Emeritus Professor Univ. of Idaho Moscow, Idaho, United States
Abstract: Are greater sage-grouse (Centrocercus urophasianus) populations cyclic? Visual inspection of 30 populations and metapopulations reconstructed from lek counts suggests that 10 show regularity of population increases and decreases commonly described as cycles. I evaluated the Snake-Salmon-Beaverhead Management Zone metapopulation of Southern Idaho and Northern Nevada statistically to test for the presence of cyclic changes in abundance. This metapopulation shows a statistically significant 8-9 year cycle of population changes imposed on a 90% long-term decline in numbers from 1965 to 1993. I used information theoretic approaches to linear models of annual rates of change over this 28-year period to test a series of hypotheses concerning the underlying causes of changes in this population: time lags in density dependence, drought, sunspots effects on soil moisture, cumulative fires across the sage-brush steppe and indices to jack rabbit and coyote population abundances. The best model based on 5 statistically significant predictors explained 67% of the variation in annual rates of change in sage-grouse numbers across this metapopulation and provided rough estimates of the relative magnitude of each predictor’s impact. How will cyclic population changes in sage-grouse challenge sage-brush ecosystem managers and researchers in developing future management actions to recover this popular gamebird indicative of ecosystem integrity in the increasingly impacted sage-brush steppe facing increased rural development, expanding oil and gas production, impact of climate change on drought and fire regimes also impacted by invasive exotic plants?
