Graduate School of Life Sciences, Tohoku University, Aobayama, Sendai 980-8578, Japan.
Conserv Biol. 2010 Aug;24(4):1141-7. doi: 10.1111/j.1523-1739.2010.01457.x. Epub 2010 Feb 22.
The influence of non-native species on native ecosystems is not predicted easily when interspecific interactions are complex. Species removal can result in unexpected and undesired changes to other ecosystem components. I examined whether invasive non-native species may both harm and provide refugia for endangered native species. The invasive non-native plant Casuarina stricta has damaged the native flora and caused decline of the snail fauna on the Ogasawara Islands, Japan. On Anijima in 2006 and 2009, I examined endemic land snails in the genus Ogasawarana. I compared the density of live specimens and frequency of predation scars (from black rats [Rattus rattus]) on empty shells in native vegetation and Casuarina forests. The density of land snails was greater in native vegetation than in Casuarina forests in 2006. Nevertheless, radical declines in the density of land snails occurred in native vegetation since 2006 in association with increasing predation by black rats. In contrast, abundance of Ogasawarana did not decline in the Casuarina forest, where shells with predation scars from rats were rare. As a result, the density of snails was greater in the Casuarina forest than in native vegetation. Removal of Casuarina was associated with an increased proportion of shells with predation scars from rats and a decrease in the density of Ogasawarana. The thick and dense litter of Casuarina appears to provide refugia for native land snails by protecting them from predation by rats; thus, eradication of rats should precede eradication of Casuarina. Adaptive strategies, particularly those that consider the removal order of non-native species, are crucial to minimizing the unintended effects of eradication on native species. In addition, my results suggested that in some cases a given non-native species can be used to mitigate the impacts of other non-native species on native species.
当种间相互作用复杂时，非本地物种对本地生态系统的影响不容易预测。物种的移除可能会导致其他生态系统组成部分产生意想不到和不期望的变化。我研究了入侵的非本地物种是否可能同时伤害和为濒危的本地物种提供避难所。入侵的非本地植物木麻黄已破坏了日本小笠原群岛的本地植物群，并导致蜗牛动物群的减少。在 2006 年和 2009 年，我在安积岛上研究了 Ogasawaraana 属的特有陆地蜗牛。我比较了在本地植被和木麻黄林中活体标本的密度和空壳上的捕食痕迹（来自黑鼠[Rattus rattus]）的频率。2006 年，本地植被中陆地蜗牛的密度大于木麻黄林中的密度。然而，自 2006 年以来，由于黑鼠捕食的增加，本地植被中陆地蜗牛的密度急剧下降。相比之下，在木麻黄林中，由于老鼠捕食的痕迹很少，Ogasawarana 的丰度没有下降。因此，木麻黄林中的蜗牛密度大于本地植被。木麻黄的去除与来自老鼠的具有捕食痕迹的贝壳的比例增加以及 Ogasawarana 的密度降低有关。木麻黄茂密而密集的凋落物似乎通过保护它们免受老鼠捕食，为本地陆地蜗牛提供了避难所；因此，应该在消灭木麻黄之前消灭老鼠。适应性策略，特别是那些考虑非本地物种的去除顺序的策略，对于最小化消灭对本地物种的意外影响至关重要。此外，我的结果表明，在某些情况下，特定的非本地物种可以用来减轻其他非本地物种对本地物种的影响。
