Rogers C M, Caro M J
Department of Biological Sciences, The University of Iowa, Iowa City, IA 52242, USA e-mail:
Department of Biology, Virginia Tech University, Blacksburg, VA 24061, USA, , , , , , US.
Oecologia. 1998 Aug;116(1-2):227-233. doi: 10.1007/s004420050583.
Ground-nesting North American landbirds have declined in the longterm, including species with a variety of migratory strategies. The mesopredator release hypothesis explains declines by suggesting that the virtual elimination of top carnivores (large-bodied canids and felids) from much of North America has "released" populations of nest-destroying mesopredators (i.e., medium-sized terrestrial omnivores such as the raccoon Procyon lotor). The hypothesis predicts (1) higher nest success in the presence than in the absence of top carnivores, and (2) a positive relationship between mesopredator abundance and nest predation. Results from a 4-year "natural experiment" in the agricultural landscape of southern Michigan tended to support prediction 1. When coyotes (Canis latrans) were absent in 1993 and present in 1994, 1995 and 1996, Mayfield nest survival in song sparrows (Melospiza melodia), a ground-nesting landbird, increased significantly during the same 4-year interval. Relative frequency of nest predation, the most common cause of nest failure, declined significantly over the four years. Coyotes may have decreased nest predation in 1994-1996 by reducing the abundance of raccoons, apparently the main nest predator in the study area. In an experiment testing prediction 2, mesopredator abundance and predation rate on artificial nests were positively related, as predicted by the hypothesis. Although the present study is not wholly conclusive by itself, we cautiously suggest it contributes to a growing body of evidence derived from a number of studies supporting the mesopredator release hypothesis.
长期以来，北美地面筑巢的陆鸟数量一直在减少，其中包括具有各种迁徙策略的物种。中层食肉动物释放假说认为，北美大部分地区顶级食肉动物（大型犬科动物和猫科动物）的几乎灭绝“释放”了破坏巢穴的中层食肉动物（即中型陆生杂食动物，如浣熊）的种群数量，从而解释了这种数量下降的现象。该假说预测：（1）存在顶级食肉动物时的巢穴成功率高于没有顶级食肉动物时；（2）中层食肉动物数量与巢穴被捕食之间存在正相关关系。在密歇根州南部农业景观中进行的一项为期4年的“自然实验”结果倾向于支持预测1。1993年郊狼（犬属）不存在，而在1994年、1995年和1996年存在，在这相同的4年期间，地面筑巢的陆鸟歌带鹀（Melospiza melodia）的梅菲尔德巢穴存活率显著增加。巢穴被捕食是巢穴失败最常见的原因，其相对频率在这四年中显著下降。郊狼可能通过减少浣熊的数量降低了1994 - 1996年的巢穴被捕食率，浣熊显然是研究区域内主要的巢穴捕食者。在一项检验预测2的实验中，正如该假说所预测的，中层食肉动物数量与人工巢穴的被捕食率呈正相关。尽管本研究本身并不完全具有决定性，但我们谨慎地认为它为越来越多支持中层食肉动物释放假说的研究证据做出了贡献。
