The effect of red, white and blue environmental noise on discrete-time population dynamics is analyzed. The coloured noise is superimposed on Moran-Ricker and Maynard Smith dynamics, the resulting power spectra are less than examined. Time series dominated by short- and long-term fluctuations are said to be blue and red, respectively. In the stable range of the Moran-Ricker dynamics, environmental noise of any colour will make population dynamics red or blue depending the intrinsic growth rate. Thus, telling apart the colour of the noise from the colour of the population dynamics may not be possible. Population dynamics subjected to red and blue environmental noises show, respectively, more red or blue power spectra than those subjected to white noise. The sensitivity to differences in the noise colours decreases with increasing complexity and ultimately disappears in the chaotic range of the population dynamics. These findings are duplicated with the Maynard Smith model for high growth rates when the strength of density dependence changes. However, for low growth rates the power spectra of the population dynamics with noise are red in stable, periodic and aperiodic ranges irrespective of the noise colour. Since chaotic population fluctuations may show blue spectra in the deterministic case, this implies that blue deterministic chaos may become red under any colour of the noise.

Abstract. Dwarf individuals are observed in many species of freshwater ®sh. This paper studies the potential causes of such stunted growth. We present a model which describes the e ect of growth conditions on the age-and size-structure of ®sh populations. The model parameters are chosen to characterize a Eurasian perch population. Two possible causes of stunting are identi®ed: resource limitation and size-or age-dependent survival probabilities. While the former mechanism often arises from intraspeci®c density dependence, the latter is of particular relevance in the context of interspeci®c interactions and ®shing. After evaluating the immediate ecological consequences of these factors, we examine the potential for life-history adaptations in stunted ®sh populations. Interactions between the ecological and adaptive mechanisms of stunting are shown to be intricate: not only does the age at maturity of individuals a ect their growth trajectories, but, in addition, alterations in growth conditions can result in di erent adaptively stable ages at maturity. We show that such adaptive responses can either alleviate or amplify stunting caused by ecological factors. Life-history adaptation may also lead to the persistence of stunting when ecological factors alone would allow for normal growth. An appreciation of the interplay between ecological and adaptive factors therefore is critical for understanding the causes and mechanisms of stunted growth.

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