Daily Decay (19th August 2014): Common Asian Toad (Duttaphrynus melanostictus) @ Clementi
I would like to see a lot more of this species in this condition.
You might think that’s a pretty harsh thing for a herpetologist to say about a frog, but in this case, I mean it sincerely.
You see, this species is native to southern Asia, where it is common and doubtless forms an integral part of the foodchain.
These toads are able to reproduce at a phenomenal rate, with some (probably ridiculous) estimates stating that females can produce up to 40,000 eggs in one year. They are also highly mobile, and quite toxic.
Earlier this year, it was revealed that this species has successfully colonised Madagascar.
People familiar with the invasion of the cane toad Rhinella marina (formerly Bufo marinus) in Australia will know just how devastating this news is. Invasive species like this have the potential to spread and effectively cause the collapse of whole ecosystems. On islands like Madagascar, invasions of this kind are particularly dangerous for the specialised and unique local fauna.
An assessment is currently under way in Madagascar to look at the feasibility of exterminating this species before it does too much damage. It is one of the main topics that we will be discussing at the ACSAM2 meeting in Madagascar in November. We can only hope it is not too late, and that something can be done before this toad spreads too far and truly becomes uncontrollable.
(YOU CAN HELP by donating just a little bit to help make the ACSAM2 meeting a success!)
And yes, I’m all too familiar with non-native and potentially invasive amphibians and reptiles; it’s a topic that I’m particularly interested in.
Here we’ve got lots of people releasing Red-eared Sliders (Trachemys scripta elegans), American Bullfrogs (Lithobates catesbeianus), and Chinese Softshell Turtles (Pelodiscus sinensis) as misguided gestures of goodwill and gaining karma through
liberating dumping pets or animals sold for human consumption in local markets.
Red-eared Sliders, Sungei Buloh Wetland Reserve;
(Photo by beggs)
American Bullfrog, Singapore Botanic Gardens;
(Photo by IngeHG)
Chinese Softshell Turtle, Bukit Batok Nature Park;
(Photo by Jerome Chua)
The Australian Green Tree Frog (Litoria caerulea) is the only amphibian allowed for sale in pet shops (but see the end of this post), and several released individuals were recently found; it’s likely that it’s more than capable of breeding in the wild here. Several other species, such as Green Iguanas (Iguana iguana), Ball Pythons (Python regius), Indian Star Tortoises (Geochelone elegans), Chinese Stripe-necked Turtles (Mauremys sinensis), Pig-nosed Turtles (Carettochelys insculpta), and Common Snapping Turtles (Chelydra serpentina), are illegal here but people somehow manage to obtain (and abandon) them. Most of the feral individuals don’t seem to represent self-sustaining populations, but given enough released/abandoned/escaped individuals and time, it’s likely that our equatorial climate will prove to be a factor in some of these species becoming established here. For instance, it’s been said that the Green Iguanas at the now-defunct Jurong Reptile Park managed to breed, and the hatchlings easily escaped their enclosures, resulting in a feral population now roaming the grounds of the neighbouring Jurong Bird Park.
Green Iguana, Jurong Bird Park;
(Photo by Ken, Ying Xu)
Common Snapping Turtle, MacRitchie Reservoir;
(Photo by budak)
In the span of three decades or so, the Changeable Lizard (Calotes versicolor) has taken over as the most common agamid in most of our parks, gardens, scrubland, and other urban green spaces. This species is suspected to have arrived in Singapore in the 1980s, possibly as stowaways in overland shipments of cargo and other goods from southern Thailand and northern Peninsular Malaysia.
And in recent years, the Brown Anole (Norops sagrei) and Günther’s Frog (Hylarana guentheri) somehow found their way here, probably through imports of ornamental plants, and it looks like they’re here to stay.
It remains to be seen whether any of these will successfully invade the remaining patches of mature secondary and primary rainforest, and whether there will be any major impacts on our native herpetofauna. One can only hope that they don’t breed or manage to be eradicated before they get established, or at worst, remain restricted to urban habitats.
My day job currently includes helping in the management of a nature reserve in Singapore, and so I have to deal with these issues on an almost-daily basis. There are all sorts of invasive species that we worry about, both plants and animals, but it’s the reptiles and amphibians that I’m personally concerned about. I get conflicted whenever I see the Red-eared Sliders in the ponds. I like turtles, but I end up wishing that I was seeing less of this non-native species and more of the native turtle species instead, like the Malayan Box Turtle (Cuora amboinensis). Just the other day, someone dumped a small Red-eared Slider in one of the raised concrete ponds (there’s no way a turtle is getting in there except through human action); my colleague adopted it.
Malayan Box Turtle, Sungei Buloh Wetland Reserve;
Even with supposedly native turtles, the situation is far from clear; some populations of Malayan Box Turtles might be descended from individuals that were imported for the pet trade or for consumption, then released, whereas a lack of earlier records suggests that sightings of several other Southeast Asian turtle species in Singapore most probably also represent former captives that have since established breeding populations here.
The Günther’s Frogs seem to be doing very well, and you can hear them calling even in the afternoon; I try my best to catch and remove as many as I can, but it does not seem to have any noticeable impact on their numbers. At the same time, it seems like the native Common Greenback Frogs (Hylarana erythraea) have declined; I wonder if there’s a link to the concurrent increased visibility of Günther’s Frog. I felt a distinct sense of dread when I spotted (and caught) a young American Bullfrog, presumably also released by someone. There are several farms in the area that raise this species for human consumption, and while they have yet to be observed successfully reproducing in the wild here, it’s worrying to think about the possible ecological consequences should all those American Bullfrogs released all over Singapore manage to breed. The Changeable Lizards are prospering and it’s unlikely that anything can be done about them at this point; I hope the Green Crested Lizards (Bronchocela cristatella) are able to persist in the presence of this larger, more aggressive rival. Nobody has done an actual study and shown that the Changeable Lizard has a negative effect on Green Crested Lizard populations, but it’s such a coincidence that the latter declined and disappeared from many of its former haunts ever since the Changeable Lizard arrived on our shores. Today, the Green Crested Lizard is largely restricted to patches of mature forest and woodland.
I concede that just because an animal isn’t native to a particular area doesn’t mean that it will only have negative impacts on the local ecology. For instance, the Banded Bullfrog (Kaloula pulchra) and Striped Keelback (Xenochrophis vittatus) are both considered to be introduced species in Singapore, and are well-established, but they seem to have become integrated and don’t appear to cause any problems (but that’s possibly because we haven’t really studied them very closely at the moment). It is possible for a non-native species to simply be a benign addition to the local biodiversity, but this is hard to predict and possibly mostly applicable to species that are native to nearly-identical ecosystems within the same region that mostly share the same suite of species. If I may hazard a guess, since Singapore’s native biodiversity is a subset of that found in the Sunda ecoregion, particularly that of the state of Johor in southern Peninsular Malaysia and the Riau Archipelago in Indonesia, any introductions of species native to this region but not formerly recorded in Singapore itself will likely have little negative impact on our biota, unless the introduced species specifically affects some endemic or otherwise locally critically endangered species. The Banded Bullfrog is widely distributed across much of Southeast Asia, whereas the Striped Keelback hails from Sumatra and Java, and so can be considered part of the suite of species native to Sundaland. Similarly, some turtle species such as the Black Marsh Turtle (Siebenrockiella crassicollis) and Asian Giant Pond Turtle (Heosemys grandis) are believed to be recent introductions to Singapore, but are naturally found in this part of the world, so their presence here is considered benign.
Banded Bullfrog, Pasir Ris;
(Photo by Noel Thomas)
It also cannot be discounted that some of our commensal geckos and amphibians, which seem to prefer disturbed habitats, are possibly ancient introductions that arrived with people who settled in this region before the 19th Century, but they are considered “native” and not a threat to other species. A large proportion of the remaining native amphibians and reptiles are dependent on mature rainforests and wetland habitats, such as mangroves and freshwater swamp forests, and already face so many challenges. Habitat destruction is still probably the most important threat to their survival, but I’m sure they would appreciate not having to deal with an influx of non-native species that could act as competitors, predators, or even as carriers of disease – Chytrid Fungus (Batrachochytrium dendrobatidis) is already in Singapore, and the trade in American Bullfrogs may play an important role in its spread in Southeast Asia.
With most of our forests and other critical habitats being little more than isolated little fragments and patches (albeit with some connected by strips of vegetation that serve as corridors for dispersal of both native and non-native species), the edge effects and pressures from all these threats will be felt even more strongly.
Hopefully, the impacts of all these non-native and invasive species will be minimal here, and that they’ll stay out of the forest reserves, the last refuge of a large proportion of our native herpetofauna; I’d really hate to see people mistakenly conclude that American Bullfrogs and Red-eared Sliders are a part of Singapore’s natural heritage.
ADDENDUM: Reptiles and amphibians as pets in Singapore
Among the reptiles and amphibians available for sale in Singapore, only the following species are allowed to be sold in licensed pet shops:
- Red-eared Slider
- Malayan Box Turtle (imported, with CITES permits)
- Australian Green Tree Frog
Juveniles of two species of amphibians are also frequently seen for sale at most pet shops, but these are usually marketed as feeders for large, predatory fishes. There is of course, nothing to stop people from buying them as pets:
- American Bullfrog
- Crab-eating Frog (Fejervarya cancrivora)
The Crab-eating Frog is native, but is typically restricted to coastal areas and mangroves. Populations found in inland water bodies and reservoirs are likely descended from those released by people.
Crab-eating Frog, Sungei Buloh Wetland Reserve;
(Photo by Jac Lau)
According to local legislation, only two species of turtle are allowed to be sold as pets in Singapore, which makes the sale of any crocodilians, lizards, snakes, tuataras, and any other turtle species illegal. By virtue of omission, all caecilians, salamanders and newts, and any other frog and toad species besides the three listed above are also not allowed in the pet trade.
Adult American Bullfrogs are routinely sold in the markets for food. The status of the Chinese Softshell Turtle is tricky; it is sold for its flesh, which is used in turtle soup, but is not listed as allowed in the pet trade, which means that the very young individuals occasionally seen in pet shops are technically illegal. Even those seen for sale live in the markets are supposed to be slaughtered on the spot once they’ve been purchased.
Several other species of turtle used to be found in pet shops, but recent crackdowns mean that these are usually no longer available (at least in the open). These include the Indian Star Tortoise, Chinese Stripe-necked Turtle, Pig-nosed Turtle, and many more. Many of our reservoirs and lakes are now inhabited by a host of exotic turtle species from all over the world, a sign of the astounding diversity of species available through the black market, and it does raise the question as to which of these are potentially able to establish breeding populations.
Pig-nosed Turtles in a home aquarium. Once commonly seen in local pet shops, trade in this species has been illegal since 2005. Ever since the ban came into effect, people who owned Pig-nosed Turtles needed to get approval from the authorities, and prove that their turtles were imported before 2005. This was determined by the turtle’s size; if it had a straight carapace length of more than 20 centimetres, it was deemed to have been imported before 2005 and hence registered as legal. Of course, there’s always the possibility of specimens exceeding this size being smuggled in and then grandfathered, although it’s likely that anyone trying to do so these days should arouse some suspicion;
(Photo by Edwin Tan)
Several other amphibian species can be occasionally found in pet shops and fish farms, even though they are technically illegal; it’s possible that they arrive with shipments of ornamental fishes and hence don’t get noticed by customs or other officials who are supposed to be monitoring the exotic pet trade:
- Oriental Fire-bellied Toad (Bombina orientalis)
- African Clawed Frog (Xenopus laevis)
- African Dwarf Clawed Frog (Hymenochirus boettgeri)
- Chinese Paddle-tailed Newt (Pachytriton labiatus)
- Chinese Fire-bellied Newt (Cynops orientalis)
- Axolotl (Ambystoma mexicanum)
Who knows if we’ll ever see any of these in the wild here; given that we now have all sorts of non-native fishes in our ponds, rivers, and reservoirs, apparently abandoned by irresponsible owners, I won’t be surprised if some of these amphibians also end up getting released.
As you may have noticed, the legislation regarding the legality of the trade in some amphibians and reptiles as pets is a little unclear. To summarise, only two species of turtle and one species of frog are allowed to be sold as pets, but two other species of frogs are apparently allowed to be sold in pet shops as feeders. An additional species of turtle cannot be sold as a pet, but can be sold for food. Every other reptile and amphibian species is supposedly illegal, but the only species explicitly mentioned in the legislation are those listed on CITES, which does raise the question as to whether trade in species not mentioned as allowed for sale in pet shops in Singapore and also not listed on CITES is legal or not. As for current levels of surveillance and enforcement, not only at customs, but also of businesses and individuals possessing and trading in exotic and illegal reptile and amphibian species, things could certainly be improved. There have been some high-profile seizures and convictions, but it’s likely that there are many more that go unreported.