Departamento de Biologia, Universidade Estadual de Maringá, Nupelia, Maringá, PR, Brazil.
PLoS One. 2013;8(3):e60004. doi: 10.1371/journal.pone.0060004. Epub 2013 Mar 25.
The role of the native species richness and density in ecosystem invasibility is a matter of concern for both ecologists and managers. We tested the hypothesis that the invasiveness of Urochloa arrecta (non-native in the Neotropics) is negatively affected by the species richness and abundance of native aquatic macrophytes in freshwater ecosystems. We first created four levels of macrophyte richness in a greenhouse (richness experiment), and we then manipulated the densities of the same native species in a second experiment (density experiment). When the native macrophytes were adults, fragments of U. arrecta were added, and their growth was assessed. Our results from the richness experiment corroborated the hypothesis of a negative relationship between the native species richness and the growth of U. arrecta, as measured by sprout length and root biomass. However, the resistance to invasion was not attributed to the presence of a particular native species with a greater competitive ability. In the density experiment, U. arrecta growth decreased significantly with an increased density of all five of the native species. Density strongly affected the performance of the Poaceae in a negative manner, suggesting that patches that are densely colonized by native macrophytes and less subject to disturbances will be more resistant to invasion than those that are poorly colonized and more commonly subjected to disturbances. Our density experiment also showed that some species exhibit a higher competitive ability than others (sampling effect). Although native richness and abundance clearly limit the colonization and establishment of U. arrecta, these factors cannot completely prevent the invasion of aquatic ecosystems by this Poaceae species.
本地物种丰富度和密度在生态系统入侵性中的作用是生态学家和管理者都关注的问题。我们检验了以下假设：即，在淡水生态系统中，非本地种 Urochloa arrecta 的入侵性会受到本地水生大型植物物种丰富度和丰度的负面影响。我们首先在温室中创造了四个层次的大型植物丰富度（丰富度实验），然后在第二个实验（密度实验）中操纵了相同本地物种的密度。当本地大型植物成年后，我们添加了 U. arrecta 的片段，并评估了它们的生长情况。我们从丰富度实验中得到的结果证实了这样一种假设，即本地物种丰富度与 U. arrecta 的生长之间存在负相关关系，这可以通过新芽长度和根生物量来衡量。然而，抗入侵性并不是由于具有更强竞争力的特定本地物种的存在而产生的。在密度实验中，随着五种本地物种密度的增加，U. arrecta 的生长显著下降。密度强烈地以负面方式影响了禾本科植物的表现，这表明，与那些受到干扰且殖民程度较低的斑块相比，那些受到干扰且殖民程度较高的斑块更能抵抗入侵。我们的密度实验还表明，一些物种比其他物种具有更高的竞争力（采样效应）。尽管本地丰富度和丰度明显限制了 U. arrecta 的定植和建立，但这些因素并不能完全阻止该禾本科物种对水生生态系统的入侵。
