Showing posts with label Florida Everglades. Show all posts
Showing posts with label Florida Everglades. Show all posts

Monday, January 30, 2012

Invasive Pythons Impact Native Wildlife: Evidence from Road Kill

The ecological damage done by the invasive brown tree snake on Guam has mad biologists, conservationists and ecologists paranoid about invasive snakes. In the United States invasive species management is estimated to exceed $120 billion annually. Invasive species, including invasive snakes alter habitat structure, competition between species, reduce native predator populations, alter the trophic structure of ecosystems, and they deplete or extirpate native prey populations. Now, Michael Dorcas and colleagues have documented the impact of the Burmese python, Python bivittatus, on the native wildlife of the Florida Everglades in a paper published today in the Proceedings of the National Academy of Sciences.

Between 1993 and 1999, prior to invasive snakes in south Florida, raccoons, opossums and rabbits were the most frequent road kill. But from 2003 to 2011, road kill surveys found a 99.3%fewer raccoons, 98.9% fewer opossums, and no rabbits or foxes; the surveys also found 94.1% fewer white-tailed deer and 87.5% fewer bobcats. During the 2003 to 2011 time frame annual removals of Burmese pythons rose from less than 50 per year to 300-400 per year. Raccoons, opossums, bobcats, deer and rabbits are all species documented in the diet of the invasive pythons in Everglades National Park. The native mammals are naive to the danger posed by the pythons, making them susceptible to python predation.

While raccoons, rabbits, and opossums are relatively common, concern for the predation pressure placed on endangered birds and mammals in south Florida has been expressed by conservationists and biologists. The entire study can be found on- line.

Dorca, ME, Wilson, JE, Reed, RN, Snow, RW, Rochford, MR, Miller, MA, Meshaka, WE, Andreadis, PT, Mazzotti, FJ, Romagosa, CM, Hart, KM. 2010. Severe mammal declines coincide with proliferation of invasive Burmese pythons in Everglades National Park. PNAS doi:10.1073/pnas.1115226109

Tuesday, March 22, 2011

Everglade Hammocks Growing on Human Middens

The following is a press release from the American Geophysical Union. The Everglade hammocks discussed in this artilce are important nesting sites for many Everglades reptiles. Kushland (1980. Copeia (4):930-932) found that hammocks were often the only dry areas in the Everglades and that they were used by alligators, turtles and lizards for depositing their eggs. 

Fixed tree island in Shark River Slough, 
Everglades. Photo Credit: Pablo Ruiz, 
Florida International University.
Ancient trash heaps gave rise to Everglades tree islands
SANTA FE, N.M.—Garbage mounds left by prehistoric humans might have driven the formation of many of the Florida Everglades' tree islands, distinctive havens of exceptional ecological richness in the sprawling marsh that are today threatened by human development.

Tree islands are patches of relatively high and dry ground that dot the marshes of the Everglades. Typically a meter (3.3 feet) or so high, many of them are elevated enough to allow trees to grow. They provide a nesting site for alligators and a refuge for birds, panthers, and other wildlife.

Scientists have thought for many years that the so-called fixed tree islands (a larger type of tree island frequently found in the Everglades' main channel, Shark River Slough) developed on protrusions from the rocky layer of a mineral called carbonate that sits beneath the marsh. Now, new research indicates that the real trigger for island development might have been middens, or trash piles left behind from human settlements that date to about 5,000 years ago.

These middens, a mixture of bones, food discards, charcoal, and human artifacts (such as clay pots and shell tools), would have provided an elevated area, drier than the surrounding marsh, allowing trees and other vegetation to grow. Bones also leaked phosphorus, a nutrient for plants that is otherwise scarce in the Everglades.

“This goes to show that human disturbance in the environment doesn't always have a negative consequence,” says Gail Chmura, a paleoecologist at McGill University in Montreal, Canada, and one of the authors of the study.

Chmura will be presenting her research tomorrow, Tuesday 22 March, at the American Geophysical Union's Chapman Conference on Climates, Past Landscapes, and Civilizations. About 95 scientists have converged on Santa Fe this week to discuss the latest research findings from archeology, paleoclimatology, paleoecology, and other fields that reveal how changes in regional and global climate have impacted the development and fates of societies.

In a previous scientific investigation of tree islands, Margo Schwadron, an archeologist with the National Park Service, cut through the elevated bedrock at the base of two islands and discovered that it was actually a so-called “perched carbonate layer,” because there was more soil and a midden below. Later, a team including Chmura's graduate student Maria-Theresia Graf performed additional excavations in South Florida and found more of the perched carbonate layers.

Chemical analysis of samples of these curious perched layers revealed that they are made up partially of carbonates that had dissolved from the bedrock below, Chmura says. The layer also contains phosphorus from dissolved bones, she adds. Her team concluded that trees are key to the formation of this layer: During South Florida's dry season, their roots draw in large quantities of ground water but allow the phosphates and carbonates dissolved in it to seep out and coalesce into the stone-like layer.

The perched carbonate plays a key role in letting tree islands rebound after fires: because it does not burn, it protects the underlying soil, and it maintains the islands' elevation, allowing vegetation to regrow after the fire. Humans are now threatening the existence of tree islands, by cutting down trees (whose roots keep the perched layer in place) and artificially maintaining high water levels year-round in some water control systems, which could cause the layer to dissolve.

Chmura's team now wants to explore exactly when trees started growing on the tree islands.

Monday, March 14, 2011

Pythons & Birds in the Everglades

You knew this was coming. The following press describes the research documenting the damage invasive pythons are doing to bird populations in Everglades National Park.

Scientists find that non-native snakes are taking a toll on native birds

Python bivittatus. JCM
The Everglades National Park in Florida is home to hundreds of species of native wildlife. It has also become the well-established home of the non-native Burmese python—known to be a predator of native species. Now scientists, for the first time, have conducted a detailed analysis of the avian component of the python's diet and the negative impact the snakes may have on Florida's native birds, including some endangered species.

The Burmese python (Python molurus bivittatus), native to Southeast Asia, was first recorded in the Everglades in 1979—thought to be escaped or discarded pets. Their numbers have since grown, with an estimated breeding population in Florida in the tens of thousands. As researchers investigate the impact of this snake in the Everglades, scientists from the Smithsonian Institution, South Florida Natural Resources Center and the University of Florida examined the snake's predation of the area's birds. They found that birds, including endangered species, accounted for 25 percent of the python's diet in the Everglades.

"These invasive Burmese pythons are particularly hazardous to native bird populations in North America because the birds didn't evolve with this large reptile as a predator," said Carla Dove, ornithologist at the Smithsonian's Feather Identification Lab in the National Museum of Natural History. "Conversely, the python is able to thrive here partly because it has no natural predator to keep its numbers in check."

The scientists collected 343 Burmese pythons in Everglades National Park as part of their study between 2003 and 2008. Eighty-five of these snakes had bird remains in their intestinal tract. From these remains the team identified 25 species of birds by comparing feathers and bone fragments with specimens in the Smithsonian's collection. The results reflected a wide variety of species, from the 5-inch-long house wren to the 4-foot-long great blue heron. Four of the species identified (snowy egret, little blue heron, white ibis and limpkin) are listed as "species of special concern" by the Florida Fish and Wildlife Conservation Commission. The team also identified the remains of a wood stork, which is a federally endangered species.

"These pythons can also inhabit a wide variety of habitats, so their impact is not restricted to just the native species within the Everglades," Dove said. "The python's high reproductive rate, longevity, ability to consume large prey and consumption of bird species are causes for serious conservation and control measures."

Dove, C. J., R. W. Snow, M. R. Rochford, F. J. Mazzotti. Birds Consumed by the Invasive Burmese Python (Python molurus bivittatus) in Everglades National Park, Florida, USA. The Wilson Journal of Ornithology, 2011; 123 (1): 126 DOI: 10.1676/10-092.1