Ecological Economics of Foraging Among Coevolving Animals and Plants

Abstract

papers presented in this symposium focus on the reciprocity between plants and their associated fauna. Some studies approach plant-pollinator interactions at generic or familial levels and treat distributions over broad expanses of evolutionary time (e.g. Beattie, Gentry, and Ramirez). Others examine selected habitats and community interactions on ecological time scales (e.g. Ayensu, Heithaus, Macior, and Strong). Generally, one goal is to document specific boundaries which allow definition of floral resources relative to specific faunal consumers. I want to relate some of these new findings to recent research on consumer switching between alternative food resources. Early studies of pollination did not consider the gathering of pollen and nectar as generalized modes of foraging, but Robertson (1899) did recognize the similarity when he stated, The relations of the host-bees to the flowers from which they get pollen are quite analogous to the relations of parasites to their hosts, of phytophagous insects to their food plants, or of predaceous insects to the insects upon which they feed .... Pollination ecologists currently use terminologies and classifications for describing pollinator behavior which are different from those applied to predatory behavior, but there is a continued recognition of the general similarity between these distinct types of foraging. For instance, a pollinator which visits a single plant species for pollen and nectar is termed monotropic, and Faegri and Pijl (1971) comment, similar to Robertson, that its relation to the blossom is more or less on the lines of a host-parasite relationship. Michener (1954) has also noted that bees which collect pollen from a few kinds of flowers (termed oligolecty) represent a form of host specificity (for a review of these terms seeLiusley, 1959). Yet, there has been little attempted transfer of methodologies from related studies on selective predation to the techniques used for studying selective pollination. In the following discussion, I propose an extension of a measure that I have recently developed for determining rate of resource substitutability among selective consumers (Covich, 1972a) to studies of pollinator energetics. Before discussing these points, I want to compare plant-pollinator and preypredator interactions. By definition, a pollinator is a dispersal agent for highly specialized pollen grains which transmit genetic information and produce sexual recombination and heterozygosis. Being direct links in the reproductive pathways of many flowering plants, pollen transporters have a strong influence on floral evolution and are tightly coupled to development of complex morphological and biochemical adaptations. Predators also have a direct effect on their prey populations, but predation (in the strict sense) can have a less intense impact if non-reproductive individuals (immature, weakened, or senescent com-