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

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.

Litter Decomposition of Spartina alterniflora and Juncus roemerianus: Implications of Climate Change in Salt Marshes

“…Insects also affect salt marsh biomass, at least in some cases (Bertness et al 1987, Bertness and Shumway 1993, Daehler and Strong 1995, Daehler and Strong 1996. Insects reduced biomass in eutrophic but not pristine New England salt marshes .…”

Frugivory by insects on mangrove propagules: effects on the early life history of Avicennia marina

“…Consequently, herbivory on propagules before they disperse from the parental plant can be an important factor limiting the supply of propagules and recruitment of seedlings (e.g., Louda and Potvin 1995). Although mostly documented for plants in terrestrial habitats (Crawley 1989(Crawley , 1992Louda 1989), herbivory by insects may also be an important factor structuring populations of plants in marine habitats such as salt marshes (Bertness et al 1987) and mangrove forests (Robertson 1991).…”

Seed production, germination rate, and seedling establishment ofScirpus pungens in tidal brackish marshes

“…Shumway and Bertness (1992) have also observed that increasing salinity inhibits germination and emergence of Juncus gerardi Loisel. Bertness et al (1987) have reported that insect herbivory on flowers and seeds of Spartina alterniflora Loisel., S. patens (>,it.) Miihl., Distichlis spicata L., and J. gerardi dramatically reduced seed production.…”