RAMHSS: Effects of Bird Predation and Interspecific Competition on Grasshoppers: A Field Experimental Study

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Predation and interspecific competition can interact to determine the distribution and abundance of species, but such interactions rarely have been studied experimentally in terrestrial ecosystems. Dactylotum is an abundant grasshopper in the grasslands of southeastern Arizona. It also is gaudily- colored, apparently distasteful, and immune from predation by birds. Other common grasshoppers in the proposed study area comprise the major prey of breeding birds. They also potentially compete with Dactylotum for food and habitat. Preliminary data indicate that birds can have a significant impact on grasshopper populations, and that Dactylotum populations can be manipulated effectively in the field. Replicated plots on a grassland preserve in southeastern Arizona will be used to exclude 1) birds, or 2) Dactylotum, or 3) both, or 4) neither. Grasshopper densities will be measured on the plots from July to October for one pre-treatment and three post-treatment years. Results will test hypotheses about the independent and interactive effects of bird predation vs. interspecific competition upon the abundances of grasshoppers in this semidesert grassland. Drs. Jane and Carl Bock will work jointly on these experiments. Their excellent research records assure a productive endeavor.