Saturday, October 13, 2012

Two recent publications on invasive snakes in the USA

Invasive species have become common place, and invasive snakes can cause considerable damage to the ecosystems they colonize. However, as ectotherms snakes are limited by temperatures and different species have evolved in different climates.

Jacobson et al. (2012) experimentally examined the ability of the Burmese python to survive winters north of southern Florida. Using daily high and low temperatures from October to February that occurred between 2005 and 2011 at Homestead, Orlando and Gainesville, Florida; and Aiken, South Carolina. And, they used minimum temperatures projected for python digestion (16 °C), activity (5 °C) and survival (0 °C). The mean low and high temperatures decreased northward from Homestead to Aiken and the number of days of freezing temperatures increased northward. They found digestion was impaired or inhibited for 2 months in the Everglades and up to at least 5 months in Aiken. The snakes' activity was increasingly limited at more northern localities during these months. A single bout of low and freezing temperatures results in python death. The capacity for Burmese pythons to successfully overwinter in more temperate regions of the USA is seemingly improbable because they lack the behaviors to seek refuge from the cold, and the physiology to tolerate the cold temperatures. Burmese pythons evolved in tropical Southeast Asia this area is the source of the Everglades Burmese pythons. The authors predict that it is unlikely the Burmese python they will be able to successfully expand to or colonize more temperate areas of Florida and adjoining states because of the lack of behavioral and physiological traits to seek refuge from cold temperatures.

The Brown treesnakes (Boiga irregularis) are perhaps the most studied invasive snake due to their colonization of Guam. A recent paper by Kahl et al. (2012) suggests that this mildly venomous, exotic snake species has the potential to become invasive in North America, Hawaii, and the Commonwealth of the Northern Mariana Islands. The brown tree snake is native to northern and eastern Australia, New Guinea, and other islands of northern and western Melanesia. The snake was first found outside its native range in 1953 on Guam. The exact date they reached the island is uncertain, but they are believed to have arrived on military cargo transport vessels some time during or just after World War II. During the years that followed, the population of brown treesnakes increased considerably on Guam. The snakes have extirpated or endangered many native animal populations, attacked pets and poultry, bitten humans, and caused power outages resulting in millions of dollars in damage. This snake species has been found on ships and aircraft, which have transported it to other islands in the Indo-Pacific, as well as Hawaii and the continental United States (i.e., Texas, Oklahoma, and Alaska) in military cargo. Because the U.S. military is expanding its bases on Guam, resulting in increased shipments and military movements from Guam to the United States, there is an increasing risk for brown treesnakes to invade the United States, as well as other islands in the Pacific. The authors note that two-thirds of the literature concerning brown treesnakes is in gray area publication outlets that can be difficult to ascertain. A literature review is offered to provide a background of past research on brown treesnakes. This review of literature elaborates on the native range, morphology, behavior, biology, ecology, venom, diet, reproduction, habitat, mortality, and control of the brown treesnakes.

Citations
Jacobson E. R., Barker, D. G., Barker, T. M., Mauldin, R., Avery, M. L., Engeman, R. and Secor, S. (2012), Environmental temperatures, physiology and behavior limit the range expansion of invasive Burmese pythons in southeastern USA. Integrative Zoology, 7: 271–285. doi: 10.1111/j.1749-4877.2012.00306.x

Kahl, S.S., Henke, S. E. , Hall, M. A. & Britton, D.K. 2012. Brown treesnakes: a potential invasive species for the United States. Human-Wildlife Interactions 6:181-203.

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