Leibold M A
Kellogg Biological Station, Department of Zoology, Michigan State University, 49060, Hickory Corners, MI, USA.
Oecologia. 1991 May;86(4):510-520. doi: 10.1007/BF00318317.
Two commonly coexisting species of Daphnia segregate by habitat in many stratified lakes. Daphnia pulicaria is mostly found in the hypolimnion whereas D. galeata mendotae undergoes diel vertical migration between the hypolimnion and the epilimnion. I examined how habitat segregation between these two potentially competing species might be affected by trophic interactions with their resources and predators by performing a field experiment in deep enclosures in which I manipulated fish predation, nutrient levels, and the density of epilimnetic Daphnia. The results of the experiment indicate that habitat use by D. pulicaria can be jointly regulated by competition for food from epilimnetic Daphnia and predation by fishes. Patterns of habitat segregation between the two Daphnia species were determined by predation by fish but not by nutrient levels: The removal of epilimnetic fish predators resulted in higher zooplankton and lower epilimnetic phytoplankton densities and allowed D. pulicaria to expand its habitat distribution into the epilimnion. In contrast, increased resource productivity resulted in higher densities of both Daphnia species but did not affect phytoplankton levels or habitat use by Daphnia. The two species exhibit a trade-off in their ability to exploit resources and their susceptibility to predation by fish. D. g. mendotae (the less susceptible species) may thus restrict D. pulicaria (the better resource exploiter) from the epilimnion when fish are common due to lower minimum resource requirements than those needed by D. pulicaria to offset the higher mortality rate imposed by selective epilimnetic fish predators. D. g. mendotae does not appear to have this effect in the absence of fish.
在许多分层湖泊中，两种常见的共存水蚤物种按栖息地进行分隔。蚤状溞大多出现在湖下层，而明多塔水蚤则在湖下层和湖上层之间进行昼夜垂直迁移。我通过在深围隔中进行实地实验，研究了这两种潜在竞争物种之间的栖息地分隔可能如何受到与它们的资源和捕食者之间的营养相互作用的影响。在实验中，我控制了鱼类捕食、营养水平以及湖上层水蚤的密度。实验结果表明，蚤状溞的栖息地利用可由与湖上层水蚤的食物竞争和鱼类捕食共同调节。两种水蚤物种之间的栖息地分隔模式由鱼类捕食决定，而非营养水平：去除湖上层的鱼类捕食者会导致浮游动物密度升高、湖上层浮游植物密度降低，并使蚤状溞将其栖息地分布扩展到湖上层。相比之下，资源生产力的提高导致两种水蚤的密度都升高，但并未影响浮游植物水平或水蚤的栖息地利用。这两个物种在利用资源的能力和对鱼类捕食的易感性方面表现出一种权衡。因此，当鱼类常见时，由于明多塔水蚤（较不易感的物种）所需的最低资源需求低于蚤状溞抵消选择性湖上层鱼类捕食者施加的较高死亡率所需的资源需求，明多塔水蚤可能会限制蚤状溞（更好的资源利用者）进入湖上层。在没有鱼类的情况下，明多塔水蚤似乎没有这种影响。
