Abrams Peter A, Rowe Locke
Department of Ecology, Evolution, and Behavior, University of Minnesota, 1987 Upper Buford Circle, Saint Paul, Minnesota, 55108.
Department of Zoology, University of Toronto, Toronto, Ontario, M5S 1A1, Canada.
Evolution. 1996 Jun;50(3):1052-1061. doi: 10.1111/j.1558-5646.1996.tb02346.x.
The effects of nonselective predation on the optimal age and size of maturity of their prey are investigated using mathematical models of a simple life history with juvenile and adult stages. Fitness is measured by the product of survival to the adult stage and expected adult reproduction, which is usually an increasing function of size at maturity. Size is determined by both age at maturity and the value of costly traits that increase mean growth rate (growth effort). The analysis includes cases with fixed size but flexible time to maturity, fixed time but flexible size, and adaptively flexible values of both variables. In these analyses, growth effort is flexible. For comparison with previous theory, models with a fixed growth effort are analyzed. In each case, there may be indirect effects of predation on the prey's food supply. The effect of increased predation depends on (1) which variables are flexible; (2) whether increased growth effort requires increased exposure to predators; and (3) how increased predator density affects the abundance of food for juvenile prey. If there is no indirect effect of predators on prey food supply, size at maturity will generally decrease in response to increased predation. However, the indirect effect from increased food has the opposite effect, and the net result of predation is often increased size. Age at maturity may either increase or decrease, depending on functional forms and parameter values; this is true regardless of the presence of indirect effects. The results are compared with those of previous theoretical analyses. Observed shifts in life history in response to predation are reviewed, and the role of size-selective predation is reassessed.
利用具有幼年和成年阶段的简单生活史数学模型，研究了非选择性捕食对其猎物最优成熟年龄和大小的影响。适合度通过成年阶段的存活率与预期成年繁殖率的乘积来衡量，而预期成年繁殖率通常是成熟时大小的增函数。大小由成熟年龄和增加平均生长率（生长努力）的代价高昂性状的值共同决定。分析包括成熟时大小固定但成熟时间灵活、成熟时间固定但大小灵活以及两个变量都自适应灵活的情况。在这些分析中，生长努力是灵活的。为了与先前的理论进行比较，分析了生长努力固定的模型。在每种情况下，捕食可能对猎物的食物供应产生间接影响。捕食增加的影响取决于：（1）哪些变量是灵活的；（2）增加生长努力是否需要增加暴露于捕食者；以及（3）捕食者密度增加如何影响幼年猎物的食物丰度。如果捕食者对猎物食物供应没有间接影响，成熟时的大小通常会随着捕食增加而减小。然而，食物增加的间接影响具有相反的作用，捕食的净结果往往是大小增加。成熟年龄可能增加或减少，这取决于函数形式和参数值；无论是否存在间接影响，都是如此。将结果与先前理论分析的结果进行比较。回顾了观察到的生活史对捕食的变化，并重新评估了大小选择性捕食的作用。
