High nutrient availability leads to weaker top-down control of stream periphyton: Compensatory feeding in Ancylus fluviatilis
High nutrient availability leads to weaker top-down control of stream periphyton: Compensatory feeding in Ancylus fluviatilis
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DOI：
10.1111/fwb.13192
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发表时间：
2019-01-01
影响因子：
2.7
通讯作者：
Fink, Patrick
中科院分区：
文献类型：
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作者：
Iannino, Alessandra;Vosshage, Alexander T. L.;Fink, Patrick
淡水生态系统中的底栖藻类生物量和分布取决于养分可用性（自下而上控制）和食草动物的放牧活动（自上而下控制）。藻类营养比例的波动可能会导致食草动物通过行为策略优化食物摄入量，以保持恒定的软体化学计量。养分有效性和藻类生物量放牧控制之间的这种联系目前还知之甚少。在这项研究中，我们测试了生活在溪流中的淡水腹足动物Ancylus Fluviatilis是否会随着附生生物营养含量的减少而增加其食物消耗率，这种行为被称为补偿性摄食。我们进行了一项全析因微观世界实验，其中两个水平的附生生物磷含量（低与高）与 12 个圆形水槽中食草动物的存在/不存在交叉。放牧1周后，通过确定放牧和未放牧水槽之间的附生生物差异来测量食物消耗率，并用变异系数描述每个水槽的附生生物生物量变异性。与高磷处理相比，低磷处理下的河曲霉的食物消耗率显着更高，支持了补偿性摄食假说。因此，在有食草动物存在的情况下，在低磷利用率下，附生生物生物量显着降低，而生物量不受无食草动物水槽中营养物富集的影响。尽管附生生物磷含量存在显着差异，但两种营养处理之间的河曲霉软体化学计量没有差异，表明具有很强的化学计量稳态。此外，在放牧的贫磷植物中，藻类生物量的分布比在富磷植物中的藻类生物量分布更加不均匀。我们的研究结果表明，营养物富集可能会导致河流生态系统中藻类生物量自上而下的控制减弱，并减少附生生物丰度的空间异质性。
Benthic algal biomass and distribution in freshwater ecosystems are determined by both nutrient availability (bottom-up control) and grazing activity by herbivores (top-down control). Fluctuations in algal nutrient ratios may cause grazers to optimise their food intake through behavioural strategies in order to maintain a constant soft body stoichiometry. Such linkages between nutrient availability and grazing control of algal biomass are as yet poorly understood. In this study, we tested whether the stream-dwelling freshwater gastropod Ancylus fluviatilis would increase its food consumption rate with decreasing periphyton nutrient content, a behaviour known as compensatory feeding. We performed a fully factorial microcosm experiment in which two levels of periphyton phosphorus content (low versus high) were crossed with grazer presence/absence in 12 circular flumes. After 1 week of grazing, food consumption rates were measured by determining the periphyton difference between grazed and ungrazed flumes, and the periphyton biomass variability in every flume was described with a coefficient of variation. The food consumption rate of A. fluviatilis was significantly higher in the low phosphorus compared to the high phosphorus treatment, supporting the compensatory feeding hypothesis. As a result, in the presence of grazers, periphyton biomass was significantly lower under low phosphorus availability, while biomass was not affected by nutrient enrichment in the grazer-free flumes. Despite the strong difference in periphyton phosphorus content, A. fluviatilis soft body stoichiometry did not differ between the two nutrient treatments, suggesting strong stoichiometric homeostasis. Furthermore, the distribution of algal biomass was significantly more heterogeneous in the grazed phosphorus-poor than in the phosphorus-rich periphyton. Our findings suggest that nutrient enrichment may lead to a weaker top-down control of algal biomass in stream ecosystems and to reduced spatial heterogeneity of periphyton abundance.