Estimating density dependence in time-series of age-structured populations.
For a life history with age at maturity alpha, and stochasticity and density dependence in adult recruitment and mortality, we derive a linearized autoregressive equation with time-lags of from 1 to alpha years. Contrary to current interpretations, the coefficients for different time-lags in the autoregressive dynamics do not simply measure delayed density dependence, but also depend on life-history parameters. We define a new measure of total density dependence in a life history, D, as the negative elasticity of population growth rate per generation with respect to change in population size, D = - partial differential lnlambda(T)/partial differential lnN, where lambda is the asymptotic multiplicative growth rate per year, T is the generation time and N is adult population size. We show that D can be estimated from the sum of the autoregression coefficients. We estimated D in populations of six avian species for which life-history data and unusually long time-series of complete population censuses were available. Estimates of D were in the order of 1 or higher, indicating strong, statistically significant density dependence in four of the six species.
Lande
R
R
Division of Biology 0116, University of California at San Diego, La Jolla, CA 92093, USA. rlande@biomail.ucsd.edu
Engen
S
S
Saether
B-E
BE
D017677:Age Distribution; D000818:Animals; D001717:Birds / Q000502:physiology*; D008954:Models, Biological; D015233:Models, Statistical; D011156:Population Density; D012044:Regression Analysis; D013997:Time Factors