Climate and the Prediction of Reproduction of Three Ungulate Species

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Abstract
The Lamb climate index was used to compare temperature and precipitation data to long term population data concerning wapiti (Cervus elaphus), mule deer (Odocoileus hemionus) and bighorn sheep (Ovis canadensis). Significant correlations between survival of young and climate were found for all 3 spp. The intensity of the climate effect was dependent upon the size of the population relation to carrying capacity (K). The wintering wapiti population was negatively correlated with the survival of bighorn sheep lambs. The temperature and precipitation over an 18 mo. period was important to the recruitment of young in both cervid species. Bighorn sheep integrated climate over a 12-mo. period, with precipitation being of prime importance to the survival of lambs. These differences, in the response to elimate, are probably related to the evolutionary history and modern geographical distribution of the species. Wapiti calf/cow ratios were correlated with the 2-yr moving hunting harvest totals at population levels below carrying capacity (K). Winter snow pack was relevant to the survival of bighorn sheep lambs, and to a lesser degree, to mule deer fawns. The results of several predictive methods were compared. Two climate based and one hunting harvest based predictions gave superior results. These point forecasts of the young to adult ratios had mean absolute errors ranging from 7.1-14.9% of the long term mean and had the highest percentage of correct trend forecasts.

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