Foraging in nature: contrasting responses to resource heterogeneity at small and large spatial scales.

A key problem faced by foragers is how to forage when resources are
distributed heterogeneously in space. This heterogeneity and associated
trade-offs may change with spatial scale. Furthermore, foragers may also
have to optimize acquiring multiple resources. Such complexity of
decision-making while foraging is poorly understood. We studied the
butterfly Ypthima huebneri to examine how foraging decisions of adults are
influenced by spatial scale and multiple resources. We predicted that, at
a small-spatial scale, the time spent foraging in a patch should be
proportional to resources in the patch, but at large-spatial scales, due
to limitations arising from large travel costs, this relationship should
turn negative. We also predicted that both adult and larval resources
should jointly affect foraging butterflies. To test these predictions, we
laid eleven plots, and sub-divided them into patches. We mapped nectar and
larval resources and measured butterfly behavior in these patches and
plots. We found that adult foraging behavior showed contrasting
relationships with adult resource density at small versus large-spatial
scales. At the smaller-spatial scale, butterflies spent more time feeding
in resource-rich patches, whereas at the large-scale, butterflies spent
more time feeding in resource-poor plots. Furthermore, both adult and
larval resources appeared to affect foraging decisions, suggesting that
individuals may optimize search costs for different resources. Overall,
our findings suggest that the variation in foraging behavior seen in
foragers might result from animals responding to complex ecological
conditions, such as, resource heterogeneity at multiple spatial scales and
the challenges of tracking multiple resources.