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Researchers investigate if the diversity of species is in equilibrium or expanding

University of Pennsylvania computational biologists are claiming that species on Earth are accumulating much more slowly now than they did in the past. Hélène Morlon and Joshua Plotkin, both of the Department of Biology in the School of Arts and Sciences at the University of Pennsylvania, conducted this study using the family trees of today's species and found that speciation rates have declined over time. 

These researchers were curious as to whether the diversity of species on Earth is in equilibrium or continually expanding. In addition, they wondered if Earth has "an invisible stop sign" that would limit species' diversity. 

To answer these questions, Morlon and Plotkin used an updated computational approach to indicate the dynamics of species diversification. Nine patterns of diversification were used as alternative models where a total of 289 phylogenies (evolutionary trees) were examined, representing arthropods, mammals, flowering plants, birds, mollusks and amphibians. The conclusion was that "diversity is generally not at equilibrium," but speciation rates have fallen over time nonetheless. This might mean that the diversification of species are somewhat restrained, and may eventually reach equilibrium. 

"What we see is diversification rates that are declining but not yet to zero," said Plotkin. "We are not yet in equilibrium. Either there is a limit to the total species number and we haven't reached it yet, or there is no such limit. But the rates of diversification are typically falling; when we will hit zero is not yet obvious."

What is obvious is that there have been recent losses of certain species because of human impact, but Morlon and Plotkin's study involves geologic time scales that are much longer, which helps them to better understand today's species. 

Despite these recent losses, researchers were surprised at the lack of extinction they observed in the evolutionary trees of species because fossil records show that several species have become extinct "over geologic time." Morlon and Plotkin found this when looking specifically at the diversity of whales. The diversity of whales has declined during the last 12 million years, but in the analyses of evolutionary trees, extinction was not obvious.  

"By taking advantage of existing data from the flood of genomic research, we hope to combine efforts with paleontologists gathering fossil data," said Plotkin. 

This study was published in PLoS One this month.

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Define "species"
By ekv on 10/1/2010 3:14:57 AM , Rating: 1
Can someone give me a (fairly precise) definition of "species"? I mean, where does one species stop and another start? What's the delineation?

RE: Define "species"
By mooty on 10/1/2010 12:52:33 PM , Rating: 2
from the wiki:
a species is defined as a separately evolving lineage that forms a single gene pool

This is probably the best definition I've read so far.

RE: Define "species"
By rangerdavid on 10/4/2010 1:26:59 PM , Rating: 2
Good question, as there are several definition of "species" because, despite our Western minds trying to name and categorize everything into discrete groups (thanks Linnaeus!), nature is a bit messier. The most commonly used is the "biological species definition." According to this, a species is:

A population of organisms among which the individuals can mate and produce viable offspring, and do-so in nature

The first clause rules out sterile hybrids, like mules (they perfectly robust, but sterile, offspring of house/donkey mating), as proving that horses and donkeys are the same species.

The second clause, "in nature," rules out something like two similar animals being caged together in a zoo (unnaturally manipulated in some way) and being able to have viable offspring, but they would never have encountered each other naturally - say, they were large cats from Africa and North America. They would still be considered separate species, even if their adorable giant hybrid kittens were viable (I don't think these examples are closely related enough, this is just an example).

This is just one, but the most commonly used, definition of species. There are morphological, phylogenetic, molecular/genetic, and other definitions as well.

We often joke that there are two kinds of biologists - "lumpers" and "splitters." Just look at all the revisions in field guides to birds, and you'll see that in one edition there are 4 species of some bird one year, and then next time the book is printed they are all just color-variants or "races" of one species - and then the next year they decide no, there are 2 species with 2 races, etc. It's all very dynamic.

My favorite problem with species definitions is called a "ring species." A good example is discussed here:

A map to help with the above article:

RE: Define "species"
By rangerdavid on 10/4/2010 1:28:19 PM , Rating: 2
Ahh, if only you could edit these submissions. "They" = "The" in the 3rd paragraph.

By DarthKaos on 10/1/2010 5:31:59 PM , Rating: 3
Seriously how could we as a species even begin to think we can tell if evolution is slowing, stopping, or increasing? We have not been on the planet for long enough to be sure of anything. Think of how many plants, animals, etc... there are on the earth today and we believe that with the handful of fossils we are able to find we can figure out all the species there use to be and how many there are now. Rubish! Humans are way to wrapped up thinking they are smarter than they are. Not to mention dating the universe is not an exact science. We could be off enough to have had our planet develop life multiple times and each time a huge solar flare or whatever could have wiped it clean. Life then started over again and again.

Punctuated Equilibrium
By Motoman on 9/30/2010 6:06:04 PM , Rating: 2
It's true
By Argon18 on 10/4/2010 12:26:17 PM , Rating: 1
Global warming killed the dinosaurs. If only those selfish caveman would have recycled and driven Priuses, we would have so many more species today. :rolleyes:

Wow, that was a waste of time
By Denigrate on 9/30/10, Rating: -1
RE: Wow, that was a waste of time
By stirfry213 on 9/30/2010 1:07:55 PM , Rating: 2
Jeez... negative nancy.

Thanks for the zero amount of productive input worth reading.

By YashBudini on 9/30/2010 1:11:04 PM , Rating: 3
negative nancy

Oh this guy is Richard Simmons compared to Mitt Romney.

RE: Wow, that was a waste of time
By Denigrate on 10/1/2010 8:23:45 AM , Rating: 2
Just taking my cue from this supposed writer.

DT has really gone down hill in the last several months. Seems like the new writers are scrambling for something to post.

RE: Wow, that was a waste of time
By YashBudini on 9/30/2010 1:07:56 PM , Rating: 1
Yeah there's no news here. Nothing can accumulate as fast as republicans. Other species simply aren't as materialistic.

RE: Wow, that was a waste of time
By Mogounus on 9/30/10, Rating: 0
By RivuxGamma on 9/30/2010 6:40:19 PM , Rating: 3
Oh, I don't know about that. They sure cling to AGW like a fat kid to mayonnaise.

Natural Selection
By Botia on 9/30/10, Rating: -1
RE: Natural Selection
By RugMuch on 9/30/2010 2:15:27 PM , Rating: 2
You're just not paying attention. I mean look at the Obese.

RE: Natural Selection
By GaryJohnson on 9/30/2010 4:14:12 PM , Rating: 2
homo obesus

or is it Eatibus almost anythingus or Grotesques appetitus?

RE: Natural Selection
By CollegeTechGuy2 on 9/30/2010 6:12:16 PM , Rating: 2

That article isn't even that old...

RE: Natural Selection
By ppardee on 9/30/2010 8:17:59 PM , Rating: 3
There is a distinct... uh... distinction between finding a new critter and a new critter being created. That spider could have been around for eons and we just happen to have stumbled across it. There was a report recently of an Oryx-type creature that had never been seen before (but somehow they knew it existed) until one was caught... and then it mysteriously 'died' in captivity.

RE: Natural Selection
By Ammohunt on 9/30/2010 2:18:38 PM , Rating: 5
you expect evolution to create a new species in 12 years?

RE: Natural Selection
By tigz1218 on 9/30/2010 2:34:31 PM , Rating: 5
There is no theory of evolution.

It's just a list of creatures Chuck Norris allows to live.

RE: Natural Selection
By Murloc on 9/30/2010 3:16:38 PM , Rating: 2
a species can go extinct in a few years, but it can take much longer. Probably the species you saw go exctint were going extict for a long time, and during your life they were at their final stage.
New species need centuries to form. It's not like you see one new species when you wake up one day, in the same manner as you don't see species go extinct because of natural selection in one day.

Also be aware that there always were times in which the biodiversity went down and down, and then BOOM, an explosion of new species of new kinds takes place, like the cambrian one.
This takes million years though.

maybe biodiversity is going down, climate is changing, and a new glacial era will come, afterwards the world will be completely different.

RE: Natural Selection
By TSS on 9/30/2010 5:48:26 PM , Rating: 5
This is not true. Several years ago, i saw my Charmander evolve into a Charmeleon.

RE: Natural Selection
By Omega215D on 10/2/2010 12:26:58 PM , Rating: 2
Charmander uses Evolution. It is super effective!

RE: Natural Selection
By Calindar on 9/30/2010 6:24:41 PM , Rating: 3
Well, you also have to look at the number of species who have been driven to extinction by humanity. We are pretty good at invading a habitat and molding/consuming the resources to our desire. I'd expect speciation to continue to remain slow until the day humans are no longer putting such a heavy burden on nature. When we are gone, a lot of niches that we have either taken over or removed, will suddenly be vacant.

RE: Natural Selection
By Argon18 on 10/4/2010 1:07:04 PM , Rating: 1
"such a heavy burden on nature"? LMAO. What a joke. Why don't you help relieve this incredible burden and go jump off a bridge. After all, by your logic, the world would be a better place with one less human.

RE: Natural Selection
By RivuxGamma on 9/30/2010 6:38:19 PM , Rating: 2
Congratulations, you're a moron.

So, just because you haven't heard of anything new means that there isn't anything new, right?

Guess that couldn't have happened, then, huh?

Or this, right?

RE: Natural Selection
By ppardee on 9/30/2010 8:26:05 PM , Rating: 2
You're assuming that these organisms did not exist until shortly before their discovery. There have likely been many times in the world's history where background radiation levels were higher than they were today. A fungus doesn't need to thrive to remain in existence. And it is possible (and likely) that the Nylon-eating bacteria were able to consume more than just the nylon byproducts, just like we are able to digest substances that had not previously existed.

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