Berlin, Feb 19 : A team of German and Sri Lankan researchers have developed a new method for measuring the impacts of species on local biodiversity, which makes it possible to determine whether a certain species promotes or suppresses species diversity.
It extends a procedure familiar to biologists that involves investigating species numbers in relation to area by adding sophisticated statistical methods so that it can be used to describe the role of individual species in their impact on biodiversity.
The researchers used their new method to evaluate unique data from two tropical rainforests in Sri Lanka and Panama that are part of a network coordinated by the Center for Tropical Forest Science.
Within this network, every single tree with a trunk thicker than a pencil has been mapped and monitored for years on about a dozen selected sample plots, some as large as 50 hectares, in tropical rainforests around the globe.
The researchers compared in their study around 40,000 larger trees in the tropical rainforest on Barro Colorado Island, Panama, with those in the Sinharaja World Heritage Site in Sri Lanka.
To their surprise, more than two third of all species did not leave identifiable signatures on spatial diversity. The other tree species had an impact on local biodiversity only in their immediate surroundings, within a radius of up to 20 metres, but not on a large scale.
These findings support the much-debated 'neutral theory', according to which species characteristics are unimportant for certain community attributes and play only a subsidiary role in the stability and diversity of ecosystems.
The study also revealed that the two tropical forests lacked any key species structuring species diversity at larger scales, suggesting that 'balanced' species-species interactions may be a characteristic of these species rich forests.
According to Dr Thorsten Wiegand, "Biodiversity researchers have not been able to agree on which processes permit a high level of species diversity to emerge, and which processes keep these complicated systems stable".
"We first used the new method in tropical rainforests, but it is universally applicable and can be used for plants in all ecosystems," said Dr Andreas Huth of the Helmholtz-Centre for Environmental Research - UFZ.