Plant-killing fungi 'drive rainforest biodiversity'

Netted stinkhorn fungus (Image: Robert Bagchi) The findings help scientists understand the mechanism that allows species to coexist in an ecosystem

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Pathogenic fungi, normally associated with killing plant life, could play a key role in driving biodiversity in tropical rainforests, a study suggests.

Researchers found that the presence of fungal pathogens limited the growth of dominant species, allowing other plants to become established.

The scientists said the study offered an insight into why rainforests are biodiversity hotspots.

The findings have been published in the journal Nature.

"The conventional wisdom in ecology suggests that if you have got more than one species competing for the same set of resources, one of those species should win and exclude the other," co-author Owen Lewis from the University of Oxford explained.

However, an idea developed by ecologists Daniel Janzen and Joseph Connell in the 1970s linked pests and diseases to high levels of biodiversity in tropical areas, which they described as negative density dependence.

"The way the hypothesis works is to give rare species an advantage - the idea is that pests and diseases tend to transmit more effectively if plants are growing close together," Dr Lewis told BBC News.

"This acts as a negative feedback mechanism, so if one species becomes too abundant locally then it tends to get hammered by the pests and diseases and this then gives rarer species a chance because they tend to be less affected.

Germinating seedlings (Image: Owen Lewis) Dominant species are targeted by fungal pathogens, allowing rarer species the opportunity to grow

"This acts as a balancing mechanism that prevents these rarer, and perhaps competitively inferior species, from being outcompeted."

Commenting on the findings, Dr Helene Muller-Landau - a scientist for the Smithsonian Tropical Research Institute - described the study as an "elegant field study" that supported the Janzen-Connell hypothesis.

"This is the first study to explicitly link a particular group of natural enemies to negative density dependence and the maintenance of species diversity in tropical forest plants," she wrote in a commentary for Nature journal.

"It clearly implicates fungal pathogens as the most important drivers of these patterns at the seedling-establishment stage."

Dr Lewis observed: "It is an interesting but almost paradoxical effect that a small group and obscure group of organisms are harming individual plant species but are ultimately good for diversity as a whole.

"And it is the plant diversity that underpins the structure of the whole ecosystem that supports the insects, birds and animals."

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