She and study co-authors Janneke Hille Ris Lambers and Josh Tewksbury of the University of Washington and Ross Miller of the University of Guam found that spiders were between two times and 40 times more plentiful on Guam than on neighboring islands.
The highly invasive brown treesnake wiped out native forest birds on the island of Guam. The effect of the loss of birds is still under investigation. View larger. (Credit: Isaac Chellman) The results are some of the first to examine the indirect impact of the brown treesnake on Guam’s ecosystem.
Historically, if ecologists wanted to study how insects reacted to the absence of birds, they would build an “exclosure,” a covering designed to keep birds out of their study area. Rogers says most exclosures cover a few branches of one tree, and, in rare cases, an entire tree. 40x more spiders.
The spider population on Guam has exploded after the loss of native forest birds, researchers report. In one of the first studies to examine how the loss of forest birds is affecting Guam’s island ecosystem, biologists from Rice University, the University of Washington, and the University of Guam found that the Pacific island’s jungles have as many ...
By the 1980s, 10 of 12 native bird species had been wiped out, and the last two live only in small areas protected by intense snake-trapping. Rogers and colleagues are investigating whether the loss of birds led to an increase in the spider population on Guam, since many birds consume spiders, compete with spiders for insect prey, ...
However, the reclusive, nocturnal reptiles are extremely hard to find. Rog ers says the average resident or tourist on Guam will never see one, and even those who actively hunt them are hard-press ed to find one, which is one reason the snakes have been impossible to eradicate from the island.
Anytime you have a re duction in insectivorous birds, the system will probably respond with an increase in spiders. With insectivorous birds in decline in many places in the world, I suspect there has been a concurrent increase in spiders.”.
Treefall gaps appear when an adult tree dies, opening up the canopy and increasing the light that reaches the forest floor. Many species rely on this increased light for germination and early growth, so these gaps are hotspots for new seedlings. Birds such as the Mariana fruit dove are a big help to the islands’ trees.
Birds such as the Mariana fruit dove are a big help to the islands’ trees. Lainie Berry, Author provided. We found that Saipan and Rota had roughly double the number of species of seedlings growing in these gaps, compared with Guam.
In 1987 the US ecologist Julie Savidge provided conclusive evidence that the two were linked: the brown tree snake was eating the island’s birds. Today, 10 of Guam’s 12 original forest bird species have been lost.
But the ecological damage doesn’t stop there. The loss of native bird species has triggered some unexpected changes in Guam’s forests. Both the establishment of new trees and the diversity of those trees is falling. These changes show how an invasive predator can indirectly yet significantly alter an entire ecosystem.
In the tropics, up to 90% of tree species rely on animals, often birds, to spread their seeds. Birds eat fruit from the trees and then defecate the undigested seeds far away from the parent tree’s canopy, where there are fewer predators and pathogens that specialise on that species , where competition for light, water and nutrients is less intense, and where seeds can take advantage of promising new real estate when old trees die.
In forests, “pioneer species” are those that rapidly colonise gaps, exploiting the increased light to grow fast and reproduce young. Crucially, we found pioneer species in all gaps on islands with birds, but in very few gaps on Guam, where these species could be at risk of being lost entirely.
Without birds, roughly 95% of seeds of two common tree species on Guam ( Psychotria mariana and Premna serratifolia) land directly beneath their parent tree. Compare that with the nearby islands of Saipan, Tinian and Rota – none of which have brown tree snakes – where less than 40% of seeds land near their parent tree.
And because Guam is so small and isolated, animals that lose their habitat really have nowhere else to go.
It’s quiet because there are virtually no birds. Brown tree snakes, an invasive species that was thought to have come to the island in the 1950s as a stowaway on a ship, feasted on the eggs of the island’s birds.
Ecologists long ago coined the term “keystone species” to describe the species without which an ecosystem could cease to function. Rogers, who let me stay in her field house on a recent visit to Guam, calls the island’s birds a “keystone functional group.”.
Trees are more likely to fall during typhoons, which hit the island every few years. Since birds aren’t dispersing the trees’ seeds as efficiently, there are fewer trees left of reproductive age, so the forest will take much longer to recover from a damaging event like a typhoon.
Birds and bats eat the fruit from trees, but don’t fully digest the seeds. Instead, the seeds pass through their digestive systems, which removes seeds’ tough outer coats and pathogens. Then, the seeds are dropped, in a nutrient-rich pile of excrement, wherever the animals happen to be at the time.
Species don’t have to go extinct for them to no longer be able to fill their ecological niche, Rogers points out. Losing a big enough proportion of the individuals in the population might be enough to reduce its ability to fulfill its ecological role.
The little fire ant ( Wasmannia auropunctata) is on the list of the top 100 invasive species in the world. It is considered the greatest invasive ant threat to the Pacific region. The bright red ant is about 1/16 of an inch. An entire little fire ant colony can fit in a macadamia nut shell.
According to Moore, the coconut rhinoceros beetle has decimated the number of coconut trees all over the island. The invasive beetle has four life stages: egg, grub, pupa and adult. Only the adult stage causes damage.
With its introduction, it can cause economic losses, environmental hardship or harm to human health. The invasive species are not ranked in any particular order; although, the experts agreed that the brown tree snake probably caused the most extensive damage so far to the island.
The pigs have also become a concern because they carry diseases, according to Post files. “People don't know when something is a problem that it can be spread unknowingly. It becomes important that people are aware of the impacts of these invasive species and also how to identify them,” Vice said.
The coconut rhinoceros beetle ( Oryctes rhinoceros) has been attacking coconut trees on Guam since it was first discovered on the island in 2007. In a 2002 U.S. Forest Service survey, the coconut was listed as the second most abundant tree on Guam.
The snake was said to have hitchhiked across the ocean to the island during the mid-20th century. The invasive snake caused the loss of native bird species on island, such as the Mariana fruit dove, Guam flycatcher, Micronesian myzomela and the rufous fantail.
From brown tree snakes to coconut rhinoceros beetles, Guam has seen a wave of invasive species that have impacted the island’s ecosystem. The damage caused by invasive species to the island has become the focal point of efforts by agencies and organizations such as the Guam Invasive Species Council.
With few native species left to eat, the snakes have moved on to eating rats and chickens. Brown tree snake electrocutions (the snakes climb power poles as well as trees) cause power outages every other day on average.
Guam—a 200-square-mile island about 1,500 miles south of Tokyo—offers one of the most severe examples anywhere of extinction caused by an introduced predator. Twenty-two species of birds and three bats lived on Guam until 1949, when a pregnant brown tree snake slithered ashore from a cargo ship. Today, hundreds of thousands ...
On Guam, the same two trees hosted a parade of beetles, ants, butterflies, honeybees, crabs, rats, praying mantises, and lizards, but not a single bird. Worse, none of the visitors showed much aptitude for collecting pollen. Most of the insects were too small to graze the flowers’ anthers.
Guam—a 200-square-mile island about 1,500 miles south of Tokyo—offers one of the most severe examples anywhere ...
The two islands have similar growing seasons, plant species, and—until recently—bird populations. On Saipan, birds made 95 percent of the visits to the two tree species (most commonly, Bridled and Golden white-eyes and the Micronesian Myzomela). On Guam, the same two trees hosted a parade of beetles, ants, butterflies, honeybees, crabs, rats, ...
Mature trees—established before birds vanished—are equally common on the two islands’ study plots, but Guam has fewer seedlings by a factor of about 50.
The few flowers that lizards or honeybees manage to fertilize simply aren’t enough to replace the trees, the research ers report. At least six more native bird- or bat-pollinated plants face the same problems, according to the article.