부산대학교 도서관

ABSTRACT Nebraska's agricultural landscape underwent dramatic changes during the last half of the 20th century. Since 1986, the Conservation Reserve Program (CRP) has led to an increase in grassland cover, but pheasant ( Phasianus colchicus) populations have been decreasing for decades. We hypothesized that if the CRP positively affected pheasant populations in Nebraska, USA, we should see effects reflected in pheasant population trend data. Thus, we examined one of the longest-running population time-series data sets in Nebraska, the rural mail-carrier survey. We averaged pheasant counts annually over the entire state during 1951-2007. We fit 4 simple demographic models to the statewide population abundance index and used information-theoretic methods to select the model with the most support. We found strong evidence that a logistic model with a 2-period decline (transition year of 1986 based on optimization) in carrying capacity described the data better than all other models (e.g., AIC c wi = 0.99). This model indicated an annual decline in our population index of approximately 15% until 1986, but then a slower annual decline of approximately 5% after 1986. The transition year (1986) corresponded with the date of implementation of the CRP. No other known effect occurred near the transition year and there is no evidence that other potential factors (e.g., disease, changes in predator communities) contributed to large-scale population declines during our study. The introduction of the CRP may have positively affected pheasant populations, but the effects are so far insufficient to reverse the decline of pheasants in Nebraska. © 2015 The Wildlife Society. [ABSTRACT FROM AUTHOR]