The status and potential distribution of Hydrocotyle umbellata L. and Salvinia auriculata Aubl. under climate change scenarios.
Aquatic ecosystems are susceptible to human-induced disturbance, including climate changes and biological invasions. The aim of this study was to assess the current and future potential distribution of two introduced aquatic species that have become invasive in some places where they were introduced. Hydrocotyle umbellata L. and Salvinia auriculata Aubl. are free-floating macrophytes native to North, Central, and South America. Both can quickly colonize aquatic environments because of their high growth rate and reproductive capacity similar to water hyacinth. Both species were introduced to Egypt for ornamental purposes. We have applied species distribution models using the Maxent approach and bioclimatic variables. Occurrence records from the entire range of the two species were obtained from the Global Biodiversity Information Facility and used for modelling their habitat suitability and assessing the potentiality of their spread in other new habitats. To project future changes in the two macrophytes' distributions with respect to climate change, we used four representative concentration pathway scenarios (RCP 2.6, 4.5, 6.0 and 8.5) of the IPCC 5th assessment, based on different assumptions of greenhouse gas emissions for the future period of 2050s. The results showed that Maxent approach has successfully predicted the distribution of the two species with test AUC > 0.92. Bioclimatic variables that contributed the most to the prediction of the two species distribution included isothermality, temperature seasonality, mean temperature of the coldest quarter, and minimum temperature of the coldest month. Results showed that the range of S. auriculata is predicted to increase by 2050 under all climatic scenarios. A decline in the current climatically suitable habitats of H. umbellata is projected to occur in its native range, especially in South America, while it is predicted to gain more suitable habitats out of its native range in Europe and Africa. Both species are predicted to gain habitats outside their native range, while their ranges are expected to face a decline in their native region. The study can help in the identification of areas with high potential vulnerability to future invasions by the two studied aquatic macrophytes and thus can assist in prioritization of monitoring actions and management plans. This can reduce any ecological and socio-economic consequences due to invasion by these two aquatic plants.