Date Published: June 17, 2019
Publisher: Public Library of Science
Author(s): Marta Rodríguez-Rey, Sofia Consuegra, Luca Börger, Carlos Garcia de Leaniz, Paulo De Marco Júnior.
Freshwater ecosystems rank among the most endangered ecosystems in the world and are under increasing threat from aquatic invasive species (AIS). Understanding the range expansion of AIS is key for mitigating their impacts. Most approaches rely on Species Distribution Models (SDMs) to predict the expansion of AIS, using mainly environmental variables, yet ignore the role of human activities in favouring the introduction and range expansion of AIS. In this study, we use five SDM algorithms (independently and in ensemble) and two accuracy measures (TSS, AUC), combined with a null modelling approach, to assess the predictive performance of the models and to quantify which predictors (environmental and anthropogenic from the native and introduced regions) best explain the distribution of nine freshwater invasive species (including fish, arthropods, molluscs, amphibians and reptiles) in a large island (Great Britain), and which species characteristics affect model performance. Our results show that the distribution of invasive species is difficult to predict by SDMs, even in cases when TSS and AUC model accuracy values are high. Our study strongly advocates the use of null models for testing SDMs performance and the inclusion of information from the native area and a variety of both human-related and environmental predictors for a more accurate modelling of the range expansion of AIS. Otherwise, models that only include climatic variables, or rely only on standard accuracy measures or a single algorithm, might result in mismanagement of AIS.
Developing a scientific basis for monitoring and managing invasive species and implementing measures to manage pathways to prevent introductions is one of the CBD Aichi Targets for 2020 . Freshwater invasions are of special concern, as freshwater ecosystems are among the most diverse and endangered ecosystems in the world , harbouring more than a quarter of all freshwater fauna threatened or recently extinct , in part due to the impact of non-native freshwater species on native biodiversity . Despite an increase in the number of studies focusing on freshwater invasions in recent years , the main drivers of the introduction and spread of aquatic invasive species (AIS) are still unknown .
Between 71% and 72% of the grid cells with watercourses in Great Britain included at least one record of a native species of the amphibian and fish groups, respectively. In the native area of the different species between a 69% and a 95% of the grids were sampled for at least a related species.
We have shown that both environmental (from the native and invaded ranges) and anthropic variables should be included in models that aim to understand and predict the distribution of aquatic invasive species. Our results also highlight the fact that different species may require different sets of predictors and that the inclusion of information about conditions in the species’ native area may be required to model their distribution accurately, making it difficult to generalize across taxa. Therefore, including as much information in the models as possible will help to find the model with the best predictive ability for the species under study, and will permit comparisons between different modelling approaches, as it is not possible to know a priori which ones might work best, in agreement with the justification of using ensemble modelling approaches .