Sammendrag
Intra-specific variability in movement behaviour occurs in all major taxonomic groups. Despite its common
occurrence and ecological consequences, individual variability is often overlooked. As a result, there is a persistent gap in knowledge about drivers of intra-specific variability in movement and its role in fulfilling life history requirements. We apply a context-focused approach to bull sharks (Carcharhinus leucas), a highly mobile marine
predator, incorporating intra-specific variability to understand how variable movement patterns arise and how
they might be altered under future change scenarios. Spatial analysis of sharks, acoustically tagged both at
their distributional limit and the centre of distribution in southern Africa, was combined with spatial analysis of
acoustically tagged teleost prey and remote-sensing of environmental variables. The objective was to test the
hypothesis that varying resource availability and magnitude of seasonal environmental change in different locations
interact to produce variable yet predictable movement behaviours across a species’ distribution. Sharks from both
locations showed high seasonal overlap with predictable prey aggregations. Patterns were variable in the centre of
distribution, where residency, small- and large-scale movements were all recorded. In contrast, all animals from the distributional limit performed ‘leap-frog migrations’, making long-distance migrations bypassing conspecifics in the
centre of distribution. By combining multiple variables related to life history requirements for animals in different
environments we identified combinations of key drivers that explain the occurrence of differing movement
behaviours across different contexts and delineated the effects of environmental factors and prey dynamics on
predator movement. Comparisons with other taxa show striking similarities in patterns of intra-specific variability
across terrestrial and marine species, suggesting common drivers.
Animal movement, Context, Intra-specific variability, Resource availability, Bull sharks, Birds, Marine
predators, Environmental change
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