Visibility of the environmental noise modulating population dynamics

Characterizing population fluctuations and their causes is a major theme in population ecology. The debate is on the relative merits of density-depend ent and density-independent effects. One paradigm (revived by the research on global warming and its relation to long-term population data) states tha t fluctuations in population densities can often be accounted for by extern al noise. Several empirical models have been suggested to support this view Mt followed this by assuming a given population skeleton dynamics (Ricker dynamics and second-order autoregressive dynamics) topped off with noise co mposed of low- and high-frequency components. Our aim was to determine to w hat extent the modulated population dynamics correlate with the noise signa l. High correlations (with time-lag -1) were observed with both model categ ories in the region of stable dynamics, but not in the region of periodic o r complex dynamics. This finding is not very sensitive to low-frequency noi se. High correlations throughout the entire range of dynamics are only achi evable when the impact of the noise is very high. Fitted parameter values o f skeleton dynamics modulated with noise are prone to err substantially. Th is casts doubt as to what degree the underlying dynamics are any more recog nizable after being modulated hv the external noise.