• Skip to primary navigation
  • Skip to main content
  • Skip to footer

Froglife

Leaping forward for reptiles and amphibians

  • Events
  • Shop
  • Donate
  • Subscribe
  • Sightings
  • Cart
  • About Us
    • Organisational structure
    • Froglife Scotland
    • Staff
    • Trustees
    • Our strategy
    • Our supporters
    • Annual reviews and accounts
    • Job vacancies
    • Contact us
  • What we do
    • Events
    • Education
      • Come Forth for Wildlife
      • Transforming Lives: Froglife Trainees
      • Green Pathways
      • Green Pathways for Life
      • Leapfrog Schools
    • Improving habitats
      • Froglife reserves
      • London Blue Chain
      • Coalface to Wildspace, Midlands
      • Discovering Dewponds
      • Come Forth for Wildlife
    • Toads on Roads
    • Campaigns and Policy
    • Research
    • Digital Amphibian and Reptile Conservation
    • Webinars
    • Virtual Reality Experience
  • Froglife Ecological Services
    • About FES
    • Training
    • FES Services
    • Research
    • Survey Calendar
  • Info & advice
    • Frequently Asked Questions
    • Reptiles and Amphibians
    • Our publications
    • Reports and research
    • Land management
  • Idea Zone
    • Pond Visualiser App
    • Fun and games
    • Education resources
    • Wildlife at home
    • Wildlife gardening
  • Support Us
    • Donate
    • Other Ways to Donate
    • Fundraise for us
    • Become a Froglife Friend
    • Legacies, in memory & celebrations
    • Become a corporate sponsor
    • Volunteer
  • What’s new
    • Events
    • Latest News and Croaks
    • Natterchat Magazine
You are here: Home / Archives for extinction

extinction

Croaking Science: How many amphibian species are there, how do we know, and how many are threatened with extinction?

November 29, 2020 by Roger Downie

I’m sure most Froglife supporters and Croaking Science readers will be aware that the world’s amphibian species are in crisis. However, you may not know just how bad the crisis is, and how we know about it. This Croaking Science article aims to show how strong the evidence is, how it is gathered, and how difficult it is to keep up to date.

Herpetologists began to become aware in the 1990s that, although all kinds of wildlife were in trouble all over the world, amphibians were a special case. Simon Stuart and colleagues put numbers to this feeling in 2004. Their Global Amphibian Assessment estimated that 32.5% of amphibian species were globally threatened (i.e. they fitted into the IUCN Red List categories Critically Endangered, Endangered or Vulnerable: see later for definitions) compared to 12% of birds and 23% of mammals. Further, 22.5% of amphibians fell into the Data Deficient category i.e. too little was known about their status to make an assessment, a substantially higher proportion than for birds and mammals whose status tends to be better known. This meant that only about 44% of amphibian species could be classed as of Least Concern.  Stuart and colleagues discussed possible reasons for amphibians being in worse shape than the other mainly terrestrial vertebrate groups (at that time, too little was known about the status of reptiles to make a similar estimate for them). Although anthropogenic habitat loss and change were the underlying main causes for all wildlife declines, amphibian populations seemed to be declining even in good quality habitat, for what Stuart et al. called ‘enigmatic’ reasons. Within a few years, it was clear that the main cause of the ‘enigma’ was the spread of the fungal disease chytridiomycosis against which many amphibian species had no or only very limited resistance. It is interesting in a time of a global pandemic affecting the human population to reflect on the causes and effects of a novel disease affecting wildlife.

Stuart et al.’s assessment was based on the then total number of described amphibian species, 5743. However, James Hanken (1999) had earlier noted the irony that, at a time when amphibian species were in severe decline, the number of known species was rapidly increasing. This trend has continued. The Amphibian Species of the World website (Frost, 2020) currently (October, 2020) lists 8226 species, a 43% increase on the number assessed by Stuart et al. in 2004. Over the last 10 years, the number of described species of amphibians (mostly anurans: frogs and toads) has increased on average by 150 per year.

How has this happened? The biggest discoveries of new species are in the tropics where amphibian diversity is highest, and where, until recently, resources and expertise for amphibian research were very limited. Amphibians are mostly small, mainly active at night, and often quite localised, all of which create difficulties in cataloguing biodiversity.  It also turns out that external appearances can conceal underlying differences, so that it is only recently, with the availability of DNA sequencing, that herpetologists can work out that some species, previously thought to have extensive ranges, should really be split into several distinct species. Over my time studying the frogs of Trinidad and Tobago, new species descriptions of this kind have occurred in several cases. For example, the stream frogs of northern Venezuela, Trinidad and Tobago (see Croaking Science September 2020 for an account of colour changes in these frogs) were earlier thought to belong to one species: now they are three, Mannophryne trinitatis, M. olmonae and M. venezuelensis. Will this process of finding new amphibian species come to an end? Presumably it will, but currently there is no sign of the new discovery trend slowing down.

How do we establish the conservation status of a species? The task of keeping tabs on amphibians falls to the IUCN Species Survival Commission’s Amphibian Specialist Group (ASG). Their aim is to ‘provide the scientific foundation to inform effective amphibian conservation around the world’. A key part of their work is the compilation and revision of the Amphibian Red List i.e. an assessment of all species relative to their status in the wild. The main Red List categories (IUCN, 2001), with their definitions, and the current proportions of amphibian species in each category (from a total of 6932 species) are shown below:

Category, definition, percentage of amphibian species  

Critically endangered (CR): extremely high risk of extinction in the wild, 8.9%

Endangered (EN): very high risk…, 14.4%

Vulnerable (VU): high risk…., 9.8%

Near threatened (NT): close to qualifying as threatened, 5.6%

Least concern (LC): widespread and abundant, 41.5%

Data deficient (DD): inadequate information available to make an assessment, 19.3%

There is a final category of ‘not evaluated’: these are mainly newly identified species for which information on their population status is often very limited. Where new species have been named from the splitting of a widespread species, this causes a particular problem for the Red Listing process. For example, the widespread small tree frog Dendropsophus minutus is an abundant neotropical LC species; the population in Trinidad is now classed as a Trinidad endemic, D. goughi, so its status now needs assessed separately.

Clearly, a species’ status can change with time, so the Red List needs regular updating. In addition, as noted above, the identification of new species means there is a constant need for new assessments. At present, the ASG is nearing completion of a major re-assessment, due for release in December 2020: it will be fascinating to find how amphibians as a whole have fared since the last major revision in 2010.

What sort of evidence goes into determining a species conservation status? The Red Listing process is as objective as possible and relies on input from experts around the world. Key questions are: have populations changed, and if so, by how much? What is the geographic range of the species, and how much of this range does it occupy? How large or small is the population?  These can be quite difficult questions to answer with any degree of certainty. Consider the UK, with its considerable resources and abundant wildlife experts. We only have a small number of amphibian species. How good is our knowledge of their population sizes and trends? Even our presence/absence distribution maps are very variable in quality, and knowledge of populations is very patchy, even for the species that are of conservation concern, like natterjack toads and great crested newts.

Now consider Venezuela: a large country in political and economic turmoil with only a small number of dedicated herpetologists, but over 300 species of amphibians. The task of Red Listing here is immense and likely to be much based on educated guesswork. I have had some involvement over the last year in re-assessing the conservation status of Trinidad and Tobago’s much smaller number (35) of species, including three previously classed as threatened, and which share their ranges with Venezuela. The process has involved several herpetologists knowledgeable about the amphibians of the three territories pooling their information to complete the IUCN’s detailed evaluation forms, and coming to a judgement. The three species are:

  • Phytotriades auratus, the golden tree frog (see Figure). Formerly CR on the basis of occurrence only on two separate Trinidad mountain peaks, where it lives among the leaves and in the water tanks of huge arboreal bromeliads. Recent discoveries of populations in northern Venezuela and on another Trinidad mountain have led us to revise the assessment to EN.
  • Hyalinobatrachium orientale, the eastern glass frog (see Croaking Science, July 2020). Found along forest streams in northern Venezuela and in north east Tobago, but not Trinidad. Previously assessed as VU. Because of its limited range in Tobago and threats from deforestation in Venezuela, we retain VU as its Red List status.
  • Flectonotus fitzgeraldi, the dwarf marsupial tree frog (see Croaking Science October 2020). Found on forest and forest edge vegetation that holds pools of water, such as bromeliads and Heliconia, in northern Venezuela, Trinidad and Tobago. The previous assessment was EN, but when we examined the evidence, it became clear that this was a case where the previous assessors had made a judgment based on very limited data. Fortunately, we had been involved in extensive surveys of the presence/absence of this species in Trinidad and Tobago, as well as population estimates at a few locations. Added to data on the species’ range in Venezuela, we have been able to publish a paper (Smith et al. in press) and to assess this species as LC.

In these three cases, we have two reductions in the estimated threats. In both cases, these are not linked to active conservation effort, but rather to better data on the numbers and distribution of species. Much of the hard work has been done, not by experts, but by students and amateur naturalists taking part in actions like Bioblitzes. Mobilising citizens in this way has been important in the UK for taxa likes birds and butterflies. It needs to be done all over the world for more taxa.

References

Frost, D.R. (2020). Amphibian Species of the World, version 6.0. Available online.

Hanken, J. (1999). Why are there so many new amphibian species when amphibians are declining? Trends in Ecology and Evolution 14, 7-8.

IUCN (2001). IUCN Red List Categories and Criteria, version 3.1. Available online.

Smith, J. et al. (in press). The distribution and conservation status of the dwarf marsupial frog (Flectonotus fitzgeraldi; Anura, Hemiphractidae) in Trinidad, Tobago and Venezuela. Amphibian and Reptile Conservation.

Stuart, S. et al. (2004). Status and trends of amphibian declines and extinctions worldwide. Science 306, 1783-1786.

Filed Under: Croaking Science Tagged With: Amphibians, Croaking Science, extinction, iucn, species

Croaking Science: Gastric-brooding frogs – a uniqueness lost forever?

November 27, 2013 by admin

Croaking science is a new way for student volunteers and scientist to explore what’s occurring in the world of Science – science facts, new research or old debates which are inspired by or affect amphibians and reptiles, and then communicate this to a wider audience in their own words. The aim of the feature is to provide a platform for those starting their foray into the world of science communications as well as established scientists.  We welcome any submissions from students and scientists. Please note that the views expressed in the articles are not those of the Froglife Trust.

This is the time of year where you may be getting together with friends and family for meals all over the world. When you do, think about what this frog went without, to look after it’s young. From one of our new Croaking Science Volunteers Hannah Graves.

Gastric-brooding frogs were discovered in Australia in the 1970’s (1). There are two known species, the Northern (Rheobatrachus vitellinus) and the Southern (R.silus) (2), neither of which has been seen in the wild since the 1980’s (3). It isn’t known exactly what caused the demise of the two species, it is believed that logging and disturbances to the water quality in their habitats may have had an effect on the Southern species (4) and wide spread forest fires and habitat destruction could be implicated in the loss of the Northern species (5). As with all amphibian populations globally, the fungal disease Chytridiomycosis can’t be ruled out (1).

As the common names suggest, this genus of frog had a very unusual way of caring for their young. After the female had mated, she swallowed her eggs! This meant that the tadpoles could develop in her stomach safe from predators (6). After six to seven weeks the tadpoles metamorphosed into young frogs and crawled back out of the female’s mouth (4). During this brooding period the female switched off the production of hydrochloric acid to prevent digesting her young (7). This meant that she couldn’t eat whilst carrying her young. Just four days after her young emerged, the female’s digestive system returned to normal and she resumed eating (4). Unfortunately, as the two species are now classified as extinct (1) (8), it is unlikely we will ever learn the secrets of how they managed to shut down their digestive systems and then start them up again.

Sadly, this story of discovering a new species only to lose them a few years later is all too common (9), and with them we lose their untold stories.

What you can do

Support initiatives to inspire the next generation of herpetologists (scientists that specialise in amphibian and reptiles) including our conservation and education work .

Even our “common” species are declining in some areas. If nothing is done now, they may not be there in the future. Use our Dragon Finder app to report any of your amphibian and reptile sightings (applicable to species found in the UK). So that the location of your local populations are recorded.

References

(1) Meyer, E.; Newell, D.; Hines, H.; May, S.; Hero, J.; Clarke, J.; Lemckert, F. (2004). Rheobatrachus silus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.1. Downloaded on 01 October 2013.

(2) IUCN (2013). IUCN Red List of Threatened Species. Version 2013.1. www.iucnredlist.org Downloaded on 01 October 2013.

(3) Hines, H. (2002) Recovery plan for Stream Frogs of South-east Queensland 2001-2005. Environmental Protection Agency, Queensland, Australia. Downloaded on 01 October 2013.

(4) Tyler, M.J. and Davies, M. 1983. The gastric brooding frog. M.J. Tyler, eds., Croom Helm, London.

(5) Hero, J. and Morrison, C. (2004). Frog declines in Australia: global implications. Herpetological Journal 14:175-186.

(6) Tyler, M.J. and Carter, D.B. (1982). Oral birth of the young of the gastric-brooding frog Rheobatrachus silus. Animal Behaviour 29:280-282.

(7) Tyler, M.J.; Shearman, D.J.C.; Franco, R.; O’Brien, P.; Seamark, R.F.; Kelly, R. (1983). Inhabitaion of gastric acid secretion in the Gastric Brooding Frog, Rheobatrachus silus. Science 220:609-610.

(8) Hero, J.; McDonald, K.; Alford, R.; Cunningham, M.; Retallick, R. (2004). Rheobatrachus vitellinus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.1.  Downloaded on 01 October 2013.

(9) Wake, D.B. and Vredenburg, V.T. (2008). Are we in the midst of the sixth mass extinction? A view from the world of amphibians. Proceedings from the National Academy of Science 105:11466-11473.

Filed Under: Uncategorized Tagged With: Australia, extinct, extinction, Froglife, Gastic-brooding Frogs, tadpoles

Croaking Science: The Golden Toad

November 18, 2013 by admin

 As our Common Toads start to enter hibernation after a tricky weather year; Becky Austin our Croaking Science Volunteer, talks about how climate change affected one of their cousins in Costa Rica.

The very first species whose extinction was blamed on climate change due to anthropogenic causes was an amphibian: the Golden Toad. Once abundant in a small area of the Costa Rican cloud forests of Central America, the last individual sighting was in 1989 and in 2004, the toad was stated as extinct.

Golden Toads, or Bufo periglenes, were only 5cm long and showed sexual dimorphism: males had bright ‘golden’ skin, whereas females had olive skin with red spots and a yellow rim. Golden toads also showed the extraordinary feature of ‘gastric breeding’, where eggs were kept in the stomach of the female until the tadpoles were ready to leave via the mouth.

How was climate change to blame for the extinction of this fascinating species? Recent discoveries may show that the toad’s extinction coincided with a very dry period of time caused by an El Niño event in 1986-7 (where a warm Pacific current affected the South American climate). This caused breeding pools to dry out and population numbers to crash as few tadpoles could survive. However, this alone may not be the cause.

Gobal warming is causing consistent atmospheric temperature changes in most parts of the world, including the toad’s home range in Costa Rica. Many scientists believe that in these highland areas, conditions are increasingly becoming more suited to the prolific growth of the chytrid fungus Batrachochytrium dendrobatidis, which may have caused the extinction of the golden toad. Even if the fungus initially spread due to the conditions the El Niño caused in the late 80s, continual warming will increase the fungus’s rate of destruction, leading to many further amphibian extinctions. Global warming must therefore be addressed as quickly as possible as the root of many species extinctions.

 

By Charles H. Smith, vergrößert von Aglarech (U.S. Fish and Wildlife Service) [Public domain]
By Charles H. Smith, vergrößert von Aglarech (U.S. Fish and Wildlife Service) [Public domain]
 

What can you do to help?

Check out our website and get clued up about chytrid fungus and what it looks like; so you can report any potential sightings of the disease.

Donate to Froglife this year and help us continue our work with amphibians and reptiles in 2014

References

Pounds, J.A., Bustamante, M.R., Coloma, L.A., Consuegra, J.A., Fogden, M.P.L., Foster, P.N., La Marca, E., Masters, K.L., Merino-Viteri, A., Puschendorf, R., Ron, S.R., Sanchez-Azofeifa, G.A., Still, C.J. and Young, B.E. (2006). Widespread amphibian extinctions from epidemic disease driven by global warming. Nature, 439: 161-167.

Anchukaitis, K.J . and Evans, M.N. (2010). Tropical cloud forest climate variability and the demise of the Monteverde golden toad. PNAS, 107: 5036-5040.

 

Filed Under: Uncategorized Tagged With: climate change, Costa Rica, Croaking Science, extinction, Froglife, Golden Toads

Footer

  • About Us
  • What we do
  • Info & advice
  • Learning zone
  • Support Us
  • What’s new
  • FAQ
  • Contact us
  • Events
  • Become a Friend
  • Our supporters
  • Privacy Information

Contact us

Froglife (Head Office)
Brightfield Business Hub
Bakewell Road
Peterborough
PE2 6XU
info@froglife.org

© 2023 · Froglife

Froglife is a Campaign title for The Froglife Trust
Registered Charity No. 1093372 (in England and Wales) and SC041854 (in Scotland)
Registered Company No. 4382714 in England and Wales

Paper Rhino logo