Paine C E Timothy, Beck Harald
Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Ecology. 2007 Dec;88(12):3076-87. doi: 10.1890/06-1835.1.
Seed dispersal and seedling recruitment (the transition of seeds to seedlings) set the spatiotemporal distribution of new individuals in plant communities. Many terrestrial rain forest mammals consume post-dispersal seeds and seedlings, often inflicting density-dependent mortality. In part because of density-dependent mortality, diversity often increases during seedling recruitment, making it a critical stage for species coexistence. We determined how mammalian predators, adult tree abundance, and seed mass interact to affect seedling recruitment in a western Amazonian rain forest. We used exclosures that were selectively permeable to three size classes of mammals: mice and spiny rats (weighing <1 kg), medium-sized rodents (1-12 kg), and large mammals (20-200 kg). Into each exclosure, we placed seeds of 13 tree species and one canopy liana, which varied by an order of magnitude in adult abundance and seed mass. We followed the fates of the seeds and resulting seedlings for at least 17 months. We assessed the effect of each mammalian size class on seed survival, seedling survival and growth, and the density and diversity of the seedlings that survived to the end of the experiment. Surprisingly, large mammals had no detectable effect at any stage of seedling recruitment. In contrast, small- and medium-sized mammals significantly reduced seed survival, seedling survival, and seedling density. Furthermore, predation by small mammals increased species richness on a per-stem basis. This increase in diversity resulted from their disproportionately intense predation on common species and large-seeded species. Small mammals thereby generated a rare-species advantage in seedling recruitment, the critical ingredient for frequency dependence. Predation by small (and to a lesser extent, medium-sized) mammals on seeds and seedlings significantly increases tree species diversity in tropical forests. This is the first long-term study to dissect the effects of various mammalian predators on the recruitment of a diverse set of tree species.
种子传播和幼苗补充（种子向幼苗的转变）决定了植物群落中新个体的时空分布。许多陆生雨林哺乳动物会食用传播后的种子和幼苗，常常造成密度依赖性死亡。部分由于密度依赖性死亡，幼苗补充阶段的多样性通常会增加，这使其成为物种共存的关键阶段。我们确定了哺乳动物捕食者、成年树木数量和种子质量如何相互作用，以影响亚马逊西部雨林中的幼苗补充。我们使用了对三种体型大小的哺乳动物具有选择性渗透性的围栏：小鼠和刺鼠（体重<1千克）、中型啮齿动物（1 - 12千克）和大型哺乳动物（20 - 200千克）。在每个围栏中，我们放置了13种树木和一种藤本植物的种子，这些种子在成年个体数量和种子质量上相差一个数量级。我们追踪种子及由此产生的幼苗的命运至少17个月。我们评估了每个哺乳动物体型类别对种子存活、幼苗存活和生长，以及存活到实验结束时的幼苗密度和多样性的影响。令人惊讶的是，大型哺乳动物在幼苗补充的任何阶段都没有可检测到的影响。相比之下，小型和中型哺乳动物显著降低了种子存活、幼苗存活和幼苗密度。此外，小型哺乳动物的捕食增加了每根茎的物种丰富度。这种多样性的增加源于它们对常见物种和大种子物种不成比例的强烈捕食。因此，小型哺乳动物在幼苗补充中产生了稀有种优势，这是频率依赖性的关键因素。小型（以及在较小程度上，中型）哺乳动物对种子和幼苗的捕食显著增加了热带森林中的树种多样性。这是第一项剖析各种哺乳动物捕食者对多种树种补充影响的长期研究。
