Concurrent density dependence and independence in populations of arctic ground squirrels.
No population increases without limit. The processes that prevent this can operate in either a density-dependent way (acting with increasing severity to increase mortality rates or decrease reproductive rates as density increases), a density-independent way, or in both ways simultaneously. However, ecologists disagree for two main reasons about the relative roles and influences that density-dependent and density-independent processes have in determining population size. First, empirical studies showing both processes operating simultaneously are rare. Second, time-series analyses of long-term census data sometimes overestimate dependence. By using a density-perturbation experiment on arctic ground squirrels, we show concurrent density-dependent and density-independent declines in weaning rates, followed by density-dependent declines in overwinter survival during hibernation. These two processes result in strong, density-dependent convergence of experimentally increased populations to those of control populations that had been at low, stable levels.
Karels
T J
TJ
Division of Life Sciences, University of Toronto at Scarborough, Ontario, Canada.
Boonstra
R
R
D000818:Animals; D001110:Arctic Regions; D006605:Hibernation; D011156:Population Density; D011157:Population Dynamics; D012589:Sciuridae / Q000502:physiology*; D012621:Seasons; D014886:Weaning