Gude Justin A, Garrott Robert A, Borkowski John J, King Fred
Ecology Department, Montana State University, Bozeman, Montana 59717, USA.
Ecol Appl. 2006 Feb;16(1):285-98. doi: 10.1890/04-0623.
Understanding the behaviorally mediated indirect effects of predators in ecosystems requires knowledge of predator-prey behavioral interactions. In predator-ungulate-plant systems, empirical research quantifying how predators affect ungulate group sizes and distribution, in the context of other influential variables, is particularly needed. The risk allocation hypothesis proposes that prey behavioral responses to predation risk depend on background frequencies of exposure to risk, and it can be used to make predictions about predator-ungulate-plant interactions. We determined non-predation variables that affect elk (Cervus elaphus) group sizes and distribution on a winter range in the Greater Yellowstone Ecosystem (GYE) using logistic and log-linear regression on surveys of 513 1-km2 areas conducted over two years. Employing model selection techniques, we evaluated risk allocation and other a priori hypotheses of elk group size and distributional responses to wolf (Canis lupus) predation risk while accounting for influential non-wolf-predation variables. We found little evidence that wolves affect elk group sizes, which were strongly influenced by habitat type and hunting by humans. Following predictions from the risk allocation hypothesis, wolves likely created a more dynamic elk distribution in areas that they frequently hunted, as elk tended to move following wolf encounters in those areas. This response should dilute elk foraging pressure on plant communities in areas where they are frequently hunted by wolves. We predict that this should decrease the spatial heterogeneity of elk impacts on grasslands in areas that wolves frequently hunt. We also predict that this should decrease browsing pressure on heavily browsed woody plant stands in certain areas, which is supported by recent research in the GYE.
了解捕食者在生态系统中的行为介导间接影响需要掌握捕食者与猎物的行为相互作用。在捕食者-有蹄类动物-植物系统中，尤其需要实证研究来量化捕食者在其他影响变量的背景下如何影响有蹄类动物的群体规模和分布。风险分配假说提出，猎物对捕食风险的行为反应取决于接触风险的背景频率，并且它可用于预测捕食者-有蹄类动物-植物之间的相互作用。我们通过对两年内调查的513个1平方公里区域进行逻辑回归和对数线性回归，确定了影响大黄石生态系统（GYE）冬季范围内麋鹿（马鹿）群体规模和分布的非捕食变量。利用模型选择技术，我们评估了风险分配以及麋鹿群体规模和对狼（犬属）捕食风险分布反应的其他先验假说，同时考虑了有影响的非狼捕食变量。我们几乎没有发现证据表明狼会影响麋鹿的群体规模，麋鹿群体规模受栖息地类型和人类狩猎的强烈影响。根据风险分配假说的预测，狼可能在它们经常捕猎的区域创造了更动态的麋鹿分布，因为麋鹿在这些区域遇到狼后往往会移动。这种反应应该会减轻麋鹿在狼经常捕猎区域对植物群落的觅食压力。我们预测，这将降低狼经常捕猎区域内麋鹿对草原影响的空间异质性。我们还预测，这将减轻某些区域中被大量啃食的木本植物林分的啃食压力，这得到了GYE近期研究的支持。
