ABSTRACT

Small cladocerans, found abundantly on surfaces of macrophytes and sediments in the littoral zone, are important prey not only for small fish but also for various invertebrates such as larvae of odonates in freshwater habitats. However, no study has documented how habitat substrates affect their behavior and vulnerability to predators and predation. We conducted laboratory experiments to examine the movement of 3 littoral cladoceran species, Chydorus sphaericus, Alona sp., and Ilyocryptus spinifer, to determine if their vulnerabilities to predation by odonate larvae changed depending on the presence or absence of bottom sediment. We observed that when sediment was present, Ilyocryptus crawled in and ceased movement. However, in the containers without sediment, they continuously swam or crawled. Similarly, Chydorus also reduced frequency of movement in a container with sediment, but Alona movement did not change regardless of the presence or absence of sediment. In the predation experiments with 2 or 3 prey species, Ilyocryptus was the most vulnerable to predation by odonate larvae in the containers without sediment but least vulnerable in those with sediment. The vulnerability of Chydorus to the odonate larvae was as low as that of Ilyocryptus in the containers with sediment. Alona was less preyed upon by odonates in containers with sediment but highly vulnerable to predation when containers had sediment with Chydorus and Ilyocryptus. These results indicate that behavior and vulnerability to predation of littoral cladocerans are species-specific and change depending on the presence of sediment and the existence of other species.

摘要

小型枝角类动物广泛存在于沿海地区的大型植物和沉积物的表面，不仅是小鱼的重要猎物，也是淡水栖息地中各种无脊椎动物的重要猎物，如无脊椎动物的幼虫。然而，没有研究记录栖息地基质如何影响它们的行为以及对捕食者和捕食的脆弱性。我们进行了实验室实验，以检查 3 种沿海枝角类动物的运动，Chydorus sphaericus、Alona sp. 和Ilyocryptus spinifer，以确定它们对齿状幼虫捕食的脆弱性是否会根据底部沉积物的存在或不存在而改变。我们观察到，当存在沉积物时，Ilyocryptus爬了进来，停止了动作。然而，在没有沉淀物的容器中，它们不断地游动或爬行。类似地，Chydorus也减少了在装有沉积物的容器中的运动频率，但无论是否存在沉积物，Alona运动都不会改变。在对2或3种猎物的捕食实验中，Ilyocryptus在没有沉积物的容器中最容易被齿状幼虫捕食，而在有沉积物的容器中则最不脆弱。Chydorus对齿状幼虫的脆弱性与在有沉积物的容器中的Ilyocryptus一样低。阿罗娜在有沉积物的容器中较少被 odonates 捕食，但当容器中含有Chydorus和Ilyocryptus 的沉积物时极易被捕食。这些结果表明，沿海枝角类动物捕食的行为和脆弱性是物种特异性的，并且根据沉积物的存在和其他物种的存在而变化。