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）的共同核心驱动，但引发此类选择的具体条件，以及选择强度产生变异的原因，目前仍未得到充分阐释。我们在爱达荷州南希尔斯区域，针对扭叶松（Pinus contorta latifolia）的三种种子散播前捕食者开展了选择强度测定。研究发现，红交嘴雀（Loxia curvirostra）与球果螟蛾（Eucosma recissoriana）在长达10年的种子结实周期中，对扭叶松不同球果与种子性状所施加的净选择强度，与另一山脉中测得的结果基本一致。我们同时观测到，选择强度随种子捕食压力的升高而增强，这一结果为种子防御机制的升级与种子捕食者种群密度之间的相关性提供了潜在作用机制。红交嘴雀的种子取食量最大，其所介导的选择压力在扭叶松所承受的总选择中占据主导地位，这为南希尔斯地区交嘴雀与扭叶松之间存在协同进化军备竞赛（coevolutionary arms race）的假说提供了新的实证支持。第三种种子捕食者多毛啄木鸟（Picoides villosus）的种子取食量仅约为交嘴雀的六分之一。在落基山脉北部区域，多毛啄木鸟的种群丰度及其由此产生的选择影响，似乎受到扭叶松强化的种子防御机制所限制。