Density dependence in rangeland grasshoppers (Orthoptera: Acrididae).
We tested for the existence of density dependence in annual adult rangeland grasshopper (Orthoptera: Acrididae) data from Montana, USA (1951-1991). Statistical density dependence was, in the sense of a stochastic equilibrium or return tendency, detected in all of the grasshopper mean density time-series from the three major physiographic regions of the state, Northern Glaciated Plains, Southern Unglaciated Plains, and Western Mountains. Parameters were estimated for a model that described the stochastic equilibrium characteristics of regional mean densities. The analyses showed that rangeland grasshopper regional densities fluctuate according to gamma distribution with a mean of 6.1-6.3 grasshoppers per m2. Further, when regions exhibit outbreaks, the resulting infestation period (duration of outbreak) is short, spanning only a few generations.
Rangeland Insect Laboratory, USDA Agricultural Research Service, 59717-0366, Bozeman, MT, USA.
William P
WP
Kemp
College of Forestry, Wildlife, and Range Sciences, University of Idaho, 83844, Moscow, ID, USA.
Brian
B
Dennis
Density dependence; Forecasting; Insecta; Logistic growth; Time series