Baird Robin W, Abrams Peter A, Dill Lawrence M
Behavioural Ecology Research Group, Department of Biological Sciences, Simon Fraser University, V5A 1S6, Burnaby, B.C., Canada.
Marine Mammal Research Group, Box 6244, V8P 5L5, Victoria, B.C., Canada.
Oecologia. 1992 Jan;89(1):125-132. doi: 10.1007/BF00319024.
Two distinct forms of killer whale (Orcinus orca) occur off the coast of British Columbia, Alaska and Washington State. These have different diets, and may be reproductively isolated. Because the primary food of transient whales (pinnipeds) is a potential competitor for the primary food of resident whales (salmon), or for the smaller fishes on which salmon feed, there should be an indirect interaction between the two forms of killer whale. We use simple mathematical models to show that this interaction will be either of a "plus-minus" type, or a "plus-plus" type (indirect mutualism), depending on whether or not pinnipeds and residents are on the same trophic level. In the case of the "plus-minus" interaction, increasing the population density or improving the environmental conditions of transients will increase the population density of residents, while increasing resident populations will reduce the equilibrium population size of transients. In the case of the "plus-plus" interaction, increasing the population density or improving the environmental conditions of transients will increase the population density of residents, while increasing resident populations will reduce the equilibrium population size of transients. In the case of the "plus-plus" interaction, increasing the population density or improving the environmental conditions of transients will increase the population density of residents, and vice versa. Such effects may not be currently manifest due to reduced populations at most levels in the food web. Regardless, considering such indirect interactions may be important for the management of many of the species involved, and can also provide a valuable framework for examining the evolution of the two forms of killer whales. Frequency-dependent indirect interactions, acting in concert with density-dependence within populations and disruptive selection on prey-type specific foraging characteristics, may have favoured reproductive isolation of the two forms of killer whales. We suggest that these two forms of whale are in the process of speciating, i.e., the two forms are incipient species.
在不列颠哥伦比亚省、阿拉斯加和华盛顿州海岸出现了两种不同形态的虎鲸（逆戟鲸，Orcinus orca）。它们有着不同的饮食结构，并且可能在生殖上相互隔离。由于过客型虎鲸（以鳍足类动物为食）的主要食物是定居型虎鲸（以鲑鱼为食）主要食物的潜在竞争者，或者是鲑鱼所捕食的小型鱼类的潜在竞争者，因此这两种形态的虎鲸之间应该存在间接相互作用。我们使用简单的数学模型表明，这种相互作用将是“正负”型，或者是“正正”型（间接互利共生），这取决于鳍足类动物和定居型虎鲸是否处于同一营养级。在“正负”相互作用的情况下，增加过客型虎鲸的种群密度或改善其环境条件会增加定居型虎鲸的种群密度，而增加定居型虎鲸的数量会减少过客型虎鲸的平衡种群规模。在“正正”相互作用的情况下，增加过客型虎鲸的种群密度或改善其环境条件会增加定居型虎鲸的种群密度，反之亦然。由于食物网中大多数层级的种群数量减少，这种影响目前可能并不明显。无论如何，考虑这种间接相互作用对于许多相关物种的管理可能很重要，并且还可以为研究两种形态虎鲸的进化提供一个有价值的框架。频率依赖的间接相互作用，与种群内的密度依赖以及对特定猎物类型觅食特征的分裂选择共同作用，可能有利于两种形态虎鲸的生殖隔离。我们认为这两种形态的虎鲸正处于物种形成的过程中，也就是说，这两种形态是初始物种。
