Siepielski Adam M, Benkman Craig W
Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
Proc Biol Sci. 2007 Aug 7;274(1620):1799-805. doi: 10.1098/rspb.2007.0449.
The importance of infrequent events for both adaptive evolution and the evolution of species interactions is largely unknown. We investigated how the infrequent production of large seed crops (masting) of a bird-dispersed tree (whitebark pine, Pinus albicaulis) influenced phenotypic selection exerted by its primary avian seed predator-disperser, the Clark's nutcracker (Nucifraga columbiana). Selection was not evident during common years of low seed abundance, whereas it was replicated among areas and favoured traits facilitating seed dispersal during infrequent years of high seed abundance. Since nutcrackers act mostly as seed predators during small seed crops but as seed dispersers during the largest seed crops, trees experienced strong selection from nutcrackers only during infrequent years when the interaction was most strongly mutualistic. Infrequent events can thus be essential to both adaptive evolution and the evolutionary dynamics of species interactions.
罕见事件对于适应性进化和物种间相互作用的进化的重要性在很大程度上尚不清楚。我们研究了一种靠鸟类传播种子的树木（白皮松，Pinus albicaulis）偶尔产生的大量种子作物（大年结实）是如何影响其主要的鸟类种子捕食者兼传播者——克拉克星鸦（Nucifraga columbiana）所施加的表型选择的。在种子产量低的常见年份，选择并不明显，而在种子产量高的罕见年份，选择在不同区域重复出现，且有利于促进种子传播的性状。由于星鸦在种子产量小的时候主要充当种子捕食者，但在种子产量最大的时候充当种子传播者，所以树木只有在这种相互作用最强烈地表现为互利共生的罕见年份才会受到星鸦的强烈选择。因此，罕见事件对于适应性进化和物种间相互作用的进化动态可能至关重要。
