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. C. 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广泛共识：物种丰富度更高的群落往往拥有更高的生物量（biomass），且其生物量随时间的波动更为稳定。然而，此类研究大多基于高度简化的食物网（food web），通常仅包含利用无机资源开展竞争的初级生产者（primary producers），且未纳入营养级相互作用（trophic interactions）。当研究纳入营养级相互作用后，多样性-生态系统功能关系的结果愈发多变，这使得“生物多样性如何影响具有更多营养级的生态系统功能”这一问题悬而未决。本研究借助淡水微宇宙（freshwater microcosms）实验，探究藻类多样性（algal diversity）（1种或4种）对群落生物量及时间变异性的影响，并设置了两种不同植食性枝角类（cladocerans）——*Ceriodaphnia dubia*与*Daphnia pulex*——的存在与缺失处理。在无植食者的对照组中，我们观测到了数百项同类研究均证实的经典模式：随着藻类物种丰富度（species richness）提升，藻类生物量增加，生物量的时间变异程度降低。当加入其中一种植食者*C. dubia*时，该经典模式得以保留。*C. dubia*对供试藻类仅表现出微弱且无选择性的啃食行为，因此多样性对生物量与变异性的影响基本未受干扰。与之形成鲜明反差的是，*D. pulex*对藻类混养群落（polycultures）表现出强烈且具有选择性的啃食，从本质上改变了两类多样性-功能关系。随着藻类丰富度提升，藻类总生物量反而下降，且时间变异程度升高。此类变化与*D. pulex*种群规模更大、种群时间变异性更低的现象相伴随。本研究结果表明，植食作用下的多样性-功能关系类型，远比仅针对单一营养级的研究所观测到的更为丰富；这也提示，在探究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。