By N. C. Stenseth, W. Z. Lidicker Jr (auth.), Nils Chr. Stenseth, William Z. Lidicker Jr (eds.)
4.1.1 Demographic importance restricted populations develop extra speedily than populations from which dispersal is authorized (Lidicker, 1975; Krebs, 1979; Tamarin et at., 1984), and demography in island populations the place dispersal is particular differs significantly from within sight mainland populations (Lidicker, 1973; Tamarin, 1977, 1978; Gliwicz, 1980), sincerely demonstrating the demographic signi ficance of dispersal. the superiority of dispersal in speedily increasing populations is held to be the simplest facts for presaturation dispersal. simply because dispersal reduces the expansion cost of resource populations, it's in general believed that emigration isn't really balanced by means of immigration, and that mortality of emigrants happens due to circulation right into a 'sink' of adverse habitat. If such dispersal is age- or sex-biased, the demo graphy of the inhabitants is markedly affected, on account of vary ences in mortality within the dispersive intercourse or age type. Habitat heterogeneity hence underlies this interpretation of dispersal and its demographic outcomes, even supposing the spatial variability of environments is never assessed in dispersal studies.
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Extra resources for Animal Dispersal: Small mammals as a model
This can take the form of (1) achieving earlier reproductive maturation; (2) finding suitable mates (both quantity and quality may be at stake); or (3) enhancing the survival of weaned offspring. All of these motivations have been described for various species of Microtus (Lidicker, 1985a), and probably occur in most other groups: for example, there is evidence that dispersing voles reach sexual maturity at a younger age than residents, adult males often disperse at the beginning of the breeding season, and in five species females have been recorded abandoning their home ranges to their weaned litters (see also Cockburn, 1988).
5 CONCLUSIONS 1. Dispersal is a key element in the understanding of many population processes. Its interdisciplinary nature bridges the fields of ecology, genetics, behaviour, and evolution in addition to several applied fields (Chapter 1). 2. Dispersers are a heterogeneous assemblage potentially including all sex and age groups in a population. In fact, dispersal occurs at a variety of times and under diverse circumstances. 3. The diversity of dispersal behaviour prompts the development of classification systems so as to organize our knowledge and to facilitate References 33 communication.
They may be searching for mates, some scarce resource, or better living conditions generally. Excursions may be preludes to actual dispersal, and occur commonly among species of small mammals (reviewed in Lidicker, 1985b). If an explorer fails to return home, it becomes indistinguishable from a disperser. Shifters are those who manage to move their home ranges by gradually adding bits of real estate to one edge while simultaneously subtracting it from another. Thus they never actually abandon completely their current home range.