PARENT SESSION
Contributed Oral Session 145: Evolutionary Ecology: Population Dynamics
Thursday, August 11, 1:30 PM - 5:00 PM, Meeting Room 524 B, Level 5, Palais des congrès de Montréal
Strong, stabilizing density dependence amplifies population variability of an insect seed predator.
Solbreck, Christer1, Ives, Anthony*,2, 1 Department of Entomology, Uppsala, Sweden2 Department of Zoology, Madison, WI, USA
ABSTRACT- Strong density-dependent regulation that rapidly returns populations to carrying capacity are generally thought to be stabilizing. However, when the carrying capacity itself fluctuates widely, strong density dependence forces populations to track the fluctuating environment, thereby increasing population variability. We demonstrate this phenomenon using long-term (22-year) data on Euphranta connexa, a dipteran seed predator of the herbaceous perennial Vincetoxicum hirundinaria in Sweden. Seed abundance is commonly limiting for E. connexa, with an average of 74% (range 11-99.5%) seed pods attacked by E. connexa per year. Furthermore, seed abundance fluctuates in a temporally uncorrelated way across two orders of magnitude. The tight coupling between V. hirundinaria and E. connexa dynamics, and the exhaustive censuses of the populations at the study sites, make it possible to fit a model to the dynamics with little residual unexplained variation. Using this model, we show how strong "stabilizing" density dependence increases the population variability of E. connexa as it tracks fluctuations in seed abundance.
Key words: population dynamics, predator-prey interactions, density dependence, model fitting