Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Robert J. Diaz
Ecologists have long known that complex habitats often provide prey with refugia from predation in a wide variety of habitat types and for a wide variety of prey species. Despite the recognized importance of structural habitat complexity, ecologists have measured complexity in many different ways. I propose four new indices of structural habitat complexity that are dimensionless, that can be applied across various habitat types and scales, and that directly measure how structural complexity interferes with a predator's foraging ability. These indices are: (1) Ct/At, the total area of cover within a habitat (Ct) divided by the area of the habitat (At), (2) Cw/Pw, the average width of the individual structures within a habitat (Cw) divided by the appropriate width of the prey organism (Pw), (3) Sp/Pr, the average inter-structural space size within a habitat (Sp) divided by the width of the predator (Pr), and Sp/Py, the average inter-structural space size within a habitat (Sp) divided by the width of the prey (Py). I predicted that prey survivorship should (1) increase hyperbolically with increasing Ct/At, (2) increase hyperbolically with increasing Cw/Pw, and (3) decrease sigmoidally with increasing Sp/Pr. I also predicted that different sized fauna should respond differently to artificial seagrass plots deployed in a seagrass bed, based upon the size of the inter-structural spaces relative to their body sizes (Sp/Py). I found that prey survivorship increased hyperbolically with increasing Ct/At, and decreased sigmoidally with increasing Sp/Pr. I found no effect of Cw/Pw on prey survivorship. I found that small fauna responded positively to increased structure in artificial seagrass plots deployed in a seagrass bed, but after controlling for structural surface area within each plot there was no difference between treatments, indicating no effect of Sp/Py on small fauna. Larger fauna responded slightly differently than the small fauna, but the pattern of their response did not support the hypothesis that Sp/Py was important. The smaller fauna also appeared to respond positively to increased water flow speeds within the seagrass bed. Overall, these indices may be useful to both ecologists and managers interested in predator-prey-habitat issues.
© The Author
Bartholomew, Aaron, "New dimensionless indices of structural habitat complexity" (2001). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1539616561.