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Empirical studies have shown that animal populations from a wide array of taxa exhibit spatial patterns of correlation in fluctuating abundance. In the search for explanations for this phenomenon it has been proposed that subpopulation interactions in the form of spatial dispersal, or variability in external factors, such as weather, would be the crucial driving forces responsible for spatial synchrony. Nevertheless, dispersal and external factors have been shown to produce different patterns of synchrony. We show here that observed patterns in synchronous dynamics can be reproduced by using a spatially linked population model. Further, we analyse how local and global environmental stochasticity and dispersal influence the pattern of spatial synchrony. We contrast our theoretical results with data on long-term dynamics of North American game animals and emphasize that the data and our spatial population dynamics models are compatible.

We describe patterns of variation in the body size of tapeworms (Cestoda) parasitizing rodents and shrews. Tapeworms display considerable interspecific variation in body size. Tapeworms also occur only in certain, species-specific parts of intestine. Empirical data on tapeworms suggest that these two phenomena are related: the biggest tapeworm species tend to occur in midgut. We put forward a hypothesis that the observed variation in body size and age-at-maturity reflects adaptation to specific levels of mortality and amount of nutrients in intestinal environment. We construct a simple energy allocation model in which we assume that optimal life-histories maximize the expected reproductive success (R0). Under realistic intestinal gradients of mortality and amount of nutrients, the predicted patterns of variation in body size resemble those observed in tapeworms of small mammals.