Body condition and pregnancy in northern Yellowstone elk: evidence for predation risk effects?
Body condition and pregnancy in northern Yellowstone elk: evidence for predation risk effects?
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北黄石麋鹿的身体状况和怀孕：捕食风险影响的证据？
DOI：
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发表时间：
2011
影响因子：
5
通讯作者：
Julie A. Cunningham
中科院分区：
文献类型：
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作者：
P. J. White;R. Garrott;K. Hamlin;R. Cook;J. Cook;Julie A. Cunningham
S. Creel等人报告了粪便孕酮浓度与较大黄石麋鹿（Cervus elaphus）群中麋鹿：狼比率之间的负相关性，并将此相关性解释为麋鹿妊娠率在狼（Canis lupus）存在下大幅下降的证据。显然，假设的机制是，减少饲料摄入量降低身体状况，导致麋鹿在秋季发情期间无法怀孕或麋鹿在冬季失去胎儿。我们通过比较北方黄石麋鹿（Creel等人采样的鹿群之一）的年龄特异性身体状况（无摄入体脂百分比）和怀孕率来验证这一假设，之前（1962-1968年）和之后（2000-2006年）狼恢复使用的指数开发和校准落基山麋鹿。在这两个时期，雌性麋鹿的平均年龄调整后体脂百分比相似（狼前9.0%-0.9%;狼后8.9%-0.8%）。估计怀孕率4-9岁麋鹿的妊娠率（母鹿妊娠率）狼前为0.91，狼后为0.87（差异的95% CI = -0.15至0.03，P = 0.46）和> 9岁麋鹿狼前和狼后分别为0.64和0.78（差异的95% CI = -0.01至0.27，P = 0.06）。因此，这些数据中几乎没有证据支持狼的存在对麋鹿怀孕的强烈影响。我们警告说，在依赖捕食者如何影响怀孕率的间接措施之前，应该考虑多条证据和/或强有力的验证。
S. Creel et al. reported a negative correlation between fecal progesterone concentrations and elk:wolf ratios in greater Yellowstone elk (Cervus elaphus) herds and interpreted this correlation as evidence that pregnancy rates of elk decreased substantially in the presence of wolves (Canis lupus). Apparently, the hypothesized mechanism is that decreased forage intake reduces body condition and either results in elk failing to conceive during the autumn rut or elk losing the fetus during winter. We tested this hypothesis by comparing age-specific body condition (percentage ingesta-free body fat) and pregnancy rates for northern Yellowstone elk, one of the herds sampled by Creel et al., before (1962-1968) and after (2000-2006) wolf restoration using indices developed and calibrated for Rocky Mountain elk. Mean age-adjusted percentage body fat of female elk was similarly high in both periods (9.0%-0.9% pre-wolf; 8.9%-0.8% post-wolf). Estimated pregnancy rates (proportion of females that were pregnant) were 0.91 pre-wolf and 0.87 post-wolf for 4-9 year-old elk (95% CI on difference = -0.15 to 0.03, P = 0.46) and 0.64 pre-wolf and 0.78 post-wolf for elk > 9 years old (95% CI on difference = -0.01 to 0.27, P = 0.06). Thus, there was little evidence in these data to support strong effects of wolf presence on elk pregnancy. We caution that multiple lines of evidence and/or strong validation should be brought to bear before relying on indirect measures of how predators affect pregnancy rates.