Research Centre for Watershed - Aquatic Ecosystem Interactions, Université du Québec à Trois-Rivières, C. P. 500, Trois-Rivières, QC, G9A 5H7, Canada.
Oecologia. 2021 Jan;195(1):77-92. doi: 10.1007/s00442-020-04822-6. Epub 2021 Feb 1.
Ecological opportunity occurs when a resource becomes available through a decrease of interspecific competition and another species colonizes the vacant niche through phenotypic plasticity and intraspecific competition. Brook charr exhibit a resource polymorphism in some Canadian Shield lakes, where a littoral ecotype feeds mainly on zoobenthos and a pelagic ecotype feeds mostly on zooplankton. The objectives of this study were to test that (i) resource polymorphism is common in these brook charr populations, (ii) the presence creek chub and white sucker, two introduced species competing with brook charr for littoral resources, will decrease the phenotypic divergence between the two brook charr ecotypes, and (iii) the ecological release from introduced species will increase population and/or individual niche widths in brook charr. The study was based on 27 lakes and five indicators of resource use (stomach content, liver δC, muscle astaxanthin concentration, pyloric caecum length, and gill raker length). Our results indicate that within-lake differences in resource use by both ecotypes are common and stable through time. When facing interspecific competition, both littoral and pelagic brook charr incorporated more pelagic prey into their diet but maintained the amplitude of their differences in resource use, which contradicts our second prediction. Finally, we did not find any significant effect of introduced species on population and individual niche widths of brook charr. We suggest that the difference in feeding mode among distantly related competitors could prevent the complete exclusion of a species from a given niche and explain the lack of response to the ecological release.
生态机会是指当一种资源由于种间竞争减少而变得可用，并且另一种物种通过表型可塑性和种内竞争占据空缺生态位时出现的机会。在一些加拿大盾状地区的湖泊中，溪红点鲑表现出资源多态性，其中浅滩生态型主要以底栖动物为食，而浮游生态型主要以浮游动物为食。本研究的目的是检验以下几点：(i) 这种资源多态性在这些溪红点鲑种群中很常见；(ii) 溪红点鲑的两种入侵物种，小口弓鱼和白鮎，与溪红点鲑争夺浅滩资源，会降低两种溪红点鲑生态型之间的表型差异；(iii) 引入物种的生态释放会增加溪红点鲑的种群和/或个体生态位宽度。本研究基于 27 个湖泊和五个资源利用指标（胃内容物、肝脏 δC、肌肉虾青素浓度、幽门盲囊长度和鳃耙长度）。我们的结果表明，两种生态型在湖泊内的资源利用差异是普遍存在且稳定的。当面临种间竞争时，浅滩和浮游生态型的溪红点鲑都会更多地将浮游猎物纳入其饮食，但保持其资源利用差异的幅度，这与我们的第二个预测相矛盾。最后，我们没有发现引入物种对溪红点鲑种群和个体生态位宽度有任何显著影响。我们认为，在给定的生态位中，由于竞争物种之间的摄食模式存在差异，可能会阻止一个物种完全被排除在外，并解释了对生态释放缺乏反应的原因。
