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9/28/2018 | 9:20 AM - 9:35 AM | Evaluating Seasonal Weather and Density as Factors Regulating Populations of Alpine-Endemic White-tailed Ptarmigan in Colorado | Eccles Conference Center Auditorium

Evaluating Seasonal Weather and Density as Factors Regulating Populations of Alpine-Endemic White-tailed Ptarmigan in Colorado

The role of intrinsic and extrinsic factors in population regulation is a long standing question in ecological studies, and effects such as density-dependence and climate are known to be important drivers of variation in abundance for many species. Interactions between these effects may be particularly important, but the type of datasets needed to detect such interactions are rare. We used two 51-year datasets for white-tailed ptarmigan in Colorado to investigate the role of climate and density on population regulation. We constructed an integrated population model (IPM) that used three sources of population data: 1) population counts, 2) capture-recapture data, and 3) the number of fledgling chicks produced per female. The IPM allowed us to estimate survival of chicks to their first spring (i.e., juvenile survival), in addition to providing a framework for examining density and climate effects on different demographic groups for which we had explicit data. We found support for negative density dependence in juvenile and breeding-age survival. Average minimum winter temperature was more strongly related to breeding-age survival than winter precipitation, and the effect was strongest at high densities. Growth estimates from the IPM indicated that one population increased an average of 2% per year while the other population declined by 3% per year. The declining population was attributed to reduced fecundity, which decreased sharply during the first few decades of the time series. Our results indicate density effects are present in white-tailed ptarmigan, and climate alone is not a particularly useful measure for predicting future viability of our populations when density is not also considered.

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Presenters/Authors

Cameron Aldridge (), United States Geological Survey, aldridgec@usgs.gov;