School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland 1010, New Zealand.
Science. 2011 Feb 25;331(6020):1068-71. doi: 10.1126/science.1199092. Epub 2011 Feb 3.
Reductions in bird numbers could hamper ecosystem services such as pollination, but experimental proof is lacking. We show that functional extinction of bird pollinators has reduced pollination, seed production, and plant density in the shrub Rhabdothamnus solandri (Gesneriaceae) on the North Island ("mainland") of New Zealand but not on three nearby island bird sanctuaries where birds remain abundant. Pollen limitation of fruit set is strong [pollen limitation index (PLI) = 0.69] and significant on the mainland but small (PLI = 0.15) and nonsignificant on islands. Seed production per flower on the mainland is reduced 84%. Mainland sites have similar adult densities, but 55% fewer juvenile plants per adult, than island sites. Seed addition experiments near adult R. solandri plants on the mainland found strong seed limitation 5 years after sowing for R. solandri but not for two other co-occurring woody species. This demonstrates a terrestrial trophic cascade.
鸟类数量的减少可能会阻碍授粉等生态系统服务，但缺乏实验证据。我们表明，新西兰北岛（“大陆”）灌木 Rhabdothamnus solandri（苦苣苔科）的鸟类传粉者功能灭绝已经减少了授粉、种子产量和植物密度，但在附近三个鸟类保护区的岛屿上，鸟类仍然丰富，这种情况并没有发生。果实结实的花粉限制很强[花粉限制指数（PLI）= 0.69]，在大陆上显著，但在岛屿上较小（PLI = 0.15）且不显著。大陆上每朵花的种子产量减少了 84%。与岛屿上的地点相比，大陆上的地点的成年植物密度相似，但每株成年植物的幼株数量减少了 55%。在大陆上成年 R. solandri 植物附近进行的种子添加实验发现，播种 5 年后，R. solandri 的种子限制很强，但另外两种共存的木本物种没有这种限制。这证明了陆地营养级联。
