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Wetland environments in many parts of the world have accumulated large inventories of anthropogenically introduced non-native flora and fauna and many of these introduced species have become invasive, causing detrimental ecological impact to the host environment. This is especially true for freshwater ecosystems that are under ever-increasing anthropogenic stress that reduces native biodiversity due to pollution, flow modification, degradation of habitat, and invasive species (as defined in ), as well as climate change and overexploitation of resident species. Modern urban and peri-urban biological communities are often degraded and filled with introduced (and sometimes invasive) species.

Our review is based on in-depth examination of the literature on RESs and our familiarity with the turtle literature in general. However, might some exotic species perform compensatory and potentially valuable ecological functions in degraded urban habitat where native species have already lost their competitive advantage? We present a case study of this apparent conundrum using the red-eared slider (RES) turtle ( Trachemys scripta elegans), now one of the most widely distributed, and vilified invasive species in the world. We agree that preservation of native biodiversity in natural habitats is an important goal of effective conservation efforts. The gulf is further widened in the literature by reference to native species as “friends,” and non-native species as “foes”. Exotic species are often labelled as “bad” and native species are considered to be “good”, with little if any middle ground. The documented negative effects of invasive species have produced a deeply entrenched dichotomy of opinions among conservation biologists. Once established, some exotic species can displace or even permanently replace native plant and animal species, as well as disrupt ecosystem processes including nutrient and fire cycles, and cause changes in patterns of plant succession. The spread of exotic species into novel habitats is considered the greatest threat to biodiversity after habitat loss and/or climate change. As early as 1958, Charles Elton stated “ We are living in a period of the world's history when the mingling of thousands of kinds of organisms from different parts of the world is setting up terrific dislocations in nature …” Modern ecologists are now even more aware of the problems caused by the invasion of exotic species into natural areas and the attendant effects on local, regional, and global patterns of biodiversity, now and in the future. Invasive exotic species have long been recognized for having negative effects on the biodiversity of native ecosystems. We also suggest research avenues to better understand the role of RESs in heavily modified wetlands. After reviewing the ecosystem functions RESs are known to provide, we conclude that in many modified environments the RES is a partial ecological analog to native turtles and removing them may obviate the ecological benefits they provide. While we do not advocate for releases outside their native range, or into natural environments, in this review, we examine the case for the RES to be considered potentially beneficial in heavily human-altered and degraded ecosystems where native turtles struggle or fail to persist.

Based on this review, we suggest that RES contribute some ecosystem functions in urban wetlands comparable to those provided by the native turtles they sometimes dominate or replace. The red-eared slider turtle (RES) has been disparaged as one of the worst invasive species. Exotic species are often vilified as “bad” without consideration of the potential they have for contributing to ecological functions in degraded ecosystems.