Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

’Fowl-howl’ ties discovered between birds, monkeys

06.08.2002


A strong and unexpected correlation between large numbers of howler monkeys and elevated counts of birds on islands created by a Venezuelan hydroelectric project has Duke University scientists looking for explanations. They say their discovery represents a prime example of the unexpected ecological insights that the science all-too-often yields.



The scientists’ working hypothesis is that excess plant-eating monkeys found on some of the smallest islands counterintuitively spur extra tree growth, which in turn boosts populations of insects that then attract all those birds, Duke investigator Kenneth Feeley reported Tuesday at the Ecological Society of America’s annual meeting.

"If you think about it, you wouldn’t expect any sort of relationship between howler monkeys and birds," Feeley said in an interview before the meeting. "It took us by surprise."


A graduate student studying for his Ph.D. at the university’s Department of Biology, Feeley was brought in to explain the strange relationship first identified by John Terborgh, a James B. Duke Professor of environmental science at Duke’s Nicholas School of the Environment and Earth Sciences.

Terborgh set up the research station on Lago Guri, a Venezuelan lake formed in 1986 by a dam impoundment, to study how plants and animals trapped on its many islands respond to the forced isolation.

The Duke professor "did a census of the bird communities in 1993 and 1995 and found that small islands had an extremely high density of birds, an average of two times what we found on the mainland, and on some islands almost 20 times as many," Feeley said.

Many of the smaller islands, only a few acres or less in size, also have howler monkey populations up to 30 times higher than those off the islands. "Wherever there are lots of howlers there are also lots of birds," Feeley noted. "So we have a strong positive correlation between the two groups."

The reasons are less than obvious, because howler monkeys are strictly vegetarians who eat leaves, flowers or fruits -- not a reason to attract birds. But "we’ve come up with several hypotheses to link them," Feeley said.

Currently favored is a hypothesis that the plant-eating monkeys are actually making the trees they feed on more productive. "It’s kind of a backward logic, but essentially it has to do with the rates of nutrient cycling," he added.

According to that view, an excess number of plant eaters increase soil fertility. "The dung of a howler monkey is recycled very rapidly, and so essentially trees benefiting from this are able to produce more vegetative matter," he explained.

Because plants are also eaten by insects, the extra growth "allows for a high density of insects, which in turn allows for a high density of insectivorous (insect eating) birds," Feeley said.

Since Terborgh’s original survey, the Duke scientists have done additional bird censuses during the last three years and expanded their research area from 12 to 31 islands. In the process, their findings have become more variant, with some otherwise similar islands found to support high bird densities and others essentially none.

"A focus is now trying to see what drives that variation," he said.

Densities of howler monkeys also vary. Numbers trapped on various islands by the flooding were "essentially determined by random chance," he said.

Still "we do have some evidence to support my hypothesis," Feeley added. "The density of birds is strongly, positively correlated with the density of howler monkeys. The growth rate of trees is also positively correlated with howler monkey densities. Finally, detailed foraging observations of the birds on small islands have shown that there do appear to be more insects available on the islands with dense bird populations."

He and other researchers are currently doing chemical and nutrient analyses of soil and growing and fallen leaves from each of the islands. That work "will hopefully allow us to look in more detail at how howler monkeys may be influencing the nutrient cycling," he said.

Monte Basgall | Duke University
Further information:
http://www.duke.edu/

More articles from Ecology, The Environment and Conservation:

nachricht Upcycling of PET Bottles: New Ideas for Resource Cycles in Germany
25.06.2018 | Fraunhofer-Institut für Betriebsfestigkeit und Systemzuverlässigkeit LBF

nachricht Dry landscapes can increase disease transmission
20.06.2018 | Forschungsverbund Berlin e.V.

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Metal too 'gummy' to cut? Draw on it with a Sharpie or glue stick, science says

19.07.2018 | Materials Sciences

NSF-supported researchers to present new results on hurricanes and other extreme events

19.07.2018 | Earth Sciences

Scientists uncover the role of a protein in production & survival of myelin-forming cells

19.07.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>