Dispersal is the spreading of individuals away from each other. Dispersal consists to three components viz., emigration (crossing habitat boundaries), transience or traversing through a landscape (like movements in non-habitat or resource poor matrix) and settlement (immigration or colonization).
Behavioural differences depend on motivation to disperse, like forced or voluntary emigration. Behavioural studies have focused mostly on dispersal propensity. Importance to behavioural variation in two other stages is mostly unknown. Variations in dispersal patterns among sexes, populations, landscapes or species are known.
Mechanistic approaches have recently been advocated to gain better understanding of dispersal. Conservation biology benefits from such understanding in manipulating patterns for conservation. Recognition of different behavioural movement contributing to dispersal study has become particularly significant in the field of habitat fragmentation (vide Dyck and Baguette, 2005).
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Various life processes along with their associated movement behaviours occur at different spatial scales from food searching in a local patch to migratory movements on regional or continental scales (1ms, 1995). Dispersal can be realized in two ways.
First, dispersal can be a byproduct of a search for daily resources by routine movements, called trivial or daily movements. Such routine movements are associated with foraging, mate location, and seeking shelter. Second, dispersal can also be realized by special movements that are designated for net displacement and settlement at some distance from natal site.
Geometry of habitat in a landscape or basically of resources will determine the probability of routine dispersal. In continuous landscapes with regularly spread resources, routine movements would contribute more to dispersal than in highly fragmented landscapes with resources in discrete patches at considerable distance relative to scale of space -use by average individual of target species. Results of experimental and empirical studies are in line with this prediction (Mennechez et al., 2003).
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In animals showing dispersal polymorphism, displacement movement is behaviourally distinguishable from routine movement. Distinct morphological variation provides an indicator of dispersal propensity of individuals and frequencies of dispersive individuals can be compared among populations and landscapes (vide Dyck and Baguette, 2005).
All individuals engage in routine movements. Propensity of special dispersal movements may vary among populations and individuals. Individuals making long-distance movements represent a non random sample of a population with respect to morphology, physiology and behaviour as exemplified by butterflies, fishes, lizards and naked mole rat. Evidence for a heritable basis for long distance dispersal in insects and birds exists.
Significant variation among individuals with respect to dispersal is not necessarily reflected in their routine, explorative movements. Colbert et al., (2004) predict that species with least environment – sensitive dispersal strategies will be specialized species in terms of habitat requirements.
Habitat fragmentation alters resource distribution from widespread and abundant to localize in discrete patches with clumped resources. Contribution of routine movements to dispersal is expected to decline with degree of habitat fragmentation.
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Dyck and Baguelte (2005) have summarized that a more accurate knowledge of dispersal behaviour is important to model dispersal with more biological realism and to better understand evolutionary consequences and conservation. Contribution of routine movements to dispersal is expected to decline with habitat fragmentation.
They further stated that species mobility is not a static trait but a multiple trait, the components of which may evolve rapidly. Possibility of uncoupled selection on routine movements and real dispersal movements remains to be evaluated. Careful treatment of behavioural components of mobility within observational and experimental studies of animal dispersal is needed.