Testing the Janzen-Connell mechanism: pathogens cause overcompensating density dependence in a tropical tree
Testing the Janzen-Connell mechanism: pathogens cause overcompensating density dependence in a tropical tree
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DOI：
10.1111/j.1461-0248.2010.01520.x
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发表时间：
2010-10-01
期刊：
影响因子：
8.8
通讯作者：
Freckleton, Robert P.
中科院分区：
文献类型：
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作者：
Bagchi, Robert;Swinfield, Tom;Freckleton, Robert P.
Janzen-Connell假说是对热带森林植物物种多样性的主要解释。这表明，在高密度下，专门的天敌降低了后代的存活率，使当地稀有物种具有优势。这种机制，在其最初的形式，假设密度依赖是过度补偿：死亡率必须在最高密度不成比例地高，很少有后代招募低于他们的父母。我们测试了这一假设，采用平行的遮荫室和现场密度系列实验的热带树木，Pleradenophora longicuspis的幼苗。我们发现强大的，过度补偿死亡率驱动的真菌病原体，造成90%（荫棚）或100%（字段）的死亡率在4周内发芽，并产生初始和最终幼苗密度之间的负相关关系。杀真菌剂治疗导致低得多，密度无关，死亡率。过度补偿性死亡非常迅速，如果没有详细的监测，可能会被遗漏。这种动态可能会阻止死树被同种替代，促进共存，如Janzen-Connell假说所设想的那样。
P>The Janzen-Connell hypothesis is a leading explanation for plant-species diversity in tropical forests. It suggests that specialized natural enemies decrease offspring survival at high densities beneath parents, giving locally rarer species an advantage. This mechanism, in its original form, assumes that density dependence is overcompensating: mortality must be disproportionately high at the highest densities, with few offspring recruiting below their parents. We tested this assumption using parallel shadehouse and field density-series experiments on seedlings of a tropical tree, Pleradenophora longicuspis. We found strong, overcompensating mortality driven by fungal pathogens, causing 90% (shadehouse) or 100% (field) mortality within 4 weeks of germination, and generating a negative relationship between initial and final seedling densities. Fungicide treatment led to much lower, density-independent, mortality. Overcompensating mortality was extremely rapid, and could be missed without detailed monitoring. Such dynamics may prevent dead trees from being replaced by conspecifics, promoting coexistence as envisioned by the Janzen-Connell hypothesis.