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Human changes to rainforests damage web of life

Reprinted from University of Canterbury Chronicle - 12/02/07

Converting the rainforests of Ecuador into intensely farmed agricultural land has had a dramatic impact on the region's web of life, according to a paper co-authored by a University of Canterbury ecologist which has been recently published in Nature magazine.

The paper, written by Dr Jason Tylianakis (Biological Sciences), Dr Owen Lewis of Oxford University and Professor Teja Tscharntke at the University of Goettingen, looks at the impact human changes to the environment have had on "food webs" the interactions between wild bees and wasps and their natural enemies in the Choco-Manabi region of Ecuador.


Human-made changes to the environment can have a huge impact on the web of life according to research by Dr Tylianakis
Human-made changes to the environment can have a huge impact on the web of life according to research by Dr Tylianakis

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Dr Tylianakis said scientists had known for some time that humans' conversion of natural habitats caused the extinction of some species but what was less clear was what happened to species that were left behind did they interact differently or did they continue as before".

Ecuador was chosen for the study as it was a country that was rapidly transforming, Dr Tylianakis said. It is one of the most biologically diverse regions in the world but, because of high levels of poverty much of the rainforest is being converted to agriculture.

"These changes are already having an impact on local climate and are affecting the country's biological diversity. Once biological diversity is altered it will affect the whole structure of species' interactions and will, down the line, affect humans." The researchers spent 17 months studying more than 7000 individual wild bee and wasp nests. They looked at how the bees and wasps were attacked by their natural enemies, mainly parasitic wasps, and whether the interaction between the species was affected by their habitats. The nests were located in tropical rainforests, agricultural areas and in coffee plantations grown beneath the forest canopy.

"We found that bees and wasps in modified agricultural areas became more heavily attacked by their parasitic enemies, which raises the question of whether bees will continue to survive and perform well in these areas," said Dr Tylianakis.

"It also raises issues for local farmers who rely on bees to pollinate their crops and use wasps as biological control agents of pests such as caterpillars.

"If wild bees and wasps are more heavily attacked by their natural enemies, farmers will have to hand-pollinate crops and use chemicals to control pests or suffer low crop yields."

However, Dr Tylianakis said the study found that coffee plantations grown under the forest canopy had a similar structure of species interactions to that of the tropical rainforest, rather than the altered structure typical of intensive agriculture such as rice or pasture.

"Coffee plantations are managed at a low intensity and while providing an income for farmers, do not significantly harm the environment. This shows that it's possible to manage habitats in a way that is compatible with agriculture and is better for the species that live in the area."

The only downside to this was the low price farmers received for coffee.

"But the increasing popularity of fair-trade coffee may help with that, and provide financial incentives for farmers to manage their crops in a sustainable way."

Similar studies have been carried out in Germany and Australia. Dr Tylianakis hoped to do research along the same lines in New Zealand, using quantitative interaction webs to look at whole communities of plants, insects and their natural enemies in natural and agricultural habitats.

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