Tag Archives: extinction

Land snails on islands: fascinating diversity, worrying vulnerability

by Piter Kehoma Boll

The class Gastropoda, which includes snails and slugs, is only beaten by the insects in number of species worldwide, having currently about 80 thousand described species. Among those, about 24 thousand live on land, where they are a very successful group, especially on oceanic islands.

The Hawaiian Islands alone, for example, have more than 750 snail species and there are more than 100 endemic species in the small island of Rapa in the South Pacific. This diversity is much higher than that in any continental place, but the reason for that is not completely understood.

Mandarina

A land snail of the genus Mandarina, endemic to the Ogasawara Islands, Japan. Photo by flickr user kmkmks (Kumiko).*

One of the most likely explanations for this huge diversity on islands is related to the lack of predators. The most common predators of snails include birds, mammals, snakes, beetles, flatworms and other snails. Most of those are not present in small and isolated islands, which allows an increase in land snail populations in such places. Without too much dangers to worry about, the community of land snails n islands can explore a greater range of niches, eventually leading to speciation.

Unfortunately, as always, the lack of danger leads to recklessness. Without predators to worry about, insular land snails tend to lay fewer eggs than their mainland relatives. If there is no danger of having most of your children eaten, why would you have that many? It is better to lay larger eggs, putting more resources on fewer babies, and so assure that they will be strong enough to fight against other snail species. Afterall, the large number of species in such a small place as an island likely leads to an increased amount of competition between species.

But why is this recklessness? Well, because you never known when a predator will arrive. And they already arrived… due to our fault.

The diversity of insular land nails was certainly affected by habitat loss promoted by humans, but also by predators that we carried with us to the islands, whether intentionally or not. These predators include rats, the predatory snail Euglandina rosea and the land flatworm Platydemus manokwari, the latter being most likely the worst of all.

800px-platydemus_manokwari

The flatworm Platydemus manokwari in the Ogasawara Islands. Photo by Shinji Sugiura.

This flatworm arrived at the Chichijima Island, part of the Ogasawara Islands in the Pacific Ocean, in the early 1990s and in about two decades it led most land snail species on the island to extinction and many more are about to face the same fate on this island and on others. Not being prepared for predators, these poor snails cannot reproduce fast enough to replace all individuals eaten by the flatworm.

We have to act quickly if we want to save those that are still left.

See also: The New Guinea flatworm visits France – a menace.

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ResearchBlogging.orgReferences and further reading:

Chiba, S., & Cowie, R. (2016). Evolution and Extinction of Land Snails on Oceanic Islands. Annual Review of Ecology, Evolution, and Systematics, 47 (1), 123-141 DOI: 10.1146/annurev-ecolsys-112414-054331

Sugiura, S., Okochi, I., & Tamada, H. (2006). High Predation Pressure by an Introduced Flatworm on Land Snails on the Oceanic Ogasawara Islands. Biotropica, 38 (5), 700-703 DOI: 10.1111/j.1744-7429.2006.00196.x

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Biological fight: Should we bring mammoths back?

by Piter Kehoma Boll

Everybody knows the amazing large animals that are found in Africa and Southeast Asia. Elephants, giraffes, rhinos, hippos, horses, lions, tigers… such large creatures, mostly mammals, are usually called megafauna, the “large fauna”.

Mammals as big as the African bush elephant once roamed the Americas. Photo by flickr user nickmandel2006*.

Mammals as big as the African bush elephant once roamed the Americas. Photo by flickr user nickmandel2006*.

The Americas once had an astonishing megafauna too, full of mastodons, mammoths, giant sloths, giant armadillos and sabertooth tigers. Nowadays it is restricted to some bears and jaguars. What happened to the rest of them? Well, most went extinct at the end of the Pleistocene, around 11,ooo years ago.

South America once had mammals as big as an African bush elephant. Picture by Dmitry Bogdanov** (dibgd.deviantart.com)

South America once had mammals as big as an African bush elephant, such as the giant sloth. Picture by Dmitry Bogdanov** (dibgd.deviantart.com)

As humans already inhabited the Americas by this time, it was always speculated if humans had something to do with their extinction. It is true that nowadays hundreds, thousands of species are endangered due to human activities, so it is easy to think that humans are the best explanation for their extinction, but 10 thousands years ago the number of humans on the planet was thousands of times smaller than today and our technology was still very primitive, so it is unlikely that we could hunt a species to extinction by that period… if we were working alone.

No, I’m not talking about humans cooperating with aliens! Our sidekick was the famous climate change. Periods of extreme warming during the pleistocene seem to have had a strong impact on the populations of many large mammals and, with the aid of humans hunting them down and spreading like an invasive species, the poor giants perished.

Le Mammouth by Paul Jamin

Le Mammouth by Paul Jamin

This happened more than 10 thousand years ago, TEN THOUSAND YEARS.

In Africa, elephants and large carnivores are well known for their importance in structuring communities, especially due to their trophic interactions that shape other populations. The extinct American megafauna most likely had the same impact on the ecosystem. As a result, suggestions to restore this extinct megafauna has been proposed, either by cloning some of the extinct species or, more plausibly, by introduced extant species with a similar ecological role.

Svenning et al. (2015) review the subject and argue in favor of the reintroduction of megafauna to restore ecological roles lost in the Pleistocene, an idea called “Pleistocene rewilding” or “trophic rewilding”, as they prefer. They present some maps showing the current distribution of large mammals and their historical distribution in the Pleistocene, which they call “natural”. They also propose some species to be introduced to substitute the ones extinct, including replacements for species extinct as long as 30 thousand years ago. Now is this a good idea? They think it is and one of the examples used is the reintroduction of wolves in the Yellowstone National Park. But wolves were not extinct for millenia there, neither are they a different species that would replace the role of an extinct one.

A wolf pack in Yellowstone National Park

A wolf pack in Yellowstone National Park

Rubenstein & Rubenstein (2016) criticized the idea, arguing that we should focus on protecting the remaining ecosystems and not trying to restore those that were corrupted thousands of years ago. They also argue that using similar species may have unintended consequences. Svenning et al. answered that this is mere opinion and that a systematic research program on trophic rewilding should be developed. The reintroduction of horses in the New World and its non-catastrophic consequences is another point used to respond to the critiques.

So what’s your opinion? Should we bring mammoths, mastodonts, giant sloths and sabertooth tigers back? Should we introduce elephants and lions in the Americas to play the role that mastodonts and smilodonts had?

My opinion is no. The idea may seem beautiful, but I think it is actually fantastic, too fabulous and sensational. Horses may have come back to the Americas without bringing destruction, but we cannot be sure with anything, even with several theoretical and small-scale studies. We all know how often introducing species goes wrong, very wrong. Look at poor Australia and Hawaii, for instance. Furthermore, those giant mammals went extinct TEN THOUSAND YEARS AGO. Certainly ecosystems have adapted to their extinction. Life always finds a way. There are worse threats to those ecosystems to be addressed, such as their eminent destruction to build more cities and raise more cattle and crops.

Get over it. Mammoths are gone. Let’s try to save the elephants instead, but without bringing them to the Brazilian cerrado. They don’t belong there. They belong in the African savannah.

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References:

Rubenstein, D. R.; Rubenstein, D. I. From Pleistocene to trophic rewilding: A wolf in sheep’s clothing. PNAS, 113(1): E1. DOI: 10.1073/pnas.1521757113

Svenning, J-C.; Pedersen, P. B. M.; Donlan, C. J.; Ejrnæs, R.; Faurby, S.; Galetti, M.; Hansen, D. M.; Sandel, B.; Sandom, C. J.; Terborgh, J. W.; Vera, F. W. M. 2016. Science for a wilder Anthropocene: Synthesis and future directions for trophic rewilding research. PNAS, 113(4): 898-906. DOI: 10.1073/pnas.150255611

Svenning, J-C.; Pedersen, P. B. M.; Donlan, C. J.; Ejrnæs, R.; Faurby, S.; Galetti, M.; Hansen, D. M.; Sandel, B.; Sandom, C. J.; Terborgh, J. W.; Vera, F. W. M. 2016. Time to move on from ideological debates on rewilding. PNAS, 113(1): E2-E3. DOI: 10.1073/pnas.1521891113

Wade, L. 2016. Giant jaguars, colossal bears done in by deadly combo of humans and heat. Science News. DOI: 10.1126/science.aag0623

Wade, L. 2016. Humans spread through South America like an invasive species. Science News. DOI: 10.1126/science.aaf9881

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The Story of the Dwarf Rhea

by Rafael Nascimento

The family Rheidae is nowadays represented by two or three (according to different authors) species of rheas, large running flightless birds, similar to the African ostriches, but having three toes on each foot instead of two. The largest one, the common rhea Rhea americana, has five subspecies distributed from northeastern Brazil to eastern Argentina and including Bolivia, Paraguay and Uruguay. The other forms, earlier put in a separate genus, Pterocnemia, are R. pennata and R. tarapacensis (commonly known as Darwin’s rhea and Puna rhea, respectively). Darwin’s rhea, which helped the British naturalist in the elaboration of his theory of natural selection, lives in the Argentinean and Chilean Patagonia. The systematic situation of the Puna rhea (and its possible subspecies), which is found in the area where Peru, Bolivia, Chile and Argentina meet, is not yet clear, and currently it is considered a distinct form based on some physical features, but more clarifying studies are necessary.

Beside these current forms and some fossil species, such as Opisthodactylus horacioperezi and Hinasuri nehensis, respectively from the Argentinian Miocene and Pliocene, another species was described in 1894 by the British Naturalist Richard Lydekker based on a small egg: Rhea nana – therefore representing a possible fourth rhea species living in historical times.

Richard Lydekker, ca 1900.

Richard Lydekker, ca 1900.

Following you can see the original text published in the journal Proceedings of the Zoological Society of London from 1894, with comments regarding this possible new species:

“Mr. R. Lydekker exhibited photographs and a model of a unique egg, the original of which had been obtained many years ago in Southern Patagonia, and now preserved in the Museum at La Plata. If not an abnormal specimen, it could not be assigned to any known species of bird.

When travelling in the district where the specimen was obtained, Dr. P. Moreno, Director of the Museum at La Plata, many years ago saw numbers of small Ratite birds, which he at first took to be small Rheas. By the natives, to whom they were well known, he was, however, assured that they were adult birds, allied to the Rheas. Desirous of confirming this information, Dr. Moreno applied to a friend acquainted with the district; who replied that not only did he well know the birds, but that he possessed an egg, that egg being the original specimen of which a model was now exhibited.

Assuming the egg to be a normal one, Mr. Lydekker was of opinion that, taken in connexion with the evidence of two independent witnesses who had been the birds, it pointed to the existence in Southern Patagonia of a small unknown Ratite bird more or less nearly allied to the Rheas.”

Illustration of Darwin's Rhea by John Gould, 1841.

Illustration of Darwin’s Rhea by John Gould, 1841.

Until today, however, no other similar egg or adult bird of a species different from the three already mentioned has been found. When we deal with potentially extinct species, only know by scarce reports or aberrant specimens, one must watch the data through a skeptical point of view. We need to be certain that those are not variations within the species or a witness confusion. The lack of extensive comparative material due to the date of the descriptions must also be taken into account, as well as the constant advancements in our understanding of science.

Normal egg of R. pennata, at Museum Wiesbaden (Germany). Photo by Klaus Rassinger/Gerhard Cammerer.

Normal egg of R. pennata, at Museum Wiesbaden (Germany). Photo by Klaus Rassinger/Gerhard Cammerer.

This egg is currently treated as an aberrant form of a Rhea pennata egg. The model cited by Lydekker, made of wax, is found in the Tring Natural History Museu, England.

del Hoyo, J., Collar, N. & Garcia, E.F.J. (2015) Puna Rhea (Rhea tarapacensis). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/467080 on 24 December 2015).

Folch, A., Jutglar, F., Garcia, E.F.J. & Boesman, P. (2015) Greater Rhea (Rhea americana). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/52399 on 24 December 2015).

Folch, A., Christie, D.A., Jutglar, F. & Garcia, E.F.J. (2015) Lesser Rhea (Rhea pennata). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/52400 on 24 December 2015).

Hume, J. P.; Walters, M. (2012) Extinct Birds. T & AD Poyser. Londres.

Knox, A. G.; Walters M. P. (1994) Extinct and Endangered Birds in the collections of The Natural History Museum. British Ornithologists’ Club Occasional Publications.

Lydekker, R. (1894) Exhibition of, and remarks upon, a photograph and model of an egg from Southern Patagonia in the La Plata Museum. Proceedings of the Zoological Society of London (1894): 654.

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The New Guinea flatworm visits France – a menace

by Piter Kehoma Boll

ResearchBlogging.orgFor as long as life exists, it spreads. Organisms move (even if only as gametes or spores) and conquer new environments if they fit. If it wasn’t so, life wouldn’t be found all over the world. Recently, however, due to human dispersion, species are much more likely to reach places far away from where they were born. We considered a species living outside its native area as exotic. And there are a lot of them. I wonder if there is any place where no exotic species exist.

In my first post in this blog, I talked about how exotic species are not always a threat to native ecosystems. But many of them are, indeed, dangerous to local diversity. The ISSG (Invasive Species Specialist Group) lists what are considered the 100 worst invasive species. Strangely, they fail to mention the top worst invasive species, Homo sapiens.

Among those 100 species, a very famous one is the giant African land snail, Achatina fulica. Native to East Africa, it has been introduced worldwide and is a major pest in gardens and agricultural sites, and can also be an intermediate host of several parasites that infect humans.

The giant African land snail Achatina fulica. Photo by Eric Guinther. Extracted from commons.wikimedia.org

The giant African land snail Achatina fulica. Photo by Eric Guinther*. Extracted from commons.wikimedia.org

As an attempt to control the populations of Achatina fulica, some “genius” decided to introduce one more exotic species in the areas where A. fulica was a pest: a voracious generalist predator of land snails.

Let's fight against an exotic pest with another exotic pest!

Let’s fight against an exotic pest with another exotic pest!

As a result, the predator snail Euglandina rosea, known as the rosy wolfsnail or cannibal snail, was introduced in areas infested by A. fulica. But E. rosea is native to North America while A. fulica is native to East Africa. In order to be effective, E. rosea had to be a generalist predator, feeding on any kind of snails. And that’s what it does…

The rosy wolfsnail Euglandina rosea. Photo by Tim Ross. Extracted from commons.wikimedia.org

The rosy wolfsnail Euglandina rosea. Photo by Tim Ross. Extracted from commons.wikimedia.org

Euglandina rosea started to prey on A. fulica, but… ops! It also attacked native land snails and led several species to extinction in Pacific Islands. It became a pest even worse than the giant African land snail…

Not satisfied by the damage caused by this predator, people decided to introduce one more species in order to control A. fulica. And the chosen one was another voracious generalist predator of land snails, the New Guinea flatworm Platydemus manokwari. As its name suggest, thee New Guinea flatworm is native to New Guinea, again a different place, and so, in order to feed on the giant African land snail, it had to feed on any kind of land snail. Thus, it became a pest as harmful as the previous one and led several species of land snails to extinction in Pacific Islands.

Until very recently it was thought that the New Guinea flatworm infestation was restricted to the Indo-Pacific Region, not so far from home. However, a recent paper by Justine et al. (2014) reports its presence in a hothouse in Caen, northern France. This report extends significantly its occurrence over the world and indicates that it may be much more spread than previously thought. Unfortunately, people are more interesting in preserving their gardens than preserving biodiversity. So those predatory pests will probably keep being introduced as biological controls, even though they pose a threat to ecosystems.

The New Guinea Flatworm Platydemus manokwari. Photo by Pierre Gros, taken from Justine et al., 2014, via commons.wikimedia.org.

Bonjour tout le monde! I came to visit Paris! The New Guinea Flatworm Platydemus manokwari. Photo by Pierre Gros**, taken from Justine et al., 2014, via commons.wikimedia.org.

Fortunately, in France, P. manokwati seems to be restricted to greenhouses. Let’s hope that it won’t be found somewhere else.

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References:

Albuquerque, F., Peso-Aguiar, M., & Assunção-Albuquerque, M. 2008. Distribution, feeding behavior and control strategies of the exotic land snail Achatina fulica (Gastropoda: Pulmonata) in the northeast of Brazil. Brazilian Journal of Biology, 68 (4), 837-842 DOI: 10.1590/S1519-69842008000400020

ISSG, Invasive Species Specialist Group. 100 of the World’s Worst Invasive Alien Species. Availabe at: < http://www.issg.org/database/species/search.asp?st=100ss >. Access on April 04, 2014.

Justine, J., Winsor, L., Gey, D., Gros, P., & Thévenot, J. 2014. The invasive New Guinea flatworm in France, the first record for Europe: time for action is now. PeerJ, 2 DOI: 10.7717/peerj.297

Sugiura, S., Okochi, I., & Tamada, H. 2006. High Predation Pressure by an Introduced Flatworm on Land Snails on the Oceanic Ogasawara Islands. Biotropica, 38 (5), 700-703 DOI: 10.1111/j.1744-7429.2006.00196.x

Sugiura, S., & Yamaura, Y. 2008. Potential impacts of the invasive flatworm Platydemus manokwari on arboreal snails. Biological Invasions, 11 (3), 737-742 DOI: 10.1007/s10530-008-9287-1

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Friday Fellow: Mauritius Fruit Bat

by Piter Kehoma Boll

So I decided to start a new category of posts here called “Friday Fellow” (yeah, kind of a silly name, but I couldn’t figure anything better!). Every friday I’ll try to bring you one interesting species among our earthling “biosiblings” and talk a bit about it.

The first one to be presented is a nice and cute guy from Mauritius, the so called Mauritius fruit bat or Mauritius flying fox (Pteropus niger).

Mauritius fruit bat (Pteropus niger). Photo extracted from batconservacy.org

However, despite its cuteness, it is the last survivor of the Mascarene-endemic fruit bats and is facing a high risk of extinction. The country has a law to protect them, but (guess what?) fruit growers from the Islands are pressing the Mauritian government to amend that law so that it would allow “culling quotas” to control the bat’s population size, reducing so the “depredation caused to fruit crops”.

Pteropus niger is already listed as an endangered species by IUCN and if its protection is not enforced instead of amended it can in fact became extinct. It’s sad to watch people concerned only about their own problems, trying to fix them in the easiest way, without looking at the aftermath that comes from it. The Mauritius fruit bat its the largest surviving frugivore in the island, having a central role to disperse seeds. Instead of simply hunting it down, the government and fruit growers should realize that protecting the bat’s natural environment (the forests) would let it have plenty of food to consume without looking for it in fruit crops.

Let’s hope that this story will have a happy ending.

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References:

Florens, F. B. V. 2012. Going to Bat for an Endangered Species. Science, 336 (6085), 1102 DOI: 10.1126/science.336.6085.1102-a

IUCN Red List:Pteropus niger. Available at <http://www.iucnredlist.org/apps/redlist/details/18743/0 >

Lubee Bat Conservacy: Africa Projects. Availabe online at <http://www.batconservancy.org/africa-projects-bat-conservation.php >

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