Determinants of establishment success: Comparing alien and native freshwater fishes in Taiwan

Abstract

Many parts of Asia, including Taiwan, have suffered severely from freshwater fish invasions. However, few studies using an assemblage approach have been conducted in the region so far that would help to prioritize suitable preventive actions. In this study, we focused on the invasion process from the import stage to the establishment stage, and defined establishment success as the success during this predefined process. We used datasets of freshwater fish assemblages in Taiwan to (1) compare established versus non-established alien species to distinguish the determinants of establishment success, and (2) to use these determinants to test a life history hypothesis which predicts that the magnitudes of the determinants should be significantly different between established alien species and native species. We collated a dataset for freshwater fish species which were imported into Taiwan (n = 118) of which some successfully established (n = 26), and another dataset for freshwater fish species native to Taiwan (n = 77). For each imported species, we collected data for 17 variables, including two phylogenetic, two human-use, two invasion history, and 11 life history variables. We then used decision tree methods, which have advantages in analyzing datasets with many variables of mixed types without the need to make assumptions about data distributions and input data for missing values. Our results showed that aquaculture use and maximum body length were the most important determinants for predicting establishment success of alien freshwater fish in Taiwan. Comparing five important determinants between established alien versus native species showed that the established alien species were significantly more often used in aquaculture, were associated with a higher number of established countries, and had a larger body length and greater highest water temperature tolerance than the native species. We thus conclude that our results provided evidence to support our stated hypothesis. We suggest that aquaculture use, measures of body size, and the number of previously invaded countries may alert researchers and conservation managers to species with a high establishment potential, especially for countries with similar conditions as those in Taiwan.

Invasive species trait-based risk assessment for non-native freshwater fishes in a tropical city basin in Southeast Asia

“…Geographical bias is also manifest in the association of successful establishment with the use of species in aquarium trade. Owing to the growing popularity of tropical aquarium fishes [ 105 , 106 ], and the common practice of discarding unwanted pets [ 6 , 7 , 106 ] (or religious release of ornamental fishes in countries such as Singapore [ 62 ] and Taiwan [ 30 ]), the aquarium trade has gained importance as an invasion pathway in many countries (e.g., [ 105 , 107 , 108 ]). In addition, aquarium trade species are often associated with a preselection of ecological traits (e.g., climate match, reproductive potential, and environmental tolerance) that increases the chance of survival within other tropical habitats [ 27 ].…”

“…physiologically suited to that environment [28,34,94]. Whereas, the negative relationship between fecundity and establishment likelihood differed from most temperate studies, which generally identified a positive association [30,40,42] (although one study by Grabowska and Przybylsk (2015) conducted in the Central European bioregion did record a negative relationship [47]). This pattern could be a result of the negative correlation between egg size and fecundity [95].…”

“…Such assessments range from the of semi-quantitative screening kits (e.g., Fish Invasiveness Screening Kit; [22]) to quantitative statistical analyses such as modelling of propagule pressure and ecological niche (e.g., [23][24][25]) and trait-based assessments (e.g., [26,27]). While many methods exist to assess the risk of a non-native species (to become invasive), trait-based risk assessment remains one of the most popular techniques available (e.g., [27][28][29][30]). Through the quantification of biological and ecological species traits that are associated with a species' ability to overcome barriers associated with each invasion stage [20], trait-based risk assessment provides a straightforward and accurate means of identifying and predicting high-and low-risk species [21,31].…”

“…Of the freshwater taxa examined, fishes appeared to be the most studied taxon, likely due to their ecological [39] and economic [18,19] importance. Among the species attributes or traits analysed, maximum size, fecundity, and native distributional range appear to be among the most commonly identified predictors of both establishment likelihood and invasiveness of freshwater species ( [27,30,32,33,[35][36][37][40][41][42][43][44][45][46][47]; S1 Table). However, although trait-based risk assessments have been performed at varying geographic scales, local assessments have mostly focused on the sub-temperate to temperate regions of the world ( [48]; S1 Table).…”

“…Focusing on multiple aspects of a species’ biology, including life history (e.g., fecundity [ 32 ] and egg size [ 36 ]) and physiological tolerance [ 30 ], as well as indicators of a species’ ecology, such as distributional range or distance to source [ 37 ], trait-based risk assessments identify a species’ innate likelihood of succeeding at an invasion stage in an introduced environment [ 21 ]. These risk assessments also allow users to account for anthropogenic factors through the use of variables such as propagule pressure [ 37 ] or human-uses [ 27 ].…”