Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
School of Biological Sciences, The University of Western Australia, Crawley, WA 6009, Australia.
Proc Biol Sci. 2022 Jun 29;289(1977):20220504. doi: 10.1098/rspb.2022.0504.
The assumption that differences in species' traits reflect their different niches has long influenced how ecologists infer processes from assemblage patterns. For instance, many assess the importance of environmental filtering versus classical limiting-similarity competition in driving biological invasions by examining whether invaders' traits are similar or dissimilar to those of residents, respectively. However, mounting evidence suggests that hierarchical differences between species' trait values can distinguish their competitive abilities (e.g. for the same resource) instead of their niches. Whether such trait-mediated hierarchical competition explains invasions and structures assemblages is less explored. We integrate morphological, dietary, physiological and behavioural trait analyses to test whether environmental filtering, limiting-similarity competition or hierarchical competition explain invasions by fire ants on ant assemblages. We detect both competition mechanisms; invasion success is not only explained by limiting similarity in body size and thermal tolerance (presumably allowing the invader to exploit different niches from residents), but also by the invader's superior position in trait hierarchies reflecting competition for common trophic resources. We find that the two mechanisms generate complex assemblage-level functional diversity patterns-overdispersion in some traits, clustering in others-suggesting their effects are likely missed by analyses restricted to a few traits and composite trait diversity measures.
长期以来，物种特征的差异反映了它们不同的生态位这一假设一直影响着生态学家如何从组合模式推断过程。例如，许多人通过分别检查外来物种的特征与当地物种的特征是否相似，来评估环境过滤与经典限制相似性竞争在驱动生物入侵中的重要性。然而，越来越多的证据表明，物种特征值之间的层次差异可以区分它们的竞争能力（例如，对于同一资源），而不是它们的生态位。这种基于特征的层次竞争是否能解释入侵和构建组合尚待进一步探讨。我们综合了形态学、饮食、生理和行为特征分析，以检验环境过滤、限制相似性竞争还是层次竞争解释了红火蚁对蚂蚁组合的入侵。我们检测到了这两种竞争机制；入侵的成功不仅可以通过体型和耐热性上的限制相似性来解释（推测允许入侵者从当地物种那里利用不同的生态位），还可以通过入侵者在反映对共同营养资源竞争的特征层次中的优势地位来解释。我们发现，这两种机制产生了复杂的组合水平功能多样性模式——在一些特征上过度分散，在另一些特征上聚类——这表明，仅通过少数特征和综合特征多样性测量进行的分析可能会忽略它们的影响。
