Froglife

Leaping forward for reptiles and amphibians

You are here: Home / Archives for invasive species

invasive species

Recent papers: Red eared terrapins and alpine newts in Scotland and their possible impact on common frog tadpoles

by

Written by Dr Andrew Smart, Conservation & Science Manager

A paper presented by Chris Catherine at the 2023 Glasgow Natural History Society Scottish Herpetological Conference has recently been published online in the Glasgow Naturalist. The paper outlines information about Scottish invasive species from a range of data sources. Catherine highlights the confusion around the status of the barred grass snake (Natrix helvetica) in Scotland with records from Dumfries and Galloway possibly of native animals or from a feral population. Catherine found 101 records of four different non-native species: alpine newt, sand lizard, Chinese pond turtle and common slider. The only record of sand lizards in Scotland is a single record form1970 on the island of Coll as part of a benign introduction programme in the 1970s, to help protect the species in the UK.  Similarly, Chinese pond turtle has only been recorded once, at Glasgow botanic gardens in 2022.

The alpine newt is a concern because of its ability to act as a vector for Batrachochytrium fungi the cause of chytridiomycosis or chytrid fungus in our native amphibians. In Scotland there appear to be four distinct populations. 

Common slider, the red-eared terrapin, is the most widely distributed invasive herpetofauna species in Scotland with records from 42 10km grid squares and 10 distinct populations. Globally, where the species reproduces it can cause significant impacts and is listed by the IUNC as one of the 100 most invasive species.  There is no breeding recorded in Scotland but  these animals can live for 20-40 years

Common slider/ red-eared terrapin, is the most widely distributed invasive herpetofauna species in Scotland

A second recent paper by Vodrazkova et al, working in the Czech republic undertook a lab based study on the impact of red eared sliders on frog tadpoles. Following up on previous research, Vodrazkova et al examined the speed of metamorphosis, size of froglets and the level of stress hormone in frog tadpole in a lab environment with or without the presence of  a red eared terrapin in the water (isolated form tadpoles but present in the tank).

The result showed that long-term and short-term presence of the terrapin in the same water increased the stress levels within the tadpoles, with hormone levels indicating the presence of chronic stress when the terrapin was present.  The tadpoles in the three treatments showed no significant difference in time taken to metamorphose but the size of the froglets in the three treatments varied, with smaller animals at metamorphosis in the treatments in the presence of the terrapin.  This indicates a developmental strategy to metamorphose at the smallest possible size to avoid the risk of predation in the waterbody.

At the moment red eared terrapins are not breeding in the UK but with a significant range, there is a risk that temperature increase due to global warming could lead to a new more widespread threat to our native species in the future.

Invasive Species Week: 20th-26th May 2024

by

Many people are unaware that alongside climate change and habitat loss, another major threat to species biodiversity is the increase in the number of non-native, invasive species appearing around the world. 

Non-native species often appear through accidental transport or by the release of pets, but they rarely survive or come into contact with con-specifics to establish a colony. If they do come into contact with others of the same species and reproduce, the outcome tends to be a small localised colony, held in place by geographical, environmental, predatory or climate barriers. 

In some cases a non-native species may not have those checks or controls in place and takes the opportunity to exploit a new niche or out-compete an existing species resulting in an invasive species becoming established and often taken for granted as a national species such as the grey squirrel, Canada goose, marsh frog or the three-cornered leek.

There are currently believed to be over 3000 non-native species living in the UK; and this graph from the JNCC shows the recent rapid increase in invasive non-native species.

A species is considered ‘invasive’ if it has the ability to spread and damage the environment, the economy, our health or the way we live. Invasives can have a significant impact as predators, competitors (for food or breeding sites) or can carry disease that impacts our native species. In 2023 the Government published a new UK invasive species strategy. Part of the strategy includes ‘horizon scanning’- the ability to look at potential ‘invasives’ that could be a problem were they to reach the UK, or that are already present and could become a problem as a result of climate change or other environmental changes.

Some species are significant risks and are considered to be GB ‘alert’ species with a request to record and notify whenever sighted; the Asian hornet, a predator of native bee colonies is one such species along with the American bullfrog. 

The Non-Native Species Information Portal (NNSIP) provides access to distribution data as well as additional information such as place or origin, date of introduction and methods of introduction. It also provides much more detailed information on 300 species, including information on identification, impacts and control methods. 

During Invasive Species Week we want to raise awareness of invasive species of reptiles and amphibians and see if we can increase our information by gathering records of non-native as well as native species using our Dragon Finder App. You can download the app for free here.

All data from the Dragon Finder App is shared with the National Biodiversity Network Atlas. 

Ban foreign soil imports to help save British wildlife – warn nature experts

by

Nature experts, from organisations including Buglife and The Wildlife Trusts are calling on the Government to phase-out imports of soils from other countries, to help prevent ‘nature invaders’ from entering the country. This is vital to stop damaging invasive non-native species from hitching a hidden ride in the plants, soils and compost bought in garden centres across the country . 

 

Soil, compost, and potted plants can host a variety of insects and microorganisms (bacteria, fungi, and viruses), and seeds from unwanted foreign plants, which can all outcompete native species. Both garden and freshwater pond plants represent a risk of introducing nature invader stowaways.

 

356,000 tonnes of plants and soils were imported into the UK during 2021 with a value of nearly £1.2bn. Of this, 287,000 tonnes were imported from EU countries, with much of the soil coming into the UK within potted plants. Since Brexit the EU does not allow imports of UK soil, either directly or in potted plant containers, with prevention of wildlife contamination a key reason for this policy. The UK, as one of the worst 10% of countries in the world for nature loss, should similarly be taking a preventative approach on soil imports, as invasive species are one of the top five drivers of nature decline.

 

Richard Benwell, CEO of Wildlife and Countryside Link, said: “Invasive species are a growing threat to wildlife in the UK. It only takes one or two eggs or a few spores hidden in imported soils to introduce organisms that can play havoc on our ecosystems. Once they have a foothold, it’s hard to stop damage spreading, but prevention is possible and so much more affordable. 

 

“Phasing out imports of soils would help prevent further disasters like ash dieback. As part of a robust strategy to hold back and root out invasive species, this is an essential part of any plan to halt the decline of nature.” 


Joan Edwards, Director of Policy & Public Affairs at The Wildlife Trusts, said:“Both the UK economy and the natural world are paying a steep price for the impact of invasive species. Nature soil invaders are already hitting British wildlife hard, out-competing and eating species from our beautiful but rare lilies and fritillaries, through to gardeners’ friends like ladybirds and earthworms. The economic cost of invasive species is more than £2 billion a year, impacting shipping, rivers, recreation, timber and even the gin industry. Closing a major route to entry to the UK, by banning soil imports, makes good economic sense and is vital for nature’s recovery.”

 

Alisha Anstee, Lead Policy Advocate – Tree Health and Invasive Species at Woodland Trust, said: “The introduction of invasive species including certain tree diseases is one of the most serious threats to trees and other wildlife in the UK. The UK is suffering the impacts of many imported invasive species, some of which can travel undetected in the soil. It is likely that Phytophthora Ramorum, which is causing larch dieback,  arrived via the plant trade and this disease is now leading to mass tree loss. Prevention is much easier and cheaper than attempting to find a cure when it comes to dealing with these invasive threats.”

 

David Smith, Advocacy and Social Change Officer at Buglife, said: “Many species that travel in soils are small, hard to detect and easily transported once on our shores. Invasive species are spreading from our gardens into wild places, impacting native species. We are quite capable of growing our own plants in the UK, effective action should be taken to boost home-grown plant production and reduce our reliance on imports. The Government must stop soil imports and only import bare-rooted plants until there is a proven way to ensure soils are free from pests and diseases.”

 

While not the only method of arrival, the import of soil and growing media is a significant route for invasive non-native species to enter the UK. A phase-out would reduce the risk of horticultural hitchhiker species entering and establishing in the UK. Current approaches focus on detection, reporting and awareness raising once a species has arrived in the UK. Yet prevention is better than cure ; preventing a species from introducing and establishing in the first place is more cost-efficient than attempting to manage or eradicate it once arrived. It is also more effective at mitigating the economic and environmental damage caused. Members of the public can also take action by buying only locally grown or bare rooted plants.

 

Current species: Experts have highlighted the destruction of British wildlife already being caused by species including the New Zealand Flatworm, Spanish Slug, Harlequin Ladybird, Red Lily Beetle and pathogens including Ash dieback, Phytophthora austrocedri and Phytophthora ramorum. These are all likely to have arrived in the UK hidden in soil, flower and tree imports.[6]  

 

The New Zealand flatworm probably arrived in the UK in the 1960s via imported soils, compost and plants. It eats native earthworms, reducing populations by up to 20%. The loss of earthworms then negatively impacts soil health, agricultural productivity, and native wildlife such as bird species, with an economic costs of tens of millions of pounds a year. Following its arrival in 2010 the Spanish Slug is now present across the country. It’s a voracious eater of crops, wild and garden plants, and numbers are difficult to control as it’s too slimy for hedgehogs and birds to eat and resistant to poisons. 

 

The Harlequin Ladybird arrived in the UK in 2004, with fruit and plant imports from the EU one of the likely routes of their introduction. It has had a devastating impact on native ladybirds, reducing numbers by around two-thirds over a ten-year period. The Red Lily beetle arrived in the UK in the 1940s probably as a hitchhiker on imported lilies, this beetle is highly destructive to both lilies and fritillaries, many species of which are in decline in the UK.

 

Ash dieback, is a fungus that was first recorded in the UK in 2012 and is likely to have been introduced via sapling imports. Its well-known impacts have seen Ash trees across the country wiped-out, with extensive felling of diseased trees necessary for public safety. It’s estimated Ash dieback will eradicate up to 95% of UK Ash trees at an economic cost of around £15 billion.  Another fungus-like pathogen Phytophthora austrocedri, which spreads through soil and water, was also likely introduced through imports. First detected in the UK in 2011 it is now present in all regions where Junipers are found. It aggressively impacts conifers, with particularly notable impacts on Junipers, affecting the Scottish gin industry. Similarly, Phytophthora ramorum arrived in 2002, likely via plant imports, and is causing mass tree death, creating huge dieback of larch trees in particular.

 

As well as the significant economic and environmental damage being caused by already established invasive species, the groups are also sounding the alarm about the further potential damage from species that could arrive if action on soil imports is not taken soon. 

 

New risk species include the Japanese Beetle, the larvae of which live in soil and could easily be accidently moved with rooted plants. These beetles have caused major damage in parts of North America – to plants including apple, birch, lime and rose. Threats to UK species would include maples, birch, apples and other stone fruits. Current summer temperatures are thought to be too low for the beetles but increasingly hot summers due to climate change could see this change. 

 

Similar to Oak Processionary Moths (which came to the UK in imported trees), Pine Processionary Moths risk spreading hidden in the soil of potted plants when they are pupae. Pupae may be present in the soil all year round as this stage can remain dormant and extend to two or three years, sometimes even longer. Worryingly, inspection is unlikely to detect pupae in the soil. They have the potential to reduce productivity of trees due to defoliation of the needles. It also weakens the tree which means it is more susceptible to other pests and diseases. Importantly these caterpillars also pose a significant threat to human health; they have toxic hairs, which can cause itching skin rashes, eye and throat irritation and breathing problems.

The Argentine Ant has been transported outside of South America through means including soil and plants. These ants have been spotted in London and Birmingham but are not thought to be established. However, a study in 2014 warned that the species could spread across regions of Britain by 2024. Studies in other countries where the species has established have shown they can displace native ants, leading to disruption of pollination and soil health.

 

New Guinea Flatworms are already found in France and are one of the “100 worst invasive alien species” in the world. It has destroyed populations of native snails across the Indo-Pacific and has the potential to similarly harm UK snail and earthworm populations. As with other flatworms the New Guinea Flatworm is likely to be distributed via the movement of plants and growing media in the horticultural trade. With no recorded natural enemies or biological or pesticide controls for non-native flatworms, the key control measure is to prevent their introduction.

 

The Government has taken some limited action on tree imports, with trees used in Government tree-planting schemes required to meet biosecurity requirements, requiring accreditation or assessments. However, this only applies to trees in Government schemes, not wider tree imports, and does not address the issue of invasive hitchhikers in imported soil and potted-plants. Coinciding with Invasive Species Week 2023 experts are calling for tougher measures to protect native wildlife, by:

  • Phasing out all soil imports – banning soil, peat and compost from other countries, including in potted plant imports, with plants to be transported soil free
  • Extending Government tree-planting scheme biosecurity requirements to all trees and potted plants entering the country
  • Requiring imported timber to undergo protective measures such as heat treatment to eradicate harmful hidden hitch-hiker species
  • Supporting the expansion of UK tree and plant growing for domestic sale, to reduce reliance on horticultural imports

Croaking Science-The Cane Toad: a cautionary tale

by

Roger Downie, University of Glasgow and Froglife

I first encountered cane toads in Trinidad (Rhinella marina, previously Bufo marinus, known locally as crapaud, the French for toad) during my initial visit there aimed at studying the variety of tropical amphibians and their life histories. The visit began in the dry season and cane toads were one of the few species around at that time of year. These large toads (a record-breaker has recently weighed in at 2.7kg in Australia) could often be found sitting in dog food dishes in back yards after consuming the food, with the hungry dog warily watching nearby, having learned that attacking these toads is not a good plan: they are well protected by the toxins in their massive parotoid glands. I also saw cane toad tadpoles – small, jet black, highly numerous and often in shoals – in slow-moving drainage ditches and low dry season rivers: the toads can breed at any time of year, their prolonged rumbling calls audible over a considerable distance. Linnaeus conferred the specific marinus on the basis of the Dutch naturalist Albertus Seba claiming they could live on land or in the sea. This was a partial error: they do not enter the sea, but can inhabit sandy beaches, feeding on the abundant invertebrates present there, and can spawn successfully in rivers close to the sea, where salinity levels may be significantly higher than in normal freshwater.

Record-breaking cane toad- Pic: Queensland Department of Environment and Science/AP

Cane toads are native to the Americas, ranging from southern Texas through central America and down into Peru and Amazonia; the islands of Trinidad and Tobago, adjacent to Venezuela, are considered part of their native range. However, the reason that cane toads are one of the most studied amphibian species is a consequence of their deliberate introduction to other parts of the world. Books and hundreds of scientific papers have been written about this species, and it must be the only anuran to feature in two full length documentary films (Cane toads: an unnatural history, 1988; Cane toads: the conquest, 2010). The toads tend to be found in open grassland areas, rather than forest, and the reason for their introductions elsewhere relates to their usual common name, cane toad: they are considered to predate the pests of sugar cane plantations. During the early 19th century, cane toads were introduced to several Caribbean islands as a control agent for pests such as rats and sugar cane beetles. Although the success of this action was patchy, positive results on the island of Puerto Rico were influential, and other introductions soon followed, to Hawaii and other Pacific islands.

The most consequential introduction was to the continent of Australia: in 1935, 102 toads sourced in Hawaii were brought to Queensland, and used to generate a population of 62,000 toadlets, which were then released into northern Queensland. The aim was to control a native beetle, considered a pest of the growing sugar cane industry. The toad’s colonisation of Australia was initially slow: not until 1959 was the coastal region of Queensland fully colonised; by 1978, the toads were moving south into New South Wales; by 1984 they were into the Northern Territories, and are now fully into Western Australia. Research by Rick Shine’s group has demonstrated rapid evolutionary changes in the characteristics of cane toads in the migration front: longer limbs, larger bodies, faster movement- allowing the front to advance now at 60 km per year.

The effects of cane toads on Australian native species are varied and changeable: they mainly relate to the toxicity of adults and tadpoles, reducing the effects of predators. Some Australian species have shown steep population declines following the arrival of cane toads: examples are the marsupial carnivore, the Northern quoll, and the varanid lizard known as the goanna. However, some predators appear to have adapted to the presence of cane toads and have found ways to avoid their toxins. In the longer term, we might expect that to progress. Overall, although there is considerable alarm over the effects of cane toads in Australia, they remain uncertain.

Many control methods have been tried, but none has been rated as successful so far. The annual Great Cane Toad Bust, lasting a week, has teams of local volunteers capturing adult toads and killing them by freezing. This is unlikely to have a significant effect on a population estimated at around 200 million. A feature that needs more research is what keeps cane toad populations in check within their native range: Lampo has estimated that native population densities are only 1-2% of those reached in Australia.

Finally, how effective were cane toads in controlling sugar cane pests in Australia? Shine’s analysis shows that the effects of cane toads have been complex, but not overall beneficial to sugar cane production. Sugar production did not increase following cane toad introduction. One reason for this is, that as a generalist predator, cane toads consume not only the beetles that are a pest of the cane, but also the ants which help control the beetles. They also poison the varanid lizards, another beetle control. Another factor is that the rodent population is unaffected by toad toxin, allowing them to consume toads and therefore grow their populations, thereby increasing their harmful effects on sugar cane. So despite the toads eating many beetles, their overall effects made matters worse for sugar cane production.

This cautionary tale should be at the forefront of thinking, whenever anyone advocates the introduction of an alien species as the answer to an ecological problem: the consequences are hard to predict.

 

References

Hinchliffe (2023). Public enemy no.1: on the hunt with Queensland’s army of volunteer toad busters. The Guardian 28/1/2023.

Lampo et al. (1998). The invasion ecology of the cane toad from South America to Australia. Ecological Applications 8, 388-396.

Phillips et al. (2010). Evolutionarily accelerated invasions: the rate of dispersal evolves upwards during the range advance of cane toads. Journal of Evolutionary Biology 23, 2595-2601.

Shine (2010). The ecological impact of invasive cane toads in Australia. Quarterly Review of Biology 85, 253-291.

Shine et al. (2020). A famous failure : why were cane toads an ineffective biocontrol in Australia? Conservation Science and Practice 2, e296.

Wikipedia articles on: The cane toad; the cane toad in Australia.

Croaking Science: should we care when we see a terrapin in the pond at our local park?

by

Abandoned turtles and terrapins; the impact they have on our native wildlife and the suffering they endure when left out in the cold. 

Pet turtles and terrapins have been regularly abandoned by their owners for decades in various ponds, rivers and canals in the United Kingdom, but despite a relatively large amount of research into the subject and the cruelty of the act, this trend continues. Perhaps this is the case, as when people buy a tiny terrapin at the pet shop when it is not much bigger than a fifty pence coin, they are often assured buy the sellers at the shop that it won’t get much bigger than that. Alternatively, maybe it is because once the said pet reaches the size of a small dinner plate, it is easier to convince oneself that you are doing the animal a kindness by releasing it into the wild, rather than committing oneself to the expensive and time consuming care that these exotic animals require. Most likely, the reason this trend continues is because people are genuinely unaware of the negative effects of the terrapin on the local environment and the distressing circumstances the animal will quickly find itself in.

A yellow bellied slider (Trachaemys scripta scripta) found at Benhill Road Nature Garden in Southwark in May 2016. Like many terrapins, this individual was an adept swimmer and it proved challenging to catch!
Figure 1: A yellow bellied slider, Trachaemys scripta scripta, found at Benhill Road Nature Garden in Southwark in May 2016. Like many terrapins, this individual was an adept swimmer and it proved challenging to catch! (Photo Credit: Alexia Fish)

Abandoned terrapins in British waters are almost always going to have their welfare compromised from the start, both in terms of health and chances of survival. The estimated annual mortality for feral terrapins and turtles in the UK is thought to be between 40-80%.

Terrapins require specific water temperatures, a good depth and flow of oxygenated water in their habitats and basking areas orientated towards the sun, not to mention good accessibility to suitable food. Furthermore, as terrapins like all reptiles are cold blooded, if they are released into an area with a lot of shade, such as tree lined banks of a canal, or a pond in a wood, they can really struggle. In cool areas, terrapins may be unable to get their body temperature high enough to move around, let alone eat and digest food. When the temperature drops below 16-18 degrees Celsius, they will not forage for food at all. This means for the majority of the year in the UK, they will be unable to forage and if there is a cold summer, they will be unlikely to build up enough fat stores to survive though hibernation.

Even in captivity, terrapins are complex and long-lived pets to maintain and often need to be supplemented with vitamins, as well as enough UV light for them to synthesise vitamin D3, which helps them absorb calcium from their food. Without supplements or enough sunshine or UV light, terrapins both feral and in captivity can suffer from ailments such as shell rot, which results in a weak and spongy shell. Vitamin A deficiency can result in swollen eyelids in terrapins which means they eventually fuse together, making them blind and unable to feed. The general cold climate of the UK means that the immune system of these animals, which are almost all adapted to the tropics or sub-tropics, is often compromised and that they are more prone to disease, such as respiratory problems and hypothermia. Inevitably, this means that the health of a large proportion of terrapins and turtles that are abandoned quickly deteriorates and they often end up and diseased or slowly starving to death.

Aside from the obvious ethical implications of abandoning terrapins and turtles, the relatively little research on them that has been done suggests that they may also have negative impacts on the environment. Though terrapins are omnivorous, they primarily eat plants, though will opportunistically take invertebrates and small mammals where they can get them. Where terrapins are released into small ponds, or where a large number of them are present, they can over consume vegetation in the pond. This may seem trivial, but not only does this mean they exhaust their own food source, but pond plants also play a vital role for our native wildlife. Newts, including the protected great crested newt, rely on plant leaves to fold over and lay their eggs in. Dragonfly and other invertebrate larvae, in addition to tadpoles, also depend on pond plants to shelter from predators, but also for food as they eat the algae that grows on them. Water fowl often make nests in and amongst plants along the margins of ponds and these areas are also important foraging and resting places for other wildlife, such as grass snakes. On a larger scale, when there is a reduction of oxygenating plants in the pond and an increase in nutrient input (for example from the faeces from a group of terrapins in a small pond), this can result in the eutrophication of the water. Eutrophication then means that the oxygen is so depleted in the pond that only organisms that can survive in oxygen poor environments, such as algae, persist. As terrapins are thought to be opportunistic feeders, they may also be directly impacting animal populations by eating invertebrates, amphibians and their larvae and possibly even young birds. To make matters worse, if a terrapin is abandoned in an urban park surrounded by roads, it is likely it will have no other ponds to go to, so it will continue to deplete the pond of its wildlife whilst it struggles to find enough to eat.

The release of non-native herpetofauna (reptiles and amphibians) has been increasing and many of these animals can also carry diseases that can be spread to our native wildlife. Though this is primarily a concern with the two chytrid fungus species being spread by invasive or exotic amphibians as well as ranavirus infection which has caused substantial mass mortality in common frogs in England, terrapins have been documented to spread the Hexamita protozoan to birds before.”

 

Unfortunately, at least 4000 terrapins are thought to be feral in the UK and rescues are struggling to keep up. London is the densest area for terrapin abandonment. In addition to this, it can be very difficult to catch and remove terrapins once they have been released. Abandoning terrapins is not only illegal, but cruel and not only does it cause suffering to the animal, but it often damages local ecosystems. Non-native species that are present in the UK are estimated to cost UK economy £1.7 billion per year. More research needs to be done into the effect of feral terrapins on the environment and awareness needs to be raised to prevent the illegal release of them.

(Alexia Fish, London Dragon Finder Ecologist)

References

Langton and Herbert, 2011. On the distribution, ecology and management of non-native reptiles and amphibians in the London Area. Part 1. Distribution and predator/prey impacts. The London Naturalist. No. 90, pp.83-156

Langton and Herbert, 2011. On the distribution, ecology and management of non-native reptiles and amphibians in the London Area. Part 2. Disease impacts, perspectives, trade exploitation and finding ethical solutions. The London Naturalist. No. 90, pp. 157-178

Croaking Science: Can blind toads teach us something new about invasive species?

by

Amphibians are currently experiencing a dramatic man-made extinction crises, with a higher percentage of endangered species than any other vertebrate groups including mammals, fish and birds. However, at the same time, some amphibians introduced by man into new territories have become phenomenally abundant and invasive, so much so that several of them are rated among the worst 100 invasive species on the planet.

Invasive species are one of the main drivers worldwide of biodiversity loss and also a major source of economic damage and as such understanding their ecology, mechanisms for invasiveness, impacts and ways to mitigate their effects are all paramount. This is especially relevant given that the ongoing and fast globalisation means that future introductions, both accidental and deliberate -mostly illegal using animals from the pet industry- are very likely to further increase.

The cane toad (Rhinella marina) in its native habitats in Central America. Photo Silviu Petrovan
The cane toad (Rhinella marina) in its native habitats in Central America. Photo Silviu Petrovan

The most famous example of an invasive amphibian is the cane toad (Rhinella marina), an imposing Central and South-American species which has been introduced into Australia in the 1930s in a misguided attempt to control a beetle in sugarcane plantations. The cane toad has now spread to most parts of north-western Australia and is causing untold damage to entire ecosystems as naïve Australian species, from monitor lizards and snakes to birds and mammals, eat the toads and die from poisoning given that it can produce large quantities of toxic secretions from its skin as a defensive mechanism. The scale of the invasion as well as the pace of the spread, currently estimated at around 40-60km per year, illustrates the remarkable potential of such species to adapt and take over a new environment following an introduction.

In another recent and fascinating example of invasive potential and adaptability of some amphibians Tolledo and Toledo (2015) report on a related species, the Cururu toad (Rhinella jimi), also from South America, which has been introduced in an effort to control the insect population, to the Fernando de Noronha archipelago, off the west coast of Brazil. The introduction was not official or state-sanctioned and therefore the information about it is scarce but most likely it took place around 100 years ago. Since then, the toad population has hugely expanded and become invasive but is suffering from a very high degree of malformations, both in tadpoles and in adults, including a very large proportion of one-eyed and even blind individuals. Despite this, both half-blind and fully blind individuals were able to survive on the island in similar numbers to normal individuals. The fact that such individuals have adapted to cope with such serious deformities and survive to hunt without relying on vision shows remarkable plasticity and adaptability, all necessary traits for invasive species. The paper describes captive experiments with both blind, half-blind and normal toads from the island where the two groups exhibited completely different foraging strategies, with the blind toads entirely switching their foraging mechanism from active hunting at night relying on vision, to sit and wait predator, relying exclusively on tactile cues and waiting for prey items to come to them and touch them. Equally, the diet composition varied significantly between the groups, with more fast-moving prey items and overall larger numbers of prey for the toads with normal eyesight.

The cause for the huge range of malformations of the Cururu toads in this island remains unknown but this represents a possibly unique experiment showing cascading effects on the toad population following introduction but also remarkable adaptability within a very short period of time.

 

References and further reading:

The Cane toad in Oz- http://www.canetoadsinoz.com/invasion.html

A BBC illustrated story about this article: http://www.bbc.com/earth/story/20150529-invasion-of-the-blind-toads

Tolledo, J. and Toledo, L. F. (2015), Blind toads in paradise: the cascading effect of vision loss on a tropical archipelago. Journal of Zoology, 296: 167–176. doi: 10.1111/jzo.12233

Please click "Accept" to use cookies on this website. More information

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.

Close