Postdispersal Seed Predation in Lomatium Spp. (Umbelliferae): Variation among Individuals and Species

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Abstract
A series of experiments in the steppe of eastern Washington and the laboratory was designed to test the hypothesis that postdispersal seed predators can distinguish among conspecific seeds derived from different plants within a population as well as between seeds of congeneric species within a community. Lomatium (Umbelliferae) seeds are eaten by ground—foraging beetles and mammals after the seeds are dispersed by wind from the plants. Field experiments showed that removal of L. dissectum seeds from seed piles was faster than removal of L. triternatum seeds in both single—species and mixed—species piles. Removal of seeds from 5—seed piles did not differ from removal from 10—seed piles. In piles containing seeds from different L. dssectum plants in the same population, seeds from certain plants were removed significantly faster than those from others. Laboratory trials using adult Eleodes nigrina beetles confirmed that plants in the L. dissectum population differed consistently in the palatability of their seeds. Beetles ate the entire seed when chewing on seeds of some plants but consistently ate only the wing surrounding the seeds of other plants, leaving the embryo and endosperm intact and viable. These results indicate that (1) postdispersal seed predators can distinguish among congeneric and even conspecific Lomatium seeds, (2) the shape of survivorship curves for the seed stage can depend upon the proximity of congeneric seeds and the mix of conspecific phenotypes (potentially genotypes) in seed piles, and (3) outcomes of interactions with E. nigrina beetles make it inaccurate to give this interaction a single typological label, since the interaction ranges from predation to commensalism among Lomatium plants within a population.