Economic growth brings in invasive species

Fish invasion--0-5 per cent, 5-25 per cent and 25-95 per cent--is classified as vulnerable, endangered and critically endangered. They are the percentages of non-native fish species compared to the total number of fish present in the river basins

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it's well known that invasion of non-native species cause biodiversity crisis by harming native species and affects ecosystem processes in the natural environment. But how they establish themselves in aquatic ecosystems is not known so far, although various hypotheses have been attempted. A recent study validates one of them and says human activities account for almost 70 per cent of the invasions.

Researchers link the invasion to economic growth; gdp contributed the most--43 per cent. Three non-exclusive mechanisms may account for this pattern, says Fabien Leprieur of cnrs -Universite Paul Sabatier, France, in the paper published in the February issue of PLoS Biology (Vol 6, No 2). "One, economically rich areas are more prone to habitat disturbances where dams and reservoirs modify river flows and facilitate invasion.Two, non-native species can invade through ornamental trade, sport fishing and aquaculture. Three, the increased demand for imported products increases the chances of unintentional invasion," says Leprieur in the paper.

Mapping invaders The researchers mapped the worldwide distribution of invasive species in every basin and compared (in percentage) them with total number of species present in that basin (see map World under). They studied 1,055 river basins covering more than 80 per cent of Earth's continental surface. The researchers declared those areas with more than 25 per cent non-native species as invasion hot spots. They identified six such hot spots.

The study found the river basins of the northern hemisphere host the highest number of invasive fish species. iucn Red List lists invasion of non-native fish species as the second major threat to biodiversity after habitat loss 20 per cent of the 680 species extinctions are due to species invasions. Freshwater fish also follow the same trend where 20 per cent of iucn listed species are threatened by invasion.

The researchers found fish invasion areas matched regions where human activities impacted most, economically. River basins of developing countries will host more non-native fish species with economic growth, they say.

"This constitutes a serious threat to global biodiversity because rivers of most developing areas (like southern Asia, western and central Africa) are characterised by high levels of endemism," says Leprieur, adding "conservation policies should be designed considering these facts".