in mean tidal height over the past 70 years has led to the fragmentation of one of the dominant species of salt marsh grasses (Spartina patens). We hypothesize that such changes in landscape structure could affect the population genetic diversity of the dominant, specialist herbivores that feed on this grass. Additionally, because predaceous hunting spiders accumulate along habitat edges, altered predator-prey interactions could further impact gene flow in specialist herbivores. We have developed 12 novel variable microsatellite loci for two S. patens specialist herbivores (Aggarwal et al. 2011) to understand how effective population size and gene flow are influenced by habitat fragmentation, which could ultimately help us better understand how fragmentation and edge effects influence genetic diversity.
