Posts Tagged ‘Aldabra tortoise’

The Lost Pleistocene World of the Seychelles Islands

September 29, 2015

The Seychelles Island group was part of the southern supercontinent Gondwanaland before the latter broke apart.  It then split away from India 60 million years ago and has been isolated from all continents ever since.  Presently, the Seychelles Islands include separate mountaintops totaling about 282 square miles, but during the last Ice Age it was 1 giant island of about 80,000 square miles…roughly the size of Georgia and half of Florida combined.  Sea level rise has inundated most of the island.

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The Seychelles Islands are located northeast of Madagascar.  They are mountain tops of  a large desert island that existed during Ice Ages.

Map of Seychelles and other islands during the Last Glacial Maximum ~29,000 BP-~15,000 BP.

A human seafarer wrecking his boat on the Pleistocene Seychelles would have discovered both a deserted and a desert island that could have inspired the setting of Robinson Crusoe.  The Seychelles Island was drier with a more sparse tree canopy than is found on the island group today.  A giant species of tortoise (Aldabrachelys gigantea) shaped the landscape into a short grass plain known as “tortoise turf.”  This long lived species (a captive specimen reached the age of 255) still occurs on 1 of the Seychelles atolls.  The Aldabra tortoise creates pathways and selects for shorter species of grasses that grow below its preferred level of foraging.

Primitive amphibians closely related to species found in India occur on the Seychelles.  Caecilians and soogloossid frogs live here.  The presence of these primitive amphibians on India and the Seychelles provides biological evidence that they were once part of the same land mass.

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There are 5 species of caecilians living on the Seychelles.  They are primitive amphibians.

The only dangerous animal for a Pleistocene Robinson Crusoe stranded on the Seychelles would have been the Australian saltwater crocodile (Crocodylus porosus).  Early European explorers reported them as “abundant” on the Seychelles, but they were extirpated here by 1819.  Naturalists wrongly assumed they were African species–either Nile crocodiles or mugger crocodiles.  But a genetic study suggests they were the Australian species.  These saltwater crocodiles occasionally do swim miles into the ocean and surface currents helped carry them to the far away Seychelles.

Saltwater Crocodile | Crocodylus porosus photo

Australian saltwater crocodiles lived on Seychelles until 1819.

At least 238 species of birds live on the Seychelles.  More species than that probably lived on the island before the Indian Ocean submerged most of it.  Sea birds like nesting on islands where few predators roam.  Many species of migratory songbirds get blown off course and learn to survive on islands.  Some evolve into new species.  Pigeons are notorious for getting blown out to sea.  The Seychelles has 5 different species of pigeons.  Settlers wiped out 1 species of parrot (Psitticula wardi) native to the Seychelles.  A fruit-eating bat known as a flying fox is the only native species of mammal on the island group.

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The Seychelles Parakeet is now extinct.

The coc-de-mer coconut palm (Ladoica maldivica) would have provided plenty of food for a stranded Pleistocene Robinson Crusoe.  It produces the largest seed in the world, weighing 50 pounds.  Unlike other coconuts, this species doesn’t float, explaining why it occurs nowhere else.  They produce a toxin that prevents other plants, including competing members of their own species, from growing near its root system.  These slow-growing plants take 800 years to reach full size.

Surviving almost impossible odds – how the Seychelles Coco-de-Mer palm parents its seeds

The coco-de-mer coconut palm is the largest seed in the world, growing to over 50 pounds.

The jellyfish tree (Medusagayune oppostifolia) is a rare species living on the granite mountaintops.  This relic was likely widespread over the Seychelles before the Indian Ocean inundated most of it.

The jellyfish tree is a rare relic that was probably more widespread on Seychelles during Ice Ages.

 

See also: https://markgelbart.wordpress.com/2011/11/11/banana-hole-fossil-sites/

Invasive Species are more Beneficial than Alarmists will Admit

January 4, 2015

Every organism that ever evolved became an invasive species.  It colonized new territory where it previously had not existed.  The concept of an invasive species that is harmful to the environment is a construct invented by man, the most environmentally damaging species to ever evolve.  The Homo sapien is such an hypocritical species.  The biogeographical history of the earth is a tale of species invading new territories.  The Bering Landbridge allowed a back and forth migration between Eurasia and North America, and the emergence of Central America offered a highway for another interchange of flora and fauna.  Man, the ultimate invader, has facilitated and accelerated the transfer of many species. Environmentalists focus on the harmful results invasive species wreak on ecology but ignore the obvious benefits that may in most cases outweigh the damage.  I mentioned 1 example on my blog last week–Burmese pythons reduce the population of predators that prey on endangered sea turtle eggs.  A recent study (referenced below) gives many more examples of beneficial invasive species that according to the authors of that study should be referred to as “recently arrived species.”

–The honeybee is not native to North America, yet without this “recently arrived species” industrial scale fruit and nut orchards would not be economically viable.

–Environmentalists mistakenly thought non native tamarisk trees were causing low water levels on the Colorado River floodplains.  Millions of dollars were spent eradicating this species.  But later studies showed tamarisk trees were not responsible for causing these low water levels.  Their misguided policy greatly reduced nesting habitat for the endangered willow flycatcher, a species that uses tamarisk in lieu of willow.

Endangered southwestern willow flycatcher’s nest in a non-native tamarisk tree.  The government and groups like the Nature Conservancy spent millions eradicating this species of tree based on the false premise that it lowers water levels.  Now this rare bird has far less nesting habitat.

–Native trees can’t be re-established on eroded Puerto Rican forestlands unless non-native trees are planted first.  With the help of non-native trees, 20 species of native trees were able to grow on badly eroded soils.

–The presence of non native honeysuckle vines increases the population of robins and catbirds that feed on the berries.  The increased bird populations acted as dispersers that helped increase native honeysuckle vine abundance.

–Non native guavas in Kenya helped increase the population of fruit-eating birds there.

–Non native grasses planted on reclaimed strip mines increased the population of endangered Henslow’s sparrows.

–Non native shad serve as forage to help feed  Pacific salmon.

–Non native mussels serve as food for raccoons.

–Butterflies utilize non native species as sources of food.

–Non native cattle maintain early successional habitat, thus helping native species dependent upon this habitat.  They’re a substitute for extinct Pleistocene megafauna.

–African honeybees traverse the areas between fragmented forests in Brazil, aiding the pollination of plant species that could become inbred and sterile.

Some regions provide refuge for species that are endangered in their land of origin.  The Aldabra tortoise is native to a Seychelles Island but is more common in Mauritia where it occupies the ecological role of a now extinct species of giant tortoise.

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The Aldabra giant tortoise has been introduced to the island of Mauritia where another species of giant tortoise was overhunted into extinction centuries ago.  It serves as an important disperser of native plants.

Banteng, an endangered species of cattle native to southern Asia, breeds successfully in northern Australia.

Banteng bull caught on camera trap in Malua BioBank. Photo by: Sabah Wildlife Department (SWD).

Banteng cattle face extinction in their homeland but have successfully established a wild breeding population in northern Australia.

Hippos (imported by a rich cocaine baron) thrive in Colombia.  Game ranches in Texas are the best hope for breeding black rhinos, currently extinct in Africa.

Recently arrived species can cause the extinction of competing native species, but they can also instigate the evolution of new species.  Non native house sparrows appear to be speciating in North America, according to the geographic region they have colonized.  Desert populations of house sparrows have distinct physical characteristics from those found in eastern woodlands.  A new species of honeysuckle fly exists today, thanks to non native honeysuckle vines.  This species resulted from the hybridization of 2 closely related flies that hosted 2 different species of native honeysuckles.  The 2 different species of fly both hosted non native honeysuckles, explaining how they began breeding with each other.

The lonicera fly is the result of hybridization between 2 different species: Rhagoletes menax X R. zephyra.  This new species resulted from the introduction of non native honeysuckles.

The authors of the below referenced study suggest recently arrived species should be more carefully evaluated and managed and not blindly eradicated, simply because they are non native.

Reference:

Schlaepfer, Martin; Dow Sax and Julian Olde

“The Potential Conservation Value of Non-Native Species”

Conservation Biology 25 (3) June 2011