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
Loss of habitat causes double damage to species richness
02.04.2019 | Deutsches Zentrum für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig
Deep decarbonization of industry is possible with innovations
25.03.2019 | Fraunhofer-Institut für System- und Innovationsforschung (ISI)
A stellar flare 10 times more powerful than anything seen on our sun has burst from an ultracool star almost the same size as Jupiter
A localization phenomenon boosts the accuracy of solving quantum many-body problems with quantum computers which are otherwise challenging for conventional computers. This brings such digital quantum simulation within reach on quantum devices available today.
Quantum computers promise to solve certain computational problems exponentially faster than any classical machine. “A particularly promising application is the...
The technology could revolutionize how information travels through data centers and artificial intelligence networks
Engineers at the University of California, Berkeley have built a new photonic switch that can control the direction of light passing through optical fibers...
Physicists observe how electron-hole pairs drift apart at ultrafast speed, but still remain strongly bound.
Modern electronics relies on ultrafast charge motion on ever shorter length scales. Physicists from Regensburg and Gothenburg have now succeeded in resolving a...
Engineers create novel optical devices, including a moth eye-inspired omnidirectional microwave antenna
A team of engineers at Tufts University has developed a series of 3D printed metamaterials with unique microwave or optical properties that go beyond what is...
17.04.2019 | Event News
15.04.2019 | Event News
09.04.2019 | Event News
18.04.2019 | Life Sciences
18.04.2019 | Physics and Astronomy
18.04.2019 | Life Sciences