DENSITY-DEPENDENT POLLINATOR FORAGING, FLOWERING PHENOLOGY, AND TEMPORAL POLLEN DISPERSAL PATTERNS IN LINANTHUS BICOLOR.

Abstract

Gene flow in flowering plant populations occurs through the dispersal of pollen and seeds. In animal-pollinated plants, the foraging behavior of pollinators can affect the distance and frequency of pollen transfer between and within plants, and thus can have an important impact on gene dispersal and outcrossing potential (Levin, 1979a, 1979b). The distribution of gene dispersal distances, the rate of outcrossing and the density of reproductive individuals in a population determine the size of a genetic neighborhood, in the sense of Wright's (1943, 1946) isolation by distance model. In general, as neighborhood size and area increase, a population's evolutionary potential for microgeographic genetic differentiation will diminish (Wright, 1943, 1946). Several authors have estimated neighborhood size and area by using pollen dispersal distances inferred from pollinator flight patterns (Kerster and Levin, 1968; Levin and Kerster, 1968, 1969; Schaal and Levin, 1978; Beattie, 1979; Beattie and Culver, 1979; Schmitt, 1980a, 1980b; Waser, 1982; Zimmerman, 1982). Recent studies of artificial populations indicate, however, that actual gene flow may often be more extensive than that estimated from pollinator movements (Schaal, 1980; Levin, 1981; Ennos and Clegg, 1982; Handel, 1982). These findings probably result from the carryover of pollen on a pollinator's body from a given plant successively to many other plants (Thomson and Plowright, 1980; Morse, 1982; Price and Waser, 1979, 1982; Waser