Data from: Resource composition mediates the effects of intraspecific variability in nutrient recycling on ecosystem processes

Despite the growing evidence for individual variation in trophic niche within populations, its potential indirect effects on ecosystem processes remains poorly understood. In particular, few studies have investigated how intraspecific trophic variability can modulate the effects of consumers on ecosystems through potential changes in nutrient excretion rates. Here, we first quantified the level of intraspecific trophic variability in 11 wild populations of the omnivorous fish Lepomis gibbosus. Outputs from stomach content and stable isotope analyses revealed that the degree of trophic specialization and trophic positions were highly variable between and within these wild populations. There was intrapopulation variation in trophic position of more than one trophic level, suggesting that individuals consumed a range of plant and animal resources. We then experimentally manipulated intraspecific trophic variability to assess how it can modulate consumer-mediated nutrient effects on relevant processes of ecosystem functioning. Specifically, three food sources varying in nutrient quality (e.g. plant material, macro-invertebrate and fish meat) were used individually or in combination to simulate seven diet treatment. Results indicated that intraspecific variability in growth and nitrogen excretion rates were more related to the composition of the diet rather than the degree of specialization, and increased with the trophic position of the diet consumed. We subsequently used microcosms and showed that critical ecosystem functions, such as primary production and community respiration, were affected by the variability in excretory products, and this effect was biomass-dependent. These results highlight the importance of considering variation within species to better assess the effects of individuals on ecosystems and, more specifically, the effects of consumer-mediated nutrient recycling because the body size and the trophic ecology of individuals are affected by a large spectrum of natural and human-induced environmental changes.

尽管种群内个体间营养生态位（trophic niche）存在差异的相关证据日益丰富，但此类差异对生态系统过程的潜在间接效应仍未得到充分解析。尤为关键的是，目前鲜有研究探讨种内营养变异性（intraspecific trophic variability）如何通过改变养分排泄速率（nutrient excretion rates），进而调控消费者对生态系统的影响。本研究首先量化了11个野生杂食性鱼类（omnivorous fish）驼背太阳鱼（Lepomis gibbosus）种群的种内营养变异性水平。胃含物分析（stomach content analysis）与稳定同位素分析（stable isotope analysis）结果显示，这些野生种群内部及种群间的营养特化（trophic specialization）程度与营养级位（trophic position）均存在显著差异。种群内部的营养级位差异可达一个以上营养级，表明该物种的个体会取食多种植物与动物资源。随后，本研究通过实验操控种内营养变异性，以探究其如何调控消费者介导的养分效应对生态系统功能相关过程的影响。具体而言，我们选取养分质量存在差异的3种食物源（例如植物材料、大型无脊椎动物与鱼肉），分别单独饲喂或组合饲喂，以模拟7种日粮处理组。研究结果表明，个体生长与氮排泄速率的种内变异性更多与日粮组成相关，而非营养特化程度，且随所取食物的营养级位升高而增强。后续我们借助生态微宇宙（microcosm）实验发现，初级生产（primary production）、群落呼吸（community respiration）等关键生态系统功能会受排泄物变异性的影响，且该效应具有生物量依赖性。上述研究结果凸显了考虑种内变异的重要性，以便更精准地评估个体对生态系统的影响，尤其是消费者介导的养分循环（consumer-mediated nutrient recycling）效应——因为个体的体型与营养生态会受到大量自然及人为环境变化的影响。