Search

Although inter‐individual heterogeneity in many aspects of dispersal behaviour is widely reported, this key life‐history trait is predominantly modelled as a dichotomous state of philopatry versus dispersal. The increasing body of evidence for dispersal syndromes (i.e. a suite of correlated morphological, behavioural and life‐history traits associated with dispersal) implies substantial but, to date, undocumented individual heterogeneity in behavioural tactics during dispersal. Using a large sample (n = 154) of GPS monitored juvenile roe deer Capreolus capreolus, we evaluated among‐individual behavioural heterogeneity in dispersal tactics, and the individual and environmental drivers of these alternative tactics. We developed a sequential three‐stage decision tree based on space use stability, exploration events and the directionality of movement. We identified six discrete alternative behavioural tactics during the dispersal period which were characterised by different timing, amplitude and duration in movement: slightly less than half of the deer were sedentary, either 'strictly philopatric' or 'explorers', which subsequently settled on their natal range; around 40% dispersed ('classic dispersal'), of which, one in six subsequently aborted, moving back to their natal range ('aborted dispersal'); finally, around 15% expressed either a 'progressive dispersal' tactic, gradually moving away from their natal area to settle elsewhere, or a 'multi‐range' tactic. The propensity to express an alternative dispersal tactic was strongly influenced by an individual's local environment. In particular, when landscape heterogeneity, resource quality and human‐related disturbance in the natal range were low, individuals were 1) more likely to adopt the alternative tactics of either progressive dispersal or multi‐ranging, but 2) also more likely to abort their dispersal attempt. Our work indicates that natal dispersal is likely not a single uniform behaviour, but that individuals may adopt a variety of alternative movement tactics which are likely governed by different selection pressures, with potentially important impacts for population dynamics and functioning. [ABSTRACT FROM AUTHOR]

Dispersal is a key life-history trait governing the response of individuals, populations and species to changing environmental conditions. In the context of global change, it is therefore essential to better understand the respective role of condition-, phenotype- and genetic-dependent drivers of dispersal behaviour. Although the importance of immune function and pathogen infestation in determining patterns of dispersal is increasingly recognised, no study to our knowledge has yet investigated the influence of immune gene variability on dispersal behaviour. Here, we filled this knowledge gap by assessing whether individual heterozygosity at five immune gene loci (one from the Major histocompatibility complex and four from encoding Toll-like receptors) influences roe deer natal dispersal. We found that dispersal propensity was affected by immune gene diversity, suggesting potential pathogen-mediated selection through over-dominance. However, the direction of this effect differed between high and low quality individuals, suggesting that dispersal propensity is driven by two different mechanisms. In support of the condition-dependent dispersal hypothesis, dispersal propensity increased with increasing body mass and, among high quality individuals only (standardized body mass > 18 kg), with increasing immune gene diversity. However, among poor quality individuals, we observed the opposite pattern such that dispersal propensity was higher for individuals with lower immune gene diversity. We suggest that these poor quality individuals expressed an emergency dispersal tactic in an attempt to escape a heavily infested environment associated with poor fitness prospects. Our results have potentially important consequences in terms of population genetics and demography, as well as host-pathogen evolution. [ABSTRACT FROM AUTHOR]

Non-consumptive effects of predators result from the cost of responses to perceived risk. Prey modulate risk exposure through flexible habitat selection at multiple scales which, in interaction with landscape constraints, determines their use of risky habitats. Identifying the relative contributions of landscape constraints and habitat selection to risk exposure is a critical first step towards a mechanistic understanding of non-consumptive effects. Here, we provide an integrative multi-scale study of roe deer spatial responses to variable hunting pressure along a landscape gradient of open habitats and dispersed refuges. Between low-risk and high-risk periods, we investigated shifts in 1) home-range location, 2) probability of using risky habitats (between-habitat scale) and 3) distance to the nearest refuge (within-habitat scale). For 2) and 3), we disentangled the contributions of landscape constraints and habitat selection to risky habitat use. We found that when risk was high, roe deer did not shift their home-range, but generally decreased their use of risky habitats, and sometimes reduced their distance to cover (particularly older animals). There was a functional response in between-habitat selection, with animals living in more open landscapes responding more than those living in landscapes with more refuges. However, individuals living in more open landscapes avoided open risky habitat less. Finally, we found that among-individual variation in risk exposure was generally, but not always, minimized by habitat selection across gradients of landscape constraints. To our knowledge, this is the first study simultaneously documenting prey responses to risk at the within-habitat, between-habitat and home-range scales. Our results support the view that between-habitat selection acts at a higher hierarchical level than within-habitat selection, and provide a framework for disentangling the contributions of habitat selection and landscape constraints to risk exposure. Selection cannot always compensate for landscape constraints, indicating a need for further investigation of the processes underlying habitat selection. [ABSTRACT FROM AUTHOR]

Parasite abundance has been shown to have major consequences for host fitness components such as survival and reproduction. However, although natal dispersal is a key life history trait, whether an individual's decision to disperse or not is influenced by the abundance of parasites it carries remains mostly unknown. Current and opposing hypotheses suggest that infected individuals should either be philopatric to avoid the energetic costs of dispersal (condition dependence) or disperse to escape from heavily parasitised habitats. From intensive monitoring of a roe deer population inhabiting a multi-use and spatially heterogeneous agricultural landscape, we evaluated the link between an individual's parasite abundance and its propensity to disperse, while accounting for confounding effects of body mass. Dispersal propensity generally decreased with both increasing nematode abundance and with decreasing body mass. Within the dispersing segment of the population, individuals with high nematode abundance left their natal home range later in the season than less parasitised deer. These results clearly show that parasite abundance is an important component of condition-dependent dispersal in large herbivores. However, unexpectedly, three individuals that were both heavily parasitised and of low body mass dispersed. We suggest that this 'leave it' response to high parasite levels in the natal habitat could represent a last ditch attempt to improve reproductive prospects, constituting a form of emergency life history strategy. [ABSTRACT FROM AUTHOR]