Disappearing Jewels: Chapter 1

February 5, 2013, 9:59 pm

Amphibians occupy an enigmatic position in the public consciousness, even among the environmentally aware. While we know that frogs, toads, and salamanders are all around us, we rarely see them. In contrast, birds regale us with their song even in the most urban of settings. Mammals live with us as household pets and companions. Even fish may brighten our aquariums or serve as the quarry of a weekend fishing expedition. Yet we simply do not encounter amphibians in our everyday lives as we do other animals. Amphibians rarely enter human habitations, with the notable exception of bathrooms in a certain class of tropical seaside hotels. Amphibians prefer bogs and swamps whereas humans, when they are outside, prefer sidewalks and dry trails. When it rains, people scurry for cover just as amphibians come out into the open. While many male frogs and toads fill the night air with their chirping, croaking, trilling, or bellowing love calls, most people are asleep. Although frogs are common in a few places, for most of us our impressions of amphibians are heavily influenced by cultural interpretations such as Kermit the Frog or talking toads in television commercials.

But if we peek into the world of real amphibians, we find some astonishing things.

  • Scientists have tallied 5,743 species of amphibians around the world, about the same as the number of mammals and more than half the number of birds. However, it is clear that many more amphibian species remain to be discovered compared with birds and mammals, with the Guianas and Peru being particularly poorly known.
  • Some species exhibit spectacular color patterns— they are the jewels of the forest. Few tropical birds can rival the colorful markings of, for example, the red-eyed leaf frog (Agalychnis callidryas) of Central America.
  • Amphibians display behaviors that defy imagination. Male Darwin’s frogs (genus Rhinoderma) from Chile and Argentina ingest their mate’s eggs and incubate them in their vocal sacs. After a few weeks, the young emerge fully formed from the father’s mouth.
  • Female strawberry poison frogs (Dendrobates pumilio) in Costa Rica carry their young from the forest floor where they hatch to tiny arboreal pools of water that form in the axils of bromeliad leaves. These miniature nurseries are free of predators, but also devoid of food for the developing tadpoles. To solve this problem, the female returns regularly to lay unfertilized eggs that become food for her young.
  • Spadefoots (genus Scaphiopus) in arid southwestern North America may spend more than 99 percent of their lives burrowed in the soil. After heavy rains finally fall, they quickly emerge for an “explosive” breeding session in which newly laid eggs develop Into fully formed toadlets in as few as eight days. The deeper we look, the more we find to challenge our preconceptions about how amphibians make a living.

What are amphibians?

Amphibians are distinguished from other four-legged vertebrates by characteristics that include moist, scale-less skin, a lack of true claws, and a remarkable retractor muscle that allows them to use their eyeballs to assist in swallowing. Although we learn as children that amphibians live part of their lives in water and part on land, a number of amphibians do not follow this pattern. Many tropical rain frogs (genus Eleutherodactylus), for example, live entirely on land, never seeing a body of water larger than what collects in a fallen palm frond. Others, such as the huge river-dwelling hellbender (Cryptobranchus alleganiensis) and permanently gilled waterdogs (genus Necturus) in the United States and the Suriname toad (Pipa pipa) of South America, never leave the water. Although humans have their own coming-of-age troubles during teenage years, most amphibians undergo a dramatic metamorphosis in which they transform from a finned creature that respires in water using gills into a four-legged, air-breathing adult.

Taxonomists recognize three major living groups of amphibians: the salamanders, the frogs and toads, and the caecilians (see Box 1). Most groups of plants and animals are very diverse in the tropics, becoming less so as one travels away from the equator. This pattern holds for frogs, toads, and caecilians, but not for salamanders. Salamanders are most diverse in the southeastern United States and Mesoamerica, well north of the equator. Only 28 species of salamanders occur in all of South America.

Amphibians in their ecosystems

Although often hidden, amphibians can be very important components of their ecosystems. For example, 132 species of frogs, toads, salamanders, and caecilians co-occur at a single site, Leticia, in southeastern Colombia[1]. In a well-studied forest in New Hampshire, United States, salamanders are the most abundant vertebrate in terms of both numbers and biomass[2]. The common coquí (Eleutherodactylus coqui), the emblematic frog of Puerto Rico, is so abundant that it can reach densities of up to 24,800 individuals per hectare[3] in prime habitat[4]. All of these adult amphibians eat large quantities of insects and help keep prey populations in check. Even tadpoles in tropical streams control algal growth and facilitate populations of mayflies, which are then consumed by other aquatic organisms[5].

Not only are amphibians important because they eat, they are also important because they are eaten. Many birds, mammals, fish, reptiles, insects, and even spiders include amphibians in their diet. The tropical fringe-lipped bat (Trachops cirrhosus) specializes on eating frogs and has even learned to differentiate the calls of palatable and poisonous species[6]. A remarkable number of snakes also prey heavily on amphibians. The false fer-de-lance (Xenodon rabdocephalus) specializes even further on toads[7]. Wading birds such as herons are well-known predators of frogs and tadpoles, but a surprising number of tropical understory birds, including woodcreepers and antbirds, also consume significant quantities of frogs[8]. Amphibians therefore play important roles in their ecosystems, performing services such as nutrient cycling and insect population control while at the same time supporting diverse predator communities.

The skin of amphibians is much more permeable to their environment than that of other vertebrate animals. All amphibians use their moist, vascular skin to obtain oxygen from their surroundings. Plethodontid salamanders, a large group of 341 species in the Americas, have no lungs at all. Because of the permeability of amphibian skin, waterborne contaminants readily enter the body and accumulate in tissue quicker than in other animals. For this reason, amphibians are exceptional indicators of environmental quality.

The problem: declining populations

Until the late 1980s, conservationists lumped the fate of amphibians with that of other wildlife. As long as we could conserve habitats in sufficient quantities, the reasoning went, we could conserve the wildlife that depended on those habitats. But then scientists began to make a puzzling observation. Even in seemingly pristine habitats, amphibian populations were mysteriously declining and disappearing. This phenomenon was not limited to a few species or a small geographic area. Declines were documented in Australia, in North, Central, and South America, in the Caribbean, and more recently in Africa and Asia[9][10][11]. In Latin America alone, nine families and 30 genera of amphibians had been affected by the late 1990s[12].

At first, some scientists were skeptical that the declines were real because amphibian populations are notorious for fluctuating widely[13]. Once powerful statistical tests showed that the declines were far more widespread than would reasonably be expected by chance, most researchers eventually agreed that something was seriously amiss[14]. Reports of declines and extinctions accelerated during the 1990s, and the mass media latched onto the story.

These observations indicated that something specific and troubling was happening to amphibians. At one site in Costa Rica, 40% of the amphibian fauna disappeared over a short period in the late 1980s[15]. Similar stories can be told about other sites[16]. The loss of amphibian species not only contributes to the world’s biodiversity crisis, but also has important implications for the ecosystems where they occur. Without amphibians, links in food webs are broken and other organisms are influenced in often unpredictable ways.

Purpose of the global amphibian assessment

Table 1. IUCN Red List Categories
Category Abbreviation Definition
Extinct EX Species for which extensive surveys show that there is no reasonable doubt hat the last individual has died.
Extinct in the wild EW Species that survive only in captivity and/or as naturalized populations.
Critically endangered CR Species that are facing an extremely high risk of extinction.
Endangered EN Species that are considered to be facing a very high risk of extinction in the wild.
Vulnerable VU Species that are considered to be facing a high risk of extinction in the wild.
Near Threatened NT Species that do not qualify for Critically Endangered, Endangered or Vulnerable now, but are close to qualifying for or likely to qualify for a threatened category in the near future.
Least Concern LC Species that do not qualify for Critically Endangered, Endangered, Vulnerable or Near Threatened. Widespread and abundant taxa are included in this category.
Data deficient DD Species for which there is inadequate information to make an assessment of extinction risk based on distribution and/or population status. A taxon in this category may be well studied, and its biology well known, but appropriate data on abundance and/or distribution are lacking. Data Deficient is therefore not a category of threat.

Clearly much research is needed to understand why amphibians are declining (see Box 2). But scientists now have new insights into the diversity and natural history of amphibians, and are now able to tell important parts of the story. Knowing the current conservation status of amphibian species is a major step in identifying important areas for research and in knowing where management and protection are most needed.

The Red List criteria developed by the Species Survival Commission of IUCN (the World Conservation Union) provide a widely accepted method for categorizing imperiled plants and animals[17][18][19]. Over the past 15 years, conservationists have refined these categories and criteria to reflect just how close to extinction a species finds itself. Although scientists have assessed all known bird and mammal species against these criteria, until recently no one has systematically examined amphibians. Because they now appear to have unique conservation problems, are often strongly tied to aquatic habitats (as opposed to most birds and mammals), and have strong sensitivity to environmental pollution, amphibians are clearly in need of a similarly exhaustive conservation assessment.

This report provides a summary of the New World portion of the Global Amphibian Assessment, an effort to assess amphibians worldwide against the IUCN criteria. Amphibians in the New World are united by evolutionary history, geography, and the economies and cultures of the people managing their habitats. By writing this report, we hope to highlight the diversity and imperiled status of the New World amphibians. We show which amphibians are most threatened and describe what threatens them. We evaluate the effectiveness of national systems of protected areas in helping to conserve amphibian faunas. Finally, we present an agenda for the conservation of amphibians. The results can be used by governments and environmental organizations to set priorities for conservation actions at regional, national, and local levels.

By highlighting the plight of amphibians, we hope to stir resource managers and the public into action so that these glittering jewels of our wild fauna receive the same long-term protection as any masterpiece painting hanging in a museum. The need is urgent, for these brilliant gems are fast disappearing. Unless we take rapid action, many will be gone forever.

Methods

 

caption Figure 1. Regional overview map of the New World. (Source: NatureServe)

 

Our analyses are based upon the application of the Red List criteria[20] to the 3,046 species of amphibians occurring in the New World. Table 1 lists the categories and their definitions (see also Box 3). We define the New World as continental North, Central, and South America, all near-shore islands, and the Caribbean. Much of the analysis is by regions of the New World (Figure 1):

South America: All countries in continental South America plus the near-shore islands of the Netherlands Antilles and Trinidad and Tobago.

Mesoamerica: Mexico through Panama.

Caribbean: All countries and territories of the Greater and Lesser Antilles plus associated islands such as Turks and Caicos, the Bahamas, and the Cayman Islands.

North America: Canada and the United States (exclusive of Hawaii and overseas possessions).

To apply the criteria, compile the supporting information, and draw range maps, we enlisted the help of numerous herpetologists from throughout the region. In most cases, a single scientist filled out a draft database, including information on distribution, abundance and population trends, natural history, threats, and conservation measures, for all species in a region. Then, in a workshop setting, other experts updated the information based on recent literature and unpublished information. Overall, 229 scientists participated in some stage of the development of the database (see Appendix 1).

Once the entire database was compiled, we reviewed the Red List category assignments for all species to ensure that the criteria were applied evenly across all regions of the New World. Spatial analyses are based on the number of species fulfilling the criteria being analyzed that occur in each quarter-degree block of latitude and longitude. Unless noted otherwise, the analyses pertain to extant native species. Native species are those that have arrived at their current distribution unaided by humans. Our analyses do not include data from 11 species that were described in previous centuries and for which type specimens have been lost or information about country of origin is in doubt.

Notes

  1. ^ Lynch, J. D. 2004. Unpublished data.
  2. ^ Burton, T. M. and G. E. Likens. 1975. Salamander populations and biomass in the Hubbard Brook Experimental Forest, New Hampshire. Copeia 1975:541-546.
  3. ^ One hectare equals about 2.5 acres.
  4. ^ Stewart, M. M. and L. L. Woodbright. 1996. Amphibians. Pages 273- 320 in P. Regan and R. B.Waide (editors), The Food Web of a Tropical Rain Forest. University of Chicago Press, Chicago, Illinois, USA.
  5. ^ Ranvestel, A. W., K. R. Lips, C. M. Pringle, M. R. Whiles, and R. J. Bixby. 2004. Neotropical tadpoles influence stream benthos: evidence for the ecological consequences of decline in amphibian populations. Freshwater Biology 49:274-285.
  6. ^ Tuttle, M. D. and M. J. Ryan. 1981. Bat predation and the evolution of frog vocalizations in the Neotropics. Science 214:677-678.
  7. ^ Savage, J. M. 2002. The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago, Illinois, USA.
  8. ^ Poulin, B., G. Lefebvre, R. Ibáñez, C. Jaramillo, C. Hernández, and A. S. Rand. 2001. Avian predation upon lizards and frogs in a Neotropical forest understory. Journal of Tropical Ecology 17:21-40.
  9. ^ Lips, K. R., J. K. Reaser, B. E. Young, and R. Ibáñez. 2001. Amphibian Monitoring in Latin America: A Protocol Manual. Society for the Study of Amphibians and Reptiles, Herpetological Circular 30:1-115.
  10. ^ Semlitsch, R. D. 2003. Amphibian Conservation. Smithsonian Books, Washington, D.C., USA.
  11. ^ Weldon C. 2004. Personal communication to K. R. Lips.
  12. ^ Young, B. E., K. R. Lips, J. K. Reaser, R. Ibáñez, A. W. Salas, J. R. Cedeño, L. A. Coloma, S. Ron, E. La Marca, J. R. Meyer, A. Muñoz, F. Bolaños, G. Chaves, and D. Romo. 2001. Population declines and priorities for amphibian conservation in Latin America. Conservation Biology 15:1213-1223.
  13. ^ Pechmann, J. H. and H. M. Wilbur. 1994. Putting declining amphibian populations in perspective: natural fluctuations and human impacts. Herpetologica 50:65-84.
  14. ^ Pounds, J. A., M. P. Fogden, J. M. Savage, and G. C. Gorman. 1997. Test of null models for amphibian declines on a tropical mountain. Conservation Biology 11:1307-22.
  15. ^ Pounds, J. A., M. P. Fogden, J. M. Savage, and G. C. Gorman. 1997. Test of null models for amphibian declines on a tropical mountain. Conservation Biology 11:1307-22.
  16. ^ Young, B. E., K. R. Lips, J. K. Reaser, R. Ibáñez, A. W. Salas, J. R. Cedeño, L. A. Coloma, S. Ron, E. La Marca, J. R. Meyer, A. Muñoz, F. Bolaños, G. Chaves, and D. Romo. 2001. Population declines and priorities for amphibian conservation in Latin America. Conservation Biology 15:1213-1223.
  17. ^ Mace, G. M. and R. Lande. 1991. Assessing extinction threats: toward a re-evaluation of IUCN threatened species categories. Conservation Biology 5:16-22.
  18. ^ IUCN. 1994. IUCN Red List Categories. Prepared by the IUCN Species Survival Commission. IUCN, Gland, Switzerland.
  19. ^ IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission, IUCN, Gland, Switzerland and Cambridge, U.K.
  20. ^ IUCN. 2001. IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission, IUCN, Gland, Switzerland and Cambridge, U.K.

 


This is a chapter from Disappearing Jewels: The Status of New World Amphibians (e-book).
Previous: Executive Summary  |  Table of Contents  |  Next: The Status of New World Amphibians
 

 

 

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Citation

International, C., Nature, T., , N., Young, B., Stuart, S., Chanson, J., Cox, N., & Boucher, T. (2013). Disappearing Jewels: Chapter 1. Retrieved from http://www.eoearth.org/view/article/151739

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