Up to one in four fish species inhabiting lakes and rivers near human settlements is foreign, according to the first global analysis of invasive species in freshwater ecosystems.
Invasive species are often called "biological pollution" because they have far-reaching effects on native wildlife. When a foreign species is introduced into a new ecosystem, it often thrives in the absence of predators, out-competes native species for a finite food source or otherwise disrupts the web of life that had evolved in that location.
Zebra mussels, native to the Caspian Sea area of Europe and Asia, for example, have invaded many freshwater ecosystems in the United States. In the Hudson River, zebra mussels have led to the extinction of native clams and so altered the ecosystem by filtering out massive amounts of plankton that young fish may not be surviving because they can't eat enough.
The new study, led by Fabien Leprieur, Olivier Beauchard and published in the Public Library of Science, found that in 1,000 river basins studied, population density, degree of urbanized land, and that area's gross domestic product were most clearly related to the number of invasive fish.
The authors of the study warned that rivers that have remained relatively unharmed are unlikely to remain so as more developing nations modernize, and world population continues to grow.
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