As populations change in size, they also change in spatial distribution of individuals. Population movement (epidemiology) across landscapes and watersheds (stream continuum) reflects integration of physiological and behavioral attributes with landscape or watershed structure. Growing populations tend to spread across the landscape as dispersal leads to colonization of new habitats, whereas declining populations tend to constrict into more or less isolated refuges. Isolated populations of irruptive or cyclic species can coalesce during outbreaks, facilitating genetic exchange.
Insect populations show considerable spatial variation in densities in response to geographic variation in habitat conditions and resource quality (Fig. 7.4).Vari-ation can occur over relatively small scales because of the small size of insects and their sensitivity to environmental gradients (e.g., Heliovaara and Vaisanen 1993, Lincoln et al. 1993). The spatial representation of populations can be described across a range of scales from microscopic to global (Chapter 5). The pattern of population distribution can change over time as population size and
Native grass Brome
Effect of surrounding matrix on rate of planthopper loss from cordgrass patch in which released (A), rate of planthopper immigration into satellite patches (B), and percentage of planthoppers lost from the central release patch that successfully immigrated into any of the eight surrounding patches. Vertical lines represent 1 SE. Bars with different letters are significantly different at P < 0.05. From Haynes and Cronin (2003) with permission from the Ecological Society of America. Please see extended permission list pg 570.
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