Data from: Causes of variation in biotic interaction strength and phenotypic selection along an altitudinal gradient

Understanding the causes of variation in biotic interaction strength and phenotypic selection remains one of the outstanding goals of evolutionary ecology. Here we examine the variation in strength of interactions between two seed predators, common crossbills (Loxia curvirostra) and European red squirrels (Sciurus vulgaris), and mountain pine (Pinus uncinata) at and below tree limit in the Pyrenees, and how this translates into phenotypic selection. Seed predation by crossbills increased whereas seed predation by squirrels decreased with increasing elevation and as the canopy became more open. Overall, seed predation by crossbills averaged about twice that by squirrels, and the intensity of selection exerted by crossbills averaged between 2.6 and 7.5 times greater than by squirrels. The higher levels of seed predation by crossbills than squirrels were related to the relatively open nature of most of the forests, and the higher intensity of selection exerted by crossbills resulted from their higher levels of seed predation. However, most of the differences in selection intensity between crossbills and squirrels were the result of habitat features having a greater effect on the foraging behavior of squirrels than of crossbills, causing selection to be much lower for squirrels than for crossbills.

阐明生物交互强度与表型选择的变异成因，仍是进化生态学领域亟待达成的核心研究目标之一。本研究针对比利牛斯山脉林线及林线以下区域，探究了两种种子捕食者——普通交嘴雀（Loxia curvirostra）与欧洲红松鼠（Sciurus vulgaris）同山松（Pinus uncinata）之间的交互强度变异，及其如何转化为表型选择。结果显示，随海拔升高与林冠愈发开阔，交嘴雀的种子捕食率呈上升趋势，而松鼠的种子捕食率则逐步下降。总体而言，交嘴雀的平均种子捕食率约为松鼠的两倍，且交嘴雀所施加的选择强度平均为松鼠的2.6至7.5倍。交嘴雀的种子捕食水平高于松鼠，与多数森林相对开阔的生境特性相关；而交嘴雀介导的选择强度更高，则源于其更高的种子捕食率。不过，交嘴雀与松鼠间选择强度的多数差异，源于生境特征对松鼠觅食行为的影响程度显著大于交嘴雀，这使得松鼠所介导的选择强度远低于交嘴雀。