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Ponds Against Climate Change

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From Antarctica to the tropics, ponds are widespread habitats found in nearly all terrestrial biomes (Jeffries, 2016). Research estimates that there are 304 million natural lakes and ponds worldwide, covering a total area of approximately 4.2 million km2 (Downing et al., 2006). This article will focus on ponds: according to limnologists, the difference between ponds and lakes is that ponds are shallow enough that plants could grow across the entire surface meaning that it has a photic zone where sun can reach the bottom. By contrast, lakes have an aphotic zone meaning there are sections deep enough that sunlight cannot reach the bottom. Ponds are biodiversity hotspots for both aquatic and terrestrial species, providing habitat for rare specialists such as fairy and tadpole shrimp. Not only are they vital for these species, but they are also vital in managing landscapes from threats such as flooding and climate change. It is known that aquatic ecosystems have a large role in managing greenhouse gases, with oceans among the most well-known of carbon sinks. However, with lakes and ponds covering such a vast expanse of area, is it possible that they are the climate’s unsung heroes?

Carbon sinks are reservoirs that absorb and store atmospheric carbon through physical and biological processes. One study concludes that ponds may be more active in nearly all of these processes than large lakes, marine ecosystems and terrestrial ecosystems (Downing, 2010). Carbon burial rates between ponds can vary depending on composition. Ponds are not ubiquitous, thus the effectiveness of carbon sequestration varies per site depending on factors such as substrate type and vegetation. Gilbert et al., (2014) found that permanent and naturally vegetated ponds were the most efficient at sequestering carbon dioxide, particularly those dominated by thick moss swards and aquatic grasses. These form a thick, moist blanket when the pond dries out, minimising the release of stored carbon into the atmosphere. The least efficient ponds were temporary, shallow arable ponds which lacked vegetation and were regularly disturbed. When discussing the value of ponds in carbon sequestration, it may be unhelpful to group all ponds together as their importance can vary considerably based on their composition. Furthermore, it is important to note that ponds can serve a variety of purposes. Whilst ponds capturing excess fertilisers and pesticides are useful in the fight against climate change, they may not make good wildlife ponds or facilitate biodiversity.

This diversity of ponds is reflected in the range of carbon sequestration rates found across the literature. One study found that small ponds sequester 79-247g of organic carbon per square meter annually, a rate 20-30 times higher than woodlands, grasslands and other habitat types (Taylor et al., 2019). Céréghino et al., (2014) suggested that some 500m2 ponds may even be capable of sequestering up to 1000kg of carbon per year, as much as a car would produce in that time. Although ponds only take up 0.0006% of land area in the UK, a tiny proportion compared to the 36% of grasslands (Carey et al., 2008), their high rates of carbon burial suggest that their overall contribution is significant – even when compared to much larger habitats. Thus their role in tackling climate change should not be overlooked.

Biological processes carried out by aquatic vegetation are pivotal in carbon sequestration in ponds. Photosynthesis contributes to the sequestration of carbon dioxide by turning it into oxygen and biomass. One kilogram of algae uses an average of 1.87 kilograms of carbon dioxide a day (Anguselvi et al., 2019). Algae in ponds also contribute to reducing additional greenhouse gases such as nitrous oxide (N2O). Nitrogen is a key component in chlorophyll and thus used in farm fertiliser. Excess nitrogen could react with oxygen in the air to become N2O. The presence of algae in farm ponds to capture this excess can prevent this reaction from occuring and limit emission of the greenhouse gas. A study has found that two thirds of farm ponds act as N2O sinks (Webb et al., 2019), making them an important contributor to combating climate change, particularly as N2O traps heat at 300x the rate of CO2. 

Ponds play an important role in mitigating climate change, however, there is evidence to suggest that they can also act as carbon sources. Does this offset their sequestering benefits? Take for instance, permafrost thaw ponds. Permafrost thaw ponds in northern regions can be particularly prominent sources of carbon. As permafrosts thaw, vast amounts of carbon dioxide and methane are released, resulting in the formation of small ponds which become carbon emission hotspots (Kuhn, 2018). Although they are releasing carbon, it is not the pond itself creating these gases. Global warming is causing the permafrosts to thaw out and release the stored carbon. Although the ponds facilitate the emissions, it is perhaps misleading to label them as a carbon source in these instances. 

Large habitats such as oceans and woodlands are well-known for their role in reducing greenhouse gasses and mitigating the effects of climate change, but ponds may play an equally important and largely underappreciated role. Ponds are also a fantastic tool against climate change because they give people a way in which to take action. People can easily create ponds in their own gardens and community spaces, and in this way play a part in reducing greenhouse gas emissions and contribute to the global fight against climate change.

Written by Mirran Trimble & Emily Robinson

 

References

Anguselvi, V., Masto, RE., Mukherjee, A., & Singh, PK. (2019) CO2  Capture for industries by algae, Algae, Yee Keung Wong, IntechOpen, DOI: 10.5772/intechopen.81800. Available from: https://www.intechopen.com/books/algae/co-sub-2-sub-capture-for-industries-by-algae

Carey, PD., Wallis, S., Chamberlain, PM., et al. (2008) Countryside Survey: UK results from 2007. Swindon, UK: Natural Environment Research Council.

Céréghino, R., Boix, D., Cauchie, HM., et al. (2014) The ecological role of ponds in a changing world. Hydrobiologia. 723, 1–6.

Downing, JA. (2010) Emerging global role of small lakes and ponds: little things mean a lot. Limnetica. 29(1), 9-24.

Downing, JA., Prairie, YT., Cole, et al. (2006) The global abundance and size distribution of lakes, ponds, and impoundments. American Society of Limnology and Oceanography. 51(5), 2388-2397.

Gilbert, PJ., Taylor, S., Cooke, DA., et al. (2014) Variations in sediment organic carbon among different types of small natural ponds along Druridge Bay, Northumberland, UK. Inland Waters. 4(1), 57-64.

Jeffries, MJ. (2016) Flood, drought and the inter-annual variation to the number and size of ponds and small wetlands in an English lowland landscape over three years of weather extremes. Hydrobiologia. 768, 255–272.

Kuhn, M., Lundin, EJ., Giesler, R., et al. (2018) Emissions from thaw ponds largely offset the carbon sink of northern permafrost wetlands. Scientific Reports. 8, 9535.

Taylor, S., Gilbert, PJ., Cooke, DA., et al. (2019) High carbon burial rates by small ponds in the landscape. Frontiers in Ecology and the Environment. 17(1), 25-31.

Webb, JR., Hayes, NM., Simpson, GL. et al. (2019) Widespread nitrous oxide undersaturation in farm waterbodies creates an unexpected greenhouse gas sink. PNAS. 116(20), 9814-9819.

 

Should we count marine turtles as members of the British fauna?

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In August 2020, the media outlet Wales On-line reported that a five-foot long marine turtle had surfaced beside a small fishing boat off the north coast and swum alongside it for an extended period before diving out of sight. The excited boat owner said that he had fished those waters for over 20 years, and never seen a turtle before. Was this an exceptional sighting? The fisherman was certainly lucky. Over the last century or so, the average number of leatherback turtles (the species observed) seen in British waters each year is around 15. However, this is bound to be a vast underestimate of the turtle numbers actually present in British waters. This is due to them being incredibly difficult to locate as they rarely emerge from the depths to breath, nor do they nest on British beaches; so the chances of actually spotting one in the huge expanses of our coastal waters are very slim.

Botterell et al. (2020) have published an analysis of marine turtle sightings, strandings (usually found dead washed up on shore) and captures (by-catch in fishing nets) since 1910. Of 1997 records, 84% are of leatherbacks; 12% of loggerheads, and 3% of Kemp’s ridleys. The remaining 13 records concern tiny numbers of three more species. Until 1980, records were small in number for all species, with substantial increases from the 1990s onwards. Mapping of the records shows that most are predominantly from the western side, including the English Channel, all around Ireland and north to the Orkneys and Shetlands. Leatherbacks and loggerheads have been recorded at all times of the year, with peaks in June-October (leatherbacks) and November-March (loggerheads). Kemp’s ridleys have only been seen from October-February. Measurements on body size, mostly from strandings and captures, suggest that most leatherbacks in British waters are adults, while loggerheads and Kemp’s ridleys are juveniles.

Although they may seem like an exotic species, these data clearly show that we should regard leatherback turtles as normal members of the migratory fauna that inhabits our surrounding seas. Adult leatherbacks manage this by generating enough heat that their body temperature is above ambient, allowing them to remain active in the cold waters of the North Atlantic; even juveniles can raise their body temperature above cold water temperatures by activity and reduction of heat loss (Bostrom et al., 2010).  For loggerheads and Kemp’s ridleys, the majority of records in British waters are strandings of juveniles in winter: these are most likely animals cold-stunned as water temperature declines. What is unknown is the number which venture into our waters, but manage to travel south and survive.

Marine turtles display what are known as cosmopolitan ranges, meaning that they are near-ubiquitous in waters globally. This has led to their incorporation into indigenous cultures around the world, with their size and habits having led to mythological status in many places. In an ecological context, the extensive migrations they undertake between foraging and nesting grounds (which often span entire oceans) are important for connecting ecosystems globally. The three species commonly found in British waters have distinct breeding and foraging grounds, with much information recently derived from satellite tracking of tagged adult females following capture at nesting sites (Fossette et al., 2014). For example, Atlantic leatherbacks consist of two separate populations. South Atlantic turtles breed either along the coast of Brazil or of West Africa, especially Gabon. Foraging takes them across the ocean and southwards, but not into the North Atlantic. The North Atlantic population breeds on the beaches of southern Florida, the islands of the Caribbean and the Guianas. They forage east and north, as far as British waters, as we have seen. Adult females return to nesting beaches every 2-4 years and lay up to 7 clutches, each 60 – 110 eggs, over several months.

Female leatherback turtle nesting on a beach in Tobago.

The males wait near the approaches to the beaches and attempt to mate with any females that turn up; however, they do not come onto land and instead spend their entire lives at sea. Leatherback females show moderately high nesting site fidelity, with all their nests in a season being laid on the same beach which they were born on or ones in close proximity. Hatchlings disperse into the sea and travel east towards open ocean to develop into juveniles. Kemp’s ridleys nest in the Caribbean, nearly all on one 16- mile Mexican beach; juveniles extend across the North Atlantic. Loggerheads are highly cosmopolitan with three distinct Atlantic populations. In the West Atlantic, they nest on beaches as far north as New Jersey and south to Parana in Brazil. Juveniles forage very widely. The Gulf Stream (also called the North Atlantic Gyre) was thought to be the primary determinant of juvenile distribution, as it carries developing individuals into east Atlantic waters. However, active dispersal has been recently documented in loggerhead, green and Kemp’s ridley turtles which suggests a more selective use of habitat than previously thought (Mansfield et al., 2014).

Sources of nutrition are a key determinant of marine turtle distribution. In other words, they go where the food is. The abundance of jellyfish in eastern Atlantic waters brings adult turtles, including loggerhead and Kemp ridley’s, but especially leatherbacks to UK and Irish coasts. As well as helping to predict the position of leatherbacks, the presence of jellyfish affects the depth at which the turtles swim. Jellyfish display a diurnal pattern of vertical migration, following their plankton prey up and down the water column. Plankton move to the water’s surface at night, when they are less visible to potential predators, and are closely followed by the jellyfish and, in turn, the turtles. Leatherbacks are so committed to pursuing their translucent prey that one intrepid individual was found swimming over 1000 metres underneath the surface during a foraging mission. This feat put leatherbacks into the top three diving animals on the planet alongside beaked whales and sperm whales. Their dedication to pursuing cnidarians was also shown by a 12,000 mile foraging journey from Indonesia to the US, which shows the determination present in their feeding habits.

It is these same feeding habits that have become a source of harm in recent times. Ingestion of marine litter, especially plastic bags, is a leading cause of turtle mortality. Particularly affected are leatherback turtles, due to their specialised diet of jellyfish which closely resemble partially degraded plastic bags hanging in the water column. One study analysed historical autopsy records spanning 123 years (1885-2007) and found plastic to be present in the digestive tracts of 34% of the dissected turtles (Mrosovsky et al., 2009). Plastic ingestion has a range of detrimental consequences, including reduced nutritional intake and asphyxiation.

There is a considerable worldwide effort to conserve marine turtle populations. One measure of this is the regularly updated IUCN Red List.  Since the 1980s, there has been a large reduction in leatherback numbers which has led to a ‘vulnerable’ classification by the IUCN. However, there are subpopulations that are doing even worse, such as those of the northwest Atlantic subpopulation who were reclassified from Least Concern to Endangered in 2019. Another case was a subpopulation based in the South China Sea that produced 10,000 yearly nests on the beaches of Malaysia. However, from the 1960s the population dwindled to the point where only two nests were laid in 2008, both of which were infertile (WWF, on-line). This decrease in numbers was partly made worse by misled conservation efforts, which collected and artificially incubated eggs at excessive temperatures, scrambling the sex determination process. As in many other reptile species, sex is determined by the temperature of incubation of the eggs. This shows the need for in depth research when developing conservation measures to deal with anthropogenic threats.

There is a wide range of barriers to the recovery of turtle numbers, with pressures both natural and anthropogenic. Among the natural threats faced by marine turtles is the impact of climate change on temperature-dependent sex determination, which disrupts reproduction and has knock-on effects on population demographics and dynamics. Another prominent challenge to successful reproduction is the predation of eggs and juveniles, which make for easy pickings for a diverse array of coastal predators.

A group of black vultures patrol a nesting beach looking for hatchlings to prey on.

Conservation efforts and scientific surveys are often based around these issues, when the turtles are onshore and accessible for data collection. Studies focused on the reproductive stage of turtle life are very valuable to the implementation of management strategies and can provide a range of insights into their life histories. The Exploration Society operating out of the University of Glasgow has run many research projects along these lines, based in the Caribbean islands of Trinidad and Tobago. These studies have contributed analyses of egg temperatures, tagging efforts to track distribution and last year uncovered a novel female behaviour for nest protection: after burying the eggs, females create a ‘decoy trail’ aimed at misleading predators over the location of the nest (Burns et al., 2020). All of these contributions are helpful to maintaining healthy populations of turtles, but there is still a large gap in the knowledge of turtle life out in the open ocean.

Leatherback hatchlings burst from a concealed nest, heading to the sea to begin their life of roaming the oceans of the world.

Marine turtles spend most of their lives navigating the oceans, across a massive geographic range and at various depths. This makes them pretty tough to track throughout their development from hatchling to mature adult, and even between nesting events. However, as we have seen, the use of satellite tracking has revealed much about adult migrations. In addition to this, the missing pieces of the puzzle can be cleared up with the help of sighting and stranding data collected from coastlines within their range, which can be acquired through citizen science projects and compiled into databases to map distributions at different stages of development. Stranded carcasses can also be inspected to gain an insight into the causes of death, and the larger scale threats to their survival. For example, carcasses with scars on their shells can show the impact of high densities of fishing vessels. The number of sightings can also be used as an indicator of population trends, as was shown by Botterell et al. (2020), summarised above. Tracking sightings and strandings off the British and Irish coasts, the study was able to attribute dips in numbers to major environmental events such as the Deepwater Horizon oil spill in 2010 and link population increases to successful conservation programmes. This shows that despite the challenges facing this fascinating group of reptiles, we can make use of the full range of analysis tools available to more fully understand their life history; from hatching through juvenile to nesting adult. From this, effective conservation strategies can be developed to protect marine turtles throughout their cosmopolitan range.

References

Bostrom, B.L. et al. (2010). Behaviour and physiology: the thermal strategy of leatherback turtles. PLoS ONE 5(11), e13925.

Botterell, Z.R.L. et al. (2020). Long-term insights into marine turtle sightings, strandings and captures around the UK and Ireland (1910-2018). Journal of the Marine Biological Association of the United Kingdom 100, 869-877.

Burns, T.J. et al. (2020). Buried treasure- marine turtles do not ‘disguise’ or ‘camouflage’ their nests but avoid them and create a decoy trail. Royal Society Open Science 7, 200327.

Fossette, S. et al. (2014). Pan-Atlantic analysis of the overlap of a highly migratory species, the leatherback turtle, with pelagic long-line fisheries. Proceedings of the Royal Society B 281, 20133065.

Mrosovsky, N. et al. (2009) Leatherback turtles: The menace of plastic. Marine Pollution Bulletin 58, 287-289.

Mansfield, K.L. et al. (2014) First satellite tracks of neonate sea turtles redefine the ‘lost years’ oceanic niche. Proceedings of the Royal Society B: Biological Sciences 281, 20133039.

WWF on-line. Search at https://www.wwf.org.my/?25625/Marine-Turtles-Malaysias-National-Heritage

Cameron Boyle, Roger Downie and Jack Rawlinson

Photos generously provided by Jack Rawlinson

University of Glasgow

The effect of the climate crisis on UK reptile populations

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Back in 2018 we discussed some of the impacts of climate change on amphibians worldwide (Froglife 2018). Since then, climate change has continued to accelerate, with global average temperatures in 2020 more than 1oC warmer relative to pre-industrial levels. The 2015 Paris Agreement has not, so far, caused nations to reduce their emissions anywhere near fast enough (Global Carbon Project 2020). The extent of future warming is projected to reach somewhere between 2 – 4oC or above, dependent upon a range of scenarios (IPCC 2014). The magnitude and speed of this change is unprecedented, and the impacts upon wildlife are already being seen.

We know that wildlife and their habitats – collectively termed the ‘biosphere’ – are in a fine, dynamic and interconnected balance. Unpicking the exact drivers of population changes is not straightforward, because they themselves are interacting in complex ways. What’s clear is that climate change is an additional stress factor for wildlife worldwide, on top of (and often accelerating) habitat loss and fragmentation, pollution and the impact of invasive species. In the UK climate change is predicted to cause hotter, drier summers and warmer, wetter winters. There will be greater extremes of weather, as well as sea level rise (Met Office 2019).

So how might the UK’s terrestrial reptiles be affected by climate change?
To begin to answer this, we can consider the direct effects of climate change on reptile physiology and behaviour, and indirect impacts from changing trophic interactions (populations of predators and prey), and from changes to reptile habitats (Le Galliard et al. 2012).

UK reptiles are more or less at the northernmost edge of the range for their species, although the adder, common lizard and slow worm have Scandinavian populations at higher latitudes. These three species are viviparous, meaning embryos develop within the body of the adult and born live. The smooth snake is ovoviviparous, which can be described as a more primitive form of viviparity, where the eggs develop within the mothers body. Sand lizards and grass snake are oviparous, meaning they lay their eggs externally, and embryos are therefore more reliant on environmental factors for their development. 

All UK reptiles however, have cousins residing in the warmer southerly climes of Iberia and Central Europe and the Balkans. So, we could assume that warmer climate here will improve survival in existing reptile populations, while enabling a northward shift of their distributions. Unfortunately, the reality is not that simple. Dunford and Berry (2012) modelled UK reptile population changes under low and high emissions scenarios for 2050 and 2080. Grass snakes appeared to be the only species consistently predicted to shift northward while maintaining the majority of their present distribution (see Cathrine, 2014 for tantalising evidence of Scottish grass snake populations), while slow worms showed a mixed northward shift with a contraction of southern populations. For all other species modelling predicted widespread population decline, greater under a higher emissions scenario (Dunford and Berry 2012).

Being ectothermic, reptiles are highly sensitive to their environment, with a tight bell curve describing their optimal climatic conditions (Le Galliard et al. 2012). Temperature and rainfall strongly influence reptile behaviour, and a changing climate has great potential to create mismatches – for example if temperature and rainfall is suboptimal either for reptiles or their prey species, especially at key points in the year such as hibernation emergence. Climate change is already affecting reptile prey populations and will continue to do so. For example Ewald et al. (2015) identified numerous invertebrate groups demonstrating sensitivity to extreme climate events over the last four decades. These trends must be considered alongside the ongoing impact of other pressures, particularly pesticide use (van Klink et al. 2020), all of which creates a complex picture. Climate impacts will vary between species groups and depend upon other biogeographical factors, meaning that impacts will not be the same everywhere for a given species.

In the UK, warming should increase reptile growth and maturation rates, due to longer periods of activity. Milder winters will likely reduce hibernation lengths for our reptiles. Earlier spring emergence, and activity extending further into the autumn and winter months would likely bring reproduction forward in the year, as gestation and incubation length is generally shorter in warmer climates. Larger body sizes in warmer climates may result in greater reproductive success (Le Galliard et al. 2012). Warm temperatures also enable a greater number of number of broods per year, observed in slow worms (Smith 1990), and common lizards (Bestion et al. 2015). However, life cycle changes may have additional impacts on population demographics and survival. Bestion et al. (2015) created experimental common lizard populations in climate-controlled chambers, with populations either subject to current average temperatures or those matching IPCC predictions for the coming century. Warming increased growth rates, brought reproduction forward, and resulted in a higher number of broods per season. However, this life cycle acceleration was coupled with a reduction in adult survival rates. Of several possible causes, the authors proposed the most likely to be greater metabolic requirements for larger individuals, with warmer temperatures increasing energetic requirements which could not be met fully by increased foraging, particularly when warm weather restricted their activity.

Our fragmented UK landscape creates major barriers for all wildlife. Reptile species are generally philopatric (tending to return to or remain near the same particular area), and so are especially sensitive to habitat loss, with populations often centred around relatively small habitat pockets or managed reserves. So even if a warmer climate could result in populations expanding northward, whether this will occur in reality depends on whether there are routes and habitats for them to do so. Araujo et al. (2006) simulated climate change driven UK reptile population dynamics under assumptions of unlimited and zero dispersal ability. Unlimited dispersal resulted in population expansion, with some local extinctions in southerly locations. Zero dispersal resulted in population contractions for all UK species, indicating climate change driven population collapse. This demonstrates the importance of considering all factors influencing population viability and dispersal in combination with climate change pressures.

Adders are usually reliant on specific habitat patches and are highly sensitive to habitat destruction and hibernation area disturbance due to their low recolonization abilities, even relative to other reptile species. On a local level, given typically small population sizes and low mobility, climate change driven habitat quality declines could result in local extinctions particularly as they may not have suitable adjacent habitat, nor the inclination to move (Gleed-Owen and Langham 2012). Although McInerny (2018) indicates that implementing appropriate mitigation can enable adder populations to persist alongside human modifications to local habitats, the adders ongoing decline nationwide is concerning (Baker et al. 2002, Gardner et al. 2019), which even a low emissions climate change scenario is likely to exacerbate (Dunford and Berry 2012).

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The dual pressures of habitat loss and climate change are even more apparent for our two most limited reptiles, the sand lizard and the smooth snake. Sand lizards can be found on lowland heath as well as coastal sand dunes. Smooth snakes are only known to be present on lowland heath in the south of England. Populations are generally isolated with little capacity for dispersal, creating a barrier to adaptation to changing conditions. Climate change could threaten habitat quality, for example increased frequency of heavy rainfall events could destroy sand lizard nests and reduce juvenile survival rates (Edgar and Bird 2006), while increased fire prevalence and sea level rise could destroy important habitat features. Dunford and Berry (2012) paint a particularly dire picture for the sand lizard, as its reliance upon highly specific landscape features such as south facing slopes and complex habitat mosaics makes the species highly sensitive to habitat loss. A small population of sand lizards has persisted on the Scottish Isle of Coll, since their introduction for research in the 1970s. Comparing the climate change resilience of this northern and relatively isolated population with that of other UK populations will be an interesting topic for study over the next few decades.

Heathland habitats are one of our most heavily impacted by urbanisation in the UK. Although direct loss through land-use change is now controlled by planning and environmental legislation, development in surrounding areas continues to increase pressure on remaining isolated heathland patches, through increased fire risk, predation by domestic animals and disturbance (Hayhow et al. 2019). Fagundez (2013) describes further pressures facing heathlands under climate change, including fires, and shifts in vegetation composition. We are used to a static conservation model for our heaths. As climate change progresses, the ideal climatic conditions for heath will likely expand in Britain (Thomas et al. 1999), and Loidi et al. (2010) point out that extensive lowland heaths throughout southern Europe support a greater diversity of reptiles than we see here. However, whether habitats will be able to expand is an entirely human choice (Coll et al. 2016, Hayhow et al. 2019).

All of the pressures we have presented here are anthropogenic in origin, born from human choices, and our expectations of how we can and should manage the land and its resources. The enormity of shifting these practices cannot be underestimated, but at least it is within our abilities to do it!

Written by Zak Mather-Gratton 

References
Araújo, M.B., Thuiller, W. and Pearson, R.G., 2006. Climate warming and the decline of amphibians and reptiles in Europe. Journal of biogeography, 33(10), pp.1712-1728.

Baker, J., Suckling, J. and Carey, R., 2002. Status of the adder Vipera berus and the slow-worm Anguis fragilis in England. English Nature.

Bestion, E., Teyssier, A., Richard, M., Clobert, J. and Cote, J., 2015. Live fast, die young: experimental evidence of population extinction risk due to climate change. PLoS Biol, 13(10), p.e1002281.

Cathrine, C., 2014. Grass Snakes (Natrix natrix) in Scotland. Glasgow Naturalist, 26(Part 1), pp.36-40.

Coll, J., Bourke, D., Hodd, R.L., Skeffington, M.S., Gormally, M. and Sweeney, J., 2016. Projected climate change impacts on upland heaths in Ireland. Climate Research, 69(2), pp.177-191.

Dunford, R.W. and Berry, P.M., 2012. Climate change modelling of English amphibians and reptiles: Report to Amphibian and Reptile Conservation Trust (ARC-Trust).

Edgar, P. and Bird, D.R., 2006. Action plan for the conservation of the Sand Lizard (Lacerta agilis) in Northwest Europe. Document T-PVS/Inf (2006), 18.

Ewald, J.A., Wheatley, C.J., Aebischer, N.J., Moreby, S.J., Duffield, S.J., Crick, H.Q. and Morecroft, M.B., 2015. Influences of extreme weather, climate and pesticide use on invertebrates in cereal fields over 42 years. Global Change Biology, 21(11), pp.3931-3950.

Fagúndez, J., 2013. Heathlands confronting global change: drivers of biodiversity loss from past to future scenarios. Annals of Botany, 111(2), pp.151-172.

Froglife 2018. Amphibians and Climate Change. Croaking Science
Gardner, E., Julian, A., Monk, C. and Baker, J., 2019. Make the adder count: population trends from a citizen science survey of UK adders. Herpetological Journal, 29, pp.57-70.

Gleed-Owen, C. and Langham, S., 2012. The Adder Status Project–a conservation condition assessment of the adder (Vipera berus) in England, with recommendations for future monitoring and conservation policy.

Report to Amphibian and Reptile Conservation. ARC, Bournemouth, UK.
Global Carbon Project. 2020. Carbon budget and trends 2020. [www.globalcarbonproject.org/carbonbudget] published on 11 December 2020

Hayhow, D.B., Eaton, M.A., Stanbury, A.J., Burns, F., Kirby, W.B., Bailey, N., Beckmann, B., Bedford, J., Boersch-Supan, P.H., Coomber, F. and Dennis, E.B., 2019. State of nature 2019.

IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

van Klink, R., Bowler, D.E., Gongalsky, K.B., Swengel, A.B., Gentile, A. and Chase, J.M., 2020. Meta-analysis reveals declines in terrestrial but increases in freshwater insect abundances. Science, 368(6489), pp.417-420.

Le Galliard, J.F., Massot, M., Baron, J.P. and Clobert, J., 2012. Ecological effects of climate change on European reptiles. Wildlife conservation in a changing climate, pp.179-203.

Loidi, J., Biurrun, I., Campos, J.A., García‐Mijangos, I. and Herrera, M., 2010. A biogeographical analysis of the European Atlantic lowland heathlands. Journal of Vegetation Science, 21(5), pp.832-842.

McInerny, C.J., 2019. The study and conservation of adders in Scotland. The Glasgow Naturalist Volume 27, p.67.

Met Office, 2019. UK climate projections: Headline findings.
Smith, N.D., 1990. The ecology of the slow-worm (Anguis fragilis L.) in southern England. Doctoral dissertation, University of Southampton.

Thomas, J.A., Rose, R.J., Clarke, R.T., Thomas, C.D. and Webb, N.R., 1999. Intraspecific variation in habitat availability among ectothermic animals near their climatic limits and their centres of range. Functional Ecology, 13, pp.55-64.

Does the reintroduction of beavers help amphibian (and reptile) populations?

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After centuries of exploitation for their fur, flesh and secretions, Eurasian beavers (Castor fiber) were extinct over much of their range, with only a few relic populations totaling about 1200 individuals by the start of the 20th Century. In Britain, they were extinct by the 16th Century. On mainland Europe, recognition of the ecosystem services beavers provide led to many countries adopting reintroduction programmes: for example, from 1922 in Sweden; 1966 in Bavaria; 1988 in Romania. Thompson et al. (2021) have evaluated the costs (to landowners) and very substantial ecosystem services provided by beaver presence, mainly in habitat and biodiversity enhancement, and in greenhouse gas sequestration. Through protection measures and reintroduction efforts, beavers have now recovered across most of their former range, with recent population estimates of 1.5 million individuals (Halley et al., 2021). Initially, Britain was resistant to beaver reintroduction, mainly because of the concerns of major landowners and forestry interests; however, more recently several high-profile projects have come into being.

In Scotland, serious discussion of the issue began in the 1990s, and the national conservation agency Scottish Natural Heritage (SNH, now NatureScot) suggested a trial reintroduction in 2000. The Government rejected this proposal, but a change of Government and more discussion led to a new proposal, which got the go ahead in 2008. The plan was for a trial reintroduction at a well-contained site in Knapdale Forest, Argyll, to be managed by the Scottish Wildlife Trust in collaboration with the Royal Scottish Zoological Society, and to be monitored independently by researchers commissioned by SNH. The Scottish Beaver Trial began in 2009, when 17 wild beavers from Telemark, Norway, were quarantined for six months in Devon, then released in May 2009 at three freshwater lochs in Knapdale. The trial continued until 2014 (Jones and Campbell-Palmer, 2014). SNH chose the monitoring topics: these included beaver ecology, otters, fish, woodland habitat and dragonflies, but NOT amphibians or reptiles (nor did they agree to permit independent study of the effects on herpetofauna). However, another population existed, formed from accidental escapes or releases in Tayside and these animals were unprotected from landowners who objected to their presence. The Tayside population generated more conflict with some landowners, especially in prime agricultural land where the damming of drainage ditches can lead to impacts on arable farming. After consideration of the data generated through the Scottish Beaver Trial, general public support and consultation with various interest groups and land management sectors, the Scottish Government agreed in November 2016 that the beavers could remain in Scotland. Going on further in May 2019 the Government granted legal protection for all beavers living in the wild (although landowners may still apply for a licence to have animals removed if they can show they are causing damage that cannot be mitigated via alternative means).

In England, the Devon Wildlife Trust received a Government licence in 2014 for a five-year study of the beaver population (origins unclear) already living in the catchment of the River Otter. The study report (Brazier et al., 2020) resulted in DEFRA’s agreeing that the population, now 15 family groups, can stay. As with the Scottish trial, herpetofauna were not a focus of the study. Nevertheless, the study concluded that the ‘effect of beaver engineering and feeding has delivered significant ecological benefits with new areas of wetland habitat created and managed, with documented benefits for amphibians, wildfowl and water-voles’. Although no regular monitoring of amphibians was carried out, in an area where beavers had constructed 13 dams along a 180 metre stretch of stream, counts of common frogspawn had increased from 10 in 2011 to 681 in 2017.

Although we lack studies on the impacts of beaver activities on amphibians in Britain, Dalbeck et al. (2020) have recently reviewed ten papers based on work in six central and eastern European countries (Switzerland, Germany, Lithuania, Denmark, Russia and Poland); they could find no reports so far from southern, western or northern Europe. They focussed on beaver impacts on streams and rivers, rather than on lakes. As is well known, beavers create dams using the logs and branches they cut down, producing ponds with low flow rates. Their tree-felling activities have several effects on local habitats: opening gaps in the forest canopy allows more light to reach the forest floor and water surface, raising temperatures and promoting primary productivity; a great quantity of rotting wood is produced and this promotes invertebrate diversity and habitat complexity. All these effects are potentially beneficial to amphibians. However, river ponds are good habitats for many species of fish, generally not considered helpful to amphibians because they consume eggs and prey on larvae. Indeed, in the UK, we do not regard streams as good amphibian habitat in general, unlike the situation in North America, where many species, especially urodeles, are primarily stream dwellers.

Central Europe supports 19 species of amphibian (six urodeles and 13 anurans). Dalbeck et al. (2020) categorised these into four groups, according to their habitat preferences: forest (6 spp.), open country (5), ubiquitous (4) and pioneers (3). All 19 species were reported from beaver ponds at least occasionally, but only forest and ubiquitous species were found frequently in such ponds. Two pioneer species (green and natterjack toads) and great crested newts were rarely found in beaver ponds. From the UK viewpoint, it is interesting that our two species of greatest conservation concern, great crested newts and natterjack toads, may not benefit significantly from beaver reintroductions. None of the reviewed studies included before and after data, but one of the German reports did compare the amphibian fauna of beaver ponds (mean 4.1 species +/-1.4 SD) with that of nearby beaver-free floodplain ponds (1.2+/-1.3) indicating a significant enhancement in the beaver ponds. Some of the studies compared the fauna of beaver ponds in headwater, small sized streams with those in wider rivers. Species richness was highest in small stream ponds, with a maximum of eight species found in a single German pond.

Sadly, the UK has a much less rich amphibian fauna than central Europe. Nevertheless, the reviewed results indicate that the habitat engineering work performed by beavers should have a positive impact on some of our species. It is, therefore, time that some relevant studies be carried out in Scotland and Devon. With beavers now having been active in Britain for some years, it should be possible to design studies that compare beaver-affected areas to similar areas that are beaver- free.

What about reptiles? The habitat changes wrought by beavers ought to be beneficial for them too, especially the creation of sunlit gaps in the forest, where animals can bask, and the habitat complexity generated producing refuges and hibernacula, and promoting invertebrate diversity. Dalbeck et al. (2020) do not report on impacts on reptiles, nor are they considered in the two British project reports. In the USA, there have been a few reports (e.g. Metts et al., 2001; Russell et al., 1999) on the impacts of beavers on reptiles (and amphibians), but they are not directly applicable to Europe since they concern a different species of beaver (C. canadensis) and a very different reptile fauna. Nevertheless, Metts et al. concluded that ‘disturbances resulting from beaver-created wetlands increase regional abundance and diversity of herpetofauna’. Another topic for research as beavers come back to Britain?

References

Brazier, R.E. et al. (2020). River Otter Beavers Trial: science and evidence report. University of Exeter, Devon Wildlife Trust and others. Available online.

Dalbeck, L., Hachtel, M. and Campbell-Palmer, R. (2020). A review of the influence of beaver Castor fiber on amphibian assemblages in the floodplains of European temperate streams and rivers. Herpetological Journal 30, 135-146.

Halley, D. J., Saveljev, A. P. and Rosell, F. (2021). Population and distribution of beavers Castor fiber and Castor canadensis in Eurasia. Mammal Review 51, ISSN 0305-1838

Jones, S. and Campbell-Palmer, R. (2014). The Scottish Beaver Trial: the story of Britain’s first licensed release into the wild. Final Report. Scottish Wildlife trust and the Royal Zoological Society of Scotland. Available online.

Metts, B.S. (2001). Evaluation of herpetofaunal communities on upland streams and beaver-impounded streams in the upper piedmont of South Ca

Russell, K.R. et al. (1999). Amphibian and reptile communities associated with beavers (Castor canadensis) ponds and unimpounded streams in the piedmont of South Carolina. Journal of Freshwater Ecology 14, 149-158.

Thompson, S. et al. (2021). Ecosystem services provided by beavers Castor spp. Mammal Review 51 (published on-line).

 Roger Downie, University of Glasgow and Froglife Trustee

Roisin Campbell-Palmer, Independent Beaver Ecologist, Associate of University of Exeter

Croaking Science: Venomous Amphibians

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Venomous animals are able to inject their toxins into another organism while poisons are ingested, inhaled and absorbed. The ability to deliver venom into another animal has distinct evolutionary advantages such as in defence, prey capture and even sexual selection.

Amphibians secrete a wide variety of compounds from their skin glands. Generally, mucous glands help provide a moist coating on their skin to facilitate cutaneous respiration while granular glands secrete substances that amphibians use as a chemical defence against predators (eg. toxic and noxious compounds) and microorganisms (eg. antimicrobial peptides). This is sometimes displayed with bright, aposematic colouration (Duellman and Trueb 1996). 

Many different toxic secretions have been found in amphibian skin which act in numerous ways to disrupt the physiology of potential enemies (Daly et al. 2005, Savitzky et al. 2012).  For example, newts in the genera Taricha and Notophthalmus synthesise tetrodotoxins in high concentrations and are co-evolving in an evolutionary arms race with Thamnophis garter snakes where toxicity is a selective pressure (Brodie et al. 2005, Mailho-Fontana et al. 2019, Hague et al. 2020).  Fire salamanders secrete samandarin alkaloids through their paratoid glands which can cause convulsions, hypertension and respiratory paralysis in potential predators.  Frogs can sequester an array of toxins such as the potent neurotoxin Zetekitoxin in the Panamanian golden frog and the batrachotoxins in highly toxic Phyllobates poison frogs (Duellman and Trueb 1996).  The bright yellow Australian corroboree frogs of the genus Pseudophryne synthesise their own pseudophrynamine toxins as well as sequestering pumiliotoxins from their environment to deter predators (Smith et al. 2002). Fossorial caecilians are also known to produce defensive toxins with poison glands being discovered on the tails of Siphonops annulatus ringed caecilians as a possible defence against predators as they burrow into the soil (Jared et al. 2019). 

Venom, however, is rare in amphibians with only a few species possessing a system to deliver their toxins into another organism. 

The Iberian ribbed newt (Pleurodeles waltii) is a fascinating salamandrid from Spain and Portugal with an incredible defence behaviour. They have the ability to use their ribs to protrude through the skin to envenomate and ‘sting’ a predator. When distressed these newts can flatten themselves or arch their backs in an antipredator posture. They will then rotate their ribs 65° forwards which increases the angle of the spine to allow its ribs to penetrate through the skin wall and project as ‘spines’. This allows them to coat their ribs with a viscous, milky substance from their skin tubercles and inject it into the mouth of the predator making them unpalatable and allowing them to escape (Heiss et al. 2010). This defence mechanism doesn’t cause any permanent damage as antimicrobial peptides are able to prevent infection in the lacerated skin and their tissue is able to regenerate remarkably quickly. The tip of the ribs are also covered with a periosteum layer which is also thought to prevent microbial infection when the ribs puncture the skin.

The Echinotriton genus of crocodile newts are a sister group to the sharp ribbed newt and are also able to use their ribs to pierce their body wall when attacked by predators (Brodie et al. 1984).  

Sharp ribbed newt (Pleurodeles walti)

Brazil is home to two tree frogs which have incredible cranial morphologies and venomous defensive mechanisms. The Greening’s frog Corythomantis greeningi live in the semi-arid caatinga ecosystem of Eastern Brazil and conceal themselves in tree hollows and rock crevices to stay moist and evade predators. Bruno’s casque headed frog Aparasphenodon brunoi is another endemic Brazilian hylid with a fascinating skull morphology. They inhabit lowland tropical forests and shrubland and like C. greeningi, will hide in water-filled tree or bamboo hollows and bromeliad phytotelmata. 

Both of these peculiar frogs have flattened, casqued heads with their skin co-ossified with underlying bones. They use their heads to aid in a behaviour known as phragmosis (Jared et al. 2006, Blotto et al. 2020).  Phragmosis occurs when an animal enters a hole and blocks the entrance with their head to defend themselves from predators. In the lab, these frogs will exhibit this behaviour by entering test tubes backwards and blocking themselves off with their casqued heads. This phragmotic behaviour along with their venomous spines means these frogs have never been observed being predated in the wild. It is also thought that cranial ossification and phragmosis also indirectly reduces water loss and prevents desiccation by creating a humid microclimate within their tree holes (Jared et al. 2006). 

These frogs have bony spines, ridges and protrusions on their skulls in areas with high concentrations of granular and mucous glands which secrete a potent venom. Their mobile heads allow the frogs to deliver the venom into animals via head-butting and jabbing with their spines which are coated with the toxic secretions as the spines pierce their venom glands. This provides a highly effective chemical defensive mechanism as the toxin coupled with the wound caused by the head spines ensures would-be predators have a bad time when they attempt to ingest these frogs (Jared et al. 2015). Their cutaneous secretions include alkaloids and steroids which can induce oedema and intense pain in predators (Mendes et al. 2016). The venom contains both proteolytic and fibrinolytic agents as well as hyaluronidase which aids the toxins in diffusing around their enemies’ bodies (Jared et al. 2015). 

The venom of Greening’s frog is thought to be twice as lethal as fer-de-lance snakes of the genus Bothrops while Bruno’s casque headed frog secretes a venom 25x as toxic as these notorious neotropical vipers with an LD50 of 94.8µg in mice. A single gram of A. brunoi venom could kill 300,000 mice or 80 humans (Jared et al. 2015)!  However, A. brunoi has smaller spines and granular glands than C. greening and so may not be able to inject as much venom when defending against a predator. 
Top: Bruno’s casque headed frog (Aparasphenodon brunoi) L: Renato Augusto Martins R: Carlos Jared 
Bottom: Greening’s frogs (Corythomantis greeningi) Carlos Jared 

 

There are many other frogs with complex cranial morphology including immense variation in skull shape and hyperossification which often relate to their interesting and diverse ecologies (Paluh et al. 2020). With an array of other anurans having mineralised and spiny skulls, it is possible that there are a few more venomous frogs which are waiting to be studied. Contenders include the fascinating shovelhead tree frog Triprion, the crowned tree frog Anotheca spinosa and Polypedates ranwellai (Jared et al. 2015). 

In a recent paper by Mailho-Fontana et al. 2020, a new set of specialised dental glands were discovered in Brazilian ringed caecilians (Siphonops annulatus) that may produce venomous enzymes – but further research is needed to confirm this. These enzymes were demonstrated to have gelatinolytic, caseinolytic and fibrinogenolytic properties. This incredible discovery may allow researchers to rethink the evolution of venom in vertebrates (since it could have evolved independently in both amphibians and reptiles) and inspire new studies about caecilian toxinology.

Through histological and biochemical analysis of saliva samples, researchers found A2 phospholipase enzymes which could mean that some fossorial caecilians inject venomous saliva via these dental glands into their earthworm prey in order to incapacitate and digest them. These enzymes are found in many other venomous creatures such as scorpions, snakes and insects. It is also worth noting that many venoms have originated as saliva such as in komodo dragons, shrews, bats and slow lorises making the prospect of venomous gymnophiones very exciting!

Other caecilians including the basal genus Rhinatrema showed similar dental glands to the ringed caecilians which could suggest that caecilians evolved to inject oral venom early on in their evolution (Jared et al. 2020). 

Written by Xavier Mahele

References

Blotto, B.L., Lyra, M.L., Cardoso, M.C., Trefaut Rodrigues, M., R. Dias, I., Marciano‐Jr, E., Dal Vechio, F., Orrico, V.G., Brandão, R.A., Lopes de Assis, C., Lantyer‐Silva, A.S., Rutherford, M.G., Gagliardi‐Urrutia, G., Solé, M., Baldo, D., Nunes, I., Cajade, R., Torres, A., Grant, T., Jungfer, K.‐H., da Silva, H.R., Haddad, C.F. and Faivovich, J. (2020) The phylogeny of the Casque‐headed Treefrogs (Hylidae: Hylinae: Lophyohylini). Cladistics

Brodie, E.D., Feldman, C.R., Hanifin, C.T. et al. (2005) Parallel Arms Races between Garter Snakes and Newts Involving Tetrodotoxin as the Phenotypic Interface of Coevolution. Journal of Chemical Ecology 31, 343–356.

Brodie, E., Nussbaum, R., & Marianne DiGiovanni. (1984) Antipredator Adaptations of Asian Salamanders (Salamandridae). Herpetologica, 40(1), 56-68.

Daly, J. W., Spande, T. F. & Garraffo, H. M. (2005) Alkaloids from Amphibian Skin:  A Tabulation of Over Eight-Hundred Compounds. Journal of Natural Products 68, 1556–1575 

Duellman, W. E. & Trueb, L. (1996) Biology of Amphibians. McGraw-Hill.

Hague, M.T.J., Stokes, A.N., Feldman, C.R., Brodie, E.D., Jr. and Brodie, E.D., III. (2020) The geographic mosaic of arms race coevolution is closely matched to prey population structure. Evolution Letters 4: 317-332.

Heiss, E., Natchev, N., Salaberger, D., Gumpenberger, M., Rabanser, A. and Weisgram, J. (2010), Hurt yourself to hurt your enemy: new insights on the function of the bizarre antipredator mechanism in the salamandrid Pleurodeles waltl. Journal of Zoology 280: 156-162.

Jared, C., Antoniazzi, M.M., Navas, C.A., Katchburian, E., Freymüller, E., Tambourgi, D.V. and Rodrigues, M.T. (2005) Head co‐ossification, phragmosis and defence in the casque‐headed tree frog Corythomantis greeningi. Journal of Zoology 265: 1-8.

Jared C, Mailho-Fontana PL, Antoniazzi MM, Mendes VA, Barbaro KC, Rodrigues MT, Brodie ED (2015) Venomous Frogs Use Heads as Weapons. Current Biology Volume 25, Issue 16,

Jared, C., Mailho-Fontana, P.L., Marques-Porto, R. et al. (2018) Skin gland concentrations adapted to different evolutionary pressures in the head and posterior regions of the caecilian Siphonops annulatus. Scientific Reports 8, 3576.

Mailho-Fontana, P.L., Jared, C., Antoniazzi, M.M. et al. (2019) Variations in tetrodotoxin levels in populations of Taricha granulosa are expressed in the morphology of their cutaneous glands. Scientific Reports 9, 18490.

Mailho-Fontana, P. L. et al. (2020) Morphological Evidence for an Oral Venom System in Caecilian Amphibians. iScience 23, 101234.

Mendes VA, Barbaro KC, Sciani JM, Vassão RC, Pimenta DC, Jared C, Antoniazzi MM. (2016) The cutaneous secretion of the casque-headed tree frog Corythomantis greeningi: Biochemical characterization and some biological effects. Toxicon Volume 122.

Paluh D, Stanley EL, Blackburn DC. (2020) Evolution of hyperossification expands skull diversity in frogs. Proceedings of the National Academy of Sciences 117 (15) 8554-8562.

Savitzky, A.H., Mori, A., Hutchinson, D.A. et al. (2012) Sequestered defensive toxins in tetrapod vertebrates: principles, patterns, and prospects for future studies. Chemoecology 22, 141–158.

Smith, B. P. et al. (2002) Evidence for Biosynthesis of Pseudophrynamine Alkaloids by an Australian Myobatrachid Frog (Pseudophryne) and for Sequestration of Dietary Pumiliotoxins. Journal of Natural Products 65, 439–447.l

 

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

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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.