Understanding scales of movement: animals ride waves and ripples of environmental change

Summary1. Animal movements are the primary behavioural adaptation to spatiotemporal heterogeneityin resource availability. Depending on their spatiotemporal scale, movements have been catego-rized into distinct functional groups (e.g. foraging movements, dispersal, migration), and havebeen studied using different methodologies. We suggest striving towards the development of acoherent framework based on the ultimate function of all movement types, which is to increaseindividual fitness through an optimal exploitation of resources varying in space and time.2. We developed a novel approach to simultaneously study movements at different spatiotem-poral scales based on the following proposed theory: the length and frequency of animalmovements are determined by the interaction between temporal autocorrelation in resourceavailability and spatial autocorrelation in changes in resource availability. We hypothesizedthat for each time interval the spatiotemporal scales of moose Alces alces movements corre-spond to the spatiotemporal scales of variation in the gains derived from resource exploita-tion when taking into account the costs of movements (represented by their proxies, forageavailability NDVI and snow depth respectively). The scales of change in NDVI and snowwere quantified using wave theory, and were related to the scale of moose movement usinglinear mixed models.3. In support of the proposed theory we found that frequent, smaller scale movements weretriggered by fast, small-scale ripples of changes, whereas infrequent, larger scale movementsmatched slow, large-scale waves of change in resource availability. Similarly, moose inhabit-ing ranges characterized by larger scale waves of change in the onset of spring migratedlonger distances.4. We showed that the scales of movements are driven by the scales of changes in the netprofitability of trophic resources. Our approach can be extended to include drivers of move-ments other than trophic resources (e.g. population density, density of related individuals,predation risk) and may facilitate the assessment of the impact of environmental changes oncommunity dynamics and conservation.Key-words: Alces alces, foraging, Fourier transform, GPS, migration, NDVI, phenology,resource, spatiotemporal scales, snowIntroduction