Modeling of the potential distribution of Eichhornia crassipes on a global scale: risks and threats to water ecosystems

Abstract The water hyacinth (Eichhornia crassipes) is listed among the 100 worst invasive plants and was ranked as the 11th worst invasive species in Europe, being a threat to aquatic biodiversity and water-provision. Predicting species distribution is the first step to understanding niche suitability, forecasting the invasion impact and building resilience against this species. In this study, we used a potential distribution model to assess the global risk of water hyacinth invasion by overlapping maps of highly suitable areas for water hyacinth occurrence and areas of biological importance and water scarcity. The MaxEnt - Maximum Entropy algorithm was used in the construction of the model and included five global bioclimatic layers and one of urbanized areas. Among the variables used, occurrence is mainly explained by urban areas, highlighting the importance of cities as a source or dispersion mechanism of the water hyacinth. Global biodiversity hotspots are predominantly situated in high suitability regions for the species. Ramsar sites and global protected areas are at a lower risk level compared to hotspots; however, future climate change and urban growth scenarios could put these areas at higher risk for invasion. Threats posed by the water hyacinth are possibly more acute in regions suffering from current or chronic drought. The results suggest that niche models that do not consider anthropic variables may be underestimating potential distribution of invasive species. Furthermore, the ecological plasticity of the water hyacinth and its close association with cities increase the concern about the impact of this species on the environment and on water security.

摘要 凤眼蓝（water hyacinth，Eichhornia crassipes）被列入全球100种恶性入侵植物名录，并在欧洲被列为第11大恶性入侵物种，对水生生物多样性及水资源供给构成威胁。预测物种分布是解析其生态位适宜性、预判入侵影响并构建针对该物种的防控韧性的首要步骤。本研究通过叠加凤眼蓝高度适生分布区、生物重要区域与缺水区域的地图，采用潜在分布模型评估其全球入侵风险。模型构建采用最大熵（MaxEnt，Maximum Entropy）算法，纳入5个全球生物气候图层与1个城市区域图层。在所采用的变量中，城市区域对物种出现的贡献度最高，凸显城市作为凤眼蓝传播源或扩散机制的重要性。全球生物多样性热点区域多分布于该物种的高度适生区内。拉姆萨尔湿地与全球保护区的入侵风险低于生物多样性热点区域，但未来气候变化与城市扩张情景或使这些区域面临更高的入侵风险。凤眼蓝所造成的威胁在当前正经历干旱或长期干旱的区域可能更为严峻。研究结果表明，未纳入人为活动变量的生态位模型可能会低估入侵物种的潜在分布范围。此外，凤眼蓝的生态可塑性及其与城市环境的紧密关联，进一步加剧了人们对该物种对生态环境与水安全影响的担忧。