Published in 01/11/2019
Amphibians: Facing Extinction
Amphibians are an old group of animals, that have developed in the Devonian period, about 370 million years ago, from lobe-finned fish which were similar to the modern coelacanth and lungfish. Amphibians are also considered the most endangered and rapidly declining group of the terrestrial vertebrates.
The Iberian Peninsula is one of the regions of Europe with the highest diversity of amphibians, with several endemic species. The reasons why this region contains such a unique herpetofauna rely on the fact that it is relatively well isolated, it displays high physiographic heterogeneity and it was a refuge for many animal and plant species in the last glaciation. In Portugal there are 19 species of amphibians of which 7 (37%) are endemic to the Iberian Peninsula.
This group of animals has a huge importance in the ecosystems in which they inhabit, maintaining their balance. Most amphibian species are predatory and important in controlling invertebrate populations, but beyond that they are also an important prey to many other animals.
Habitat destruction and fragmentation, infectious diseases, pollution, climate change and the introduction of exotic species are some of the factors that threaten amphibians across the planet. Many populations have declined even in intact areas, showing that these animals are extremely sensitive to any kind of human activity, even if they are many kilometres away.
Certain diseases such as chytridiomycosis and ranavirus have alarmingly reduced populations and even possibly driven to extinction various species across the planet.
Chitridiomycosis is an infectious disease caused by the chytrid fungus, Batrachochytrium dendrobatidis, which infects amphibian skin. In affected individuals, the skin becomes impermeable to electrolytes, such as sodium and potassium, which usually is associated with potential cardiac arrest. The fact that the prevalence of this disease is extremely high outside its region of origin and that rarely affected individuals survive, makes the situation even more worrying.
In 1938, in the African continent was discovered in the species Xenopus laevis the first known case, being the disease endemic to this region. Through the trade of amphibians, chytridiomycosis has spread to all continents except Antarctica, and is known to be pathogenic to at least 508 species. The most serious outbreaks of the disease are reported to have occurred in Neotropical America, where the disease was responsible for the extinction of 110 species of Atelopus spp. frogs (67%) and to have caused the rapid loss of amphibian biodiversity across eight families of frogs and salamanders at El Cope, Panama.
*This image does not represent amphibians infected by the disease.
In Europe the fungus is spread over a vast and irregular area and has been found in several species and Portugal is no exception. The most problematic example occurred in the Serra da Estrela Natural Park in August 2009, where hundreds of common midwife toads (Alytes obstetricans) were found dead.
Ranavirus is a disease caused by viruses of the genus Ranavirus and usually affects amphibians during larval state. This epidemic disease is associated with extremely high mortality and is responsible for population reductions worldwide, including Europe, namely in the United Kingdom.
Change Since the formation of planet Earth, the climate has undergone successive changes, but in the last century the pace between these climatic variations has accelerated abruptly, due to human activity, and the tendency is to take even greater proportions if we don’t act. This sudden climate change prevents organisms from adapting to new conditions, resulting in the mass extinction of species.
The natural balance between water availability and temperature are the most important abiotic conditions for the fitness and dynamics of amphibian populations. Water regime plays a vital role in determining the patterns of reproductive activity and determining the distribution of populations. A change in precipitation patterns and unusually long periods of drought may result in the decreasing of breeding sites, with a consequent increase in competition and predation levels. It may also lead to increased vulnerability to diseases.
The impacts of climate change on ecological systems are observed at all levels, from population level, to changes in geographical distribution, leading species to extinction and disruption of structure and functionality of ecosystems.
Direct change on ecological systems is a major cause of global biodiversity loss. Apart from complete habitat destruction, there are other subtle changes that can have significant consequences for amphibians.
Habitat fragmentation considerably increases the likelihood of a local population becoming extinct, because the distance between populations is also increased, isolating them.
We are currently dealing with an unprecedented percentage of illegal wildlife trade, threatening to reverse decades of conservation work. This activity is a big business, comparable to illegal gun and drug trade, worth millions of euros.
Amphibians are marketed as food, as pets, and for traditional medicines. This illegal business is responsible for the decline of several amphibian species and many have been collected in large numbers for centuries.
Although wildlife trade is prohibited and regulated by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), amphibian trade represents a threat to at least 281 species, of which 153 (54%) are classified with one of the following conservation status, “Vulnerable”, “Endangered”, or “Critically Endangered”.
Environmental Contamination and Exotic Species
Certain contaminants increase the larval stage period and make juveniles more susceptible to predation and drying of the pond in which they inhabit. Exposure to contaminants can also lead to poor development (eg, body malformations and metabolic disorders), decreasing their capacity of reproducing.
Another big problem is the introduction of exotic species. Some of the species introduced by man can quickly adapt to new environments and produce offspring. This easy adaptation often results in the complete elimination of native species through competition by exclusion. Invasive species not only decrease population numbers within a community, but can also drive them to extinction, which is a modifying factor of an entire healthy ecosystem.
Some carnivorous fish, introduced in the Portuguese rivers, have proved to be authentic pests for native amphibians, because they prey on their eggs, larvae and even adults. The same is true for the Louisiana red crayfish (Procambarus clarckii), which was introduced in the mid-twentieth century in Portugal and now is distributed throughout the country.
Amphibians are animals very susceptible to any changes in their habitat. Therefore, on a planet that is constantly and profoundly changing due to human activities, it is crucial to protect them and we should all contribute to their conservation.
Thank you for reading this article. Feel free to comment and to share it. If you would like to know more about this issue, please contact me.
- Almeida, N., Almeida, P., Gonçalves, E., Sequeira, F., Teixeira, J. & Almeida, F. (2001). Guia FAPAS Anfíbios e Répteis de Portugal. Porto: FAPAS
- Boone, Cowman, D., Davidson, C., Hayes, Hopkins, Relyea, R., Schiesari, L., & Semlitsch, R. (2005). Chapter 6. Evaluating the Role of Environmental. Contamination in Amphibian Population Declines. Pp. 26-31 In: Gascon, C., Collins, J.P., Moore, R.D., Church, D.R., Mackay, J.E., Mendelson, J., (eds.), Amphibian Conservation Action Plan. IUCN/SSC Amphibian Conservation Summit 2005. IUCN, Gland, Switzerland
- Carpenter, Dublin, H., Lau, M., G. Syed, McKay, J., & Moore, R. (2005). Chapter 5. Over-harvesting. Pp. 26-31 In: Gascon, C., Collins, J.P., Moore, R.D., Church, D.R., Mackay, J.E., Mendelson, J., (eds.), Amphibian Conservation Action Plan. IUCN/SSC Amphibian Conservation Summit 2005. IUCN, Gland, Switzerland
- Daszak, P., Lips, K., Alford, R., Carey, C., Collins, J., Cunningham, A., Harris, R., & S. Ron. (2005). Chapter 4. Infectious diseases. Pp. 21-25 In: Gascon, C., Collins, J.P., Moore, R.D., Church, D.R., Mackay, J.E., Mendelson, J., (eds.), Amphibian Conservation Action Plan. IUCN/SSC Amphibian Conservation Summit 2005. IUCN, Gland, Switzerland
- Gardner, T. (2001). Declining amphibian populations: a global phenomenon in conservation biology. Animal Biodiversity and Conservation 1578-665X 24 (2) : 25 – 44
- Mooney, H., & Cleland, E. (2001). The evolutionary impact of invasive species. PNAS 98 (10) : 5446 – 5451
- Pounds, A., Carnaval, A., & Corn, S. (2005). Chapter 3. Climate Change, Biodiversity Loss, and Amphibian Declines. Pp. 19-20 In: Gascon, C., Collins, J.P., Moore, R.D., Church, D.R., Mackay, J.E., Mendelson, J., (eds.), Amphibian Conservation Action Plan. IUCN/SSC Amphibian Conservation Summit 2005. IUCN, Gland, Switzerland
- Rosa, G., Anza, I., Moreira, P., Conde, J., Martins, F., Fisher, M. & Bosch, J. (2012). Evidence of chytrid-mediated population declines in common midwife toad in Serra da Estrela, Portugal. Anim. Conserv. 1367-9430 (16) : 306 – 315
- Schlaepfer, M., Hoover, C., & kenneth Dodd, C. (2005). Challenges in Evaluating the Impact of the Trade in Amphibians and Reptiles on Wild Populations. BioScience 55 (3) : 256 – 264
- Trenton, W., Garner, Walker, S., Bosch, J., Hyatt, A., Cunningham, A., & Fisher, M. (2005). Chytrid Fungus in Europe. Emerg Infect Dis. 11 (10) : 1639 – 1641
- Vargas, J. M., Real, R. & Guerrero. J. C. (1998). Biogeographical regions of the Iberian Peninsula based on freshwater fish and amphibian distributions. Bcographv (21) : 371 – 382
- Weldon, C., Preez, L., Hyatt, A., Muller, R., & Speare, R. (2004). Origin of the Amphibian Chytrid Fungus. Emerg Infect Dis. 10 (12) : 2100 - 2105
- No Comments