Department of Botany, University of British Columbia, 6270 University Boulevard, Vancouver, BC, V6T 1Z4, Canada.
Mol Ecol. 2017 May;26(9):2407-2409. doi: 10.1111/mec.14078.
Wet tropical forests are among the most diverse ecosystems on Earth and can host several hundreds of tree species per hectare. To maintain such diversity, the community must contain large numbers of relatively rare species rather than be dominated by a few very common trees, as is often the case in temperate forests. Explaining the mechanisms preventing dominance by common species has been a major task of tropical forest ecology. One of the most promising mechanisms is negative density dependence (NDD) of tree abundance driven by pests, including fungal diseases ('pest pressure'). NDD entails that the chance of survival of a sapling increases with the distance from a mature tree of the same species, thus preventing species from becoming locally dominant. Curiously, the strength of NDD is negatively correlated with abundance, meaning that tree species that are more common generally show weaker NDD (Comita et al. ). Interactions between plants and soil pathogens have been shown to play an important role in NDD (Klironomos ), and rare species are apparently more strongly affected (Mangan et al. ). However, the genetic mechanisms underlying this phenomenon have remained obscure. In this issue of Molecular Ecology, Marden et al. () suggest that reduced diversity of the genes involved in pathogen recognition (Resistance genes or R genes) could explain why NDD is stronger in locally rare species.
湿热带森林是地球上生物多样性最丰富的生态系统之一，每公顷可容纳数百种树种。为了维持这种多样性，群落中必须包含大量相对较少的稀有物种，而不是像在温带森林中那样，由少数几种非常常见的树木主导。解释防止常见物种占主导地位的机制一直是热带森林生态学的主要任务之一。最有希望的机制之一是由害虫（包括真菌疾病）驱动的树木丰度的负密度依赖性（NDD）。NDD 意味着幼苗的存活机会随着与同一物种的成熟树木的距离增加而增加，从而防止物种在当地占主导地位。奇怪的是，NDD 的强度与丰度呈负相关，这意味着更常见的树种通常表现出较弱的 NDD（Comita 等人）。已经表明，植物与土壤病原体之间的相互作用在 NDD 中起着重要作用（Klironomos），而稀有物种显然受到更强的影响（Mangan 等人）。然而，这一现象背后的遗传机制仍然不清楚。在本期《分子生态学》中，Marden 等人（）提出，参与病原体识别的基因（抗性基因或 R 基因）多样性减少可能解释了为什么在当地稀有种中 NDD 更强。
