Lau Jennifer A
Center for Population Biology, University of California-Davis, California 95616, USA.
Evolution. 2006 Jan;60(1):56-63.
Both ecological and evolutionary processes can influence community assembly and stability, and native community members may respond both ecologically and evolutionarily as additional species enter established communities. Biological invasions provide a unique opportunity to examine these responses of native community members to novel species additions. Here, I use reciprocal transplant experiments among naturally invaded and uninvaded environments, along with experimental removals of exotic species, to determine whether exotic plant competitors and exotic insect herbivores evoke evolutionary changes in native plants. Specifically, I address whether the common native plant species Lotus wrangelianus has responded evolutionarily to a series of biological invasions by adapting to the presence of the exotic plant Medicago polymorpha and the exotic insect herbivore Hypera brunneipennis. Despite differences in selection regimes between invaded and uninvaded environments and the presence of genetic variation for traits relevant to the novel competitive and plant-herbivore interactions, these experiments failed to reveal evidence that Lotus has responded evolutionarily to the double invasion of Medicago followed by H. brunneipennis. However, when herbivory from H. brunneipennis was experimentally reduced, Lotus plants from source populations invaded by Medicago outperformed plants from uninvaded source populations when transplanted into heavily invaded destination environments. Therefore, Lotus showed evidence of adaptation to Medicago invasion but not to the newer invasion of an exotic shared herbivore. The presence of this exotic insect herbivore alters the outcome of evolutionary responses in this system and counteracts adaptation by the native Lotus to invasion by the exotic plant Medicago. This result has broad implications for the conservation of native communities. While native species may be able to adapt to the presence of one or a few exotics, a multitude of invasions may limit the ability of natives to respond evolutionarily to the novel and frequently changing selection pressures that arise with subsequent invasions.
生态过程和进化过程都会影响群落的组装和稳定性，当新物种进入已建立的群落时，本地群落成员可能会在生态和进化两个方面做出响应。生物入侵提供了一个独特的机会来研究本地群落成员对新物种加入的这些反应。在这里，我通过在自然入侵和未入侵环境之间进行相互移植实验，以及对外来物种进行实验性清除，来确定外来植物竞争者和外来昆虫食草动物是否会引发本地植物的进化变化。具体来说，我探讨了常见的本地植物物种兰氏百脉根是否通过适应外来植物多花苜蓿和外来昆虫食草动物褐翅豆长管蚜的存在，而对一系列生物入侵做出了进化反应。尽管入侵环境和未入侵环境之间的选择机制存在差异，并且存在与新的竞争和植物 - 食草动物相互作用相关的性状的遗传变异，但这些实验未能揭示兰氏百脉根对多花苜蓿随后被褐翅豆长管蚜双重入侵做出进化反应的证据。然而，当通过实验减少褐翅豆长管蚜的食草作用时，来自被多花苜蓿入侵的源种群的兰氏百脉根植株在移植到重度入侵的目的地环境中时，表现优于来自未入侵源种群的植株。因此，兰氏百脉根显示出适应多花苜蓿入侵的证据，但没有适应更新的外来共享食草动物的入侵。这种外来昆虫食草动物的存在改变了该系统中进化反应的结果，并抵消了本地兰氏百脉根对外来植物多花苜蓿入侵的适应。这一结果对本地群落的保护具有广泛的意义。虽然本地物种可能能够适应一种或几种外来物种的存在，但大量的入侵可能会限制本地物种对随后入侵所带来的新的且频繁变化的选择压力做出进化反应的能力。
