Do Spur-Throated Grasshoppers, Melanoplus spp. (Orthoptera: Acrididae), Exert Top-Down Control on Smooth Cordgrass Spartina alterniflora in Northern New England?
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Recently, strong top-down (consumer) control of cordgrass (Spartina alterniflora) has been demonstrated. Here, we manipulated the densities of cordgrass consumers, acridid grasshoppers (Melanoplus bivittatus and Melanoplus femurrubrum), to examine their impact on cordgrass in the Plum Island Estuary (PIE), MA, USA. After 1 month, there was no detectable effect of grasshopper density on S. alterniflora biomass and grasshoppers at the highest densities (34 individuals per square meter) consumed only ~14% of the standing stock biomass. However, significant impacts of grasshopper density on grazing damage were seen. For example, plant damage and scarring length increased by 160% and 6,156%, respectively, at the highest grasshopper densities relative to exclusion (zero grasshoppers) densities. Plant height was significantly reduced with increasing grasshopper densities, although this may be a function of leaf tip removal instead of reduced plant growth. No other strong consumers of cordgrass (e.g., Littoraria irrorata, Prokelisia marginata) were observed in PIE and we suggest that consumer regulation of cordgrass is weak in this system.
KeywordsSpartina alterniflora Top-down control Chewing insects Melanoplus spp. Acridid grasshoppers Salt marsh
We thank C. Kennedy and C. E. Goranson for field assistance. J.W. Fleeger, M.A. Grippo, K.A. Galván, R. S. Warren, and three anonymous reviewers provided helpful manuscript comments. This work was supported in part by the National Science Foundation under Grants No. 0213767 and 9726921.
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