Impending Global Amphibian Extinctions: A Review of the Literature

So something I've been studying lately is how amphibians are declining worldwide. Now you're probably laughing, thinking why the hell is she writing a blog about amphibians? But it really is a concern. These species are facing extinction. Many species already have gone extinct. Not to mention it kind of tells us that maybe the environment isn't in that great of shape for our own health. I'm making a website about it for english, so i'll post it once it's published. But here's a literature review I had to write for english as well. It summarizes and comments on several publications about the subject. Kind of long for a blog, but if it interests you, you can read it. It's something I care about, and in the paper, I argue why you should care about it too.






Impending Global Amphibian Extinctions: A Review of the Literature





Imagine our world ravaged by an incurable disease, an environment subjected to intolerable climate change, individuals poisoned by foreign toxins, and populations stripped of their homes. This may seem to be a catastrophic end of the world scenario only found in science fiction books. But for amphibian populations, it is a present reality. Amphibian populations are declining at an alarming rate, and for complex, difficult to fix reasons. Additionally, their plight may be a harbinger for the state of our own environment. This review intends to address the worldwide amphibian decline – why it is happening, what it means, and what conservation efforts may be able to halt it. The following questions will be addressed by the literature reviewed:





* Why are amphibians declining to such an alarming degree?
* For how long have amphibians been declining?
* To what degree are amphibians declining?
* What can be done about the amphibian decline?
* Why should something be done about this?
* What will happen if amphibian populations are not protected?
* What amphibians are currently threatened/endangered in AZ?
* What conservation efforts are most effective?
* How does the evolution of amphibians affect the current extinction problem?
* How can conservation work take the complicated environments (both terrestrial and aquatic) of amphibians into account?




The Amphibian Crisis





Collins and Storfer (2003) reported that amphibians were becoming threatened at an alarming rate, and for a variety of causes. While officially found to be declining in 1990, evidence shows that this has been occurring since before the 1980's. This is for a variety of reasons, including introduction of foreign species, hunting of frogs, "land use change", global change in chemical concentration, climate change, and diseases. The chytrid fungus has been especially deadly to amphibians and currently has no cure.



Since the latter three (called Class II hypothesis) are difficult to remedy with conservation methods, the authors argue that traditional efforts may not be enough. This is also seen in that even protected habitats are losing amphibians. An increase in research regarding the amphibian decline is needed, and it is a matter of urgency, as it may serve as a warning that the sustainability of the environment is at risk overall. This piece is very useful in understanding the complex nature of this issue, as well as its importance.





Norris (2007) estimated that, at minimum, 43% of amphibians are declining and 40% are endangered, and less than 1% are increasing. This statistic is unmatched by birds, mammals, or other such groups of animals. This not only has an effect on the amphibians themselves, but it can also change the stability of the ecosystem, as animals that prey on amphibians will become endangered as well. Amphibians may represent the declining sustainability of the environment humans depend on. And if amphibians do become extinct, the many medicinal uses of their poison glands will be inaccessible.



Chytrid fungus is striking an overwhelming amount of amphibian populations, and it is one of the main causes for the amphibian decline. It seems the only option is to remove species from the wild; however these conservation efforts are riddled with problems. Even though captive breeding keeps populations from absolute extinction, it is not successfully reintroducing species back into the wild. Overall, the author argues that this issue should be of great concern, as not only are we losing entire species, but if such a disease were to occur at the mammalian level, the results would be catastrophic.





Blaustein and Bancroft (2007) argue that the amphibian decline needs to be considered from an evolutionary standpoint, as it is apparent that the adaptations that once made amphibians fitter are no longer helpful in an environment altered by human activities. For example, their need for light for thermoregulation has caused them to constantly expose themselves to the sun, which now gives off more harmful UVB rays due to ozone depletion. Another adaptation is that amphibians lay their eggs in water. While the environment may have been conducive to this at one time, the toxins introduced to the water by humans are causing a high rate of tadpole malformations. The "communal" laying of eggs also encourages spread of disease.



Researchers must look at the amphibian decline from the perspective of evolutionary adaptations. While evolution takes a lengthy amount of time, the climate changes and introduction of toxins has happened extremely quickly. Thus, amphibians are unable to adapt and are facing extinction. This is another manner of looking at the amphibian extinction, which can be useful in understanding its causes.




Conservation





Baldwin, et. al (2006) studied the efficacy of current conservation methods for the wood frog, Rana sylvatica. The wood frog is threatened by deforestation. Since it needs both vernal pools for breeding and forest wetlands for post-breeding migrations, it is difficult to protect enough habitat without protecting too much habitat, resulting in overspending of limited funds. They therefore studied how frogs chose their habitat, using radio transmitters.



Finding that the frogs preferred humid, closed canopy, forested areas, protection can be more focused. Instead of simply surrounding the vernal pools with a large enough protected area, which may be impossible in urban areas or at best expensive on private lands, only the habitat experimentally proven to be needed by the frogs is protected. Thus the complexity of conserving species requires extensive study. This study gives a practical example of conservation efforts that can help save amphibians. Habitat loss is one of the causes of this decline that can be remedied, and it is important to determine how to best implement habitat protection programs.





Schmidt, et. al (2005) argue that the global amphibian decline requires not only the common practice of focusing on the larval stages in assessing population declines, but also the analyzing of the adult stages. This hypothesis was studied by capturing adult salamanders, recording their unique markings, and re-releasing them into the wild. Over a twenty year period, the salamanders were recaptured to record how many individuals were still in that habitat, and thus the stability of the population could be assessed. While one population remained stable, the other became nearly extinct (or possibly all migrated). This was probably due to changes in the forest habitat of this group.



According to the authors, this study shows the need to focus on more than the aquatic habitats of larvae. Terrestrial habitats, which are the primary habitats for adult amphibians, also need to be protected, as populations will be subject to loss if affected at adult stages in addition to the larval stages. Individual, adult salamanders were dying at a higher rate in one population, which demonstrates that changes to terrestrial habitat can affect amphibians negatively. This study was useful in that it stressed the importance of protecting both types of habitats, as the aquatic habitats often receive the most attention.





Anderson and Arruda (2006) discuss how change in the way humans use land can negatively affect amphibians, particularly a type known as anurans. By studying breeding pools where the surrounding land had different uses, such as mining and agricultural, any differences in amphibian populations, as well as tadpole malformations, could be studied. Natural sites showed the most anurans, and mined sites showed the least. The same was true in density of species. Natural sites also had the fewest malformations of tadpoles. This may be due to water contamination, as agriculture introduces pesticides, and mining introduces metals into the water.



It is important to understand how human usage of amphibian habitat affects this class of animals. These activities must be monitored, and land must be protected, in order to keep amphibians from decline. This is one of the many reasons for the amphibian declines, and this article demonstrates how human activities can affect the fate of amphibians.





The U.S. Fish and Wildlife Service (2002) has written a detailed conservation plan for the endangered Sonoran tiger salamander, an amphibian found in Arizona. This can be done by monitoring the habitat itself, such as instituting policies to limit water pollution and managing the water quality (pH, etc.) chemically. Alien species that threaten the salamander should also be removed. Salamander populations also need to be monitored, and the wildlife and fish department can work with private landowners to conduct surveys on their land. Salamander life cycles, etc., also need to be researched so that conservation plans will better understand this animal. Finally, the public needs to be educated on the laws regarding the salamander, as well as on its endangered state.



Overall, several things can be done to save the salamander from extinction. By working with the stakeholders involved, such as law enforcement and private landowners, the salamander population can return to normal. This is a very practical plan for how to protect an amphibian currently endangered.




Conclusion



Amphibians are declining at an alarming rate, and if nothing is done, many will face extinction. Many species have already become extinct due to disease, and many other factors are contributing to their decline as well. Amphibians have not had enough time to adapt to the changes in climate and habitat, and their sudden decline may be a warning regarding the sustainability of the environment for mammals.



Conservation is complicated but possible. By creating practical plans and taking the complicated factors regarding amphibians into account, amphibians still have hope of being saved. Both terrestrial and aquatic habitats need protecting, and it is important to acquire the cooperation of the stakeholders in this issue if conservation is to be successful. Questions on how best to protect amphibians still remain, and this is the reason that more research is required. However, conservation efforts must begin immediately if valuable species are to be preserved. Amphibians have specific uses to humans, and they also represent millions of years of evolution which cannot be regained if lost.





Literature Cited



Anderson, Lewis and Arruda, Joseph. (2006) Land use and anuran biodiversity in southeast Kansas, USA. Amphibian and Reptile Conservation. Vol. 4, no. 1, pp. 46-59.



Baldwin, Robert F.; Calhoun, Aram J. K.; and DeMaynadier, Philip G. (2006) Conservation Planning for Amphibian Species with Complex Habitat Requirements: A Case Study Using Movements and Habitat Selection of the Wood Frog Rana sylvatica. Journal of Herpetology. Vol. 40, no. 4, pp. 442-453.



Blaustein, Andrew R. and Bancroft, Betsy A. (2007) Amphibian Population Declines: Evolutionary Considerations. Bioscience. Vol. 57, no. 5, pp. 437-444.



Collins, James P. and Storfer, Andrew. (2003) Global amphibian declines: sorting the hypotheses. Diversity and Distributions. Vol. 9, pp. 89-98.



Norris, Scott. (2007) Ghosts in Our Midst: Coming to Terms with Amphibian Extinctions. Bioscience. Vol. 57, no. 4, pp. 311-316.



Schmidt, Benedikt R.; Feldmann, Reiner; Schaub, Michael. (2005) Demographic Processes Underlying Population Growth and Decline in Salamandra salamandra. Conservation Biology. Vol. 19, no. 4, pp. 1149-1156.



U.S. Fish and Wildlife Service. (2002) Sonora tiger salamander (Ambystoma tigrinum stebbinsi) recovery plan. U.S. Fish and Wildlife Service, Phoenix, Arizona. iv + 67 pp.