Abstract
Biological invasions have created detrimental impacts in freshwater ecosystems. As non-native freshwater species include economically beneficial, but also harmful, species, trait-based risk assessments can be used to identify and prevent the import of potentially invasive species. Freshwater fishes are one of the most evaluated freshwater taxa to date. However, such assessments have mostly been done in sub-temperate to temperate regions, with a general lack of such research in the tropics. In view of this knowledge gap, this study aims to determine if a different set of traits are associated with successful establishment of non-native fishes within the tropics. In tropical Southeast Asia, Singapore represents a suitable model site to perform an invasive species trait-based risk assessment for the tropical region given its susceptibility to the introduction and establishment of non-native freshwater fishes and lack of stringent fish import regulation. A quantitative trait-based risk assessment was performed using random forest to determine the relative importance of species attributes associated with the successful establishment of introduced freshwater fishes in Singapore. Species having a match in climate, prior invasion success, lower absolute fecundity, higher trophic level, and involvement in the aquarium trade were found to have higher establishment likelihood (as opposed to native distributional range and maximum size being among the commonly identified predictors in subtropical/temperate trait-based risk assessments). To minimize invasive risk, incoming freshwater fishes could be screened in future for such traits, allowing lists of prohibited or regulated species to be updated. The findings could also potentially benefit the development of invasive species action plans and inform management decisions in the Southeast Asian region. Considering a geographical bias in terms of having relatively less documentation of biological invasions in the tropics, particularly Asia, this study highlights the need to perform more of such risk assessments in other parts of the tropics.
Highlights
Before causing any substantial harmful effects in a new environment, introduced species must pass through several invasion stages and overcome anthropogenic, biological, and environmental barriers [13, 14]
With a relative lack of research efforts in the tropics [49, 50], and the potential variation in identified traits at the local level ([51]; see S1 Table), it is unclear if risk assessments performed within tropical regions would identify similar patterns or suites of traits as those conducted in other climatic regions. In light of this paucity of information, and a noted difference in invasibility of tropical ecosystems [52, 53], this study aims to determine if non-native species within tropical climates are associated with a different set of traits in overcoming the barriers in the invasion process
The identification of climate match, absolute fecundity, and trophic level as the three most important variables consistently in all full as well as reduced random forest (RF) models suggests that these attributes are strong predictors of establishment success
Summary
Before causing any substantial harmful effects in a new environment, introduced species must pass through several invasion stages and overcome anthropogenic, biological, and environmental barriers [13, 14]. This process first involves a species being transported and introduced into an area outside of its native range, surviving and reproducing to form an established or self-sustaining population before spreading to other habitats [14]. Not every species is able to overcome the barriers associated with each stage of the invasion process, and even if they do, such species can turn out to be benign (e.g., [16, 17])
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