Department of Ecology and Evolution, Universidade Federal de Santa Maria, Santa Maria, Rio Grande do Sul, Brazil.
Université de Bordeaux, INRAE, BIOGECO, Pessac, France.
Glob Chang Biol. 2024 Sep;30(9):e17513. doi: 10.1111/gcb.17513.
Human activities and climate change have accelerated species losses and degradation of ecosystems to unprecedented levels. Both theoretical and empirical evidence suggest that extinction cascades contribute substantially to global species loss. The effects of extinction cascades can ripple across levels of ecological organization, causing not only the secondary loss of taxonomic diversity but also functional diversity erosion. Here, we take a step forward in coextinction analysis by estimating the functional robustness of reef fish communities to species loss. We built a tripartite network with nodes and links based on a model output predicting reef fish occupancy (113 species) as a function of coral and turf algae cover in Southwestern Atlantic reefs. This network comprised coral species, coral-associated fish (site occupancy directly related to coral cover), and co-occurring fish (occupancy indirectly related to coral cover). We used attack-tolerance curves and estimated network robustness (R) to quantify the cascading loss of reef fish taxonomic and functional diversity along three scenarios of coral species loss: degree centrality (removing first corals with more coral-associated fish), bleaching vulnerability and post-bleaching mortality (most vulnerable removed first), and random removal. Degree centrality produced the greatest losses (lowest R) in comparison with other scenarios. In this scenario, while functional diversity was robust to the direct loss of coral-associated fish (R = 0.85), the taxonomic diversity was not robust to coral loss (R = 0.54). Both taxonomic and functional diversity showed low robustness to indirect fish extinctions (R = 0.31 and R = 0.57, respectively). Projections of 100% coral species loss caused a reduction of 69% of the regional trait space area. The effects of coral loss in Southwestern Atlantic reefs went beyond the direct coral-fish relationships. Ever-growing human impacts on reef ecosystems can cause extinction cascades with detrimental consequences for fish assemblages that benefit from corals.
人类活动和气候变化加速了物种的丧失和生态系统的退化，达到了前所未有的水平。理论和经验证据都表明，灭绝级联在全球物种丧失中起着重要作用。灭绝级联的影响可以在生态组织的各个层次上扩散，不仅导致分类多样性的二次损失，还导致功能多样性的侵蚀。在这里，我们通过估计珊瑚礁鱼类群落对物种丧失的功能稳健性，在共灭绝分析方面迈出了一步。我们建立了一个三分网络，节点和链接基于一个模型输出，该模型输出预测了西南大西洋珊瑚礁中珊瑚礁鱼类的占有（113 个物种）作为珊瑚和草坪藻类覆盖率的函数。这个网络包括珊瑚物种、与珊瑚相关的鱼类（与珊瑚覆盖率直接相关的栖息地占有）和共同出现的鱼类（与珊瑚覆盖率间接相关的栖息地占有）。我们使用攻击-容忍曲线和估计的网络稳健性（R）来量化珊瑚物种损失的三种情景下的珊瑚礁鱼类分类和功能多样性的级联损失：中心度（去除与更多珊瑚相关的鱼类的第一种珊瑚）、白化脆弱性和白化后死亡率（最脆弱的先去除）和随机去除。与其他情景相比，中心度产生了最大的损失（最低的 R）。在这种情景下，虽然功能多样性对与珊瑚相关的鱼类的直接损失具有稳健性（R=0.85），但分类多样性对珊瑚的损失并不稳健（R=0.54）。直接鱼类灭绝的分类和功能多样性都显示出低稳健性（R=0.31 和 R=0.57）。对 100%珊瑚物种损失的预测导致区域特征空间面积减少了 69%。西南大西洋珊瑚礁中珊瑚的损失影响超出了珊瑚-鱼类的直接关系。人类对珊瑚礁生态系统的影响不断增加，可能会引发灭绝级联，对依赖珊瑚的鱼类群落造成不利影响。
