Climate Change
(February, 22 2006; V.Vredenburg)
Several accounts of declining amphibian populations have been from relatively pristine areas such as designated wilderness areas and national parks (Pounds and Crump 1994, Lips 1998, Lips et al. 2006). In these areas, global climate change may be directly and indirectly responsible for declines (Donnelly and Crump 1998, Pounds et al. 1999). For example, one study suggests that global climate change has made conditions more favorable for a new disease (chytridiomycosis) thus indirectly leading to extinctions and declines of amphibians(Pounds et al. 2006); however another study contests this and suggests that the disease spread and associated species extinctions do not require a change in climate to explain the emergence and spread of the disease (Lips et al 2006). Direct consequences of climate change can also be excpected because amphibians may be more sensitive to climate change than other species. Because of their permeable skin, biphasic lifecycles and unshelled eggs, amphibians are extremely sensitive to small changes in temperature and moister (Carey and Alexander 2003). Here we summarize some of the evidence that climate change has directly and indirect affected amphibian populations around the world.
Global warming and amphibian breeding phenology
The timing of amphibian breeding is largely driven by environmental cues such as temperature and moisture (Carey and Alexander 2003); because of this, their breeding phenology may be directly affected by global warming. Amphibians in temperate regions may be even more susceptible to increases temperatures. Most temperate species spend a large portion of the year inactive, escaping either cold winters or hot summers. Subtle increases in temperature or moisture trigger them to immerge from their hibernacula. Immediately upon immergence, they migrate to ponds or streams to breed. Thus, one hypothesized direct affect of global warming on amphibians is a trend towards early breeding as the average temperatures increase. If amphibians breed too early in the season they may be more vulnerable to early snowmelt induced floods and early season freezes that are usually less common later in the season. To test his hypothesis, researchers from Europe and North America have analyzed long-term data sets looking for trends towards earlier breeding. Some amphibians do show a trend towards earlier breeding but not all species do (Beebee 1995, Blaustein et al. 2001, Gibbs and Breisch 2001). In addition, this trend may vary regionally for a single species. For example, the spring peeper (Pseudacris crucifer) is breeding earlier in Ithaca, New York in the 1990’s than it did in 1900’s (Gibbs and Breisch 2001) but does not appear to be breeding earlier in Germfask, Michigan (Blaustein et al. 2001). In the table below, we list the amphibians in North America and the United Kingdom that are showing a trend towards earlier breeding and those that are not breeding earlier based on studies from Beebee 1995, Blaustein et al. 2001 and Gibbs and Breisch 2001 (table modified from Blaustein et al. 2003).
| Species: |
natterjack toad Bufo calamita © 2000 Arie van der Meijden |
edible frog Rana esculenta © 2000 Arie van der Meijden |
Palmate newt Triturus helveticus © 2002 John P. Clare |
| Where: | Hampshire, England | Sussex, England | Sussex, England |
| Reference: | (Beebee 1995) | (Beebee 1995) | (Beebee 1995) |
| Species: |
smooth newt T. vulgaris © PENSOFT Publishers |
great-crested newt T. cristatus © PENSOFT Publishers |
grey treefrog Hyla versicolor © 1998 Joyce Gross |
| Where: | Sussex, England | Sussex, England | Ithaca, New York, USA |
| Reference: | (Beebee 1995) | (Beebee 1995) | (Gibbs and Breisch 2001) |
| Species: |
spring peeper Pseudacris crucifer © 2001 John White |
American bullfrog R. catesbeiana © 2002 William Flaxington |
wood frog R. sylvatica © 2003 John White |
| Where: | Ithaca, New York, USA | Ithaca, New York, USA | Ithaca, New York, USA |
| Reference: | (Gibbs and Breisch 2001) | (Gibbs and Breisch 2001) | (Gibbs and Breisch 2001) |
Amphibians not breeding earlier
| Species: |
common toad Bufo bufo © 2000 Arie van der Meijden |
common frog Rana temporaria © 2003 Twan Leenders |
American toad B. americanus © 2003 Brad Moon |
| Where: | Purbeck Hills in south Dorest, England | Sussex, England | Ithaca, New York, USA |
| Reference: | (Reading 1998) | (Beebee 1995) | (Gibbs and Breisch 2001) |
| Species: |
western toad B. boreas © 2000 Joyce Gross |
Fowler’s toad B. fowleri © 1979 Alan Resetar |
spring peeper Pseudacris crucifer © 2001 John White |
| Where: | Lost Lake, Three Creeks and Todd Lake, Oregon, USA | Long Point, Ontario, Canada | Germfask, Michigan, USA |
| Reference: | (Blaustein et al. 2001) | (Blaustein et al. 2001) | (Blaustein et al. 2001) |
| Species: |
Cascades frog R. cascadae © 1998 Harry Greene |
green frog R. clamitans © 2003 John White |
| Where: | Site One and Todd Lake, Oregon, USA | Ithaca, New York, USA |
| Reference: | (Blaustein et al. 2001) | (Gibbs and Breisch 2001) |
Other direct effects of climate change on amphibians
To date, there is limited data available to answer questions concerning the effects of climate change on amphibians and most of the data that exists are for relatively short time periods, but hopefully, with monitoring programs in place all over the world, we will have more data to better answer question associated with amphibian declines and climate change. However, even with large data sets, it is difficult to determine causal relationships, because other environmental factors vary concurrently.
A handful of studies, mostly from the tropics, have analyzed available data, and have found casual relationships between declines and irregular climate conditions. In Brazil between 1979 and 1982, Heyer et al. (1988) found that sever frosts correspond to the extinction of five frog species. Also, Brazil, Weygoldt (1989) found that other declines were associated with dry winters. In eastern Australia, Ingram (1990) and Laurance (1996), both found a correlation between drought and massive declines of stream-dwelling rain forest amphibians. In North America, Corn and Fogleman (1984), found a correlation between the extinction of montane populations of the northern leopard frog, Rana pipiens and drought. In Puerto Rico, Stewart (1995) found that the dramatic population declines in 1983 of the Puerto Rican coqui, Eleutherodactylus coqui, and other Puerto Rican frog species corresponded to an increased number of extended dry periods (i.e. multiple consecutive days with less than 3mm of rainfall). In other words, it was the length of dry periods that had noticeably increased instead of an overall decrease in the annual precipitation. Finally, in the cloud forests of Monteverde, Costa Rica, Pounds et al. (1999 and 1994) found a correlation between the pattern of dry mist frequency associated with highland forests and the decline and likely extinction of several species of amphibians, including the popular golden toad, Bufo periglenes, the poster child for amphibian declines. More recently Pounds et al. (2006) report amphibian declines following regional warming periods.
It is likely that climate change is affecting amphibian populations in subtle more complex ways. For example, local changes in the environment can decrease immune function and lead to pathogen outbreaks and elevated mortality. Or conditions can change to become more favorable for growth of a pathogen. For example, the chytrid fungus (Batrachochytrium dendrobatidis ) grows best in culture between 6-28 degrees C (Bradley et al 2002) and dies at 32 degrees C (Berger 2001). In Costa Rica, Pounds et al (2006) report that global warming is leading to warmer nighttime temperatures and mistier daytime temperatures, resulting in a better growth spectrum for B. dendrobatidis . Or the situation can be even more complex, involving three or more factors. Kiesecker et al. (2001) found that in extreme dry years, reduced pond depth increases exposure of amphibian embryos to ultraviolet (UV-B) radiation. This increased exposure to UV-B, increases their vulnerability to an infectious disease, Saprolegnia ferax, which causes egg mortality (Kiesecker et al. 2001).Literature Cited
Beebee, T. J. C. 1995. Amphibian Breeding and Climate. Nature 374:219-220.
Berger, L. 2001. Diseases in Australian frogs. PhD thesis, James Cook University, Townsville.
Blaustein, A. R., L. K. Belden, D. H. Olson, D. M. Green, T. L. Root, and J. M. Kiesecker. 2001. Amphibian breeding and climate change. Conservation Biology 15:1804-1809.
Blaustein, A. R., A. C. Hatch, L. K. Belden, E. Scheessele, and J. M. Kiesecker. 2003. Global Change: challenges facing amphibians. Pages 199-213 in R. D. Semlitsch, editor. Amphibian Conservation. Smithsonian Institution, Washington.
Bradley, G. A., Rosen, P. C., Sredl, M. J., Jones, T. R. and Longcore, J. E. 2002. Chytridiomycosis in native Arizona frogs. - Journal of Wildlife Diseases 38: 206-212.
Carey, C., and M. A. Alexander. 2003. Climate change and amphibian declines: is there a link? Diversity and Distributions 9:111-121.
Corn, P. S., and J. C. Fogleman. 1984. Extinction of Montane Populations of the Northern Leopard Frog (Rana-Pipiens) in Colorado. Journal of Herpetology 18:147-152.
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