Density dependence, compensation, and environmental effects on elk calf mortality in Yellowstone National Park
Density dependence, compensation, and environmental effects on elk calf mortality in Yellowstone National Park
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黄石国家公园麋鹿幼崽死亡率的密度依赖性、补偿和环境影响
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发表时间：
1997
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通讯作者：
M. Coughenour
中科院分区：
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作者：
F. J. Singer;A. Harting;K. Symonds;M. Coughenour
我们研究了1987-1990年黄石国家公园射彩麋鹿(Cervus Elaffus)幼崽的存活情况，以及根据1968-1992年种群估计计算的幼鹿存活率。我们假设，夏季和冬季小麋鹿的存活率和新生幼崽的数量与种群大小、环境严重程度的衡量标准和出生时间呈负相关。基于冬季计数、报告的收获量和鹿群分类的全群生存估计表明，小麋鹿的冬季存活率与冬季估计的麋鹿种群数量呈负相关(P=0.0002)，但我们发现与冬季严重程度指数没有相关性(P=0.51)。麋鹿幼崽的夏季存活率与前一个冬季估计的麋鹿种群数量呈负相关(P=0.03)。1987~1990年间，平均夏季存活0.65头(127头)，主要是捕食造成的损失(22%)。小牛的越冬存活率平均为0.72(88头标记小牛进入越冬期)，损失主要是由于营养不良(58%)。小牛夏季存活率与估计初生重呈正相关(P=0.001)。1987年至1990年冬季放牧小牛的存活率与初产羔数和冬季温和程度呈正相关(与整个群体的存活率估计值相反)，与当年估计的麋鹿种群数量呈负相关(P=0.006)。1988年至1989年，在干旱和大火之后，射胶犊的越冬存活率低于其他3个冬季(P<；0.001)。在1988年的干旱和火灾之后，夏季对麋鹿幼崽的捕食增加了一倍(火灾前因捕食而损失的幼鹿比例为13%，而火灾后为29%)。幼崽死亡率的构成因素之间存在潜在的补偿关系：捕食者杀死较轻(P=0.041)和较晚出生的幼崽(P=0.146)；恶劣天气条件下出生较晚且较轻(P=0.048)的幼崽；较重出生的幼崽的存活率较高(P=0.006)。我们的结果与这样的假设是一致的，即由于营养不良导致的幼崽冬季死亡率与密度相关，以及夏季由于捕食造成的死亡率是部分补偿的，但严酷的环境条件在很大程度上增加了夏季(捕食增加)和冬季(营养不良增加)死亡率的附加成分。
We studied survival of radiocollared elk (Cervus elaphus) calves in Yellowstone National Park from 1987 to 1990, and survival of calves computed from population estimates from 1968 to 1992. We hypothesized that summer and winter survival of elk calves and mass of neonates were inversely related to population size, measures of environmental severity, and timing of births. Herd-wide survival estimates based on winter counts, reported harvests, and herd classifications, suggested that winter survival of elk calves was related inversely to estimated size of the elk population during winter (P = 0.0002), but we found no correlation with an index of winter severity (P = 0.51). Summer survival of elk calves also was correlated inversely with the estimated size of the elk population the previous winter (P = 0.03). Summer survival of radiocollared calves averaged 0.65 (n = 127 marked calves) from 1987 to 1990, the losses mostly due to predation (22%). Winter survival of calves averaged 0.72 (n = 88 marked calves entered the winter period), with losses due mostly to malnutrition (58%). Summer survival of radiocollared calves was positively correlated with estimated birth weight (P = 0.001). Survival of radiocollared calves during winters 1987-90 was correlated positively with early calving and mildness of the winter (in contrast to herd-wide survival estimates), and was inversely correlated with estimated elk population size that winter (P = 0.006). Winter survival of radiocollared calves was lower during 1988-89 following the drought and large fires than the other 3 winters (P < 0.001). Predation on elk calves during summer doubled after the drought and fires of 1988 (13% calf losses to predation before the fires vs. 29% after the fires). Potential compensation existed between components of calf mortality: predators killed more light (P = 0.041) and more late born calves (P = 0.146); calves were born later and lighter (P = 0.048) following severe weather conditions; and heavier born calves survived at a higher rate (P = 0.006). Our results are consistent with the hypothesis that density-dependent mortality of calves during winter due to malnutrition, and summer mortality of calves due to predation were partially compensatory but severe environmental conditions produced largely additive components to both summer (increased predation) and winter (increased malnutrition) mortality.