The question of which forces control terrestrial ecosystems lies at the heart of a long-standing debate among ecologists. One theory, the so-called bottom-up theory, suggests that plant defense mechanisms exert control by limiting food availability for herbivores. Top-down theorists, however, suggest that predators limit the numbers of herbivores and hence their impact on the vegetation. Now new findings in the current issue of the journal Science that describe animal communities isolated for 15 years weigh in on the side of predators as crucial to controlling an ecosystem.
An international team of 11 authors studied a dozen predator-free islands isolated since 1986 by rising water in a hydroelectric impoundment in Venezuela. Two of the large islands, together with two mainland sites, served as control systems. The smaller islands, the authors write, are "highly aberrant, consisting of a suite of consumers without predators." As such, they provide a unique opportunity to test top-down control.
The researchers found highly inflated numbers of consumer animals on some of the islands as compared with the mainland—including 35 times more rodents, 25 times more howler monkeys, 10 times more iguanas and 100 times more leafcutter ants. "This is very strong evidence for top-down regulation," says lead author John Terborgh of Duke University. "If predators are gone, then the number of these consumers explodes." Hinting at the complexity of ecosystem control, however, the reproductive rates of the howler monkey on one island did exhibit bottom-up control, in that the birth rate was one quarter of that found on a less-populated island.
Sarah Graham | Scientific American
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Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
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In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
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Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
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