Showing posts with label invasive species. Show all posts
Showing posts with label invasive species. 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

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.

Saturday, April 9, 2011

Invasive Herps & Brain Size

Why is it that some amphibian and reptile species become invasive, while others do not? The anwer to this question may rest in the relative brain size of the species. This question is addressed in a new article by Joshua J. Amiel, Reid Tingley, and Richard Shine of the University of Syndney.  They report that amphibians and reptiles have smaller forebrains than birds and mammals, and are often viewed to have less behavioural complexity. In an effort to examine the relationship between larger brain size and capacity to thrive in a novel environment, the authors analysed data on human introductions of amphibians and reptiles to areas outside of their native geographic ranges. They assumed that if a larger brain facilitates dealing with new challenges, success in establishing feral populations following a human introduction will be higher in amphibians and reptiles with large brains relative to their body sizes.

They found brain size relative to body size was, in fact, larger in species of amphibians and reptiles reported to be successful invaders, compared to species that failed to thrive after translocation to new sites.
This was the same evolutionary trend previously found in birds and mammals suggesting that larger brain size enhances the ability to deal with novel environmental challenges in all major clades of terrestrial vertebrates. Interestingly, this pattern was present in all biogeographic regions, except Australasia. Introduced amphibians and reptiles with smaller (rather than larger) brains were more successful at establishing populations in Australasia. This may result from environmental factors selecting against larger brain size where a lack of resources exacerbates the energetic costs of maintaining such an energy expensive organ. The authors prpose that low resource availability in Australasia may favour small brain size and other traits that reduce an animal's total energy requirements. They note evolutionary trends towards reduced fecundity levels in rodents and in birds that have invaded Australia over longer time periods reinforce this hypothesis.

Amiel JJ, Tingley R, Shine R (2011) Smart Moves: Effects of Relative Brain Size on Establishment Success of Invasive Amphibians and Reptiles. PLoS ONE 6(4): e18277. doi:10.1371/journal.pone.0018277

Tuesday, April 5, 2011

Tadpoles and an Invasive Crustacean

After 30 years, the common frog can not activate their defenses against the American crayfish.

Iván Gómez Mestre and Carmen Díaz Paniagua, biologists from the Biodiversity Research Unit of the Principality of Asturias CSIC-Universidad de Oviedo and Station Biological relevance of Doñana (CSIC) respectively have confronted two groups of tadpoles with the American crayfish and have compared the degree of activation of their defenses. The researchers note that, despite the common frog tadpoles activated when they detect predators, are unable to perceive the American crayfish, which leaves no recourse for this invasive species.

"The common frog in the Doñana National Park has not yet adapted to the American red crayfish (Procambarus clarkii ) [photo]," said Iván Gómez Mestre. Both the common frog tadpoles in the wetlands of Donana, a town three decades has been in contact with this predator (between 10 and 15 generations), and tadpoles from populations that are faced by first time crab responded the same way: "The degree of activation of defenses is the same in both cases: null," says the biologist.

Tadpoles, explains, they have many defenses available to it, but when they detect the chemical signals (the smell dissolved in water) of a predator such as dragonfly larvae can morphological and behavioral changes.
"The changes in shape result in a wider tail and more pigmented, which attracts the predator to her leaving intact the vital organs and no tears or loss of tail have such serious consequences, since they can regenerate. And changes in behavior resulting in a reduction of activity that passed over unnoticed, "said Iván Gómez Mestre.

But these changes, despite improved survival in case of predators, have a price: "By reducing its activity, the tadpoles were fed less, grew more slowly and faced with the progress of your pond dry season, addition to give advantage to competitors for food, "says the researcher. Hence, the activation of defenses is not permanent and depend on the detection of the predator species by the tadpoles.
An evolutionary race

The results published today contribute to better understand the series of changes that occur in the Iberian ecosystems that invasive crab, native to the Southeastern U.S. and present from Doñana to Asturias. As indicated by Iván Gómez Mestre, among other effects "are known to be in areas that present the American crayfish is a proliferation of predatory birds, so that the pressure on amphibians increases even more."
"The question is whether common frog populations exposed to American crayfish have enough time before dying to adapt to the presence of an introduced predator so voracious. Can not venture a period in evolutionary terms, because each species responds differently, but a reference can be detected cases in the U.S. adaptation of bullfrog tadpoles by introduced fish against the man after 110 years of contact, "says researcher.

The species was detected 15 years ago in Asturian rivers. The American crayfish damage native ecosystems and particularly harmful to salmonids, small fish, amphibians, and vegetation waters. It has also displaced the native crayfish ( Austropotamobius pallipes lusitanicus) in almost all waterways.

This situation has led to initiatives such as the Crab Project:

Ivan Gomez-Mestre and Carmen Díaz-Paniagua. (2011)  Invasive predatory crayfish do not trigger inducible defences in tadpoles Proc. R. Soc. B published online 30 March 2011doi:10.1098/rspb.2010.2762

Saturday, February 26, 2011

The Invasive Python Problem, Climate Modeling, and a Revised Map

The following is based upon Rodda et al. 2011. It is taken from their introduction and has been slightly edited for readability.It should be pointed out that Python molurus and Python bivittatus are now regarded as distinct species.

In 2008 the U.S. Fish and Wildlife Service (USFWS) solicited advice from the general public on the potential merits of restricting the importation of nine exotic species of giant constricting snakes. The intent was to reduce the risk of introducing the invasive species into the USA. The species list included the Indian Python (Python molurus) and what at the time was considered to be its subspecies. The best known of which is the Burmese Python, Python molurus bivittatus. At about the same time, Rodda et al. published results of an analysis of the areas of the U.S. that are climatically matched to the native range of the Indian Python. The publication of the map and the USFWS Notice of Inquiry were connected in the sense that USFWS had joined the U.S. National Park Service in funding the U.S. Geological Survey (USGS) study. Some sections of the public perceived the work as interagency collaboration in support of regulation of trade in giant constrictors, despite the fact that USGS had no policy position on invasive species regulation, and was under no pressure, either imposed by the funding sources or self-imposed, to support regulation, or bias the size or extent of the U.S. area that climatically matched the python’s native range. The climate match study was to inform the discussion. Pyron et al. (2008) countered with an alternate map showing areas of the U.S. that climatically matched the python’s native range; their map was embraced by opponents of regulation because it showed a much smaller area of climatic agreement – the area that could be inhabited by the pythons. And,  Pyron et al. concluded that ‘‘The Burmese python is strongly limited to the small area of suitable environmental conditions in the United States it currently inhabits…’’ They also averred, ‘‘The proposed expansion of the python into the continental United States would require an expansion of the actual tropical marshland habitat comprising most of the Everglades, not simply the presence of similar temperature and precipitation conditions.’’ If either of these claims were true, no further areas of the U.S. would be at risk of colonization, and regulation of U.S. trade in this species would be largely moot. Although Pyron et al. did not expressly tie their climate match to policy, they did lay claim to the policy high ground by asserting that, ‘‘The alarmist claims made by USGS could potentially hamper scientific discourse and inquiry into the problem, especially with regard to policy-making.’’ The notice of inquiry and subsequent proposed rulemaking generated a substantial public response, with a large number of comments received (55,600), and most of the criticism focused on the climate matching result for one of the nine species under consideration, the Indian Python. The intensity of the public’s reaction can be used to document climate matching can be a key element in establishing environmental policy. Also, differences among approaches to climate modeling are critical for evaluating the scientific basis for the policy. One element of this controversy is the herpetological facts that were the basis for the models. In these, Rodda et al. and Pyron et al. did not noticeably differ and the herpetological facts will not be discussed further. Another element of the controversy is the modeling approach, for which the two teams took divergent approaches: Rodda et al. adopted a climate suitability algorithm based on first principles, and Pyron et al. used a statistical tool to discover a climate suitability algorithm. Ideally, one would have some method for validating the projections, but there is no obvious way to validate the likelihood of a hypothetical event. Furthermore, the validity of these specific models might rest on factors unique to the Indian Python, and therefore be of limited interest.

Species distribution models are often used to characterize a species’ native range climate, so as to identify sites elsewhere in the world that may be climatically similar and therefore at risk of invasion by the species. Rodda et al. have evaluated a number of species to assess MaxEnt’s  (Maximum Entropy model) utility for vertebrate climate matching.

They found MaxEnt models to be very sensitive to modeling choices and selection of input localities and background regions. As used, MaxEnt invoked minimal protections against data dredging, multicollinearity of explanatory axes, and overfitting. As used, MaxEnt endeavored to identify a single ideal climate, whereas different climatic considerations may determine range boundaries in different parts of the native range. MaxEnt was extremely sensitive to both the choice of background locations for the python, and to selection of presence points: inclusion of just four erroneous localities was responsible for Pyron et al.’s conclusion that no additional portions of the U.S. mainland were at risk of python invasion. When used with default settings, MaxEnt overfit the realized climate space, identifying models with about 60 parameters, about five times the number of parameters justifiable when optimized on the basis of Akaike’s Information Criterion.

Rodda et al. (2011) concluded that when used with default settings, MaxEnt may not be an appropriate vehicle for identifying all sites at risk of colonization. Model instability and dearth of protections against overfitting, multi-collinearity, and data dredging may combine with a failure to distinguish fundamental from realized climate envelopes to produce models of limited utility. A priori identification of biologically realistic model structure, combined with computational protections against these statistical problems, may produce more robust models of invasion risk. The entire article can be found by the linked reference below.

Rodda, G. H., C. S. Jarnevich R. N. Reed. (2009, online 2008) What parts of the US mainland are climatically suitable for invasive alien pythons spreading from Everglades National Park? Biological Invasions 11: 241–252. 10.1007/s10530-008-9228-z.

Rodda G. H., C. S. Jarnevich, R. N. Reed. 2011. Challenges in Identifying Sites Climatically Matched to the Native Ranges of Animal Invaders. PLoS ONE 6(2): e14670. doi:10.1371/journal.pone.0014670

Pyron R.A., F. T. Burbrink, 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. 10.1371/journal.pone.0002931.