DENSITY DEPENDENT FORAGING ON LIATRIS PYCNOSTACHYA.

Abstract

One of the distinguishing features of flowering plants is the reliance of many species on animal vectors, particularly insects, for cross pollination. For an outcrossing entomophilous plant, the behavior of pollinators directly determines the mating relations within a population and strongly affects the overall pattern of gene dispersal (Levin and Kerster, 1974). In their studies of gene dispersal in several entomophilous species, Levin and Kerster (1969a,b) have shown that within a plant population, the pollen component of gene dispersal is non-random and density dependent. Bee pollinator moves on Liatris aspera are predominantly to near-neighbor plants (Levin and Kerster, 1969a). As the distance between the plant near neighbors increases, the flight distance of the pollinators also increases. Thus, at a given density, the probability of two plants crossing is proportional to the distance between them; mating within an entomophilous plant population can conform to an isolation by distance model. When mating in a population is non-random as in some entomophilous plants, the population may become genetically divided into neighborhoods. Studies on genetic structure in the entomophilous species Liatris cylindracea have shown that subdivision does occur and that genetic differentiation conforms to an isolation by distance model (Schaal, 1974, 1975). Since genetic subdivision is known to exist in some entomophilous plant populations, and because, according to Wright (1969) it is an important characteristic that affects the evolutionary potential of a population, further studies of pollinator behavior, particularly the near-neighbor foraging pattern, seem to be warranted. The following is a report of density-dependent near-neighbor foraging of Bombus pennsylvanicus on Liatris pycnostachya.