Rudolf Volker H W
Department of Biology, University of Virginia, Charlottesville 22904-4327, USA.
Ecology. 2006 Feb;87(2):362-71. doi: 10.1890/05-0961.
Nonlethal indirect interactions between predators often lead to nonadditive effects of predator number on prey survival and growth. Previous studies have focused on systems with at least two different predator species and one prey species. However, most predators undergo extreme ontological changes in phenotype such that interactions between different-sized cohorts of a predator and its prey could lead to nonadditive effects in systems with only two species. This may be important since different-sized individuals of the same species can differ more in their ecology than similar-sized individuals of different species. This study examined trait-mediated indirect effects in a two-species system including a cannibalistic predator with different-sized cohorts and its prey. I tested for these effects using larvae of two stream salamanders, Gyrinophilus porphyriticus (predator) and Eurycea cirrigera (prey), by altering the densities and combinations of predator size classes in experimental streams. Results showed that the presence of large individuals can significantly reduce the impact of density changes of smaller conspecifics on prey survival through nonlethal means. In the absence of large conspecifics, an increase in the relative frequency of small predators significantly increased predation rates, thereby reducing prey survival. However, with large conspecifics present, increasing the density of small predators did not decrease prey survival, resulting in a 14.3% lower prey mortality than predicted from the independent effects of both predator size classes. Small predators changed their microhabitat use in the presence of larger conspecifics. Prey individuals reduced activity in response to large predators but did not respond to small predators. Both predators reduced prey growth. These results demonstrate that the impact of a predator can be significantly altered by two different types of trait-mediated indirect effects in two-species systems: between different-sized cohorts and between different cohorts and prey. This study demonstrates that predictions based on simple numerical changes that assume independent effects of different size classes or ignore size structure can be strongly misleading. We need to account for the size structure within predator populations in order to predict how changes in predator abundance will affect predator-prey dynamics.
捕食者之间的非致命间接相互作用通常会导致捕食者数量对猎物生存和生长产生非加性效应。先前的研究主要集中在至少有两种不同捕食者物种和一种猎物物种的系统上。然而，大多数捕食者在表型上会经历极端的个体发育变化，以至于同一捕食者不同大小群体与其猎物之间的相互作用可能会在仅包含两个物种的系统中导致非加性效应。这可能很重要，因为同一物种不同大小的个体在生态学上的差异可能比不同物种相似大小的个体之间的差异更大。本研究在一个两物种系统中检验了性状介导的间接效应，该系统包括一种具有不同大小群体的自相残杀的捕食者及其猎物。我通过改变实验溪流中捕食者大小类别的密度和组合，使用两种溪流蝾螈的幼虫，即多纹脊口螈（捕食者）和卷尾真螈（猎物）来测试这些效应。结果表明，大型个体的存在可以通过非致命手段显著降低较小同种个体密度变化对猎物生存的影响。在没有大型同种个体的情况下，小型捕食者相对频率的增加显著提高了捕食率，从而降低了猎物的生存率。然而，在有大型同种个体存在时，增加小型捕食者的密度并没有降低猎物的生存率，导致猎物死亡率比根据两种捕食者大小类别独立效应预测的低14.3%。小型捕食者在有大型同种个体存在时改变了它们对微生境的利用。猎物个体对大型捕食者做出反应而减少活动，但对小型捕食者没有反应。两种捕食者都降低了猎物的生长。这些结果表明，在两物种系统中，捕食者的影响可以通过两种不同类型的性状介导的间接效应显著改变：在不同大小的群体之间以及在不同群体与猎物之间。本研究表明，基于简单数值变化（假设不同大小类别具有独立效应或忽略大小结构）的预测可能会产生严重误导。我们需要考虑捕食者种群内部的大小结构，以便预测捕食者数量的变化将如何影响捕食者 - 猎物动态。
