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Nash Turley spent the past summer working at the Savannah River Site National Environmental Research Park in South Carolina. The Savannah River Site, or SRS, is home to a large-scale and long-term experiment on the efficacy of habitat corridors as thoroughfares for organisms moving between like landscape patches, especially remnant parcels of native habitat. Corridors have long been thought to help preserve and promote biodiversity in fragmented landscapes by providing a clear, navigable path for organisms and propagules such as seeds or pollen to move between patches.
SRS was traditionally a longleaf pine savannah ecosystem. All of the original longleaf pines were logged and the region was replanted with loblolly pine for timber production. Now, in partnership with the US Forest Service, a group of researchers, including Biology professor Josh Tewksbury, are in the process of restoring forty one hundred meter-squared patches of longleaf pine savannah. The patches are in groups of five, with each group of five comprising an experimental unit. By grouping the patches the experimental design is replicated eight times, thus strengthening the results of each study. The patches within an experimental unit vary in pattern so the patch perimeter-to-area ratio varies. The various patch designs allow researchers to determine which patch shape does the best job of preserving biodiversity. Corridors connect some of the patches, while others are isolated islands amidst a sea of loblolly pine, which permits the researchers to ask the central question of this project: Do corridors work?
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Prior to this group’s investigations, there were few experimentally controlled studies with data to suggest corridors were effective at facilitating the movement of different organisms between patches, and none at scales large enough to be useful for management. But the first papers published with data from SRS suggest that corridors are in fact beneficial, providing statistical power to a concept long touted by conservation biologists.
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Working with Josh Tewksbury, Nash is investigating whether patch shape or connectivity or a plant’s distance from a patch edge affect herbivory. To test this, Nash and a group of researchers planted 80 Solanum americanum (American nightshade) seedlings in each experimental unit this spring and monitored them for growth and herbivory throughout the summer. In addition to recording visible herbivore damage to the 640 plants, Nash also documented the presence of arthropod species on plants, some of which feed on plants but typically leave no visible signs of herbivory (e.g., aphids). At the end of the season he tallied the total number of fruits produced by each plant as an approximate measure of a plant’s success in producing offspring. With these data he can determine how different patch parameters (shape, connectivity, distance from edge) affect herbivory (leaf damage, number of arthropods on a plant). He can then determine how the correlated effects of herbivory and patch parameters influenced each plant’s relative reproductive success, or fitness, the most informative measure in biology. In a world where landscapes are becoming increasingly fragmented due to destruction and conversion, data from studies such as Nash’s are incredibly valuable to conservation planners charged with designing landscape preserves that effectively manage biodiversity.
Nash was awarded the Department of Biology’s Frye-Hotson-Rigg Award to support a portion of his research. The Frye-Hotson-Rigg Endowment was established in honor of former Botany professor Frye, Hotson, and Rigg and supports Biology undergraduates working on a plant system with costs associated with fieldwork. If you would like to support more students participating in research by contributing to this endowment, please fill out the gift form on the last page of this newsletter and specify that you would like to contribute to the Frye-Hotson-Rigg Endowment, or please feel free to call (206) 685.2185 for more details.