Climate Change

Does climate change affect amphibians?

Yes! Climate change is having a huge impact on amphibians.  Below is a figure illustrating some of the cascading effects global climate change has on amphibians according to research on climatic impacts on amphibians from scientific literature listed at the bottom of the page.





Figure by Heidi Rockney illustrating cascading effects of climate change on amphibian populations.

Amphibians are ectotherms, they rely on their environment to regulate their internal heat. They also generally require damp environments because they need their skin to stay damp in order to breathe through their skin. They use weather patterns to tell them when to initiate breeding and/or hibernate. The present course of climate change has disrupted many environmental conditions that affect the health and reproductive success of amphibians. One of the most obvious issues that surround amphibian survival is the interruption of changing climate on their biphasic reproductive cycle.

The reproductive success of amphibians is directly related to weather and seasonal changes. They are dependent on cues such as precipitation levels to initiate breeding. When the hydrology cycle in an environment shifts, many species are cued at different times than normal. This can have numerous consequences. The general pattern for change has been earlier spring weather; this disrupts the normal flow of reproductive niches that have been established by multiple species. Instead of having just one or a few species breeding, many are now competing for the same water source at the same time. This lowers the reproductive success for all amphibian species involved.

Dessicated eggs. Photo credit:flickr

Changing precipitation and temperature patterns alters water levels in amphibian habitats. Since amphibians rely on water for laying and maturation of their eggs, the water quantity and quality affect the rate of survival for amphibian eggs and juveniles. Varying levels of precipitation not only affect the pattern and frequency of water sources available for breeding, but also the depth of the water in which the eggs are laid. In Yellowstone National Park, temporary breeding ponds have decreased and water levels in remaining ponds have decreased in water depth. Fewer water sources increase competition between amphibian species. The competition and stress usually increases juvenile amphibian mortality. Lower water levels also affect the solute levels in the water and the amount of nutrients available for developing young. The lower water levels and higher temperatures cause juveniles to have a shorter time for development, if the eggs and young are able to survive to maturation; the emerging froglets are often smaller than normal and not as able to withstand predation. Increased temperatures can cause water sources to dry up earlier and desiccate eggs (see photo of dessicated amphibian eggs on right) before they are able to hatch. The aspect of altered water levels due to changing climate not only impacts the amount of amphibians that are able to survive, but also the actual physiology of those that do survive.

 

The quantity of water in breeding sites and local temperature ranges plays a direct role in the development of the amphibian immune system. Two factors play a major role in development regarding water levels; the amount of UV exposure and the size of the developing juveniles. Water is a great source of UV protection. The lower the water levels are, the more UV radiation that reaches developing amphibian eggs. Increased UV exposure in studies of the Xenopus species have shown that UV directly alters the expression of normal immune system development and function. Temperature alterations in these studies have also show depressed development of their immune system. These factors combined have devastating effects on the ability of eggs and juveniles to be resistant to normal exposure to pathogens. An increase in amphibian deaths related to fungus, bacteria, parasitic and virus infection is a phenomenon that is consistent across the entire global range of amphibians. Amphibians that are smaller than normal at maturation have severely compromised immune function, making them highly susceptible to massive death from pathogens. The fact that amphibians are also more localized due to the decrease in suitable breeding habitats creates an environment that allows pathogens to spread quickly and devastate entire populations. The role of local ecology dynamics plays a huge role in the ability of amphibians to recover and thrive given these stressors.

Prediction of future extinction rates with climate change

Climate plays an essential role in maintaining the integrity of local habitats. When changes in the local hydrological cycle and temperatures occur, ecosystem dynamics are thrown out of balance. Species who cannot survive in changing environments relocalize to other environments that are more suitable. Incoming invasive species often devastate established local species. Amphibians are exposed to new competition for sources and new predators. The ability for amphibians to adapt is often unsuccessful, especially taking into account their smaller emerging froglet size and lower immunity function. Not only are there new predators, but new pathogens generally accompany shifting ecosystems. For example, altering temperature ranges can allow the chytrid fungus to thrive more heavily and attack weakened eggs/juvenile and adult amphibians. Once infected, amphibians are also susceptible to secondary pathogens like bacteria and viruses. The fact that amphibians often have small home ranges means that once an infection or invasive species wipes out a population, amphibians are not able to recover population numbers. Photo to the right is a prediction of future extinction rates with climate change assessments according to Millenium Ecosystem Assessment.

Amphibians have difficulties relocating to adjust to new ecological system changes, because they are thwarted by the impact of anthropogenic habitat destruction and local species that are well established and more able to adapt. Amphibians are extremely adapted to their local environments and often unable to find other suitable places of habitation that fit their specific habitat criteria. The redefinition of ecological niches brought on by climate change does not favor a species that is so sensitive to environmental conditions like amphibians.

The infographic below, from information is beautiful, is a sobering compilation of the consequences of our carbon emmissions.

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References:

Carey, Cynthia, Cohen, Nicholas, Rollins-Smith, Louise. 1999. Amphibian declines: an immunological perspective. Development and Comparative Immunology. 23, pp459-472.

Kiesecker, Joseph M., Blaustein, Andrew R., Belden, Lisa K. 2001. Complex causes of amphibian population declines.Nature. 410 (6829) pp639-40.

McMenamin, Sarah K., Hadly, Elizabeth A., Wright, Christopher K. 2008. Climatic change and wetland desiccation cause amphibian decline in Yellowstone National Park. PNAS. 105 (44) pp. 16988-16993.Pounds, J. Alan, Fogden, Michael, P.L., Campbell, John H. 1999. Biological response to climate change on a tropical mountain.Nature.398. Pp. 611-615.

Pounds, J. Alan, Bustamante, Martin R., Coloma, Luis A., Consuegra Jaime A., Fogden, Michael P.L. Foster, Pru N., La Marca, Enrique, Masters, Karen L., Merino-Viteri, Puschendorf, Robert., Ron, Santiago R., Sanchez-Azofeifa, Arturo. Still, Christopher J., Young, Bruce E. 2006. Widespread amphibian extinctions from epidemic disease driven by global warming. Nature 439.

Raffel, T.R., Rohr, J.R., Kiesecker, J.M., Hudson, P.J. 2006. Negative effects of changing temperature on amphibian immunity under field conditions. Functional Ecology. 20 pp819-828.

Skerratt, Lee Francis, Berger, Lee, Speare, Richard, Cashins, Scott, Raymond McDonald, Keith, Phillott, Andrea Dawn, Hines, Harry Bryan, Kenyon, Nichole. 2007. Spread of chytridiomycosis has caused the rapid global decline and extinction of frogs. Ecohealth. 4pp125-134.

Wake, David B., Vredenburg, Vance T. 2008. Are we in the midst of the sixthmass extinction? A view from the world of amphibians. PNAS. 105.

Walther, Gian-Reto, Post, Eric, Convey, Peter, Menzel, Annette, Parmesan, Camille, Beebee, Trevor J.C., Fromentin, Jean-Marc., Hoegh-Guldberg, Ove., Bairlein, Franz. 2002.Ecological responses to recent climate change. Nature. 416.Pp389-395.

http://www.namos.ca/NAMOS_conservation.htm