Date of Award:

5-1-1990

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology/Ecology

Committee Chair(s)

James W. Haefner

Committee

James W. Haefner

Committee

James A. MacMahon

Committee

Fred Post

Committee

Ronald Sims

Committee

Darwin Sorensen

Committee

Wayne Wurtsbaugh

Abstract

Competition for resources can influence patterns of species abundance. Disturbances can alter the outcome of competition, and affect species diversity. In this study, a competition experiment was designed to quantify the effects of disturbance intensity and frequency on the outcome of algal competition for phosphorus. The disturbance chosen was an intermittently supplied limiting resource, phosphorus. The two algal species used represented divergent life history strategies. Pediastrum, a colonial, green alga, is adapted to exploit periods of high phosphorus concentration, while Staurastrum is the superior competitor in phosphorus poor environments. The competition experiment included five treatments that received phosphorus pulses throughout the experiment at one of three intensities (2.25, 4.50 or 9.00 µg SRP liter-1) and two frequencies (3 and 6 days between pulses). Two other treatments were not pulsed and received phosphorus only at the start of the experiment. The outcome of competition was dependent upon the measurement unit used. Pediastrum outcompeted Staurastrum in the unpulsed treatments, while Staurastrum was the dominant species in the pulsed treatments when examining cell densities. Using biovolume or surface area to evaluate the outcome of competition, indicated that Pediastrum outcompeted Staurastrum in one or both of the high intensity pulsed treatments, respectively. Statistical tests (MANOVA, ANOVA and planned comparisons) indicated pulse intensity, frequency and total amount of phosphorus delivered affected cell densities and biomass of both algae. Pulse intensity was the most important of these factors and had a significant effect throughout the experiment. Species densities increased with increasing intensity, and frequency in the pulsed treatments. Algal responses to pulses changed during the experiment as cell densities increased. Resource based competition models were used to predict the species density dynamics of the competition experiment. Model parameters were estimated from single species batch and semicontinuous culture experiments for the Monod and Droop growth equations, and the Michaelis-Menton nutrient uptake equation. All of the resource based competition models failed to quantitatively predict cell densities observed in the competition experiment. The Monod and Droop models qualitatively predicted the outcome of competition in five of seven treatments. Mechanistically both models failed to describe the process of cell division.

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