Mello Thayná Jeremias, Oliveira Alexandre Adalardo de
Departamento de Ecologia, Universidade de São Paulo, São Paulo-SP, Brazil.
Fernando de Noronha Marine National Park, Instituto Chico Mendes de Conservação da Biodiversidade, Fernando de Noronha-PE, Brazil.
PLoS One. 2016 Mar 24;11(3):e0152070. doi: 10.1371/journal.pone.0152070. eCollection 2016.
Biological invasions pose a significant threat to biodiversity, especially on oceanic islands. One of the primary explanations for the success of plant invaders is direct suppression of competitors. However, indirect interactions can also be important, although they are often overlooked in studies on biological invasion. The shrub Leucaena leucocephala is a widespread island invader with putative allelopathic effects on the germination and growth of other species. We quantified the impact of Leucaena on plant communities richness on an oceanic Brazilian island and, through nursery experiments, investigated the potential for allelopathic effects on the germination of Erythrina velutina, a native species that is often absent from stands of Leucaena. Additionally, in a manipulative field experiment, we examined the direct and indirect effects (mediated by the native species Capparis flexuosa) of the invader on the development of Erythrina. The species richness in invaded sites was lower than in uninvaded sites, and Capparis was the only native species that was frequently present in invaded sites. In the nursery experiments, we found no evidence that Leucaena affects the germination of Erythrina. In the field experiments, the odds of Erythrina germination were lower in the presence of Leucaena litter, but higher in the presence of Leucaena trees. However, the survival and growth of Erythrina were considerably inhibited by the presence of Leucaena trees. The isolated effect of native Capparis on the germination and growth of Erythrina varied from positive to neutral. However, when Capparis and Leucaena were both present, their combined negative effects on Erythrina were worse than the effect of Leucaena alone, which may be attributed to indirect effects. This study provides the first empirical evidence that the balance of the interactions between native species can shift from neutral/positive to negative in the presence of an exotic species.
生物入侵对生物多样性构成重大威胁，尤其是在海洋岛屿上。植物入侵者成功的主要原因之一是对竞争者的直接抑制。然而，间接相互作用也可能很重要，尽管它们在生物入侵研究中常常被忽视。银合欢是一种广泛分布于岛屿的入侵植物，对其他物种的发芽和生长具有潜在的化感作用。我们量化了银合欢对巴西一个海洋岛屿上植物群落丰富度的影响，并通过苗圃实验，研究了其对绒毛刺桐发芽的化感作用潜力，绒毛刺桐是银合欢林分中通常不存在的本土物种。此外，在一项控制性田间实验中，我们研究了入侵者对绒毛刺桐生长发育的直接和间接影响（由本土物种弯果山柑介导）。入侵地点的物种丰富度低于未入侵地点，弯果山柑是唯一在入侵地点经常出现的本土物种。在苗圃实验中，我们没有发现银合欢影响绒毛刺桐发芽的证据。在田间实验中，有银合欢凋落物时绒毛刺桐发芽的几率较低，但有银合欢树时发芽几率较高。然而，银合欢树的存在显著抑制了绒毛刺桐的存活和生长。本土弯果山柑对绒毛刺桐发芽和生长的单独影响从积极到中性不等。然而，当弯果山柑和银合欢都存在时，它们对绒毛刺桐的综合负面影响比银合欢单独的影响更严重，这可能归因于间接影响。这项研究提供了首个实证证据，即在外来物种存在的情况下，本土物种之间相互作用的平衡可能从中性/积极转变为消极。
