Data from: Herbivores control effects of algal species richness on community biomass and stability in a laboratory microcosm experiment

Hundreds of studies that have explored how biodiversity affects the productivity and stability of ecosystems have produced a consensus that communities composed of more species tend to have higher biomass that is more stable through time. However, the majority of this work stems from studies performed using highly simplified food webs, often composed of just primary producers competing for inorganic resources in the absence of trophic interactions. When studies have incorporated trophic interactions, diversity-function relationships have been more variable, leaving open the question of how biodiversity affects the functioning of ecosystems with more trophic levels. Here we report the results of a laboratory experiment that used freshwater microcosms to test for effects of algal diversity (one or four species) on community biomass and temporal variability in the presence and absence of two different herbivore species (cladocerans Ceriodaphnia dubia and Daphnia pulex). When no herbivores were present, we found the classic pattern observed in hundreds of other studies – as species richness of algae increased, algal biomass increased, and the temporal variation in biomass decreased. This pattern was retained when one of the herbivores (C. dubia) was present. Ceriodaphnia dubia exhibited weak and non-selective grazing on the focal algae, leaving the effect of diversity on biomass and variability essentially intact. In contrast, D. pulex exhibited strong and selective grazing in algal polycultures that qualitatively altered both diversity–function relationships. As algal richness increased, total algal biomass decreased and variation through time increased. These changes were coupled with larger and less variable populations of D. pulex. Our results show that herbivory leads to a richer array of diversity–function relationships than often observed in studies focused on just one trophic level, and suggests trophic interactions should be given more attention in work that seeks to determine how biodiversity impacts the functioning of ecosystems.已有数百项探索生物多样性（biodiversity）如何影响生态系统生产力与稳定性的研究达成共识：物种组成更丰富的群落，其生物量通常更高，且随时间推移的稳定性更强。然而，这类研究大多基于高度简化的食物网模型，通常仅包含在无营养级相互作用的条件下竞争无机资源的初级生产者。当研究纳入营养级相互作用后，多样性-功能关系的表现则更为多变，这使得生物多样性对多营养级生态系统功能的影响这一问题仍未得到解答。本研究报告一项实验室微宇宙实验的结果：我们利用淡水微宇宙（freshwater microcosms），设置不同藻类多样性梯度（单物种或四物种组合），并在有/无两种不同植食性枝角类[角突网纹溞（Ceriodaphnia dubia）与蚤状溞（Daphnia pulex）]的条件下，探究藻类多样性对群落生物量及其时间变异性的影响。在无植食性动物的对照组中，我们观测到了数百项同类研究均报道的经典模式：随着藻类物种丰富度提升，藻类生物量增加，而生物量的时间变异性降低。当加入其中一种植食性动物（角突网纹溞）时，该经典模式得以保留。角突网纹溞对受试藻类的取食行为较弱且无选择性，因此多样性对生物量及其变异性的影响基本未受干扰。与之形成鲜明对比的是，蚤状溞在藻类多物种组合中表现出强烈且具有选择性的取食行为，从本质上改变了两类多样性-功能关系。随着藻类物种丰富度提升，总藻类生物量反而下降，而其时间变异性则升高。这类变化与蚤状溞种群规模更大、种群波动更小的现象相伴随。本研究结果表明，与仅聚焦单一营养级的研究相比，植食作用会催生更为多样的多样性-功能关系模式；同时也提示，在旨在探明生物多样性如何影响生态系统功能的研究中，应给予营养级相互作用更多关注。