Showing posts with label snakes. Show all posts
Showing posts with label snakes. Show all posts

Wednesday, November 9, 2011

The First Exotic Animal Amnesty Day In Florida

Human's, particularly males under the age of 25 are quite impulsive, and it is not uncommon to find them buying large pythons as well as venomous snakes.  The Florida Wildlife and Conservation Department (FWC)  held its first Exotic Pet Amnesty Day on November 6, 2011 - an event for exotic pet owners looking to get rid of those impusive buys, and opportunity to give up their animals, no questions asked. The FWC collected 64 animals, including a leopard gecko, two Madagascar giant chameleons, pythons, boas, turtles, fish, and about 30 Australian sugar gliders. On Exotic Pet Amnesty Day pet owners can turn in their animals without consequences. But FWC officials said most people who turned in animals were just not prepared to keep them. One woman impulsively bought a sugar glider and then a couple more for breeding. She turned in 25 of them, including a few newborns.

An event like this is a great idea and should be copied by other states and cities. Veterinarians gave advice and tips as to how to care for the animals, but the main goal is to prevent people from  releasing the animals into the wild once they can no longer care for them. If the pet industry was think towards the future they would be encouraging, supporting, and organizing exotic animal amnesty days across the county.

Monday, July 25, 2011

Why Are Some Snakes More Common Than Others?

Ringnecked Snakes, Diadophis punctatus 
reach some of the most dense populations 
found in snakes. JCM

There is a reason why more people study lizards than snakes, snakes are notorious for being difficult to find. Undoubtedly their cryptic nature and in some cases low population densities are likely contributors to this situation. A paper in Science this week by Hechinger et al. examined parasites (there are no known parasitic snakes), but the authors produced two general rules that they suggest can be applied to animal abundance – for any species. The following quotes were taken from a press release associated with this article. 

First they said that, "In addition to body size, the general rule for animal abundance must factor in the food chain and let both small and large animals be top consumers." The second rule was, "that the amount of biomass produced by a population does not depend on the body size of the animals in the population, or on what type of animal -- bird, fish, crab, or parasite. So, "If this rule is general, it means an aphid population can produce the same amount of biomass as a deer population," said Lafferty. "Furthermore, tapeworms that feed on the deer population produce less biomass than the deer, but can produce the same as a mountain lion population that also feeds on the deer. Predicting animal abundance is one of the most basic and useful things ecological science can provide for management and basic research," said Hechinger. "This simple rule helps with that because it may apply to all life forms and can easily be applied to complex ecosystems in the real world." So, does this apply to snakes? Snakes are all predators or facultative scavengers. Does it explain why many snakes are very difficult to find, while other species seem quiet abundant in their habitats?

Parker and Plummer (1987) compiled a table of population densities of snakes, undoubtedly many more have been published since - but this information was readily available for this post. I added column for size.

In looking at the table below, Hechinger et al seem to be correct, the snakes with the most dense populations are small species (Carphophis and Diadophis), species feeding on invertebrates that are close to their food source - a short food chain; or they are piscivorous species that are probably taking prey that are feeding on autotrophic protists, scavenging decomposing material, or have other abundant food resources. The rarer snakes tend to feed on mammals, have larger body sizes, or live in environments with low productivity (Lampropeltis, Pantherophis, Eryx).

Size (m)
Acrochordus arafurae
Eryx tataricus
Carphophis amoenus
Coronella austriaca
Diadophis punctatus
Elaphe dione
Pantherophis obsoleta
Elaphe quadrivirgata
Pantherophis vulpina
Heterodon nasicus
Heterodon platirhinos
Lampropeltis calligaster
Lampropeltis triangulum
Lycodonomorphus bicolor
Protobothrops flavoviridis
Vipera berus
Vipera ursinii

Hechinger, R. F., K. D. Lafferty,. A. P. Dobson, J. H. Brown, A. M. Kuris. 2011. A Common Scaling Rule for Abundance, Energetics, and Production of Parasitic and Free-Living Species. Science, 2011; 333 (6041): 445-448 DOI: 10.1126/science.1204337.

Parker, W. S. and M. V. Plummer. 1987. Population Ecology. Pages 253-301 In: R. Seigel et al. (eds.) Snakes, Ecology and Evolutionary Biology. New York: McMillian Publishing.

Wednesday, June 15, 2011

Looking For Squamates in the Bocas

Between working in the UWITT Museum and running around Trinidad to find supplies we do occasionally get into the field for some serious collecting and fun. On Tuesday, Stevland Charles, Mike Rutherford, and Josh Traub, and I visited two of the Bocas Islands – Gaspar Grande and Monos  - the major goal was to find more coral snakes from each of the islands. However, snakes are notoriously difficult to find no matter how much ground cover you turn. Keeping that in mind we hoped to at least add some footnotes to the islands’ herpetology, and collect some specimens that could supply tissue for molecular studies. Mike was also interested in adding land snails to the UWITT collection. The Bocas Islands (Bocas del Dragon) lie between Trinidad and Venezuela, in the  “Dragons' Mouth”.
Our first stop was Gaspar Grande, a small island composed mostly of limestone. After exiting the boat and a short hike we were at the opening of a sinkhole that descended into a cave; local people had used this as a dump. Using a rope all of us were soon exploring the sink and collecting land snails for Mike and Gonatodes for Stevland. 
Mike and Josh looking for snails in the sinkhole on Gaspar Grande.
Leaf-nosed bats would occasionally brush us. Out of the hole and walking up the trail Gymnopthalmus and Ameiva were quickly getting out of our way. At the top of the  hill were  several relicts of World War II, anti-aircraft gun emplacements, now covered with graffiti and inhabited by some of the island’s lizards. Despite several hours of looking we collected only Gymnopthalmus, a Gonatodes vittatus, and some snails.
We met the boatman at noon and headed for Monos, just a few minutes away.
Stevland directing the boatman to the landing site.
 Landing on Monos, was a bit tricky, the boatman let us off on a crumbling concrete wall several hundred feet from shore. The required us to scramble over slippery, broken concrete to reach shore. As we approached the beach the volume of plastic litter and other man-made junk was alarming. Stevland had been to this location before, and we walked through the coastal palms in to a more seasonal dry forest to a house. As if he knew where to look - an outhouse- Stevland produced a Hemidactylus palichthus within a minute of arrival. This gecko's presence in the Western Hemisphere is a biogeographical puzzle, all of its close living relatives are in Africa, and it is the only Western Hemisphere Hemidactylus that is endemic. All other Western Hemisphere Hemidactylus are  introduced.  
The gecko, Hemidactylus palichthius.

We walked along a stream bed only to encounter a large bamboo die-off that made following the gully exceptionally difficult. As we got deeper into the forest Plica plica became more obvious and abundant, these arboreal and scansorial tropidurid lizards are quite social and on some of the larger tree trunks 3 or 4 individuals were obvious. 

Josh  with a Plica plica on the tree buttress.

Monos has a large amount of human made garbage washing up on its beaches.

Snakes eluded us until we got out of the gully onto the hillside, within a few minutes a Mastigodryas was spotted, but despite being in contact with the hands of two of us it escaped. As we headed back to the beach Mike spotted a Boa constrictor laid out along a broken palm frond. It was a male, about 1.3 m long and had two blood swollen ticks attached to its head. 

Boa constrictor with ticks.

Boa constrictor after tick removal.
After removing the ticks, and a photo session, we were out of water and it was time to met the boatman for the return trip to Trinidad. Despite the fact that we did not find any Bocas coral snakes, the day was not a total loss.

Saturday, January 22, 2011

Detecting Snakes: Experimental Results

Early in my teaching career I kept a captive born squirrel monkey in a classroom laboratory along with a variety of lizards and snakes. Once the monkey realized snakes were present, it would scream, race back and forth in its cage and literally bounce off-the-walls in a display that was impossible to ignore. After seeing the snakes the monkey respond with the same display towards completely harmless objects that were snake-shaped, like ropes and garden hoses. Research over the past 20 years has suggested humans have evolved the ability to detect snakes as a threat – an attentional bias – that has served to warn humans of a snake’s presence before it has an opportunity to bite.  This mechanism involves fear of snakes as well as a visual sensitivity to objects shaped like snakes, most likely a detection mechanisms similar to the ones found in monkeys.

Vanessa Lobue, of Rutgers University, and Judy Deloache, at the University of Virginia, have recently published the results of a series of experiments using touch screen technology with preschool children and adults. The subjects were presented with 3x3 matrices of color photographs and asked to touch a target on the screen as quickly as possible. Based on previous research, parallel results were expected for the adult and the preschool participants; they expected adults would respond more rapidly than the children, but that the two age groups would display the same pattern of performance. The subjects responded to snakes much more rapidly than frogs as expected. In one experiment they found the color of the snake was not important in detection; but other experimental sets suggest recognizing a coiled object (coiled snake vs. a coiled wire vs. flower); the coiled snake and coiled wire were detected more rapidly than the flower. But the differences between detecting the snake and detecting the wire were not statistically significant. In another experimental set and one using a snake stretched out, the coiled snake was detected more rapidly.

It seems likely that human fear as well as human obsession with snakes have an evolutionary origin and will keep psychologists busy for sometime trying to understand the impact of snakes on the human brain.

Lobue, V. and J. S. Deloache. 2011. What's so special about slithering serpents? Children and adults rapidly detect snakes based on their simple features. Visual Cognition, 19(1):129-143

Tuesday, January 18, 2011

Convergence of Infrared Vision in 3 Snake Clades

Three families of snakes use infrared waves to detect prey and differences in environmental temperatures. The mechanism involved in this has only been recently discovered to involve the transient receptor potential (TRP) ion channels. TRPs are involved in various biological processes, including calcium and magnesium homeostasis, neuronal growth, temperature sensation, and pain sensation. The sensations caused by the pungent agents of wasabi and other mustard plants are generated by our transient receptor potential ankyrin 1 (TRPA1) channel. Recently, it has been discovered that the orthologous receptors (receptors sharing a common ancestral gene) of the western diamondback rattlesnake (Crotalus atrox), ball python (Python regius), and garden tree boa (Corallus hortulanus) detect infrared radiation, while those the Texas rat snake (Pantherophis obsoletus lindheimeri) does not. The genetic mechanism of infrared sensitivity of these snake-specific TRPA1 proteins is unknown. Yokoyama et al. (2011) have now identified the amino acid changes that are responsible for the dramatic functional changes in the three groups of snakes. They suggest three parallel amino acid changes (L330M, Q391H, and S434T) are responsible for the development of infrared vision in the three groups of snakes. Protein modeling shows that the three amino acid changes alter the structures of the central region of their ankyrin repeats. The article can be found on-line.

Yokoyama, S., A. Altun, and D. F. DeNardo. 2011. Molecular convergence of infrared vision in snakes. Molecular Biology and Evolution  28(1): 45-48. doi:10.1093/molbev/msq267

Wednesday, January 12, 2011

Thoughts on Invasive Snakes

The USA has more than 160 invasive species of vertebrates (Witmer et al., 2007). Rarely do you see people complaining about feral horses, starlings, or bullfrogs. But, the level of emotion involved in discussing invasive giant snakes during 2010 rivals rhetoric directed at the reintroduction of wolves to Yellowstone National Park. Giant snakes and wolves are both apex predators capable of killing humans and their domesticated species as well as a reminder that humans are not on the top of the food chain.

The USGS’ report on invasive giant constricting snakes by Reed and Rodda was released in October of 2009. Rotella et al. (2010) studied the public reaction to the release on the Internet, using news stories based on the report for one month. They analyzed the news items in terms of key points and interpretational errors. Key points of the original publication were identified by consensus and then tallied through critical reading of the news items. Errors in the news items were categorized as: factual errors, exaggerations, conclusions beyond the data, and political.

Rotella and colleagues results revealed 26 unique news stories produced by 11 syndicated news agencies, and 15 blog posts, newsletters, or as items released by net forums for special interest groups. The articles had a mean word count of 621 (the original report was 302 pages). The team identified the key points as: threat to humans, invasion range, effects of climate change, risk assessment, pet release, removal/capture, reproduction/growth, rights of pet owners, biology in the native habitat, and extinction risk for competing species. The key points mentioned most frequently in the news items were: threat to humans, snake removal/capture, reproduction/growth, and pet release. Nineteen of the 26 news items (73%) had errors. The most frequent errors were exaggerations (13 items), unsubstantiated conclusions (11 items), and factual errors (10 items). Two of the news items included parodies based on the original publication.

Other criticism of the report comes from David and Tracy Barker (2010a, b), who run VPI, a python breeding facility in Texas. They argue for less regulation on the captive snake breeding industry and criticize the report on a variety of levels which range from style and grammar to methodology and conclusions drawn from the study.

Python bivittatus, JCM
Some of the problem with the USGS report and its critics rests in the lack of knowledge and confusion concerning the systematics of the Python molurus complex. It is now relatively clear that the Indian Python, P. molurus is a peninsular Indian species, while the Burmese Python (P. bivittatus) is a Myanmar- Indochinese species. They undoubtedly shared a common ancestor, and are thus morphologically similar, but are in all likelihood distinct species (despite the fact they can reproduce with each other). See Jacobs et al. 2009. The failure to recognize this in the USGS report is understandable give the morphological similarity of the species and the fact that large snakes are poorly studied in their native countries. Much of the literature on these species is a tangled mess that results from writers reworking what others have previously said about the natural history of large snakes. Murphy and Henderson (1997) attempted to unravel part of this by using direct quotes from earlier literature, but even this was only partially successful. Biological field work for western researchers is virtually impossible in countries like Myanmar (Burma). Therefore, advancing knowledge about these snakes is left to observation of captive specimens and the few field studies that do get done within the snake's natural distribution.

Predicting the future is always difficult. The climate modeling work done by Pyron et al, (2008) suggests that pythons won’t be able to expand their distribution much beyond what it is today during the course of this century. And, the study done by Dorcas et al. (2010) would seem to support this – although nobody is talking about sample size. The special interests have latched on to this study in an attempt to find support for their view point.

The well documented ecological disaster brought about by the Brown Treesnake in Guam is certainly a wake-up call to prevent invasive snakes from eating their way through the native fauna of southern Florida or any other place they might survive and thrive.

As for giant snakes surviving and spreading –natural selection will be finding those individuals that can withstand cold temperatures (assuming a small percentage can - it may be only a fraction of 1%). Those individuals will be leaving more offspring in the next generation, so as time goes on it seem probable that the Florida populations of Python bivittatus and Python sebae, as well as the Boa constrictor will be adapting to cold snaps. Any reduction in the Florida giant snake populations due to die off from cold weather in southern Florida is at best temporary and offers only a short reprieve to the native vertebrate fauna.

From my perspective the government should be working to minimize invasive species and protect the native fauna - an important natural resource. Perhaps the snake breeding industry should be working on developing designer snake morphs that self-destruct when they escape or are released from captivity. Or, perhaps more realistically sterile designer snake morphs should be produced. So, escapees and released pets at least cannot reproduce.

As for the danger of snakes to humans, in the USA, it pales in comparison to deaths from auto accidents or firearms. In the United States there are more than 250 million privately owned firearms and that the number increases by about 4 million per year. The CDC estimates 75,000 annual human deaths from firearms. Therefore, outrage or even loud concern about snakes that kill less than a dozen people per year seems a bit over the top. Not that the loss of human life should not be a concern, only that statically being killed and or eaten by a giant snake in the USA is a non-issue.

Barker, D. G. and T. M. Barker. 2010a. A critique of the analysis used to predict the climate space of the Burmese Python in the United Snakes by Rodda et al. (2008, 2009) and Reed and Rodda (2009). Bulletin of the Chicago Herpetological Society 45(6):97-106.

Barker, D. G. and T. M. Barker. 2010b. The Tympanum. Bulletin of the Chicago Herpetological Society 45(9):144-149. Bulletin of the Chicago Herpetological Society 45(12):97-106.

Barker, D. G. and T. M. Barker. 2010c. A review of: Dorcas, M. E., J. D. Willson, and J. WE. Gibbons. 2010. Can Invasive Burmese Pythons Inhabit Temperate Regions of the Southeastern United States? Biological Invasions. Online at doi10.107/s10530-010-9869-6. Bulletin of the Chicago Herpetological Society 45(12):187-189..

Beschta, R. L., and Ripple, W. J. 2009. Large predators and trophic cascades in terrestrial ecosystems of the western United States. Biological Conservation 142, 2009: 2401-2414.

Jacobs, H. J., M. Auliya and W. Böhme. 2009. Zur Taxonomie des Dunklen Tigerpythons, Python molurus bivittatus KUHL, 1820, speziell der Population von Sulawesi. Sauria, Berlin, 2009, 31 (3): 5–16.

Murphy, J. C. and R. W. Henderson. 1997. Tales of Giant Snakes. Krieger Publishing, Malabar, Florida.

Pyron, R. A., F. T. Burbrink, and T. J. Guiher. 2008. Claims of potential expansion throughout the U.S. by invasive python species are contradicted by ecological niche models. PLoS ONE 3:e2931 [doi:10.1371/journal.pone.0002931]

Reed, R. N. and G. H. Rodda. 2009. Giant constrictors: biological and management profiles and an establishment risk assessment for nine large species of pythons, anacondas, and the boa constrictor: U.S. Geological Survey Open-File Report 2009-1202, Washington, D.C., USA.

Rotella, A. R., R. A. Connelly, M. D. Marsh, C. C. Wessel, J. W. Murphy, L. L. Canton, and J. O. Luken. 2010. Snake Invasion: Evaluation of an Online News Frenzy. Bulletin of the Ecological Society of America 91:438–441. [doi:10.1890/0012-9623-91.4.438]

Witmer, G. W. et al. 2007. Management of invasive vertebrates in the United States, An Overview. USDA National Wildlife Research Center Symposia. 12 pages.

Wednesday, December 1, 2010

A Giant in a Genus of Small Snakes

Atractus gigas
Perhaps the most specious genus of snakes is Atractus (Family Dipsididae) with about 130 species.  Atractus are commonly known as ground snakes, and tend to be small to medium snakes that feed on earthworms, arthropods, and mollusks. They are distributed from Panama to Argentina and overall knowledge about their natural history is at best very incomplete. They occur from sea level to 4,500 m in elevation and many, if not most of them, are known only from the type specimens. They are closely related to the Middle American and northern South American fossorial and cryptozoic genera Adelphicos and Geophis. Atractus range in size from snakes that are less than 200 mm at maturity to the giant, Atractus gigas that exceeds 1000 mm. Myers and Schargel (2006) described Atractus gigas from a single specimen collected on the west side of the Ecuadorian Andes, Tolhurst et al. (2010) recently reported a second specimen of A. gigas about 50 km from the type locality on the basis of photographs.  Now, Passos et al (2010) discovered additional specimens of this poorly known snake in museum material and collected new specimens during fieldwork in the northeastern Peruvian Andes. The largest female was 1040 mm in body length, while the largest male was 255 mm in body length (presumably this was a subadult). The female’s body size makes this species the largest in the genus. The authors describe the juvenile and adult color patterns and detail the sexually dimorphic scale counts. They encountered this snake at Santuario Nacional Tabaconas Namballe, San Ignacio, Peru, on a coffee plantation and in nearby montane forest. Individuals were observed from early morning to late afternoon. Thus, Atractus gigas inhabits primary and secondary cloud and montane forest as well as coffee plantations between 600 and 2300 m on both sides of the Andes. The diurnal activity of this snake is also unusual for the genus, since many others ground snake species are known to be nocturnal. One female contained 12 oviductal eggs, this is an exceptionally large clutch size for an Atractus [other Atractus with known clutch sizes, i.e. A. reticulatus and A. trilineatus, have 1-6 eggs]. Many Atractus show sexual dimorphism with large females and smaller males. Thus this clade of snakes may make an excellent study group to test hypotheses about sexual dimorphism in snakes - given the number of species it is likely one or more has males that are larger than females.

Myers, C. W. and W. E. Schargel. 2006. Morphological extremes – Two new snakes of the genus Atractus from northwestern South America (Colubridae: Dipsadinae). American Museum Novitates, 3532: 1‑13.

Passos, P., M. Dobiey, and P. J. Venegas  2010. Variation and Natural History Notes on Giant Groundsnake, Atractus gigas (Serpentes: Dipsadidae). South American Journal of Herpetology 5(2):73-82.

Tolhurst, B.; M. Peck; J. N. Morales; T. Cane and, I. Recchio. 2010. Extended distribution of recently described dipsadine colubrid snake: Atractus gigas. Herpetology Notes, 3: 73‑75.

Wednesday, February 24, 2010

Invasive Constrictor Hunt in Florida

A 22 February 2010, Miami Herald story by By Susan Cocking states that the Florida Fish and Wildlife Conservation Commission will open a special hunting season targeting invasive constricting snakes on state lands in South Florida March 8 through April 17. A hunting license and a $26 management area permit are required to take the snakes and the invasive Nile Monitor Lizard. Hunters may use firearms but not remove the snakes alive. The harvest area includes the Everglades, Francis S. Taylor, Holey Land, and Rotenberger wildlife management areas. The harvest is timed to follow the close of small game season and enable hunters to target the reptiles during cooler months when they are out in the open and easier to spot.