Movement behaviour of woodland caribou at multiple temporal scales.

摘要

I investigated movement by forest-dwelling woodland caribou ( Rangifer tarandus caribou) at multiple temporal scales, to clarify how, when and where they move and to determine the extent to which caribou movement behaviour may be influenced by variation in extrinsic and intrinsic conditions. First, I developed a formal methodology for characterizing annual movements by mobile organisms and applied it to caribou space use patterns to determine whether movement was consistent with round-trip migration or other forms of movement. I also assessed whether annual, regional and individual variation in movement at the annual scale was consistent with a fixed or conditional basis for annual movement patterns. 1tligration was the dominant form of space use at both population and individual scales. While there was limited evidence for partial migration, caribou exhibited considerable annual variation in migration distance, as well as considerable between and within-individual variation in migration distance, consistent with the hypothesis that the migratory behaviour of individual caribou is conditional and strongly influenced by environmental variability. Next, I applied a behaviour-driven approach to evaluate caribou movement behaviour at several spatio-temporal scales (i.e., step, path and range) to determine whether round-trip annual migrations by caribou were produced by seasonal switches in movement behaviour. Net displacement and linearity of caribou movements defined four distinct seasons and three types of movement behaviour: sedentary "station-keeping" in summer and late winter, directed "migration" in spring and exploratory "ranging" in late autumn-early winter. Finally, I looked at the relationship between environmental conditions and caribou movement at the step scale to determine which conditions were most strongly associated with seasonal and within-season variation in caribou movement behaviour and whether variation in the timing and duration of behavioural seasons was more consistent with facultative or obligatory behaviour. Seasonal switches between different types of movement behaviour were associated with changes in photoperiod, snow depth and NDVI (Normalized Difference Vegetation Index), consistent with hypotheses both of "facultative" and "obligatory" changes in behaviour. A substantial influence of variable environmental conditions (i.e., snow depth and NDVI) suggested that caribou movement within seasons was strongly influenced by these factors. In general, at each scale at which behaviour Was examined, caribou movements were consistent with a high degree of facultative responsiveness to immediate experiences of resources and conditions. Consequently, it appears as though stochastic environmental conditions do not just form the evolutionary basis for migratory behaviour, but for woodland caribou, they also exert a strong proximate influence on the movements of migrants at both coarse and relatively fine temporal scales.