Masters Theses
Date of Award
8-2000
Degree Type
Thesis
Degree Name
Master of Science
Major
Mathematics
Major Professor
Louis J. Gross
Committee Members
Mark Kot, Daniel Simberloff
Abstract
The keystone species concept has helped advance food web theory, differentiating functional versus trophic roles and strong versus weak interactors. Although early work tended to neglect spatio-temporal variability within and among communities, recent empirical and theoretical work on interaction strength and community importance recognize the context dependency of species interactions. These include the effects of disturbance, productivity, species associations, temporal variability, and spatial scale on species interactions. Spatio-temporal variability in the density of a keystone species affects the persistence, spatial extent, and degree of community effects. Moreover, the spatial extent and resolution the examiner chooses may affect estimates of interaction strength and their interpretation. Sixteen model scenarios of a simple consumer-prey interaction were examined to assess the effects of spatial structure and scale on the measurement and interpretation of interaction strengths. Four common interaction strength indices (raw difference, community importance, Paine's index, and dominance index) were calculated for each simulation to determine patterns associated with each index. Model scenarios assessed the dependence of interaction strength on 1) the spatial distribution of predators, 2) the degree of predator and prey movement, 3) the spatial extent, resolution, and location of the study area, and 4) characteristics of the prey and predator populations, such as density and predator capture ability. Results indicate in general that interaction strengths were strongest when predators were uniformly distributed and weakest when predator distribution was limited, regardless of the length of the experiment. When high prey densities interfered with the ability of predators to capture prey, however, interaction strengths for the different predator spatial distributions depended on the length of the experiment, initial prey density, and rarity of prey Interaction strengths also depended on the dispersal ability of prey. reflecting a balance between prey entering and escaping predator patches as the predator spatial distribution varied. The spatial extent examined should be large enough to account for the degree of prey and predator movement, otherwise interaction strengths may be overestimated. The most reliable estimate of interaction strength, when prey dispersal is not too high, is found by measuring prey and predator populations in the local area in which they interact, rather than taking an average over a large spatial area. Theoretical models, empirical studies, and management strategies should account for the effects of spatial structure and scale. Neglecting these effects can lead to underestimates or overestimates of interaction strength, and possible misidentification of keystone species.
Recommended Citation
Harrell, Susan M., "Spatio-temporal variability in keystone species and implications for quantifying interaction strengths. " Master's Thesis, University of Tennessee, 2000.
https://trace.tennessee.edu/utk_gradthes/9398