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Individual Differences, Parasites, and the Costs of Reproduction for Bighorn Ewes (Ovis canadensis)
Journal of Animal Ecology
Vol. 58, No. 3 (Oct., 1989), pp. 785-795
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/5124
Page Count: 11
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(1) The consequences of reproduction for subsequent survival and reproductive success of individually marked bighorn ewes (Ovis canadensis) were examined over 8 years in south-western Alberta, Canada. (2) Ewes that raised sons did not experience a decrease in reproductive success the following year, but their faecal output of lungworm (Protostrongylus spp.) larvae increased relative to ewes that raised daughters. (3) Ewes were seldom known to produce sons in consecutive years. Because lamb sex was not determined at birth, this result could be explained by either an alteration of the birth sex ratio, or differential mortality of sons born in the year after their mother had produced a son. (4) Ewes that lactated at 2 years of age appeared to be in better condition, and were more likely to lactate at 3 years of age, than ewes that did not lactate at 2 years. Overall, reproductive success in one year did not aversely affect reproduction the following year. (5) Lactating ewes had greater faecal counts of lungworm larvae than non-lactating ewes. Ewes that had produced a lamb at 2 years of age were more likely to die during a pneumonia epizootic than ewes that had not lambed at 2 years. A decrease in resistance to parasites and pathogens appears to be a consequence of reproduction.
Journal of Animal Ecology © 1989 British Ecological Society