In this new post, Camille Bernery and Clara Marino—a Post doctorate and PhD student, respectively, at the Ecology, Systematic and Evolution (ESE) lab, Université Paris-Saclay, CNRS, AgroParisTech, Gif-sur-Yvette, France—share their recently published paper titled: Relative importance of exotic species traits in determining invasiveness across levels of establishment: Example of freshwater fish. They discuss the characteristics that explain differences in invasion success of freshwater fish, challenges of collecting and analysing global data, as well as their journeys towards becoming ecologists.

A French translation of this blogpost is available to read here!

About the paper

The main goal of our paper was to identify the characteristics that differentiate exotic fish established worldwide in many locations, from other fish established in very few and restricted locations. Indeed, with the increase of international trade, it is well known that numerous exotic freshwater fish were introduced worldwide and now have big ecological, sanitary, and economic impacts in their new environment. Thus, understanding the characteristics leading to some exotic species successfully establishing and invading new environments is an important question. This question has already been addressed multiple times in the literature on several taxa, across plants and animals (e.g., mammals, birds, reptiles, and fish). However, previous studies have often ignored that species can be successful in different ways: some can spread all over the world while others will be restricted to a few areas close to their native ranges. But are these species different in terms of behavior, traits, or morphology? Do some characteristics explain these differences in invasion success?

We address these questions by assessing the ecological, morphological, and behavioral traits of 222 exotic freshwater fish species along four levels of establishment, defined by the number of basins and the location of establishment. We found that the super-established species were indeed different from species established in a handful of locations. Super-established species tended to have multiple diets and a high level of parental care, while other groups had no parental care and were more specialized in terms of diets, mostly showing a zoobenthic diet (i.e., comprising animals living in the bottom of the river or lake). Our findings highlight the importance of considering trait variability when thinking of species’ ability to establish and invade new environments. Therefore, policymakers and managers should consider our results when developing relevant strategies and policies for controlling biological invaders by identifying the most impactful species to manage in priority.

About the research

Previous studies recognized exotic species as successful and unsuccessful, while our study emphasizes the importance of considering different levels of establishment defined by the number of basins and the location of establishment. Thus, our study on freshwater fish species advances the understanding of invasion dynamics and represents an innovative way to study the factors of invasion success. Ultimately, being able to identify the traits that promote varied levels of establishment of exotic species can help us to identify species that are most invasive and thus help to prevent their potential introduction and impacts. However, this kind of study is not easy to develop. We conducted this research by gathering data from open databases online on a global scale, meaning we needed information on a vast number of species worldwide.

Having a complete and clean database was the most challenging task for being able to answer our research question with an adequate sample size. For instance, we decided to focus on 222 fish species while more than 500 are known to have an exotic population somewhere—data on the remaining (ca. 300 species) were not available or sufficient. Consequently, one of the following steps would be to collect more data on species to expand our findings to most exotic fish in the world. Another follow-up work for completing our study would be exploring similar research questions but with other taxa (like vertebrates such as mammals or birds, or invertebrates such as insects or molluscs). These taxa are also widely transported and introduced, with some invasive species having tremendous ecological impacts on native biodiversity. Therefore, it would be relevant to see if our findings are congruent with other life forms or specific to freshwater vertebrates. Ultimately, this would help build an adapted conservation response to the global issue of biological invasions threatening biodiversity.

About the authors

Camille: I started my Ph.D. one year before Clara—with whom I shared my office for two years—along with one of our thesis directors, Céline Bellard, the last author of this article. At the beginning of my Ph.D., Céline and I wanted to build a project together with Clara because we were good friends, and we also saw the potential of combining our skills on a project that would motivate us. I had skills concerning the specificities of the model (fish), and I mastered the database on fish traits and the generalised linear model part of the analysis. In contrast, Clara mastered the building of functional spaces, a method that I never used before in a study. Céline was a mentor for us, as well as the perfect person to supervise us. I have now completed my PhD thesis, and I proudly presented this study during my PhD viva. This study is, for me, the perfect example of successful cooperation in research, and I am proud to have completed it with one of my close friends. I am now a postdoctoral researcher, still in conservation ecology but on another topic: the study of the effects of agricultural practices on arthropod-bat food webs. To me, being an ecologist is one of the most interesting jobs. When I was little, I was always outside and very motivated to understand the behaviour of animals I saw during the day—I was always wondering weird questions about them. Nature documentaries were not enough for me; I wanted to answer these questions myself. Ecology is also a subject that is garnering greater interest and popularizing this subject is one of my main passions. It is important for me that the general public hear about what we do in science and understand the world we live in, especially during a time when issues about the loss of biodiversity are making headlines.

Clara: I am in the final year of my PhD and I work on the ecological consequences of invasive alien species on terrestrial vertebrates, on a global scale. To echo Camille, this project was the perfect opportunity to join our complementary skills while enjoying working with a good friend. This project is now also a chapter of my thesis, and I am very happy to be defending this work soon during my PhD viva. Once I graduate, I will start a postdoc position in Montpellier for two years, working on the vulnerability of insular ecosystems. I started studying ecology in 2015, the year of the Paris Agreement (COP21), when a lot of people around me started to talk about environmental and climate crises. What I love about ecology is its complexity and its perpetual dynamic that prevent us from capturing everything in words and numbers. The living world will always somehow surprise us and that fascinates me. However, I don’t like the fact that I’m constantly reminded of the extent to which human activities are degrading biodiversity and the global environment. After having spent my whole thesis working with data and code on a computer, I could not pretend to be a field ecologist, and I am surely not a naturalist who could identify any living creature. Yet, I really enjoy spending time on the outside looking at nice landscapes while cycling.

Enjoyed the blogpost? Read the research here!