Tuesday, August 7, 2007

PS 35-170: Gradients of grasshopper species composition and size in Atlantic coast salt marshes

Elizabeth L. Wason and Steven C. Pennings. University of Houston

Changes in species composition can alter the way otherwise similar communities function.  Although grasshoppers are a common salt marsh herbivore, we know little about geographic variation in their species composition.  Tettigoniids (N=740 adults) were collected from the Spartina alterniflora zone of 31 Atlantic Coast salt marsh sites across a latitudinal range of 13.19 degrees (Florida to Maine), with an additional 52 individuals collected from the Juncus roemerianus zone of low-latitude marshes for comparative purposes.  Eight species were collected, but some were common only at a few sites, or rare throughout the entire collection range.  The tettigoniid community was dominated by Orchelimum fidicinium at low latitudes and Conocephalus spp. at high latitudes.  Several factors might explain this shift, including changes in climate, plant phenology, and plant zonation patterns.  Because Orchelimum fidicinium readily eats grasses, while Conocephalus spp. mainly consume seeds and flowers, geographic variation in species composition of grasshoppers may help explain documented patterns of geographic variation in plant palatability and plant-herbivore interactions.  Grasshopper body size followed the Converse to Bergmann’s Rule.  In three of the four most common tettigoniid species, body size significantly decreased with increasing latitude (the fourth species showed a trend toward the same pattern).  Thus, larger body size at low latitudes could also help explain the increase in herbivore pressure on plants at low latitudes.  Finally, because it can be difficult to identify tettigoniids to species, we present a guide to aid future workers in identifying the tettigoniid species common in Atlantic Coast salt marshes.

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