Efecto de la interferencia parcial en la depredación natural sobre una comunidad de acrídidos en un pastizal del Desierto Chihuahuense.

Perturbation on natural predation in a driest year (1988) on eight grasshopper species assembly during an outbreak of one of them (Boopedon nubilum) in a toboso arid grassland in Chihuahuan Desert was analyzed. We used a four blocks trial with a treatment (predators’ decreased) and a control. Predators recorded were five mammals, five reptiles, two amphibians, 20 birds, six diurnal Insects, six spiders and four nocturnal arthropods. The vertebrate predators presence (principally raptors) inhibited invertebrate predators action, the most important predators were birds. Results showed no significative effect of date and treatment on grasshopper density (pooled data). The effect of predation on the most abundant grasshopper species (B. nubilum) was observed, changing the species composition of the assembly and the use of plant stratification by grasshoppers. The graminicole species showed an escape strategy of jumping between grasses, tussocks, bunches or to bare soil, or only keep down into the grass, using this strategy, vulnerability (detection risk by predators) depends on their coloration and final position adopted to avoid predators. The short time effect results were due by short time response in treatment add to the predation satiation phenomena by over offer of meal in this specific patch by the outbreak grasshopper species. Where control and treatment showed clearly negative tendency on the population records of B. nubilum and a natural effect of predation, but our statistical analysis showed no significative differences, suggesting it is more adequate to do this kind of trials, considering a larger remotion of predators and monitoring and evaluating on next generation of grasshopper species.