Data from: Genetic variation in invasive species response to direct and indirect species interactions

Biotic resistance to invasion arises from strong species interactions that decrease the fitness and population growth rates of potential invaders. Strong, direct interactions such as predation and competition are typically thought to drive biotic resistance, but in diverse communities, indirect interactions among species may also affect biotic resistance. Further, genetic variation in traits of the invading species that affect species interactions may allow some genotypes to overcome biotic resistance. We investigated the direct and indirect effects of a native legume (Acmispon wrangelianus) and insect herbivores on the fitness of different genotypes of an invasive legume (Medicago polymorpha) in a California grassland. Insect herbivores decreased Medicago fitness, but only in the presence of Acmispon, suggesting that indirect interactions mediated through insects and Acmispon are important for deterring Medicago invasion. Some Medicago genotypes were less affected by interactions with other species, however. This genetic variance suggests that while biotic resistance reduced the reproductive success of most genotypes, a few genotypes were able to overcome these complex interactions. However, Medicago invasion was unsuccessful in all treatments at several of our sites, suggesting that factors beyond those manipulated here also play a key role at many sites. At sites where biotic resistance is important, spatial and temporal variation in community composition and the genetic composition of the invasion pool may explain the invasion success of Medicago into this community.生物入侵抗性源于强烈的物种间相互作用，此类作用可降低潜在入侵物种的适合度与种群增长速率。传统认知中，捕食、竞争等强直接种间相互作用被认为是驱动生物入侵抗性的核心因素，但在物种多样的群落中，物种间的间接相互作用同样可能影响入侵抗性。此外，入侵物种中影响种间相互作用的性状遗传变异，或可使部分基因型突破生物入侵抗性。本研究于加利福尼亚草原生境内，探究了本土豆科植物（Acmispon wrangelianus）与昆虫植食者，对入侵豆科植物（Medicago polymorpha）不同基因型适合度的直接与间接影响。实验结果显示，昆虫植食者仅在本土豆科植物存在时，才会降低入侵苜蓿的适合度，这表明由昆虫与本土豆科植物介导的间接相互作用，对阻遏入侵苜蓿的入侵过程具有关键作用。不过，部分入侵苜蓿基因型受到其他物种相互作用的影响相对更弱。该遗传变异特征表明：尽管生物入侵抗性降低了多数基因型的繁殖成功率，但仍有少数基因型能够突破这些复杂的种间相互作用。但在本研究的多个样地中，所有处理组均未出现入侵苜蓿成功定植的情况，这表明除本实验所操控的因子外，尚有其他因素在多数样地中发挥关键作用。在生物入侵抗性发挥核心作用的样地中，群落组成的时空变异以及入侵种群库的遗传组成，或可解释入侵苜蓿在该群落中的入侵成功现象。