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 dynamics across geographical ranges: Time-series analyses of three small game species.
Williams, Christopher 1, Ives, Tony1, Applegate, Roger2, 1 Department of Zoology, Madison, WI, USA2 Department of Wildlife and Parks, Emporia, KS, USA
ABSTRACT- Little is known about how density-independent and density-dependent processes affecting population dynamics vary geographically across species ranges. To address this problem for three vertebrate species (northern bobwhite, ring-necked pheasants, and Eastern cottontails), we examined long-term (1966-2001) seasonal (January, April, July, and October) time-series data from the Kansas Rural Mail Carrier Survey, USA. All three species have range boundaries in Kansas, with population abundances declining towards the periphery of their ranges. We quantified the strengths of density-dependent and density-independent processes affecting the dynamics of 10 populations of each species ranging from low to high mean abundance using first-order autoregressive models with measurement error. Peripheral populations with lower mean abundance tended to have greater population variability. This pattern could potentially be explained by peripheral regions experiencing weaker density dependence or greater environmentally driven density-independent fluctuations in per capita population growth rates. In general, density dependence did not vary among geographic regions, although there was a trend for smaller, peripheral populations to exhibit stronger density dependence. Density-independent variability in per capita population growth rates was higher in peripheral populations. Furthermore, density-independent fluctuations in per capita population growth rates were weakly correlated with temperature and precipitation, and were highest for the period October-January, identifying fall as the period of greatest environmentally driven variability in population dynamics. Per capita population growth rates fluctuated in moderate synchrony among regions, especially for more abundant, non-peripheral populations in close geographical proximity. The strong density-dependent and stronger density-independent processes in smaller, peripheral populations suggest that the greater variability in peripheral populations densities are caused by greater population sensitivity to environmental fluctuations. This may make peripheral populations more likely to go extinct and leads to the prediction that potential population declines will be accompanied by a contraction in their geographic ranges.
Key words: core, density-dependence, population, periphery