Limnology/Aquaripária Lab, Department of Ecology, IB, University of Brasília (UnB), Brasília, Brazil.
Faculty of Science and Technology, University of the Basque Country (UPV/EHU), Leioa, Spain.
J Anim Ecol. 2018 Sep;87(5):1465-1474. doi: 10.1111/1365-2656.12876. Epub 2018 Jul 16.
Understanding how biodiversity loss influences plant litter decomposition-that is, the biologically mediated conversion of coarse to fine particulate organic matter-is crucial to predict changes in the functioning of many stream ecosystems, where detrital food webs are dominant. Rates of litter decomposition are influenced by detritivore diversity, but the mechanisms behind this relationship are uncertain. As differences in detritivore body size are a major determinant of interspecific interactions, they should be key for predicting effects of detritivore diversity on decomposition. To explore this question, we manipulated detritivore diversity and body size simultaneously in a microcosm experiment using two small (Leuctra geniculata and Lepidostoma hirtum) and two large detritivore species (Sericostoma pyrenaicum and Echinogammarus berilloni) in all possible 1-, 2- and 4-species combinations, and litter discs of Alnus glutinosa. We expected that larger species would facilitate smaller species through the production of smaller litter fragments, resulting in faster decomposition and greater growth of smaller species in polycultures containing species of different body size. To examine this hypothesis, we used a set of "diversity-interaction" models that explored how decomposition was affected by different interspecific interactions and the role of body size, and quantified the magnitude of such effect through ratios of decomposition rates and detritivore growth between polycultures and monocultures. We found a clear positive effect of detritivore diversity on decomposition, which was mainly explained by facilitation and niche partitioning. Facilitation of small animals by larger ones was evidenced by a 12% increase in decomposition rates in polycultures compared to monocultures and the higher growth (20%) of small species, which partly fed on fine particulate organic matter produced by larger animals. When the large species were together in polycultures, decomposition was enhanced by 19%, but there were no changes in growth; niche partitioning was a plausible mechanism behind the increase in decomposition rates, as both species fed on different parts of litter discs, only one species being able to eat less palatable parts. Our study demonstrates that interspecific differences in body size should be taken into account in diversity-decomposition studies. Future studies should also consider differences in species' vulnerability to extinction depending on body size and how this might affect ecosystem functioning in different scenarios of detritivore diversity and more complex food webs.
理解生物多样性丧失如何影响植物凋落物分解——即粗颗粒有机物质通过生物介导转化为细颗粒有机物质——对于预测许多溪流生态系统功能的变化至关重要，因为碎屑食物网在这些生态系统中占主导地位。凋落物分解的速度受碎屑分解者多样性的影响，但这种关系背后的机制尚不确定。由于碎屑分解者的体型差异是种间相互作用的主要决定因素，因此它们应该是预测碎屑分解者多样性对分解作用影响的关键。为了探讨这个问题，我们在一个微宇宙实验中同时操纵了碎屑分解者的多样性和体型，使用了两种小型（Leuctra geniculata 和 Lepidostoma hirtum）和两种大型碎屑分解者物种（Sericostoma pyrenaicum 和 Echinogammarus berilloni），并使用 Alnus glutinosa 的凋落物圆盘，所有可能的 1、2 和 4 种组合。我们预计，较大的物种会通过产生较小的凋落物碎片来促进较小的物种，从而导致在包含不同体型物种的多物种培养物中更快的分解和较小物种的更大生长。为了检验这个假设，我们使用了一组“多样性-相互作用”模型，该模型探讨了分解如何受到不同种间相互作用和体型的影响，并通过多物种培养物和单物种培养物之间的分解速率和碎屑分解者生长比来量化这种影响的程度。我们发现，碎屑分解者多样性对分解有明显的正效应，这主要是由促进作用和生态位分化解释的。较大的动物对小型动物的促进作用表现在多物种培养物中分解速率比单物种培养物中增加了 12%，并且小型动物的生长（20%）更高，这部分是由较大动物产生的细颗粒有机物质喂养的。当大型物种在多物种培养物中一起时，分解作用增强了 19%，但生长没有变化；生态位分化是分解速率增加的一个合理机制，因为两种物种都以凋落物圆盘的不同部分为食，只有一种物种能够吃不太可口的部分。我们的研究表明，在多样性-分解研究中应考虑体型的种间差异。未来的研究还应考虑物种对灭绝的脆弱性取决于体型的差异，以及这可能如何影响不同碎屑分解者多样性和更复杂食物网情景下的生态系统功能。
