Data from: Consistency and variation in phenotypic selection exerted by a community of seed predators

Phenotypic selection that is sustained over time underlies both anagenesis and cladogenesis, but the conditions that lead to such selection and what causes variation in selection are not well known. We measured the selection exerted by three species of predispersal seed predators of lodgepole pine (Pinus contorta latifolia) in the South Hills, Idaho and found that net selection on different cone and seed traits exerted by red crossbills (Loxia curvirostra) and cone borer moths (Eucosma recissoriana) over 10 years of seed crops was similar to that measured in another mountain range. We also found that the strength of selection increased as seed predation increased, which provides a mechanism for the correlation between the escalation of seed defenses and the density of seed predators. Red crossbills consume the most seeds and selection they exert accounts for much of the selection experienced by lodgepole pine, providing additional support for a coevolutionary arms race between crossbills and lodgepole pine in the South Hills. The third seed predator, hairy woodpeckers (Picoides villosus), consumed less than one-sixth as many seeds as crossbills. Across the northern Rocky Mountains, woodpecker abundance and therefore selective impact appears limited by the elevated seed defenses of lodgepole pine.

长期持续的表型选择（phenotypic selection）是前进演化（anagenesis）与分支演化（cladogenesis）的共同基础，但介导此类选择形成的条件，以及引发选择差异的原因，目前仍未得到充分阐明。我们针对爱达荷州南丘陵地区的扭叶松（Pinus contorta latifolia）的3种种子前捕食者展开了选择压力测定。研究发现，在10年的种子结实周期中，红交嘴雀（Loxia curvirostra）与球果蛀蛾（Eucosma recissoriana）对扭叶松不同球果及种子性状所施加的净选择压力，与另一山脉中的测定结果基本一致。我们还发现，选择强度随种子捕食率的提升而升高，这为种子防御机制升级与种子捕食者密度之间的相关性提供了作用机制。红交嘴雀的种子取食量最大，其所施加的选择压力占扭叶松所承受选择压力的绝大部分，进一步为南丘陵地区红交嘴雀与扭叶松之间存在协同进化军备竞赛（coevolutionary arms race）的观点提供了额外佐证。第三种捕食者多毛啄木鸟（Picoides villosus）的种子取食量尚不足红交嘴雀的六分之一。在整个落基山脉北部区域，扭叶松强化的种子防御机制似乎限制了多毛啄木鸟的种群丰度，进而限制了其选择影响效应。