Can Daphnia lumholtzi invade European lakes?

The cladoceran Daphnia lumholtzi is a subtropical and tropical zooplankter, and an invasive species in North America. Thus far, D. lumholtzi has not been detected in Europe. Here we investigated whether a hypothetical introduction to Europe could result in a successful invasion, either now or in the near future when facilitated by climate change. In laboratory experiments, we tested whether different clones of D. lumholtzi can invade a resident community consisting of native Daphnia from lake Klostersee, Germany, and how invasion success depends on temperature and the presence or absence of planktivorous fish. In some treatments, invasion success was consistently high, and D. lumholtzi reached densities similar to the native competitors by the end of the experiment. Surprisingly, the presence of a planktivorous fish inhibited the invasion of D. lumholtzi, and a clone with an inducible defense against fish predation was a more successful invader than a permanently defended clone. Of the three temperatures tested in this study (15, 20, and 24°C), invasion success was highest at 20°C. To understand the competitive interaction between native and introduced Daphnia, we fit a Lotka-Volterra-type competition model to the population dynamics. Our experimental and modeling results suggest that D. lumholtzi can invade European lakes and can cause substantial declines in the population size of native Daphnia, with potential consequences for higher trophic levels.

枝角类（Cladocera）的卢氏溞（Daphnia lumholtzi）是亚热带与热带浮游动物，同时也是北美地区的入侵物种。迄今为止，欧洲尚未检出该物种。本研究旨在探讨：若将该物种假设性引入欧洲，无论在当前还是受气候变化推动的近期，是否能够实现成功入侵。本研究通过室内实验，测试了不同克隆株的卢氏溞能否入侵由德国克洛斯特湖（Lake Klostersee）本土溞属物种构成的本地群落，并探究了入侵成功率如何受温度以及浮游动物食性鱼类存在与否的影响。部分实验组的入侵成功率始终较高，实验结束时，卢氏溞的种群密度已与本土竞争者趋近一致。令人意外的是，浮游动物食性鱼类的存在反而抑制了卢氏溞的入侵；且相较于具备永久防御机制的克隆株，带有可诱导型鱼类捕食防御机制的克隆株入侵成功率更高。本研究设置的三个测试温度（15、20与24℃）中，入侵成功率在20℃时达到最高。为解析本土与引入溞属物种间的竞争互作关系，本研究将洛特卡-沃尔泰拉（Lotka-Volterra）型竞争模型拟合至种群动态数据中。本研究的实验与建模结果表明，卢氏溞可入侵欧洲湖泊，并会导致本土溞属物种的种群规模大幅下降，进而对更高营养级的群落结构产生潜在影响。