Date of Award
Doctor of Philosophy
Ecology and Evolutionary Biology
Arnold G. van der Valk
Kirk A. Moloney
I designed and implemented three studies exploring the factors controlling the development of vegetative zonation in prairie wetlands. In the first study, I used growth chamber experiments to examine the effects of water depth and temperature on seedling recruitment from a wetland seed bank. Regression analysis indicated that both water depth and temperature affected the composition of the seedling community. Annual species richness declined in richness. Perennial species richness increased in richness with decreasing temperature. Species that were found in deep water as adults germinated at higher rates in the flooded treatments, while species that occurred at higher elevations as adults germinated at their highest rates in the unflooded treatments;In the second study, I used field surveys of vegetation and topography to compare the variation in diversity along elevational gradients in natural wetlands and five to seven year old restored wetlands. Natural wetlands had higher local diversity ([alpha] diversity) than restored wetlands, but there was no difference in species turnover rates ([beta] diversity). The highest potential levels of species richness occurred 20 cm above the highest point of flooding in both wetland types. Changes in [beta] diversity along the elevational gradient suggested that [alpha] diversity was constrained by environmental stress at low elevations and by biotic interactions at high elevations;In the third study, I compared the accuracy of a statistical model with no dispersal component to a spatial rule-based model that incorporated dispersal, using data from a ten year field experiment of the effects of water level changes on wetland vegetation. The spatial model was more accurate than the niche model at predicting species' abundance and distribution patterns;In summary, adult distributions are a function of the current environment and the environment during historical recruitment events. Adult distributions in wetlands will be strongly affected by the elevational gradient soon after a wetlands forms, but local species richness will be lower in younger wetlands. Direct environmental effects associated with the elevational gradient will be strongest at low elevations. Dispersal is important in determining the abundance and pattern of species' distribution along a water depth gradient.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Eric William Seabloom
Seabloom, Eric William, "Vegetation dynamics in prairie wetlands " (1997). Retrospective Theses and Dissertations. 12243.