Study enables more accurate predictions around invasive species immigration in freshwater fish communities

Invasive species are considered a major threat to global biodiversity. Scientists from the Center for Advanced Systems Understanding (CASUS) at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) have now used North American freshwater fish communities to find out what makes the success of invasive fish species likely: on the one hand, high fecundity, a longer lifespan and the size of the species are crucial for their survival. On the other hand, the existing fish communities must also have open functional spaces in which the newcomers can establish themselves, the experts write in a study for the journal Nature Communications (doi: 10.1038/s41467-023-38107-2).

The immigration of invasive species – i.e. animal and plant species that conquer a new habitat far from their original range – often has negative consequences: They displace native species, transmit diseases or change the gene pool by interbreeding with native species. It is not much different in fish communities either: invasive fish species that have been unintentionally introduced to new regions of the world via ship tanks, for example, or deliberately introduced by the fishing industry and anglers, can displace native fish species and lead to their local disappearance, bring diseases with them or change the ecological balance of the ecosystem. “Many alien species are introduced with good intentions, but at some point it turns out that this new species has some kind of negative impact on the environment,” says co-author Prof. Justin Calabrese, who has been researching at the interface of ecology and data science at CASUS since 2020.

Investigation from two different perspectives

For the studies, the CASUS team used an extensive, freely accessible US database, which contains data on more than 1,800 fish communities, primarily in North American rivers. The researchers investigated the immigration of invasive fish species into river ecosystems from two different perspectives. On the one hand, they analyzed the morphological and physiological characteristics or behavioural traits of the alien species that have found a niche in an existing species community in an ecosystem. These include, for example, the size of the species, estimates of reproduction, diet, salt and temperature tolerance or the care of their own offspring. Secondly, they investigated how permeable an existing fish community is so that a new fish species can establish itself there. “We wanted to understand which arrangement of functional characteristics enables invasive species to enter an existing species community,” says Calabrese.

The result of the extensive data analysis: if an invasive fish species has a higher fecundity, a longer lifespan and is also significantly larger than comparable native species, the probability of successful invasion is high. “These are parameters that make a lot of biological sense for an invasive species,” says the lead author of the study, Dr. Guohuan Su, who worked at CASUS until January 2023. For example, high fecundity with many eggs and offspring is a clear advantage for a fish species to become established in an unfamiliar environment. This has already been proven in earlier studies for the European carp in Australia. According to the CASUS team’s data analysis, however, it is less important whether, for example, the invasive species is at the top of the food chain as a predator. However, these functional characteristics of the species are only one aspect of their colonization success. “We were also able to establish that the distribution of fish species is concentrated on certain resources and that there is a peak of resources that make this area attractive,” says Calabrese. It therefore makes sense for invasive species to become established where there is sufficient food, suitable temperatures or the absence of predators.

At the same time, however, the functional characteristics of the newcomers must not be too similar to those present in the existing species community. “If the differences are only slight, the invasive species have to compete with the species living there. This is exhausting and does not necessarily promise successful colonization”. If an alien species manages to blend into the resource-rich area, it has a good chance of becoming a permanent resident. “It is therefore the combination of these characteristics that enables an invasive species to colonize successfully,” concludes fish ecologist Su.

Predicting the establishment of invasive species

These findings are useful because they can be used to optimize the prediction of invasive species immigration into freshwater fish communities in the future. “We now have a better understanding of what makes a species community potentially susceptible to new species. We can now analyze rivers and lakes and estimate how likely it is that new fish species will establish themselves there,” says Calabrese. This makes it possible to identify those bodies of water that are particularly at risk from invasive species. It is also possible to identify those invasive fish species that are likely to be very successful in taking over new habitats and ensure that they do not spread. “Our results provide useful information on how to deal with invasive species before they establish themselves anywhere,” concludes Su. Because one thing is well known about invasive species, whether fish, mammals or plants: once a new species has gained a foothold, it is almost impossible for humans to drive it out of its habitat again. It would therefore be better if it did not settle in the first place.


Guohuan Su, Adam Mertel, Sébastien Brosse, Justin M. Calabrese: Species invasiveness and community invasibility of North American freshwater fish fauna revealed via trait-based analysis, Nature Communications (2023), doi: 10.1038/s41467-023-38107-2

About the Center for Advanced Systems Understanding

CASUS was founded 2019 in Görlitz/Germany and pursues data-intensive interdisciplinary systems research in such diverse disciplines as earth systems research, systems biology or materials research. The goal of CASUS is to create digital images of complex systems of unprecedented fidelity to reality with innovative methods from mathematics, theoretical systems research, simulations as well as data and computer science to give answers to urgent societal questions. The founding partners of CASUS are the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the Helmholtz Centre for Environmental Research in Leipzig (UFZ), the Max Planck Institute of Molecular Cell Biology and Genetics in Dresden (MPI-CBG), the Technical University of Dresden (TUD) and the University of Wrocław (UWr). CASUS, managed as an institute of the HZDR, is funded by the German Federal Ministry of Education and Research (BMBF) and the Saxon State Ministry for Science, Culture and Tourism (SMWK).