Data from: Competition, seed dispersal, and hunting: what drives germination and seedling survival in an Afrotropical forest?

Disentangling the contributions of different processes that influence plant recruitment, such as competition and seed dispersal, is important given the increased human-mediated changes in tropical forest ecosystems. Previous studies have shown that seedling communities in an Afro-tropical rainforest in Southeastern Nigeria are strongly affected by the loss of important seed dispersing primates, including Cross River gorillas (Gorilla gorilla diehli), chimpanzee (Pan troglodytes elioti), and drill (Mandrillus leucophaeus). Here we study how germination and survival of tree seedlings are affected by competition and reduced seed-dispersal in three contiguous forest reserves, in Southeastern Nigeria, with similar mature tree species composition and structure. We use an experimental design aimed at manipulating the effect of competition among seedlings in three protected and three hunted sites within the reserves. We use a total of sixty 5×5 m plots of three types: plots cleared of all seedlings, plots selectively cleared of all primate-dispersed seedlings and control plots. All seedlings were identified, measured, assigned to dispersal mode, and tagged, and after one year we evaluated survival, mortality and new recruits. We found that in hunted sites germination of abiotically dispersed species was over four times higher in cleared plots compared to control plots, whereas germination of primate dispersed species was the same, which indicated that dispersal limitation was the dominant force in seedling recruitment in hunted sites. This was supported by the fact that the germination of all dispersal modes in the selectively cleared plots in protected sites was similar to the control plots in the same sites, but germination of abiotically dispersed species was significantly lower than in cleared plots in hunted sites. Competition among seedlings was mostly evident from the fact that 75% more seedlings of primate dispersed species germinated in cleared compared to control plots in protected sites. We conclude that inter-seedling competition may be irrelevant to seedling recruitment in hunted sites, where dispersal limitation appears to be a much stronger force shaping the seedling plant community, and thus hunting indirectly reverses the importance of competition and dispersal limitation in structuring seedling communities.鉴于热带森林生态系统正日益受到人类活动介导的改变，解析影响植物补充的不同过程（如种间竞争与种子扩散）的相对贡献，具有重要意义。既往研究显示，尼日利亚东南部非洲热带雨林中的幼苗群落，受重要种子扩散灵长类动物丧失的影响显著，这些灵长类包括克罗斯河大猩猩（Gorilla gorilla diehli）、埃利奥特黑猩猩（Pan troglodytes elioti）以及鬼狒（Mandrillus leucophaeus）。本研究聚焦尼日利亚东南部三处连续的森林保护区，这些区域的成熟乔木物种组成与结构均较为相似，旨在探究种间竞争与种子扩散能力下降如何影响林木幼苗的萌发与存活。我们设计了实验方案，在保护区内的3个受保护样点与3个受狩猎干扰样点中，对幼苗间的竞争效应进行操控。本研究共设置60个5×5米的样方，分为三类：清除所有幼苗的样方、选择性清除所有灵长类扩散型幼苗的样方，以及对照样方。研究人员对所有幼苗进行物种鉴定、形态测量、扩散模式归类并佩戴标签；在实验开展一年后，我们对幼苗的存活、死亡情况以及新补充的幼苗进行了评估。我们发现，在受狩猎干扰的样点中，非生物扩散型物种的萌发率在清除幼苗的样方中较对照样方高出4倍以上，而灵长类扩散型物种的萌发率则无显著差异，这表明在受狩猎干扰的样点中，扩散限制是驱动幼苗补充的主导因素。这一结论得到了以下结果的支撑：在受保护样点中，选择性清除样方内所有扩散模式的幼苗萌发率与同区域的对照样方无显著差异，但非生物扩散型物种的萌发率显著低于受狩猎干扰样点中的清除幼苗样方。幼苗间的竞争效应在受保护样点中体现得尤为明显：灵长类扩散型物种在清除幼苗的样方中的萌发率较对照样方高出75%。综上，我们认为在受狩猎干扰的样点中，幼苗间的种间竞争与幼苗补充过程无关；此类样点中的幼苗群落构建主要受扩散限制的主导作用，因此狩猎活动间接逆转了种间竞争与扩散限制在塑造幼苗群落结构中的相对重要性。