Desmarais Kristen H, Tessier Alan J
W.K. Kellogg Biological Station and Department of Zoology, Michigan State University, 3700 E Gull Lake Dr., Hickory Corners, MI 49060, USA e-mail:
Oecologia. 1999 Jul;120(1):137-146. doi: 10.1007/s004420050842.
An important environmental factor determining both phytoplankton and zooplankton community composition is lake depth and thermal stratification. However, there is little information on how the interaction between zooplankton grazers and their phytoplankton food changes along an environmental gradient of lake depth. We contrasted resource availability for daphniid zooplankton populations living in two shallow, unstratified lakes and in two deep, stratified lakes using a novel growth bioassay. Stratified lakes had consistently lower resource richness than shallow unstratified lakes. To test whether resources were important in explaining differences in daphniid composition of shallow and deep lakes, we performed reciprocal transplant experiments. We raised daphniids typical of shallow (Ceriodaphnia reticulata) and deep (Daphnia dentifera) lakes in the resources from replicate shallow and deep lakes and monitored survival and reproduction. The two species exhibited a performance trade-off, measured by life table r and R , across a gradient in natural resource richness. D. dentifera had higher relative fitness than C. reticulata when raised in the poorest resource environment from a deep lake. However, under richer resource conditions typical of shallow lakes, C. reticulata outperformed D. dentifera. We further created a gradient in natural resource quantity (by dilution) to test whether this trade-off in species relative fitness involved aspects of resource quality. No trade-off in species performance was evident across the dilution gradient, indicating that resource quality was important to the trade-off. We conclude that shifts in daphniid species composition along a gradient of lake depth involve an adaptive trade-off in ability to exploit rich versus poor resource quality.
决定浮游植物和浮游动物群落组成的一个重要环境因素是湖泊深度和热分层。然而，关于浮游动物食草动物与其浮游植物食物之间的相互作用如何沿湖泊深度的环境梯度变化，目前几乎没有相关信息。我们使用一种新颖的生长生物测定法，对比了生活在两个浅水、未分层湖泊和两个深水、分层湖泊中的水蚤浮游动物种群的资源可利用性。分层湖泊的资源丰富度始终低于浅水未分层湖泊。为了测试资源是否对解释浅水湖和深水湖之间水蚤组成的差异很重要，我们进行了相互移植实验。我们在来自重复的浅水湖和深水湖的资源中培养浅水湖典型的水蚤（网纹船卵溞）和深水湖典型的水蚤（齿状溞），并监测其生存和繁殖情况。在自然资源丰富度的梯度上，这两个物种通过生命表r和R衡量表现出一种性能权衡。当在来自深水湖的最贫瘠资源环境中培养时，齿状溞的相对适合度高于网纹船卵溞。然而，在浅水湖典型的更丰富资源条件下，网纹船卵溞的表现优于齿状溞。我们进一步通过稀释创造了自然资源数量的梯度，以测试物种相对适合度的这种权衡是否涉及资源质量方面。在稀释梯度上，物种表现没有明显的权衡，这表明资源质量对这种权衡很重要。我们得出结论，水蚤物种组成沿湖泊深度梯度的变化涉及在利用丰富与贫瘠资源质量能力方面的适应性权衡。
