Feeds:
Posts
Comments

Posts Tagged ‘Extinction’

A news story has been circulating a fair bit in the past couple of weeks. This story has been picked up by numerous news and science outlets. How it is being reported and explained is just plain misleading and inaccurate.

Image result for aldabra rail

The Aldabra Rail is a subspecies of the White-throated Rail.

Here are a few titles that show how the subject is being covered.

Science Magazine – Evolution Brings Extinct Island Bird Back into Existence

Smithsonian Magazine – How Evolution Brought a Flightless Bird Back from Extinction

CBS News – An Extinct Bird Species Has Evolved Back into Existence, Study Says

From these titles, and from the bodies of the articles themselves, readers would think that the same species of bird existed at some point in the past, went extinct (as in died out completely), and then re-evolved!

That does not happen.

Here is what actually did occur.

The small atoll of Aldabra is a pretty spectacular spot. It is very remote. It is quite beautiful. It is home to a bunch of unique animals found no where else on earth. It has one of the longest fossil records on any island in the Indian Ocean.

That fossil record includes a lot of the animals that have called the atoll home over the past few million years. One of those animals was the Aldabra Rail. This rail was a small flightless bird that was probably found hunting through reed beds along the edges of water. The Aldabra Rail went extinct about 136,000 years ago at about the same time that global sea level was rising and submerging oceanic islands like Aldabra. After a few thousand years, sea level dropped and Aldabra became an exposed island once more. Not long after that fossils of a rail on Aldabra start showing up again.

There are a couple of possible explanations. One is that some remnant population of the Aldabra Rail hung on, some how, and did not die. These were flightless birds, so it is not clear how this might have happened, but perhaps a small population managed to survive on a floating raft of vegetation long enough to reach an exposed bit of land. This seems like a very long shot. It is much more likely that the Aldabra Rail simply died out completely. It went extinct.

The other possible explanation is much more likely and widely understood and accepted, and it is this: the Aldabra Rail went extinct when the atoll went under water. Then after it re-emerged, a group of birds likely from the same parent stock of the original Aldabra Rail re-colonized the atoll (quite probably from Madagascar). This new group of colonizers eventually became flightless and filled the same, or very similar, ecological niche as the original Aldabra Rail.

This is a process called iterative evolution and it is pretty rare. The definition of iterative evolution is: the evolution of similar or parallel structures in the development of the same main line.

But iterative evolution does not produce the same species twice. It may produce similar species, but to produce the same species twice would require starting with the same gene pool twice. The group of birds that first colonized Aldabra, and became the Aldabra Rail 1.0, had a unique combination of genes to work with. The group of birds that later colonized Aldabra, and became the Aldabra Rail 2.0, had a unique combination of genes to work with. Those two combinations of genes may have been similar, but they were not the same. Therefore the decedents of those two groups would not be the same.

I really think that the implications of how this story is being reported is really misleading and possible even damaging.

Misleading because they imply that a species can evolve twice. To go back to the definition of  iterative evolution, it the evolution of “similar or parallel structures…” Similar or parallel structures are not the same as identical species. Two rails that evolved at different times in the same place and that are both flightless, are not the same species.

Damaging because there is weight to the idea of extinction. Extinction is forever. It means that an entire evolutionary lineage has ended, and any potential future that that lineage may have had is gone. If the idea of extinction becomes an impermanent one, it looses its urgency and tragedy. People may well not worry about extinction as that species can just re-evolve. No harm, no foul.

Again, no species can ever occur twice. Once a species goes extinct, that is it for that evolutionary lineage. Even if some other lineage emerges that is close, it will not be the same and will not have the same evolutionary trajectory or potential.

When reporting on science, I feel strongly that the ideas behind the science should be accurately represented. I think it is especially distressing when the sources of the misrepresentations are otherwise reputable sources for science.

I hope the current Aldabra Rail has a long future filled with descendants, and I mourn the loss of the previous rail of Aldabra and the lineage it might have left behind, but never will.

Read Full Post »

A sad landmark has been reached.

A fellow species has fallen.

Let us each take a quiet moment to consider what we have lost.

Pyrocephalus dubius 2

A male San Cristobal Flycatcher

The landmark that has been reached is the first extinction of an endemic Galapagos bird species. For a long time, many species of animals found on the Galapagos Islands, and no where else on earth, have been declining. Biologists have warned for years that if dramatic steps are not taken, many of these species will go extinct and the ecosystems of the Galapagos Islands will be impoverished forever. Exactly this has now happened. The San Cristobal Flychatcher (Pyrocephalus dubius) is the first species to fall. Found only on a couple of the Galapagos Islands, this stunning flycatcher used to be thought of as a subspecies of the more widely distributed Vermillion Flycatcher (Pyrocephalus rubinus). Recent studies, however, have shown that it and the Galapagos Flycatcher (Pyrocephalus nanus), also a former subspecies of the Vermillion, both warranted elevation to full species status. And now, surveys of the islands have found that there are no San Cristobal Flycatchers to be seen.

Pyrocephalus dubius 1

A female San Cristobal Flycatcher

The reason for this tragic loss is not completely known, but it is likely due in part to invasive Brown and Black Rats and in part to the parasitic fly Philornis downsi. The rats have been transported to the islands unintentionally by humans. They climb up trees and eat the eggs out of the nests of many songbird species. The flies were another accidental introduction to the islands by humans when their eggs were brought to the islands on imported fruit. The fly larva infect nestling songbirds feeding on blood and tissue. Infestations frequently become severe enough to kill the nestlings.

How many more species will go extinct before sufficient actions are taken? How many more species can go extinct before the ecosystems of these fragile islands collapse into a ghost of their former selves?

I leave that to your consideration.

Read Full Post »

One hundred years ago today (September 1st, 1914) Martha died in her cage at the Cincinnati Zoo. She was the last member of a species that had once been the most numerous species of bird in the world, the Passenger Pigeon. Flocks of these birds would darken the sty when they passed, and streaming flocks of Passenger Pigeons could take days to go by. Martha’s death marked a moment that often goes unnoticed and unremarked. The moment of extinction. The moment when a lineage of organisms, children to parents to grandparents, through millions of generations, ends, never to continue. it is a sobering moment. A moment for reflection. What is the cost of a species going extinct? For the Passenger Pigeon, there were certainly economic costs. Many people gained their livelihoods by hunting huge numbers of these birds for sale to restaurants and individuals. Railways made money transporting these birds from the field to cities. Restaurants made money selling dishes of Passenger Pigeon to their customers. These economic venues might still be operating if the Passenger Pigeon had been harvest sustainably, and not wiped out as fast as the hunters could kill them. But there are other costs as well. You and I will never get to see a live Passenger Pigeon. My daughter will never get to see one. There is a cost to the limiting of experiences. An impoverishment of exposure. It is hard to impossible to put a dollar amount on this cost, but it is a cost none the less. And what did we gain? Aldo Leopold, speaking at the dedication of the Passenger Pigeon Monument, said “This, then, is a monument to a bird we have lost, and to a doubt we have gained.” The doubt Leopold went on to explain, was the doubt that the gains of human progress were always worth the costs. That increasing human demands, and the associated increasing pressures on wilderness and all other species, were worth it if the lives of humans became better. But what if those gains are not worth it? What if we could be happier with what we have and not strive for more, always more? Is there some point when making a few more things go a little bit faster is not worth the loss of a pigeon? I think there is. I think we need to remember Martha and the rest of her species and doubt the actions of our species a bit more.

Read Full Post »

The phylum Mollusca is one of the most diverse groups of animals in the world.  It includes familiar organisms, like the snail in our gardens, and not-so-familiar organisms, like the recently discovered Colossal Squid that cam grow to up to 33 ft long and weight 1,100 lbs!  This group is comprised of three major classes the Gastropods (slugs and snails), the Cephalopods (squid, octopus, cuttlefish, nautilus), and the Bivalves (clams, mussels, oysters, scallops).  Several more smaller groups exist as well.  In total, all these groups combined account for about 200,000 living species!  Ecologically, molluscs interact in many complex and important ways from decomposers to predators to prey.

Of the 200,000 species of molluscs, most are marine, but as we all know from everyday lives there are plenty of terrestrial molluscs as well.  At least for now.  Terrestrial molluscs have been experiencing dramatically high rates of extinction in the past half century.  The International Union for the Conservation of Nature (IUCN) publishes a Red List which identifies the conservation status of all species every five to ten years.  The IUCN has identified about 800 in the last 500 years, and of those about 300 are molluscs.  That means that about 40% of all extinctions belong to this one group, and some people have estimated the number of molluscs we have lost to be as much as double the IUCN estimate.

Most of these extinctions have taken place on small oceanic islands which is not surprising.  Ecosystems on oceanic islands are notoriously delicate, and extinctions often occur in response to ecological disturbances such as the introduction of some new predator, the clearing of land for agriculture, or competition with other newly introduced species.  Their fragility makes oceanic islands the canaries in the coal mines giving us early warnings of what might befall continents if we do not stop, or at least slow, the current rates of ecosystem disturbance.  On the Gambier Islands, for example, there were 46 species of terrestrial snail.  Of those 46 species, 43 are now extinct.  Many of them have not even been given names.

An interesting footnote is that while terrestrial molluscs are disappearing disturbingly quickly, marine molluscs are not.  Is there something about the marine environment that makes species that live there less prone to extinction?  Is it just that there have been fewer introduced pests and predators to oceans and to land (since land is where humans spend most of their time)?

Read Full Post »