PARENT SESSION
Contributed Oral Session 14: Evolutionary Ecology: Theory; Modeling
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 521 A, Level 5, Palais des congrès de Montréal

Scaling up habitat size clarifies deterministic dynamics through a reduction in demographic stochasticity.

Costantino, Robert^*,1, Desharnais, Robert², ¹ University of Arizona, Tucson, AZ² California State University, Los Angeles, CA

ABSTRACT- An assumption in ecological theory is that the relative magnitudes of population fluctuations due to demographic stochasticity (chance variation in individual births and deaths) decrease with increases in population size. We provide experimental support for this assumption. Building on a validated deterministic model for flour beetles (the LPA model), we use binomial and Poisson distributions to describe the survival and reproduction of insects. The binomial and Poisson distribution parameters are modeled as nonlinear functions of the state variables in such a way that the mean trend for the system predicted over one time unit is the deterministic model. The departures of data from the deterministic model skeleton are well described by this formulation of demographic stochasticity. We tested the predicted change in the relative magnitude of population fluctuations using six replicate beetle populations maintained for 108 weeks (approximately 18 generations) in 20g and 60g of media with chaotic dynamics acheived under standard culturing techniques. We quantified the observed changes in population fluctuations using the residual one-step forecasts and the mean minimum distance of the observations from the underlying deterministic chaotic attractor. Our results support the hypothesis that increasing population size reduces demographic stochasticity with an accompanying increase in the clarity of the deterministic dynamics of population densities. This places the scaling rule for demographic stochasticity on a firmer empirical footing.

Key words: stochastic, dynamics, nonlinear