Foraging in nature: Contrasting responses to resource heterogeneity at small- and large-spatial scales

摘要

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 butterflyYpthima huebnerito 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.