4.1.1 Demographic significance Confined populations grow more rapidly than populations from which dispersal is permitted (Lidicker, 1975; Krebs, 1979; Tamarin et at., 1984), and demography in island populations where dispersal is restricted differs greatly from nearby mainland populations (Lidicker, 1973; Tamarin, 1977, 1978; Gliwicz, 1980), clearly demonstrating the demographic signi ficance of dispersal. The prevalence of dispersal in rapidly expanding populations is held to be the best evidence for presaturation dispersal. Because dispersal reduces the growth rate of source populations, it is generally believed that emigration is not balanced by immigration, and that mortality of emigrants occurs as a result of movement into a 'sink' of unfavourable habitat. If such dispersal is age- or sex-biased, the demo graphy of the population is markedly affected, as a consequence of differ ences in mortality in the dispersive sex or age class. Habitat heterogeneity consequently underlies this interpretation of dispersal and its demographic consequences, although the spatial variability of environments is rarely assessed in dispersal studies.

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Theimer, an accomplished ecologist.

Fresh concepts in the study of seed dispersal are spurring a host of exciting new questions, new answers to old questions, new methods and approaches, and a reinvigoration of the field.Seed Dispersal: Theory and its Application in a Changing World presents both recent advances and reviews of current knowledge demonstrating the vigour and vibrancy of the field. It provides new perspectives and directions at a time when efforts to meet growing environmental challenges threatening natural systems are of utmost importance.

Now that so many ecosystems face rapid and major environmental change, the ability of species to respond to these changes by dispersing or moving between different patches of habitat can be crucial to ensuring their survival. Understanding dispersal has become key to understanding how populations may persist. Dispersal Ecology and Evolution provides a timely and wide-ranging overview of the fast expanding field of dispersal ecology, incorporating the very latest research. The causes, mechanisms, and consequences of dispersal at the individual, population, species, and community levels are considered. Perspectives and insights are offered from the fields of evolution, behavioural ecology, conservation biology, and genetics. Throughout the book theoretical approaches are combined with empirical data, and care has been taken to include examples from as wide a range of species as possible - both plant and animal.

An outline of the principles of animal dispersion. The integration of social groups by visible signals. Dispersion in the breeding season: birds. Display characters and natural selection. Fourther consideration of castes in animal societies. Timing and synchronisation. Vertical migration of the plankton. Fluctuations, irruptions and emigrations. Recruitment through reproduction. Socially-induced mortality. Deferment of growth and maturity.