Testing for enemy-mediated density-dependence in the mortality of seedlings: field experiments with five Neotropical tree species
Testing for enemy-mediated density-dependence in the mortality of seedlings: field experiments with five Neotropical tree species
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DOI：
10.1111/j.1600-0706.2013.00835.x
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发表时间：
2014-02-01
期刊：
影响因子：
3.4
通讯作者：
Lewis, Owen T.
中科院分区：
文献类型：
--
作者：
Gripenberg, Sofia;Bagchi, Robert;Lewis, Owen T.
在物种丰富的热带森林中，物种丰富的植物物种的共存可以通过特殊的敌人以负密度依赖的方式来促进。虽然热带树苗的存活往往与密度负相关，但其原因很少被发现。我们在中美洲伯利兹的五种森林树种上测试了昆虫和植物病原体是否导致依赖密度的幼苗招募和存活。我们在靠近果树的小块(1米(2)或0.25米(2))中操纵种子或新萌发的幼苗的密度。使用析因设计，我们从含有杀菌剂和杀虫剂的地块的子集中排除了敌人。在植物最容易受天敌影响的时期，对种子萌发(对两个物种)和早期幼苗存活(对所有物种)进行了大约每周一次的监测，最长可达八周。在水曲柳中，种子萌发与密度呈负相关，排除昆虫后种子萌发率增加。然而，杀虫效果的大小与密度无关。密度对幼苗存活率的唯一显著影响是多叶相思；与预期相反，高密度的幼苗存活率更高。在少数情况下，施药对苗木成活率有显著影响，但只有一种情况下，施药与密度存在显著互作。我们的结果告诫不要对在单一时间和地点进行的单一物种的研究进行概括，并说明了在实验中测试敌人中介的负密度依赖的挑战。实验结果可能取决于主要天敌分散的空间尺度和对植物密度的反应，以及它们行动的时间尺度。收集有关这些变量的信息将提高我们对热带森林物种自然历史的理解，并有助于为未来实验的设计提供信息。
The coexistence of plant species in species-rich tropical forests can be promoted by specialised enemies acting in a negatively density-dependent manner. While survival of tropical tree seedlings is often negatively density-dependent, the causes have rarely been identified. We tested whether insects and plant pathogens cause density-dependent seedling recruitment and survival in five forest tree species in Belize, Central America. We manipulated densities of seeds or newly germinated seedlings in small (1 m(2) or 0.25 m(2)) plots close to fruiting conspecific trees. Using a factorial design, we excluded enemies from subsets of the plots with fungicides and insecticides. Seed germination (for two species) and early seedling survival (for all species) were monitored at approximately weekly intervals for up to eight weeks, during the period when plants are likely to be most susceptible to natural enemies. In Terminalia amazonia, seed germination was negatively density-dependent and the proportion of seeds germinating increased when insects were excluded. However, the magnitude of the insecticide effect was independent of density. The only significant density effect for survival of young seedlings was in Acacia polyphylla; counter to expectation, seedling survival was higher at high densities. In a few cases pesticide application had a significant effect on seedling survival, but in only one case (Terminalia amazonia) was a significant pesticide x density interaction detected. Our results caution against generalising from studies conducted on a single species at a single time and place and illustrate the challenges of experimentally testing for enemy-mediated negative density-dependence. Experimental outcomes are likely to depend on the spatial scale at which the principal enemies disperse and respond to plant density, and the timescales over which they act. Gathering information on these variables will improve our understanding of the natural histories of tropical forest species and help inform the design of future experiments.