Dispersal range analysis: quantifying individual variation in dispersal behaviour

Abstract

A complete understanding of animal dispersal requires knowledge not only of its consequences at population and community levels, but also of the behavioural decisions made by dispersing individuals. Recent theoretical work has emphasised the importance of this dispersal process, particularly the phase in which individuals search the landscape for breeding opportunities. However, empirical advances are currently hampered by a lack of tools for quantifying these dispersal search tactics. Here, we review existing methods for quantifying movement that are appropriate for the dispersal search process, describe several new techniques that we developed for characterising movement and behaviour through an individual's dispersal range, and illustrate their use with data from Australasian treecreepers (Climacteridae). We also describe how the quantitative parameters we discuss are calculated in a freely available computer software package that we designed. Specifically, we present methods for calculating the area searched during dispersal, search rate, thoroughness, intensity, philopatry of search, timing of exploration, and surreptitiousness. When we applied this approach to the study of dispersal in treecreepers, we found that search area, philopatry and timing of exploration showed the greatest individual variation. Furthermore, search area, search rate, thoroughness and philopatry of search were all correlated, suggesting they may be useful parameters for further research on the causes and consequences of different dispersal search tactics. Finally, we make recommendations for modifying radiotracking protocols to facilitate more accurate assessment of individual variation in the dispersal process, and suggest future directions for this type of empirical work at the interface of population and behavioural ecology.

The Combined Effects of Remnant Vegetation and Tree Planting on Farmland Birds

“…For example, several studies have raised concerns about the decline of the Brown Treecreeper and highlighted problems with the dispersal ability of the species (Walters et al 1999;Doerr & Doerr 2005). We identified a strong positive relationship between the remnant native-vegetation index and the probability of occurrence of the Brown Treecreeper (Table 2).…”

Dispersing brush mice prefer habitat like home

“…This discrepancy in results occurred because animals that did not venture far from home had a much higher a priori probability of settling within natal habitat than did animals that moved across long distances prior to selecting a new habitat; as a result, the individual test was much more conservative than the landscape test. Given growing evidence of considerable inter-individual variation in movement behaviour in a wide range of species ( Fraser et al 2001;Diffendorfer et al 2005;Doerr & Doerr 2005;Sheppard et al 2006), our results imply that researchers who do not consider individual differences in movement patterns when estimating habitat availability may inadvertently find stronger support for NHPI than is warranted. Other researchers have investigated NHPI in free-living mammals (i.e.…”

“…Throughout this study, we use 'dispersal' to refer to the complete process of dispersal (including departure from the natal area, search and settlement in an adult home range; Bowler & Benton 2005;Doerr & Doerr 2005), rather than a movement of a particular distance. We apply this terminology due to the increasing recognition that in many species (including brush mice), dispersal is not necessarily a single movement between natal and breeding sites (Bowler & Benton 2005;Doerr & Doerr 2005). Rather, dispersal is a process that may occur over a period of days, weeks or even longer periods, and includes the movements of juveniles prior to selecting a place to settle.…”

Animal movement in dynamic landscapes: interaction between behavioural strategies and resource distributions

“…Rather, it is more likely that variability results from individuals making different choices about how to interact with resource distributions. Factors such as breeding status, energy reserve dynamics, competition, predation risk and experience may influence those choices, making any given movement pattern a complex, condition-dependent behavioural strategy (Conradt et al 2003;Doerr and Doerr 2005;Lima 1999, 2005). Moreover, there is evidence that differences in past experience may combine with spatial memory to create differences in current movement patterns (Sheppard et al 2006;Klaassen et al 2007), providing access to resources beyond the immediate perceptual range of the individual.…”