Inman-Narahari Faith, Ostertag Rebecca, Asner Gregory P, Cordell Susan, Hubbell Stephen P, Sack Lawren
Department of Ecology and Evolutionary Biology, University of California 621 Charles E. Young Drive South, Los Angeles, California, 90095-1606.
Department of Biology, University of Hawaii 200 W. Kawili Street, Hilo, Hawaii, 96720.
Ecol Evol. 2014 Oct;4(19):3755-67. doi: 10.1002/ece3.1196. Epub 2014 Sep 9.
For niche differences to maintain coexistence of sympatric species, each species must grow and/or survive better than each of the others in at least one set of conditions (i.e., performance trade-offs). However, the extent of niche differentiation in tropical forests remains highly debated. We present the first test of performance trade-offs for wild seedlings in a tropical forest. We measured seedling relative growth rate (RGR) and survival of four common native woody species across 18 light, substrate, and topography microhabitats over 2.5 years within Hawaiian montane wet forest, an ideal location due to its low species diversity and strong species habitat associations. All six species pairs exhibited significant performance trade-offs across microhabitats and for RGR versus survival within microhabitats. We also found some evidence of performance equivalence, with species pairs having similar performance in 26% of comparisons across microhabitats. Across species, survival under low light was generally positively associated with RGR under high light. When averaged over all species, topography (slope, aspect, and elevation) explained most of the variation in RGR attributable to microhabitat variables (51-53%) followed by substrate type (35-37%) and light (11-12%). However, the relative effects of microhabitat differed among species and RGR metric (i.e., RGR for height, biomass, or leaf area). These findings indicate that performance trade-offs among species during regeneration are common in low-diversity tropical forest, although other mechanisms may better explain the coexistence of species with small performance differences.
为了使生态位差异维持同域物种的共存，每个物种必须在至少一组条件下（即性能权衡）比其他物种生长得更好和/或存活得更好。然而，热带森林中生态位分化的程度仍存在激烈争论。我们首次对热带森林中的野生幼苗进行了性能权衡测试。我们在夏威夷山地湿林的2.5年时间里，测量了四种常见本地木本物种在18种光照、基质和地形微生境中的幼苗相对生长速率（RGR）和存活率，夏威夷山地湿林因其物种多样性低和物种栖息地关联强，是一个理想的地点。所有六对物种在微生境之间以及微生境内RGR与存活率之间都表现出显著的性能权衡。我们还发现了一些性能等效的证据，在微生境间的26%的比较中，物种对具有相似的性能。在所有物种中，低光照下的存活率通常与高光照下的RGR呈正相关。当对所有物种进行平均时，地形（坡度、坡向和海拔）解释了可归因于微生境变量的RGR变化的大部分（51 - 53%），其次是基质类型（35 - 37%）和光照（11 - 12%）。然而，微生境的相对影响在物种和RGR指标（即高度、生物量或叶面积的RGR）之间有所不同。这些发现表明，在低多样性热带森林中，物种在再生过程中的性能权衡很常见，尽管其他机制可能更好地解释性能差异较小的物种的共存。
