Hamer A, Lane S, Mahony M
Discipline of Biological Sciences, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia.
Oecologia. 2002 Aug;132(3):445-452. doi: 10.1007/s00442-002-0968-7. Epub 2002 Aug 1.
The introduction of fish has decimated many amphibian populations through increased predation, primarily on their larvae. Some amphibian species now occupy marginal habitats as a response to the presence of introduced fish predators. Such habitats may include ephemeral water bodies where fish do not usually occur, although breeding in these suboptimal environments may incur some cost to a species if its larvae are not adapted to develop under these conditions. We investigated this scenario of amphibian decline using the endangered green and golden bell frog (Litoria aurea) and the introduced mosquitofish (Gambusia holbrooki) in a factorial experiment to determine the responses of tadpoles to declining water levels and the introduced predator. Tadpoles metamorphosed asynchronously but did not accelerate development in declining water or when housed with mosquitofish. Mass at metamorphosis was 30% less in declining water. Mass increased with time to metamorphosis in constant water-level treatments, but decreased in declining water. Tadpoles did not respond to mosquitofish and were therefore assumed to be naive to this predator. These results suggest that ephemeral habitats may be suboptimal for breeding, and tadpoles appear better suited to develop in permanent water bodies free of introduced fish. Intra-clutch variability in larval development (i.e. bet-hedging) may allow L. aurea to cope with unpredictable pond duration, whereby even permanent water bodies may occasionally dry out. The responses observed in L. aurea suggest that introduced fish may have reduced the suitability of permanent water bodies as breeding sites for other pond-breeding amphibian species. The use of less favourable ephemeral habitats as breeding sites may be responsible for some of the declines reported in amphibians since the 1970s.
鱼类的引入通过增加捕食，主要是对两栖动物幼体的捕食，导致许多两栖动物种群数量锐减。一些两栖动物物种现在占据边缘栖息地，以应对引入的鱼类捕食者的存在。此类栖息地可能包括临时性水体，鱼类通常不会出现在这些水体中，不过如果某个物种的幼体不适应在这些条件下发育，在这些不太适宜的环境中繁殖可能会给该物种带来一些代价。我们使用濒危的绿金铃蛙（Litoria aurea）和引入的食蚊鱼（Gambusia holbrooki）进行了析因实验，以研究两栖动物数量下降的这种情况，从而确定蝌蚪对水位下降和引入的捕食者的反应。蝌蚪异步变态，但在水位下降时或与食蚊鱼一起饲养时并没有加速发育。在水位下降的情况下，变态时的体重减少了30%。在恒定水位处理中，变态时的体重随变态时间增加而增加，但在水位下降时则减少。蝌蚪对食蚊鱼没有反应，因此被认为对这种捕食者缺乏经验。这些结果表明，临时性栖息地可能不太适合繁殖，蝌蚪似乎更适合在没有引入鱼类的永久性水体中发育。幼体发育的窝内变异性（即风险分摊）可能使绿金铃蛙能够应对不可预测的池塘持续时间，即使是永久性水体偶尔也可能干涸。在绿金铃蛙中观察到的反应表明，引入的鱼类可能降低了永久性水体作为其他池塘繁殖两栖动物物种繁殖地的适宜性。自20世纪70年代以来，两栖动物数量下降的部分原因可能是使用了不太有利的临时性栖息地作为繁殖地。
