Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Brown Tree Snake Could Mean Guam Will Lose More than Its Birds

11.08.2008
Brown tree snakes have come to embody the bad things that can happen when invasive species show up where they have few predators. But new research suggests that indirect impacts might be even farther reaching, possibly changing tree distributions and altering already damaged ecosystems.

In the last 60 years, brown tree snakes have become the embodiment of the bad things that can happen when invasive species are introduced in places where they have few predators. Unchecked for many years, the snakes caused the extinction of nearly every native bird species on the Pacific island of Guam.

A variety of other damage has been directly attributed to brown tree snakes, including large population losses among other native animal species in Guam's forests, attacks on children and pets, and electrical power outages.

But new research by University of Washington biologists suggests that indirect impacts might be even farther reaching, possibly changing tree distributions and reducing native tree populations, altering already damaged ecosystems even further.

"The brown tree snake has often been used as a textbook example for the negative impacts of invasive species, but after the loss of birds no one has looked at the snake's indirect effects," said Haldre Rogers, a UW doctoral student in biology.

"It has been 25 years since the birds disappeared. It seems to me the consequences are going to keep reverberating throughout the community if birds are fundamental components of the forest," she said.

Birds typically make up a small part of the life of a forest, but they are important for pollination, spreading seeds around the forest and controlling insects that feed on plants. Guam, an island 30 miles long and 5 to 15 miles wide about 3,800 miles west of Hawaii, lost most of its native birds after the brown tree snake was introduced by accident from the Admiralty Islands following World War II. The snake has few predators on Guam, so its population density is quite high – estimated at more than 3,000 per square mile – and some individuals there grow to an unusual size of 10 feet long.

Before introduction of the brown tree snake, Guam had 12 species of native forest birds. Today 10 of those are extinct on Guam, and the other two species have fewer than 200 individuals. Though Guam has some non-native bird populations, few other birds moved in when native species died out, and none of them live in the forest. That leaves few birds to consume tree seeds and then drop them away from the trees.

That could have two possible negative impacts on the native forests, Rogers said. First, some plant species need birds to handle their seeds to ensure effective germination. In addition, seed predators and fungi that kill seeds are often found in high density directly beneath a parent tree, so the trees rely on birds to disperse seeds beyond the range of those negative effects. If native birds performed those functions on Guam, tree populations could suffer from the loss of birds. It appears 60 percent to 70 percent of tree species in the native forests are dispersed, at least in part, by birds, she said.

To test the effects of the loss of native birds on seed distribution, Rogers devised seed traps that look a bit like satellite dish receivers, with tubing bent into a circular shape and covered with fine mesh screen-door netting. She set 119 traps beneath and near Premna obtusifolia, or false elder, trees on Guam and the nearby island of Saipan, which does not have brown tree snakes. For each tree sampled, she set two traps directly beneath the tree's canopy, two about 3 feet away, three at 16 feet, three at 33 feet and seven at 65 feet.

On Saipan, Rogers and her colleagues found seeds in nearly every trap at each distance, though more seeds were found in closer traps and fewer farther away. However, on Guam the seeds appeared only in traps directly beneath the canopy. What's more, most of the farther-dispersed seeds from traps on Saipan had the seed coats removed, a factor that could speed seedling germination and the growth of new trees and something that likely could only be accomplished in the gut of a bird. None of the seeds found on Guam had seed coats removed.

In addition, the scientists randomly selected points in native forests on Guam, Saipan and two other nearby islands, Tinian and Rota, searching for seedlings of a tree called Aglaia mariannensis and each seedling's most likely parent, the closest adult of that species. On Guam all seedlings were found within 16 feet of the nearest adult tree, most within 6 feet. On the other islands the nearest adult trees were found two to three times farther away from the seedlings.

"These findings could have global implications, since forests in areas that have had a decline in bird populations instead of outright extinction might show effects similar to those in the forests of Guam," Rogers said.

She notes that recent studies show bird populations are declining worldwide, and that as many as 25 percent of U.S. species face the threat of extinction.

Rogers presents her data Friday (Aug. 8) at the Ecological Society of America meeting in Milwaukee. Co-authors are Joshua Tewksbury and Janneke Hille Ris Lambers, both UW assistant professors of biology.

Further research, Rogers believes, could turn up other indirect impacts the brown tree snake has had on Guam. For example, she notes anecdotal evidence that there is a substantially higher spider population on Guam than on other nearby islands, and she speculates that could largely be because the native bird population has been decimated.

But the biggest indirect impact, she said, could be altered seed scattering that in turn might, in the near future, transform the remaining forest from a diverse mixture of tree species to clumps of trees of the same species, separated by open space. That could have serious consequences, including extinction, for plant and animal species that still live in the forests.

"It seems logical that if there are no birds then seeds are not able to get away from their parent trees, and that is exactly what our research shows," Rogers said. "The magnitude of difference between seed dispersal on Guam and Saipan is alarming because of its implications for Guam's forests, and for forests worldwide experiencing a decline or complete loss of birds."

For more information, contact Rogers at (206) 491-2573 or haldre@u.washington.edu.

Vince Stricherz | Newswise Science News
Further information:
http://www.washington.edu

Further reports about: Brown tree snake invasive species native forest birds

More articles from Ecology, The Environment and Conservation:

nachricht International network connects experimental research in European waters
21.03.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

nachricht World Water Day 2017: It doesn’t Always Have to Be Drinking Water – Using Wastewater as a Resource
17.03.2017 | ISOE - Institut für sozial-ökologische Forschung

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: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

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.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

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...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Argon is not the 'dope' for metallic hydrogen

24.03.2017 | Materials Sciences

Astronomers find unexpected, dust-obscured star formation in distant galaxy

24.03.2017 | Physics and Astronomy

Gravitational wave kicks monster black hole out of galactic core

24.03.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>