Population dynamics of large and small mammals

We offer an evaluation of the Caughley and Krebs hypothesis Chat small mamm als are more likely than large mammals to possess intrinsic population regu lating mechanisms. Based on the assumption that intrinsic regulation will b e manifest via direct density-dependent feedbacks, and extrinsic regulation via delayed density-dependent feedbacks, we fit autoregressive models to 3 0 time series of abundance for large and small mammals to characterize thei r dynamics. Delayed feedbacks characterizing extrinsic mechanisms, such as trophic-level interactions, were detected in most time series, including bo th small and large mammals. Spectral analyses indicated that the effect of such delayed feedbacks on the variability in population growth rates differ ed with body size, with large mammals exhibiting predominantly reddened and whitened spectra in contrast with predominantly blue spectra for small mam mals. Large mammals showed less variance and more stable dynamics than smal l mammals, consistent with, among other factors, differences in their poten tial population growth rates. Patterns of population dynamics in small vers us large mammals contradicted those predicted by the Caughley and Krebs hyp othesis.