Findings: Amphibians are our friends

April 25, 2003

Severely declining amphibian populations could lead to a rise in potentially deadly human diseases, writes Natasha Gilbert.

According to researchers from Australia, mosquito larvae and tadpoles are often found in the same ponds and have similar diets - bacteria, detritus, protozoans and algae. Rick Shine and Allie Mokany at the School of Biological Sciences, University of Sydney, investigated how these species might affect each other's growth rate and survival.

They found that tadpoles reduced the growth rate and survival of mosquito larvae. The researchers suggested that tadpoles might delay mosquito metamorphosis - reducing larval survival and adult body size and hence limit their disease-carrying potential and ability to reproduce.

The findings indicate that the fall in amphibian populations could diminish natural controls of mosquito populations. Dr Shine told The THES: "There are grounds for concern that the decline in amphibian populations may have an unexpected impact on human health."

The researchers reported that the effect tadpoles had on mosquito larvae were present even when food was in abundance. These findings suggest that mosquito larvae and tadpoles affect each other in more complex ways than just competition for resources.

"The mechanisms of competition affect how much influence one species has on the other," Dr Shine said. "Even a few tadpoles might be able to reduce mosquito viability."

But, Tim Halliday, international director of the Declining Amphibian Population Task Force, department of biological sciences, Open University, suspects there may be only limited impacts on mosquito populations because they often breed in the absence of tadpoles.

Dr Shine said his research was a reminder of the connectedness of species.

"You can't take away one bit of the jigsaw without affecting the other parts."

These findings are published in the journal Community Ecology.

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