Consumer pressure and seed set in a salt marsh perennial plant community

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Abstract
Seed predation can be an important determinant of plant success, but has received little attention in wetland plant communities. Here, we examine the role of flower and seed predators in limiting the seed production of the dominant perennial plants in a salt marsh plant community. Of the four perennial investigated, direct ovule loss to consumers ranged from 51 to 80%, resulting in seed set reductions ranging from 50% to over 20-fold. Most losses were due to generalist grazing by the grasshopper, Conocephalus spartinae. More species-specific losses were inflicted by planthoppers, and microlepidopteran and dipteran larval seed parasites. Insect abundance and consumer pressure on flowers and seeds increased over the early summer, peaked in the middle of July, and declined through August, and this temporal pattern was reflected in the natural consumer damage incurred by each of the marsh perennials. Juncus gerardi flowers earlier than other marsh perennials and largely escapes heavy consumer losses. Spartina patens and Distichlis spicata flower in the middle of the summer during the peak consumer activity and incur extremely heavy seed losses. Spartina alterniflora flowers late in the summer as consumer pressure is subsiding, which appears to minimize its seed loss. In addition to destroying seeds directly, consumers also markedly reduce the frequency and affect the timing of sexual expression in these plants. In particular, predation drastically reduces the frequency of male flowers, which could lead to pollen limitation of seed set. Intense flower and seed predation on these marsh perennials may be an important determinant of the success of marsh plant populations as well as a potent selective force on their flowering phenologies and reproductive effort.