Ecological divergence in estuarine transition zone fishes

河口常常被描述为恶劣的环境，在那里，物理特性的陡峭梯度和强烈的潮汐混合只允许少数宽容，但丰富的居民物种共存。在河口过渡区（ETZ），淡水首先与海水混合的观察，怀疑这种一般范式的有效性。首先，在一些主要河口的ETZ中，鱼类和浮游动物是丰富的，这表明ETZ是一个重要的苗圃区。在圣劳伦斯河，ETZ支持高浓度的胡瓜鱼和小鳕鱼的所有生命史阶段，胡瓜鱼的早期生命史阶段在ETZ的浑浊沃茨中享有显着的增长和生存优势。第二，ETZ食物网在水生生态系统中似乎是独特的。消费者对当地初级生产表现出强烈的选择性，而初级生产只占总碳生产的一小部分。第三，我们已经证明了一个令人惊讶的程度，种内栖息地分区和分歧，尽管ETZ的分散性。这些观察结果表明，ETZ促进了比以前推测的更大程度的生物多样性的存在。我的长期发现资助的研究计划的最终目标是评估潜在的种内群体利用不同的资源，以适应不同的栖息地，并最终分化为不同的人口在高度动态的环境中的圣劳伦斯ETZ。我们将扩大我们的胡瓜鱼种群的研究，并扩大研究范围，包括其他种类的鱼类，以验证我们的主要假设的一般性。此外，我们将测试的假设，这些相同的环境梯度结构的整个鱼类群落。最后，碳、氮和硫的稳定同位素分析也将用于评价种内生境划分。该计划的结果将提供与河口栖息地分区相关的自然选择的强度的第一次估计，并将是非常宝贵的关键栖息地的指定和加拿大最重要的河流之一的生物多样性保护。

Estuaries are often depicted as hostile environments where steep gradients in physical characteristics and strong tidal mixing permit the co-existence of only a small number of tolerant, yet abundant, resident species. Observations in the estuarine transition zone (ETZ), where freshwater first mixes with seawater, cast doubt on the validity of this general paradigm. Firstly, fishes and zooplankton are abundant in the ETZ of a number of major estuaries, indicating that the ETZ is an important nursery zone. In the St. Lawrence River, the ETZ supports high concentrations of all life-history stages of smelt and tomcod, with the early-life history stages of smelt enjoying significant growth and survival advantages in the turbid waters of the ETZ. Secondly, the ETZ food web appears to be unique among aquatic ecosystems. Consumers show strong selectivity for local primary production that constitutes only a minor fraction of total carbon production. Thirdly, we have demonstrated a surprising degree of intraspecific habitat partitioning and divergence in spite of the dispersive nature of the ETZ. These observations suggest that the ETZ fosters the existence of a far greater degree of biodiversity than previously surmised. The ultimate objective of my long-term Discovery-funded research program is to assess the potential for intraspecific groups to exploit different resources, to adapt to distinct habitats and ultimately to diverge as distinct populations within the highly dynamic environment of the St. Lawrence ETZ. We will extend our studies of the smelt populations and expand the scope of the study to include other species of fish to verify the generality of our major hypothesis. In addition, we will test the hypothesis that these same environmental gradients serve to structure the entire fish community. Finally, stable isotope analyses of carbon, nitrogen and sulphur will also be used to evaluate intraspecific habitat partitioning. The results of this program will provide the first estimates of the strength of natural selection associated with the partitioning of habitat in estuaries and will be invaluable for the designation of critical habitat and the conservation of biodiversity in one of Canada's most important rivers.