PARENT SESSION
Oral Session # 7: Populations and Genetics.
Presiding: E Sotka
Monday, August 4. 8:00 AM to 11:30 AM, SITCC Meeting Room 106.
Population growth rate as a general predictor of the strength of density dependence.
Agrawal, Anurag1, Underwood, Nora2, 1 University of Toronto, Toronto, Ontario, Canada2 Florida State University, Tallahassee, Florida
ABSTRACT- Although ecological studies of density dependence have yielded highly variable results, little is known about the conditions that may promote strong versus weak density dependence. Thus, a critical hurdle in developing a predictive framework for population dynamics is understanding the causes of this variation. Here we present experimental evidence for positive, negative, and no density dependence from 12 independent density manipulations of milkweed aphids in laboratory and field experiments. A general pattern emerged from these highly variable results: greater experiment-wide per capita growth rate of aphids was associated with stronger density dependence (a more negative slope of the relationship between density and per capita growth rate). This pattern was robust across a broad range of aphid densities; the initial or final mean aphid density for experiments did not predict the strength of density dependence. Experimental manipulation of temperature demonstrated that shifts in population growth rates were associated with changes in the strength of density dependence. These results suggest a general hypothesis: as density independent factors increase mean per capita growth rates, the slope of density dependence decreases. Given certain assumptions, this prediction follows from the definition of density dependence that is included in many widely used models of population dynamics. Thus, the relationship between population growth rate and density dependence is likely to be broadly applicable as a determinant of variation in the strength of density dependence.
Key words: oleander aphid Aphis nerri, population dynamics, common milkweed Asclepias syriaca, density dependence