PARENT SESSION
Poster Session # 21: Biogeography, Biodiversity, Populations, and Genetics.

Thursday, August 7 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.

Seasonal changes in density dependent population growth rate of feral house mouse populations.

Davidson, R. Scott^*,1, Steen, Harald², ¹ University of Otago, Dunedin, Otago, New Zealand² University of Oslo, Blindern, Oslo, Norway

ABSTRACT- Density dependence is difficult to detect in wild populations. The effect of density on population growth rates can easily be obscured by habitat heterogeneity and environmental stochasticity. By measuring vital rates on replicate populations under a variety of conditions we are better able to take these factors into account and isolate any effect of density. We examined the relationship between density and population growth rate in seasonally breeding populations of feral house mice (Mus musculus) living in coastal dune vegetation near Dunedin, New Zealand. Our study design consisted of eight live-trapping grids that we trapped every second month from February 2000 to June 2002. The experimental design allowed us to measure vital rates with both temporal and spatial replication. Mark-recapture data were analysed with program MARK. Mouse apparent survival was estimated using the Cormack-Jolly-Seber model, and recruitment into the population was estimated using the Pradel models. For each grid at each trapping session we produced a population projection matrix from the survival and recruitment estimates, and calculated the population′s asymptotic growth rate. We fitted a generalised linear model to the growth rates to analyse how they varied with density and the time of year. While there was no overall relationship between the population′s growth rate and the density of the mice, there was a seasonal density-dependent effect. The population′s growth rate during winter was inversely related to the log of population density. This occurred early in the non-breeding period just after the mice reached their seasonal peak population density in autumn. This result is consistent with mortality from starvation following the depletion of summer foods. We did not find a significant relationship between the population′s growth rate and the population′s density at any other time.

Key words: population growth rate, seasonal population dynamics, density dependence, Mus musculus