Résumé
1. Dispersal is a key mechanism enabling species to adjust their
geographic range to rapid global change. However, dispersal is costly and
environmental modifications are likely to modify the cost-benefit balance
of individual dispersal decisions, for example, by decreasing functional
connectivity. 2. Dispersal costs occur during departure, transience and
settlement, and are levied in terms of energy, risk, time and lost
opportunity, potentially influencing individual fitness. However, to the
best of our knowledge, no study has yet quantified the energetic costs of
dispersal across the dispersal period by comparing dispersing and
philopatric individuals in the wild.3. Here, we employed animal-born
bio-loggers on a relatively large sample (N = 105) of juvenile roe deer to
estimate energy expenditure indexed using the vector of dynamic body
acceleration (VeDBA) and mobility (distance travelled) in an intensively
monitored population in the south west of France. We predicted that energy
expenditure would be higher in dispersers compared to philopatric
individuals. We expected costs to be i/ particularly high during
transience, ii/ especially high in the more fragmented areas of the
landscape, and iii/ concentrated during the night to avoid disturbance
caused by human activity. 4. There were no differences in energy
expenditure between dispersers and philopatric individuals during the
pre-dispersal phase. However, dispersers expended around 22% more energy
and travelled around 63% further per day than philopatric individuals
during transience. Differences in energy expenditure were much less
pronounced during the settlement phase. The costs of transience were
almost uniquely confined to the dawn period, when dispersers spent 23%
more energy and travelled 112% further than philopatric individuals.
Finally, the energetic costs of transience per unit time and the total
distance travelled to locate a suitable settlement range were higher in
areas of high road density. 5. Our results provide strong support for the
hypothesis that natal dispersal is energetically costly and indicate that
transience is the most costly part of the process, particularly in
fragmented landscapes. Further work is required to link dispersal costs
with fitness components so as to understand the likely outcome of further
environmental modifications on the evolution of dispersal behaviour.