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Top predators govern multitrophic diversity effects in tritrophic food webs
Ecology ( IF 4.8 ) Pub Date : 2021-05-03 , DOI: 10.1002/ecy.3379
Ruben Ceulemans 1 , Christian Guill 1 , Ursula Gaedke 1
Affiliation  

It is well known that functional diversity strongly affects ecosystem functioning. However, even in rather simple model communities consisting of only two or, at best, three trophic levels, the relationship between multitrophic functional diversity and ecosystem functioning appears difficult to generalize, because of its high contextuality. In this study, we considered several differently structured tritrophic food webs, in which the amount of functional diversity was varied independently on each trophic level. To achieve generalizable results, largely independent of parametrization, we examined the outcomes of 128,000 parameter combinations sampled from ecologically plausible intervals, with each tested for 200 randomly sampled initial conditions. Analysis of our data was done by training a random forest model. This method enables the identification of complex patterns in the data through partial dependence graphs, and the comparison of the relative influence of model parameters, including the degree of diversity, on food-web properties. We found that bottom-up and top-down effects cascade simultaneously throughout the food web, intimately linking the effects of functional diversity of any trophic level to the amount of diversity of other trophic levels, which may explain the difficulty in unifying results from previous studies. Strikingly, only with high diversity throughout the whole food web, different interactions synergize to ensure efficient exploitation of the available nutrients and efficient biomass transfer to higher trophic levels, ultimately leading to a high biomass and production on the top level. The temporal variation of biomass showed a more complex pattern with increasing multitrophic diversity: while the system initially became less variable, eventually the temporal variation rose again because of the increasingly complex dynamical patterns. Importantly, top predator diversity and food-web parameters affecting the top trophic level were of highest importance to determine the biomass and temporal variability of any trophic level. Overall, our study reveals that the mechanisms by which diversity influences ecosystem functioning are affected by every part of the food web, hampering the extrapolation of insights from simple monotrophic or bitrophic systems to complex natural food webs.

中文翻译:

顶级捕食者控制三营养食物网中的多营养多样性效应

众所周知,功能多样性强烈影响生态系统功能。然而,即使在仅由两个或最多三个营养级组成的相当简单的模型群落中,多营养功能多样性与生态系统功能之间的关系似乎也难以概括,因为它具有高度的背景性。在这项研究中,我们考虑了几种不同结构的三营养食物网,其中功能多样性的数量在每个营养水平上独立变化。为了获得可概括的结果,在很大程度上独立于参数化,我们检查了从生态合理区间采样的 128,000 个参数组合的结果,每个组合测试了 200 个随机采样的初始条件。我们的数据分析是通过训练随机森林模型完成的。该方法可以通过部分依赖图识别数据中的复杂模式,并比较模型参数(包括多样性程度)对食物网特性的相对影响。我们发现自下而上和自上而下的效应在整个食物网中同时级联,将任何营养级别的功能多样性的影响与其他营养级别的多样性数量密切相关,这可能解释了统一先前研究结果的困难. 引人注目的是,只有在整个食物网中具有高度多样性,不同的相互作用才能协同作用,以确保有效利用可用营养并将生物量有效转移到更高的营养水平,最终导致高生物量和顶级产量。随着多营养多样性的增加,生物量的时间变化表现出更复杂的模式:虽然系统最初变得不太可变,但最终由于越来越复杂的动态模式,时间变化再次上升。重要的是,影响顶级营养级的顶级捕食者多样性和食物网参数对于确定任何营养级的生物量和时间变异性至关重要。总体而言,我们的研究表明,多样性影响生态系统功能的机制受到食物网每个部分的影响,阻碍了将见解从简单的单营养或双营养系统外推到复杂的自然食物网。最终,由于日益复杂的动态模式,时间变化再次上升。重要的是,影响顶级营养级的顶级捕食者多样性和食物网参数对于确定任何营养级的生物量和时间变异性至关重要。总体而言,我们的研究表明,多样性影响生态系统功能的机制受到食物网每个部分的影响,阻碍了将见解从简单的单营养或双营养系统外推到复杂的自然食物网。最终,由于日益复杂的动态模式,时间变化再次上升。重要的是,影响顶级营养级的顶级捕食者多样性和食物网参数对于确定任何营养级的生物量和时间变异性至关重要。总体而言,我们的研究表明,多样性影响生态系统功能的机制受到食物网每个部分的影响,阻碍了将见解从简单的单营养或双营养系统外推到复杂的自然食物网。
更新日期:2021-07-01
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