Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
Desert Laboratory on Tumamoc Hill, University of Arizona, Tucson, Arizona, USA.
Ecology. 2022 Jun;103(6):e3675. doi: 10.1002/ecy.3675. Epub 2022 Apr 11.
Competition is often highlighted as a major force influencing plant species diversity. However, there are multiple facets of competition (e.g., strength, intransitivity, and size asymmetry) that may have independent and differential impacts on diversity, making understanding the degree to which competition structures communities difficult. Unfortunately, field-based experiments that decouple multiple facets of competition are lacking, limiting our ability to test theoretical frameworks and reducing understanding of the actual linkages among competition and coexistence. Here, we experimentally manipulate the size structure of local grassland communities to examine the relative impacts of competitive size asymmetry (i.e., competitive advantage based on relative size) and intensity (i.e., mean effect of neighbors on plant growth) on species loss and gain. Increased competitive size asymmetry was associated with increased species loss and decreased species gain, while no relationship was found between competitive intensity and species loss and gain. Furthermore, the probability of loss was not dependent on a species initial size, suggesting that small species may not always be the losers of size-asymmetric interactions. Instead, loss was dependent on species rarity, where loss was higher for rare species. Overall, these results suggest that competitive size asymmetry may be more important for species loss than intensity in some plant communities and demonstrates the importance of decoupling different aspects of competition to better understand their drivers and ecological consequences.
竞争常被强调为影响植物物种多样性的主要力量。然而，竞争有多个方面（例如，强度、非传递性和大小不对称性），它们可能对多样性有独立和不同的影响，这使得理解竞争如何构建群落变得困难。不幸的是，缺乏分离竞争多个方面的现场实验，限制了我们测试理论框架的能力，并降低了对竞争与共存之间实际联系的理解。在这里，我们通过实验操纵当地草原群落的大小结构，研究竞争大小不对称性（即基于相对大小的竞争优势）和强度（即邻居对植物生长的平均影响）对物种损失和获得的相对影响。竞争大小不对称性的增加与物种损失的增加和物种获得的减少有关，而竞争强度与物种损失和获得之间没有关系。此外，损失的概率不依赖于物种的初始大小，这表明小物种不一定总是大小不对称相互作用的失败者。相反，损失取决于物种的稀有性，稀有物种的损失更高。总的来说，这些结果表明，在某些植物群落中，竞争大小不对称性可能比强度对物种损失更为重要，并证明了分离竞争的不同方面以更好地理解其驱动因素和生态后果的重要性。
