Department of Environmental Science and Policy, Università degli Studi di Milano, Via Celoria 26, 20133 Milano, Italy.
Laboratoire Evolution et Diversité Biologique, UMR5174, Université Paul Sabatier, CNRS, IRD, 118 route de Narbonne, 31062 Toulouse, France.
Proc Biol Sci. 2023 Sep 13;290(2006):20231130. doi: 10.1098/rspb.2023.1130.
Understanding how anthropization impacts the assembly of species onto communities is pivotal to go beyond the observation of biodiversity changes and reveal how disturbances affect the environmental and biotic processes shaping biodiversity. Here, we propose a simple framework to measure the assembly processes underpinning functional convergence/divergence patterns. We applied this framework to northern Amazonian fish communities inventoried using environmental DNA in 35 stream sites and 64 river sites. We found that the harsh and unstable environmental conditions characterizing streams conveyed communities towards functional convergence, by filtering traits related to food acquisition and, to a lower extent, dispersal. Such environmental filtering also strengthened competition by excluding species having less competitive food acquisition traits. Instead, random species assembly was more marked in river communities, which may be explained by the downstream position of rivers facilitating the dispersion of species. Although fish assembly rules differed between streams and river fish communities, anthropogenic disturbances reduced functional divergence in both ecosystems, with a reinforcement of both environmental filtering and weaker competitor exclusion. This may explain the substantial biodiversity alterations observed under slight deforestation levels in Neotropical freshwater ecosystems and underlines their vulnerability to anthropic disturbances that not only affect species persistence but also modify community assembly rules.
了解人类活动如何影响物种在群落中的组装对于超越对生物多样性变化的观察并揭示干扰如何影响塑造生物多样性的环境和生物过程至关重要。在这里，我们提出了一个简单的框架来衡量功能趋同/发散模式背后的组装过程。我们将该框架应用于使用环境 DNA 对 35 个溪流站点和 64 个河流站点进行的北亚马孙鱼类群落的调查。我们发现，溪流的恶劣和不稳定的环境条件使群落向功能趋同方向发展，因为它过滤了与食物获取相关的特征，在较小程度上也过滤了扩散特征。这种环境过滤还通过排除具有较少竞争食物获取特征的物种来加强竞争。相反，河流中的随机物种组装更为明显，这可能是由于河流下游位置有利于物种的扩散。尽管溪流和河流鱼类群落的鱼类组装规则不同，但人为干扰减少了这两个生态系统的功能发散，同时加强了环境过滤和较弱的竞争者排除。这可能解释了在新热带淡水生态系统中轻微森林砍伐水平下观察到的大量生物多样性变化，并强调了它们对人为干扰的脆弱性，这些干扰不仅影响物种的生存，还改变了群落的组装规则。
