The difficulty of deducing behavior from resource use: an example from hilltopping in checkerspot butterflies

Resource preferences of individuals cannot be deduced from patterns of resource use at the population level. For example, a particular pattern of resource use can be produced by a variety of preference distributions in an animal population. The strength of the association between resource preference (a behavioral parameter) and resource use (an ecological parameter) detemines the extent to which natural selection acting on resource use translates into selection acting on preference. However, the mechanism underlying the evolution of resource use is the evolution of preference (unless the resource itself is evolving). Therefore, a clear distinction between ecological and behavioral parameters is necessary for any evolutionary prediction. We apply these principles to the use of a particular spatial resource, hilltops, by the butterfly Euphydryas editha. We distinguish between the occupation of a hilltop location (resource use) and preference for these locations, or "hilltopping" behavior. Previous authors estimated that the mating success of male E. editha on a hilltop was lower than that on the slopes below. In consequence, hilltopping by these males was labeled "maladaptive." We argue that the evidence presented by these authors fails to demonstrate (1) that hilltopping behavior occurred, (2) that, if it did occur, it was variable among individuals, and (3) that, if variation of hilltopping was present, it was associated with mating success. Thus, discussion of the evolutionary significance of intrapopulation variation of hilltopping behavior is premature. In our own study of a different population of the same species, we failed to find evidence of hilltopping.