Peacor Scott D, Schiesari Luis, Werner Earl E
Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan 48824, USA.
Ecology. 2007 Jun;88(6):1536-47. doi: 10.1890/06-1066.
Understanding the factors responsible for generating size variation in cohorts of organisms is important for predicting their population and evolutionary dynamics. We group these factors into two broad classes: those due to scaling relationships between growth and size (size-dependent factors), and those due to individual trait differences other than size (size-independent factors; e.g., morphology, behavior, etc.). We develop a framework predicting that the nonlethal presence of predators can have a strong effect on size variation, the magnitude and sign of which depend on the relative influence of both factors. We present experimental results showing that size-independent factors can strongly contribute to size variation in anuran larvae, and that the presence of a larval dragonfly predator reduced expression of these size-independent factors. Further, a review of a number of experiments shows that the effect of this predator on relative size variation of a cohort ranged from negative at low growth rates to positive at high growth rates. At high growth rates, effects of size-dependent factors predominate, and predator presence causes an increase in the scaling of growth rate with size (larger individuals respond less strongly to predator presence than small individuals). Thus predator presence led to an increase in size variation. In contrast, at low growth rates, size-independent factors were relatively more important, and predator presence reduced expression of these size-independent factors. Consequently, predator presence led to a decrease in size variation. Our results therefore indicate a further mechanism whereby nonlethal predator effects can be manifest on prey species performance. These results have strong implications for both ecological and evolutionary processes. Theoretical studies indicate that changes in cohort size variation can have profound effects on population dynamics and stability, and therefore the mere presence of a predator could have important ecological consequences. Further, changes in cohort size variation can have important evolutionary implications through changes in trait heritability.
了解导致生物群体大小变化的因素对于预测其种群和进化动态至关重要。我们将这些因素分为两大类：一类是由于生长与大小之间的比例关系（大小依赖因素），另一类是由于除大小之外的个体性状差异（大小独立因素；例如形态、行为等）。我们构建了一个框架，预测捕食者的非致命存在会对大小变化产生强烈影响，其影响的程度和方向取决于这两类因素的相对影响。我们展示的实验结果表明，大小独立因素可对无尾两栖类幼虫的大小变化产生重大影响，而蜻蜓幼虫捕食者的存在会降低这些大小独立因素的表现。此外，对一系列实验的综述表明，这种捕食者对群体相对大小变化的影响在低生长速率下为负，在高生长速率下为正。在高生长速率下，大小依赖因素起主导作用，捕食者的存在会导致生长速率随大小的比例增加（较大个体对捕食者存在的反应不如小个体强烈）。因此，捕食者的存在导致大小变化增加。相反，在低生长速率下，大小独立因素相对更重要，捕食者的存在会降低这些大小独立因素的表现。因此，捕食者的存在导致大小变化减少。我们的结果因此表明了一种非致命捕食者效应可在猎物物种表现上体现的进一步机制。这些结果对生态和进化过程都有重要意义。理论研究表明，群体大小变化的改变可对种群动态和稳定性产生深远影响，因此仅仅是捕食者的存在就可能产生重要的生态后果。此外，群体大小变化的改变可通过性状遗传力的变化产生重要的进化影响。
