Berger Kim Murray
Teton Field Office, Wildlife Conservation Society, North America Program, P.O. Box 985, Victor, ID 83455-0985, USA.
Conserv Biol. 2006 Jun;20(3):751-61. doi: 10.1111/j.1523-1739.2006.00336.x.
Despite the importance of carnivores in terrestrial ecosystems, many nations have implemented well-coordinated, state-funded initiatives to remove predators, largely because of conflicts with humans over livestock. Although these control efforts have been successful in terms of the number of carnivores removed, their effects on the viability of the industries they seek to protect are less understood. I assessed the efficacy of long-term efforts by the U.S. government to improve the viability of the sheep industry by reducing predation losses. I used regression analysis and hierarchical partitioning of a 60-year data set to explore associations among changes in sheep numbers and factors such as predator control effort, market prices, and production costs. In addition, I compared trends in the sheep industry in the western United States, where predator control is subsidized and coyotes (Canis latrans) are abundant, with trends in eastern states that lack federally subsidized predator control and that were (1) colonized by coyotes before 1950 or (2) colonized by coyotes between 1950 and 1990. Although control efforts were positively correlated with fluctuations in sheep numbers, production costs and market prices explained most of the model variation, with a combined independent contribution of 77%. Trends in sheep numbers in eastern and western states were highly correlated (r > or = 0.942) independent of the period during which they were colonized by coyotes, indicating either that control has been ineffective at reducing predation losses or that factors other than predation account for the declines in both regions. These results suggest that government-subsidized predator control has failed to prevent the decline in the sheep industry and alternative support mechanisms need to be developed if the goal is to increase sheep production and not simply to kill carnivores.
尽管食肉动物在陆地生态系统中具有重要地位，但许多国家仍实施了协调良好、由国家资助的清除食肉动物的举措，主要原因是与人类在牲畜问题上存在冲突。虽然这些控制措施在清除食肉动物数量方面取得了成功，但它们对其所试图保护的产业的生存能力的影响却鲜为人知。我评估了美国政府长期努力通过减少捕食损失来提高养羊业生存能力的成效。我使用回归分析和对一个60年数据集的层次划分，来探究绵羊数量变化与诸如捕食者控制力度、市场价格和生产成本等因素之间的关联。此外，我比较了美国西部养羊业的趋势，那里捕食者控制得到补贴且郊狼（犬属）数量众多，与东部各州的趋势，东部各州缺乏联邦政府补贴的捕食者控制，且（1）在1950年之前被郊狼占据，或（2）在1950年至1990年之间被郊狼占据。尽管控制力度与绵羊数量的波动呈正相关，但生产成本和市场价格解释了模型变化的大部分，两者的独立贡献合计为77%。东部和西部各州绵羊数量的趋势高度相关（r≥0.942），与它们被郊狼占据的时期无关，这表明要么控制措施在减少捕食损失方面无效，要么除捕食之外的其他因素导致了两个地区绵羊数量的下降。这些结果表明，政府补贴的捕食者控制未能阻止养羊业的衰落，如果目标是增加绵羊产量而不仅仅是捕杀食肉动物，就需要开发替代支持机制。
