Choo Juanita, Carasco Cecilia, Alvarez-Loayza Patricia, Simpson Beryl B, Economo Evan P
Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Okinawa, Japan 904-0495.
Universidad Nacional San Antonio Abad del Cusco, Jr. Victoria Palestina FF-2 Santiago, Departamento de Cusco, Peru.
Ann Bot. 2017 Jul 1;120(1):147-158. doi: 10.1093/aob/mcx051.
Natural enemies are known to be important in regulating plant populations and contributing to species coexistence (Janzen-Connell effects). The strength of Janzen-Connell effects (both distance- and density-effects) varies across species, but the life history traits that may mediate such a variation are not well understood. This study examined Janzen-Connell effects across the life stages (seed through adult stages) of two sympatric palm species with distinct phenologies and shade tolerances, two traits that may mediate the strength and timing of Janzen-Connell effects.
Populations of two common palm species, Attalea phalerata and Astrocaryum murumuru , were studied in Manu National Park, Peru. Seed predation experiments were conducted to assess Janzen-Connell effects at the seed stage. In the post-seed stages, spatial point pattern analyses of the distributions of individuals and biomass were used to infer the strength of distance- and density-effects.
Seed predation was both negative distance- and density-dependent consistent with the Janzen-Connell effects. However, only seedling recruitment for asynchronously fruiting Attalea phalerata was depressed near adults while recruitment remained high for synchronously fruiting Astrocaryum murumuru , consistent with weak distance-effects. Negative density-effects were strong in the early stages for shade-intolerant Attalea phalerata but weak or absent in shade-tolerant Astrocaryum murumuru.
Distance- and density-effects varied among the life stages of the two palm species in a manner that corresponded to their contrasting phenology and shade tolerance. Generalizing such connections across many species would provide a route to understanding how trait-mediated Janzen-Connell effects scale up to whole communities of species.
已知天敌在调节植物种群和促进物种共存（简森-康奈尔效应）方面发挥着重要作用。简森-康奈尔效应（包括距离效应和密度效应）的强度因物种而异，但对可能介导这种差异的生活史特征却了解甚少。本研究考察了两种同域分布的棕榈物种在不同生活阶段（从种子到成年阶段）的简森-康奈尔效应，这两种棕榈物种具有不同的物候特征和耐荫性，而这两个特征可能介导简森-康奈尔效应的强度和时间。
在秘鲁的马努国家公园对两种常见棕榈物种阿塔莱棕（Attalea phalerata）和穆鲁穆鲁星果棕（Astrocaryum murumuru）的种群进行了研究。开展种子捕食实验以评估种子阶段的简森-康奈尔效应。在种子萌发后的阶段，利用个体和生物量分布的空间点格局分析来推断距离效应和密度效应的强度。
种子捕食呈现出与简森-康奈尔效应一致的负距离依赖性和负密度依赖性。然而，只有异步结果的阿塔莱棕在成年植株附近的幼苗补充受到抑制，而同步结果的穆鲁穆鲁星果棕的幼苗补充率仍然很高，这与较弱的距离效应一致。对于不耐荫的阿塔莱棕，早期的负密度效应很强，而对于耐荫的穆鲁穆鲁星果棕，负密度效应较弱或不存在。
两种棕榈物种在不同生活阶段的距离效应和密度效应各不相同，这种差异与它们不同的物候特征和耐荫性相对应。在多个物种中归纳此类联系将为理解性状介导的简森-康奈尔效应如何扩展到整个物种群落提供一条途径。
