PARENT SESSION
Oral Session #6: Insect Population and Community Ecology: Interactions, foodwebs.
Presiding: M. Hunter
Monday, August 5. 8:00 AM to 11:30 AM. Apache Meeting Room, TCC.
Resource limitation in a generalist grasshopper: the importance of resource abundance and diversity .
Suttle, Blake*,1, Sapp, Joseph1, Power, Mary1, 1 University of California, Berkeley, Berkeley, CA
ABSTRACT- We investigated resource limitation influences on the generalist grasshopper Melanoplus devastator in a northern California meadow community to assess the importance of resource limitation and the advantages of polyphagy for this species. In replicate field cages we manipulated the abundance and breadth of forage available to M. devastator nymphs and monitored growth, development, and survival over fifty days. Resource biomass had little effect on any biotic response measured. In contrast, resource composition had marked effects on grasshopper performance. Nymphs reared on mixed-resource, annual forb, or perennial forb diets showed significantly higher growth, development, and survival than those reared on annual or perennial grasses. Surprisingly, a diet consisting exclusively of the annual forb Trichostema lanceolatum maximized grasshopper growth relative to all other treatments, including a mixed diet containing T. lanceolatum. Grasshoppers in cages containing this single resource may have profited from an inability to choose among plant species, as those in mixed cages foraged on the less nutritive grasses in addition to forbs. The grasshoppers' improved performance on T. lanceolatum, a plant which is highly unapparent in space and time, suggests that polyphagy may have evolved in M. devastator primarily as a bet-hedging strategy rather than a means by which to maximize nutrient balance or dilute harmful plant secondary compounds.
KEY WORDS: polyphagy, resource limitation, California grassland, Melanoplus devastator