Radny Janina, Meyer Katrin M
Department of Ecosystem Modelling, Georg-August-Universität Göttingen, Göttingen, Germany.
PeerJ. 2018 Aug 8;6:e5342. doi: 10.7717/peerj.5342. eCollection 2018.
Establishment success of non-native species is not only influenced by environmental conditions, but also by interactions with local competitors and enemies. The magnitude of these biotic interactions is mediated by species traits that reflect competitive strength or defence mechanisms. Our aim was to investigate the importance of species traits for successful establishment of non-native species in a native community exhibiting biotic resistance in the form of competition and herbivory.
We developed a trait-based, individual-based simulation model tracking the survival of non-native plants in a native community. In the model, non-native plants are characterized by high or low values of competition and defence traits. Model scenarios included variation of initial number of non-natives, intensity of competitive interaction, density of herbivores and density as well as mixture of the native community.
Traits related to competition had a much greater impact on survival of non-native species than traits related to defence. Survival rates of strong competitors never fell below 50% while survival of weak competitors averaged at about 10%. Weak competitors were also much more susceptible to competitive pressures such as community density, composition and competition intensity. Strong competitors responded negatively to changes in competition intensity, but hardly to composition or density of the native community. High initial numbers of non-native individuals decreased survival rate of strong competitors, but increased the survival rate of weak competitors. Survival under herbivore attack was only slightly higher for plants with high defensive ability than for those with low defensive ability. Surprisingly, though, herbivory increased survival of species classified as weak competitors.
High survival rates of strong non-native competitors relate to a higher probability of successful establishment than for weak competitors. However, the reduced survival of strong competitors at high initial numbers indicates a self-thinning effect, probably mediated by a strongly competitive milieu. For weak competitors, our model emphasizes positive effects of high propagule pressure known from field studies. General effects of herbivory or defence abilities on survival were not supported by our model. However, the positive effect of herbivory on survival of weak competitors indicated side effects of herbivory, such as weakening resident competitors. This might play an important role for establishment of non-natives in a new community.
非本地物种的定殖成功不仅受环境条件影响，还受与本地竞争者和天敌相互作用的影响。这些生物相互作用的强度由反映竞争强度或防御机制的物种特征介导。我们的目的是研究物种特征对于在以竞争和食草形式表现出生物抗性的本地群落中成功定殖非本地物种的重要性。
我们开发了一个基于特征的、基于个体的模拟模型，追踪非本地植物在本地群落中的存活情况。在模型中，非本地植物以竞争和防御特征的高值或低值为特征。模型情景包括非本地物种初始数量的变化、竞争相互作用的强度、食草动物的密度以及本地群落的密度和组成。
与竞争相关的特征对非本地物种存活的影响远大于与防御相关的特征。强竞争者的存活率从未低于50%，而弱竞争者的平均存活率约为10%。弱竞争者也更容易受到诸如群落密度、组成和竞争强度等竞争压力的影响。强竞争者对竞争强度的变化反应为负，但对本地群落的组成或密度几乎没有反应。非本地个体的高初始数量降低了强竞争者的存活率，但提高了弱竞争者的存活率。在食草动物攻击下，具有高防御能力的植物的存活率仅略高于防御能力低的植物。然而，令人惊讶的是，食草作用提高了被归类为弱竞争者的物种的存活率。
强非本地竞争者的高存活率表明其成功定殖的概率高于弱竞争者。然而，在高初始数量下强竞争者存活率的降低表明存在自疏效应，可能由强烈竞争的环境介导。对于弱竞争者，我们的模型强调了实地研究中已知的高繁殖体压力的积极影响。我们的模型不支持食草作用或防御能力对存活的一般影响。然而，食草作用对弱竞争者存活的积极影响表明了食草作用的副作用，如削弱本地竞争者。这可能对非本地物种在新群落中的定殖起重要作用。
