Findlay, C. S.,Clarke, Paul D.2009-03-252009-03-2519961996Source: Masters Abstracts International, Volume: 35-06, page: 1719.9780612199378http://hdl.handle.net/10393/10051http://dx.doi.org/10.20381/ruor-8108Animal population densities are thought to be "regulated" by density-dependent processes (Haldane, 1953; Royama, 1977: Berryman, 1991). The perceived importance of these processes to biologists is evident from the vast amount of research dedicated to this idea (Inchausti, 1994). Most of this research addresses the problem(s) of detecting the effect of density-dependent regulatory processes using time series data. However, the question of the relative importance of density-dependent factors upon rates of change of population abundances is rarely addressed. In this thesis, I quantify the importance of density-dependent factors in 303 natural animal populations. I found that, on average, only $\approx$19% of the temporal variability in per capita growth rate could be statistically related to population density. Yet research effort concentrates overwhelmingly on density-dependent processes. I conclude that the effects of density-dependent processes within natural animal populations are generally weak and disproportionately studied. Because many, if not all, ecological processes act on some characteristic temporal or spatial scale (O'Neill et al., 1986; Wiens, 1989; Pimm, 1991; Maurer, 1994; Fleishman, 1995) I also address the question of how the characteristic time of density-dependent regulatory processes might affect the estimates of the influence of regulatory processes on a population's per capita growth rate. I hypothesized that if density-dependent regulatory processes operate on a characteristic temporal scale that sampling with a sampling period commensurate with the characteristic time of these processes would yield the maximal amounts of variability in the per capita growth rate statistically related to the variability in N. Simulated population time series were generated using a logistic growth model with a stochastic term added. Based on the analysis of the simulated time series, the characteristic time of density-dependent regulatory processes is predicted to be independent of life-history traits correlated with body size. The characteristic times are predicted to be integral multiples of 1 year (1, 2, 3 and 4 years) for all modelled body sizes. These predictions, regarding characteristic times, were found to be suspect after further testing supported the contention that these results may be methodological artifacts. I suggest that these results are due to the pragmatic criteria imposed to constrain the number of possible subsamples to be analyzed. I further suggest that to better address the characteristic time hypothesis, time-slices with different time periods between successive population densities are required.290 p.Biology, Ecology.Thesis