Chavarie Louise, Harford William J, Howland Kimberly L, Fitzsimons John, Muir Andrew M, Krueger Charles C, Tonn William M
Center for Systems Integration and Sustainability Michigan State University East Lansing MI USA.
Department of Biological Sciences University of Alberta Edmonton AB Canada.
Ecol Evol. 2016 Oct 5;6(21):7727-7741. doi: 10.1002/ece3.2506. eCollection 2016 Nov.
A generalist strategy, as an adaptation to environmental heterogeneity, is common in Arctic freshwater systems, often accompanied, however, by intraspecific divergence that promotes specialization in niche use. To better understand how resources may be partitioned in a northern system that supports intraspecific diversity of Lake Trout, trophic niches were compared among four shallow-water morphotypes in Great Bear Lake (N65 56' 39″, W120 50' 59″). Bayesian mixing model analyses of stable isotopes of carbon and nitrogen were conducted on adult Lake Trout. Major niche overlap in resource use among four Lake Trout morphotypes was found within littoral and pelagic zones, which raises the question of how such polymorphism can be sustained among opportunistic generalist morphotypes. Covariances of our morphological datasets were tested against δC and δN values. Patterns among morphotypes were mainly observed for δN. This link between ecological and morphological differentiation suggested that selection pressure(s) operate at the trophic level (δN), independent of habitat, rather than along the habitat-foraging opportunity axis (δC). The spatial and temporal variability of resources in Arctic lakes, such as Great Bear Lake, may have favored the presence of multiple generalists showing different degrees of omnivory along a weak benthic-pelagic gradient. Morphs 1-3 had more generalist feeding habits using both benthic and pelagic habitats than Morph 4, which was a top-predator specialist in the pelagic habitat. Evidence for frequent cannibalism in Great Bear Lake was found across all four morphotypes and may also contribute to polymorphism. We suggest that the multiple generalist morphs described here from Great Bear Lake are a unique expression of diversity due to the presumed constraints on the evolution of generalists and contrast with the development of multiple specialists, the standard response to intraspecific divergence.
作为对环境异质性的一种适应策略，泛化策略在北极淡水系统中很常见，然而，它通常伴随着种内分化，这种分化促进了生态位利用的特化。为了更好地理解在支持湖红点鲑种内多样性的北方系统中资源是如何分配的，我们比较了大熊湖（北纬65°56′39″，西经120°50′59″）四种浅水形态型湖红点鲑的营养生态位。对成年湖红点鲑进行了碳和氮稳定同位素的贝叶斯混合模型分析。在四种湖红点鲑形态型中，发现它们在沿岸带和中上层带的资源利用上存在主要生态位重叠，这就提出了一个问题：在机会主义泛化形态型中，这种多态性是如何维持的。我们对形态学数据集的协方差与δC和δN值进行了测试。主要在δN方面观察到形态型之间的模式。这种生态和形态分化之间的联系表明，选择压力作用于营养级（δN），独立于栖息地，而不是沿着栖息地-觅食机会轴（δC）。北极湖泊（如大熊湖）中资源的时空变异性，可能有利于沿着弱的底栖-中上层梯度出现多种不同程度杂食性的泛化者。形态型1-3比形态型4具有更泛化的摄食习性，它们同时利用底栖和中上层栖息地，而形态型4是中上层栖息地的顶级捕食者特化型。在所有四种形态型中都发现了大熊湖频繁发生同类相食的证据，这也可能导致多态性。我们认为，这里描述的来自大熊湖的多种泛化形态型是多样性的一种独特表现形式，这是由于泛化者进化过程中可能存在的限制，并且与多种特化型的发展形成对比，后者是种内分化的标准响应。
