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Offline DoctorBeaver

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Highest extinction rate
« on: 04/10/2007 07:11:13 »
Yes... I know all extinctions are 100%, but that's not what I mean. I want to know if mammals, reptiles, insects, birds, fish or whatever have suffered the most species extinctions.

I realise this is a very difficult, if not impossible, question to answer as many species do not leave traces. I was just wondering if they are any theories about it.

My gut feeling is that it would be insects as there are more insect species alive today than any other. In my weird way of thinking, that would point to their having been more in the past also.


 

another_someone

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Highest extinction rate
« Reply #1 on: 04/10/2007 13:24:33 »
I would tend to believe likewise.  Insects seem to be able to create new species (or what are superficially regarded as species - since for the most part, I don't know of any rigorous test to prove they are separate species, or even rigorous definition of what a species is) far more rapidly, if only because they have shorter life spans, but also many species do not seem to interbreed between colonies very much, so again making divergent genetic paths more likely.
 

Offline JimBob

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Highest extinction rate
« Reply #2 on: 05/10/2007 04:57:32 »
Lets get this straight - you mean extinction now, not in the past? If in the past it would be the Permian extinction. But what we are doing now far exceeds that. By habitat destruction, over hunting, pollution, disease, competition for specialized niches between species and other cause we are causing the biggest mass extinction the world has ever seen - across the board for all species. That is based on documented evidence - not opinion.

http://en.wikipedia.org/wiki/Holocene_extinction_event

 

another_someone

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Highest extinction rate
« Reply #3 on: 05/10/2007 05:18:36 »
Lets get this straight - you mean extinction now, not in the past? If in the past it would be the Permian extinction. But what we are doing now far exceeds that. By habitat destruction, over hunting, pollution, disease, competition for specialized niches between species and other cause we are causing the biggest mass extinction the world has ever seen - across the board for all species. That is based on documented evidence - not opinion.

http://en.wikipedia.org/wiki/Holocene_extinction_event

Yes, but the point is that there are more extinctions now than ever before because there are more species now than ever before (if we had as many extinctions at the end of the Permian period we'd probably have had a negative number of species left, so it is inevitable that we could not have had this number of extinctions any time in the past.

The number that probably matters is the percentage of species going extinct rather than the number of species going extinct.
 

Offline Ophiolite

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Highest extinction rate
« Reply #4 on: 05/10/2007 16:14:57 »
Yes, but the point is that there are more extinctions now than ever before because there are more species now than ever before
I don't believe this is correct and I am not quite sure why you think this would be so. We may know of more species now, but that is for two reasons: a) many species are not readily preserved b) there are more biologists than paleaontologists.
 

another_someone

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Highest extinction rate
« Reply #5 on: 05/10/2007 18:56:55 »
Yes, but the point is that there are more extinctions now than ever before because there are more species now than ever before
I don't believe this is correct and I am not quite sure why you think this would be so. We may know of more species now, but that is for two reasons: a) many species are not readily preserved b) there are more biologists than paleaontologists.

There are two issues in this - whether I am actually correct in my belief (I will explain why it seems to me a rational belief, but that is not to say it is an unquestionably provable belief); and whether the actuality of its accuracy really matters nearly as much as the fact that it appears to be true.

I believe it is rational to believe it to be true as all the evidence is that the general trend is that life gets more complex as it progresses (by this, I don't mean that every organism is more complex, but that some organisms get more complex, in general DNA gets more complex (even where some of that complexity is redundant), and that the interaction between organisms gets more complex).  If life is more complex, then the number of permutations, and number of opportunities to find a novel niche increases.

Now, to look at the issue of comparing apparent numbers of palaeontological species and true numbers of palaeontological species.  The Permian–Triassic extinction is believed to have killed 90% of all known species.  If it is your assertion that we actually only know about 10% of the species existed at the time, then what happened to the other 90% of the species.  One could speculate that 100% of the species we do not know about, all survived the extinction event, and so in reality the extinction event only killed 9% of the species that actually existed - it is possible, but to my mind exceedingly improbable.  The opposite extreme, that 100% of all the unknown species were killed together with the 90% of the known species, thus making the overall extinction rate to be 99% rather than 90%.  This is a slightly more probable scenario than 100% survival of the unknown species, but to my mind still not the most probable outcome.  To my mind, the most likely outcome is that if the extinction event killed 90% of the known species, then it probably killed a similar percentage of the unknown species.  Thus what still remains in that what is important is not the number of species that appear to be dying, but rather the percentage of species that appear to be dying.
« Last Edit: 05/10/2007 19:18:11 by another_someone »
 

Offline Ophiolite

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Highest extinction rate
« Reply #6 on: 06/10/2007 18:20:17 »
I believe it is rational to believe it to be true as all the evidence is that the general trend is that life gets more complex as it progresses
This was the conventional view, and it is applicable over the entire span of the history of life on the Earth. It is not, however, generally though to be valid for life since the Cambrian explosion, and certainly not since the occupation of terrestrial environments. A simple illustration of this, by way of example, is that all of the current phyla were in place in the Cambrian - no new ones have emerged since.
I don't mean that every organism is more complex, but that some organisms get more complex, in general DNA gets more complex (even where some of that complexity is redundant), and that the interaction between organisms gets more complex).
I readily confess that I am not, by training, a biologist, however this statement runs counter to my understanding. For example, one of the surprises to emerge from the human genome project is how few genes homo sapiens actually has.
Now, to look at the issue of comparing apparent numbers of palaeontological species and true numbers of palaeontological species.  The Permian–Triassic extinction is believed to have killed 90% of all known species.  If it is your assertion that we actually only know about 10% of the species existed at the time, then what happened to the other 90% of the species.  One could speculate that 100% of the species we do not know about, all survived the extinction event, and so in reality the extinction event only killed 9% of the species that actually existed - it is possible, but to my mind exceedingly improbable.
I am certainly not arguing that. As you say, the best current estimate is that the Permo_Triassic MEE eliminated 90% of known species. It is wholly reasonable - and I know of nobody in the field who would argue otherwise - to believe that it also killed 90% of unknown species.
The point is that preservation of any remains is a very chancy event and the probability of then discovering the remains even less. Consequently we can only expect to discover a small fraction of the species that were extant at any time. Consider the situation with current species - taxonomists observe that we have stil failed to identify many millions of species, even although these are out there today - visible for us all.
Add in the problem of preservation of creatures largely composed of soft components, in environments that do not lend themselves to preservation, and we just are not going to get to know more than that very small fraction of species.
 

Offline DoctorBeaver

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Highest extinction rate
« Reply #7 on: 06/10/2007 19:52:54 »
b) there are more biologists than paleaontologists.

That may be the case, but they are not all looking for new species.

Quote
For example, one of the surprises to emerge from the human genome project is how few genes homo sapiens actually has.

Indeed, but the manner in which the genes work together is incredibly complex. That is not necessarily true of species with more genes. So, you have to decide what "complexity" means.

As an example, take a computer program. You can write it as 1 instruction following another from start to finish. If a particular function is needed more than once, it is coded in each place. Such a program will have many lines of code but will be very easy to follow as it is linear.

Then take the same program written as a series of separate functions which are called as & when required. You will end up with far fewer lines of code as all duplicate coding will have been removed. But the flow of the program, and how different parts of it interact, will be more complex. Function A can call Function B which calls Function C which could call Function A with different parameters, and so on.

The same could be true of DNA. Larger amounts of DNA could mean more duplication (or redundancy?) and may act in a more linear, autonomous fashion, whereas fewer genes could mean that they interact a lot more with each other (which does seem to be the case).
« Last Edit: 06/10/2007 20:04:18 by DoctorBeaver »
 

another_someone

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Highest extinction rate
« Reply #8 on: 07/10/2007 00:22:09 »
I believe it is rational to believe it to be true as all the evidence is that the general trend is that life gets more complex as it progresses
This was the conventional view, and it is applicable over the entire span of the history of life on the Earth. It is not, however, generally though to be valid for life since the Cambrian explosion, and certainly not since the occupation of terrestrial environments. A simple illustration of this, by way of example, is that all of the current phyla were in place in the Cambrian - no new ones have emerged since.

Maybe not new phyla, but certainly many new species (you may debate whether the new species were matched one for one by previous species that became extinct, but I would suggest that this is probably not the case).

The fact is that the vast majority of species alive today are heterotrophs, and this includes all animals and fungi.  This fact alone means that none of these could have existed until the prior existence of autotrophs (but this ofcourse was all there long before the the first entity that left a fossil existed on this planet); but the point is what this shows is that each new species of life generally depends upon existing species to pre-exist in order to create a niche for it to be able to survive.  It therefore follows that each layer of life can create a new set of niches for a new set of autotrophs to live within.  Thus it follows that the relationship of these species of life must in general become more complex as one has ever more complexity of interrelationship between pre-existing organisms and newer species.

I suppose it is possible to argue that the increase in complexity of life (not of individual organisms, but of the over interrelationship of organisms) is a medium term trend, and is to some extent reset by each major extinction event.  I would accept this caveat to a degree, but I am not convinced that the effects of the increased complexity prior to the extinction event does not leave its mark on the survivors of the extinction event, thus making the re-establishment of complexity after the extinction event more rapid, and allowing a longer term underlying trend in the increase of complexity to continue.

I don't mean that every organism is more complex, but that some organisms get more complex, in general DNA gets more complex (even where some of that complexity is redundant), and that the interaction between organisms gets more complex).
I readily confess that I am not, by training, a biologist, however this statement runs counter to my understanding. For example, one of the surprises to emerge from the human genome project is how few genes homo sapiens actually has.


My understanding of that (again, I too am not a biologist) is not so much a statement of how little DNA we have, but rather how little of it codes for identifiable genes.  What the survey told us nothing about is what was the function of that extra 'noise'.

But what I have said throughout is that I was not suggesting that organisms were themselves more complex (and thus necessarily requiring more genes to code for them), but rather, that the number of distinct specialisations that individual organisms addressed was greater (i.e. that each organism is like a transistor in a larger circuit of life, and each transistor remains as simple as before, but the way they are connected together gets ever more complex).  In that respect, each species may not necessarily have more genes, but the way the genes interplay may themselves be more novel as each species uses its genes to create different specialisations.  As I say, what this 'noise' component has to do with that is pure speculation, but I would not at all be surprised if that 'noise' does increase over time, even as the number of active genes may remain similar.

The other thing to bear in mind is Eth's (DoctorBeaver's) comment about subroutines.  We know that many genes do little more than trigger other genes (i.e. they invoke a subroutine of genes).  In this way, we are dealing with a set of low level functionality that is the same for humans and for bananas, but then over the top of that you have a higher level macro programming language that invokes these low level functions in different ways to do different things.  Thus the real complexity can be invoked be a very few very high level genes that invoke powerful macro functions, thus making little correlation between the number of instructions and the complexity of outcome.

I am certainly not arguing that. As you say, the best current estimate is that the Permo_Triassic MEE eliminated 90% of known species. It is wholly reasonable - and I know of nobody in the field who would argue otherwise - to believe that it also killed 90% of unknown species.
The point is that preservation of any remains is a very chancy event and the probability of then discovering the remains even less. Consequently we can only expect to discover a small fraction of the species that were extant at any time. Consider the situation with current species - taxonomists observe that we have stil failed to identify many millions of species, even although these are out there today - visible for us all.
Add in the problem of preservation of creatures largely composed of soft components, in environments that do not lend themselves to preservation, and we just are not going to get to know more than that very small fraction of species.

I don't believe that to be true (for reasons given above), but it is a statement of belief rather than of proven fact.

But the point is, if that is true, we are still well short of killing 90% of all presently known species, so if the number of species that existed in the permian epoch was similar to the number we have today, it means that the statement that we have a higher extinction rate than at any time in the past is a false statement (although the caveat is that we actually know even less about the short term rate of extinction in the past, and the extinction rates can only be compared over the granularity of time for which we can judge past events - over very short periods of time, we can only say for this statement, that we have absolutely no idea whether it is true or false).
 

Offline Ophiolite

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Highest extinction rate
« Reply #9 on: 08/10/2007 08:31:33 »
The analogy that used to be used was of a large vat filled with boulders, each boulder representing a particular environmental niche. You can then fill the spaces between the boulders with apples. There will be a lot more apples, representing more particualr environmental niches. Then you can fill the spaces between apples and boulders with peas, then with sand grains. The idea is that the biosphere becomes increasingly complex over time as micro niches develop on the backs, as it were, of macro niches.
I understand this concept. I think I was taught this when studying paleaontology and ancient environments. However, that was four decades ago. The science has moved on. This view is, to the best of my knowledge, no longer considered valid. (Since this I now take this as read I do not have to hand citations that would address this. I'll try to locate some.)
Where I do agree with you is on two points:
a) Any large scale extinction will simplify the biosphere for a time. It seems (shades of Gaia) that the biosphere can recover its complexity in a remarkably short (geological) time.
b) Jim Bob's estimate of the size of the current mass extinction we are visiting on the planet is overstated. Moreover, unlike prior mass extinctions we may not be significantly reducing the biomass. Prior MEEs, I suspect, involved not only loss of species, but loss of biomass.
 

Offline JimBob

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Highest extinction rate
« Reply #10 on: 12/10/2007 20:38:23 »
Take the time to read the following - I think you may change you collective mnds.

http://atlas.aaas.org/
 

another_someone

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Highest extinction rate
« Reply #11 on: 12/10/2007 21:35:35 »
Take the time to read the following - I think you may change you collective mnds.

http://atlas.aaas.org/

In what way - I have not read cover to cover, but it still seems to be talking about no more than a few percent loss of species (yes, in absolute numbers, they may look big, but in percentage terms, is still well short of many of the historic extinction events, and it seems to pretty much accept that).  The most extreme projections it claims seem to be a long term 25% loss of species (it actually says "over the next quarter century, when between 2 and 25 percent of species could be lost" - so there is a 10 fold uncertainty even in that).  Certainly, well short of the 90% loss in the Permian extinction.

It also makes all sorts of jumbled up claims - mixing historic and current issues.  For instance, it says "Approximately 118 out of the top 150 prescription drugs sold in the United States are laboratory versions of chemicals found by "bioprospectors" in the wild" - but this covers drugs such as aspirin, which are very old, as well as newer drugs, and ignores the fact that the tendency today is towards designer drugs (this is partly because we are better able to target and understand these drugs, but also because they are far easier to patent).  It also does not seem mention about the loss of the smallpox virus, or that Malaria, which was endemic in Northern Europe in past centuries is now no longer existing in that part of the world.  This is clearly part of the loss of biodiversity - but is it something we should shed tears over?

Ofcourse, if we take conservation to its logical limit, we should also look at racial conservation in humans - which amounts to apartheid.  We do this for a few native tribes of humans in the Amazonian forest, but on a broader scale it is very much out of political favour.  I am not myself suggesting that is the way to go, but it does apply the same standards to humans that conservationists apply to other species.  Certainly, over the centuries and millennia, there has been the loss of many independent isolated human breeding populations, and with this, arguably a loss of biodiversity in the human population.  Is this a good thing, or a bad thing?  If we look at the way conservationists regard biodiversity in non-human species, it maybe should be something we should concern ourselves over.
 

Offline Ophiolite

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Highest extinction rate
« Reply #12 on: 15/10/2007 13:10:00 »
Take the time to read the following - I think you may change you collective mnds.
http://atlas.aaas.org/
JimBob, I haven't read it yet, but it is unlikely to change my mind. I already believe the current extinction rate we have foisted on the planet and more especially the destruction of habitat, is the one of the two most serious consequences of our unacceptable population expansion. I just think, based upon facts, that your numbers are exagerated. And that, I believe, carries with it the risk of getting the problem ignored when the non-believers demonstrate your numbers are wrong. Just a thought
 

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Highest extinction rate
« Reply #12 on: 15/10/2007 13:10:00 »

 

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