transition land between two habitats, known as ecotones could actually be the womb of the priceless diversity of the rainforests according to new research. Where previously these areas on the fringes of rainforests, for instance, were ignored, now they are considered zones of evolution for various life-forms.

According to a report published this fortnight in the New York Times (1.7.97), this new theory could also explain the mystery behind the generation of diverse species in the tropical rainforests. "This is a wake-up call,' said Thomas B Smith, an evolutionary biologist at San Francisco State University, us , to scientists who harbour the impression that by protecting the rainforests they were also protecting the evolutionary forces that generated the species within them. Added Smith, who headed the team of four that produced the new study, "...if we don't stop ignoring these transition areas, we may be preserving the pattern of biodiversity, but not the processes that produce it.'

Smith and his team began taking ecotones seriously to understand why they were so often home to unusual looking populations in a number of species. Further, birds of the same species living in forest patches in the ecotone and in the deep forest were different. Smith and his team focussed on the little greenbull, an abundant, dull-green, robin-sized bird that feeds on fruits and insects in the forest. They examined birds living in six populations from the deep forest and six from forest patches in ecotones.

Results showed that there was a healthy amount of interbreeding between those greenbulls living in ecotones and those in the deep rainforests. However, in spite of this genetic relationship, weights, wing lengths, leg lengths and bill depths in the offsprings were quite different. The researchers concluded that with habitats not being the same, the offsprings had evolved differently, in spite of continued mating. Wings of the greenbulls in ecotones were significantly longer probably to escape from predators in the more open habitat of the ecotone. According to researchers, this divergence in species despite continued interbreeding is suggestive of the kind of diversification that can lead to the origin of new species.

Several scientists have welcomed the study. Calling it "convincing', Dolph Schluter, an evolutionary biologist at the University of British Columbia in Vancouver, said it was "a significant step in the attempt to understand the generation of variation, the variety of biodiversity.' The new theory questions the current understanding of how the rainforests evolved. According to this hypothesis, as global climate cooled in the ice ages, huge tropical rain forests shrank in size and broke up into much smaller tracts, which survived only in the few regions still hospitable for such plants and animals. The theory says that groups of unique species evolved in these isolated patches of remaining forest, known as refugia. Further, these patches of forest expanded and grew together after the ice ages ended, their unique complements of species gathering into what is the overwhelming biodiversity seen in tropical rain forests today. However, this controversial