Ewel John J, Mazzarino María Julia
Department of Biology, University of Florida, Gainesville, FL 32611, USA.
Proc Natl Acad Sci U S A. 2008 Dec 2;105(48):18836-41. doi: 10.1073/pnas.0807216105. Epub 2008 Nov 20.
Chance events such as seed dispersal determine the potential composition of plant communities, but the eventual assemblage is determined in large part by subsequent interactions among species. Postcolonization sorting also affects the ultimate composition of communities assembled by people for restoration, horticulture, or conservation. Thus, knowledge of the mechanisms controlling interspecific interactions in plant communities is important for explaining patterns observed in nature and predicting success or failure of utilitarian combinations. Relationships among species, especially those from studies of biological diversity and ecosystem functioning, are largely based on studies of short-lived, temperate-zone plants. Extrapolation to perennial plants in the humid tropics is risky because functional relationships among large-stature species change with time. Shifts in competitive relationships among 3 life forms--trees, palms, and perennial herbs--occurred during 13 yr in experimental tropical ecosystems. In 2 cases the novel competitive mechanism responsible for the shift was reduction in crown volume, and therefore light-capturing capability, of overtopping deciduous trees by intrusive growth from below a palm. In a third case, complementary resource use developed between 2 evergreen life forms (overstory tree and palm), probably because of differential nutrient acquisition. Species-level traits and adequate time for shifts in interspecific relationships to emerge are crucial for predicting community trajectories.
诸如种子传播这样的偶然事件决定了植物群落的潜在组成，但最终的组合在很大程度上取决于物种间随后的相互作用。殖民后筛选也会影响人们为恢复、园艺或保护而组建的群落的最终组成。因此，了解控制植物群落种间相互作用的机制对于解释自然界中观察到的模式以及预测功利性组合的成败至关重要。物种间的关系，尤其是那些来自生物多样性和生态系统功能研究的关系，很大程度上基于对短命的温带植物的研究。将其外推到潮湿热带地区的多年生植物是有风险的，因为高大物种间的功能关系会随时间变化。在实验性热带生态系统中，三种生活型——树木、棕榈和多年生草本植物——之间的竞争关系在13年里发生了变化。在两个案例中，导致这种变化的新竞争机制是棕榈从下方侵入生长，使落叶乔木的树冠体积减小，从而降低了其采光能力。在第三个案例中，两种常绿生活型（上层树木和棕榈）之间形成了互补性资源利用，这可能是由于养分获取的差异。物种水平的特征以及种间关系转变出现的足够时间对于预测群落轨迹至关重要。
