Habitat loss = extinctions??

[Paralith]

I feel like this thread happened twice. First, SkepticLance tells us what Lomborg says about habitat loss. Then some of us (myself included) respond with anger at the idea that habitat loss isn't a major cause of extinction. Then SkepticLance tells us that if we're so darn sure, go and find clear cut examples. So, we go looking for examples, because we know they must be out there somewhere. Lucaspa did a better job than I did, but all in all most cases brought up do have some other contributing factors involved. We come to the conclusion that habitat loss is the weakening blow that allows other contributing factors to really hurt, but which do we blame for the extinction in the first place? Finally, SkepticLance agrees that habitat loss is bad thing (but a general, major contributing cause? he never quite concedes it), and then says that it's all about prioritizing conservation efforts.

 

My conclusion so far, is that we should concentrate on conserving habitat when the habitat is what is precious. However, we should concentrate on stopping poachers and controlling alien introductions, when preventing extinction is the goal.

 

But what makes habitat precious? And what are non-precious habitats? Isn't a habitat precious because of the treasure of species diversity it holds within it, that cannot be found in other habitats? Or just because photos of the place make for good wall art? And once the poachers are stopped and alien species aren't coming in, how does the endangered species in question make a comeback if it's living in an area too small to support a strong, stable population? Habitat loss is important, and it needs to be addressed. If conservation efforts are the ultimate subject of this thread, I think that much can be said with certainty.

[SkepticLance]

To Paralith

 

No-one disputes yourt statement that habitat is important. Conservation must address that problem also, and work to stop loss of vital habitat. This is especially true for certain places (such as South East Asian rain forest)where the remaining habitat is looking to become scarce.

 

However, that is not what this thread was about. In my own view, as I said before, it is more about prioritising effort. If the goal is to prevent an extinction, where do we put our efforts?

 

As I see it, the biggest causes of extinctions, in order of importance, and approximately, are :

 

1. Over-hunting/over-fishing by humans.

2. Introduction of alien species into ecosystems that have not adapted to their presense.

3. Habitat loss.

4. Pollution.

5. Global warming.

 

1 and 2 are the biggest by far. This statement is based on the number of species we know have been made extinct by these two factors.

 

There appears to be a big gap between 2 and 3. Habitat loss seems to be more important as a contributing factor than as a direct cause of extinctions, in most cases. The last one, global warming, probably has had little effect so far.

 

Quantifying these, of course, is probably an impossible task, and my list remains open to debate.

[lucaspa]

To Lucaspa

 

I think there may be a misunderstanding here. I am not looking for proof that loss of habitat is the sole cause of all extinctions. Nor was Lomborg suggesting we needed that. The suggestion was that loss of habitat is a minor cause.

 

This means that over-hunting/over-fishing by humans, and introduction of alien species into an ecosystem are far more important causes of extinction than loss of habitat.

 

Define "minor" and "far more important". These terms imply quantification of number of species that go extinct due to loss of habitat vs the number that go extinct by other causes.

 

Lomborg should have been able to go thru the literature and tote up the number of extinctions due to loss of habitat vs other causes where a cause has been determined. Did he? If not, then his hypothesis is junk, because he never attempted to TEST it.

 

From what you have told us, Lomborg ONLY went looking for supporting evidence. That isn't the way you are supposed to do science. You are supposed to look for data that FALSIFIES your hypothesis. In this case, it would be adding the numbers like I suggested.

 

Although, when your references are looked at more closely, it appears that in any cases there are other major causes at work, as well.

 

I went thru the references eliminating many that indicated other major causes. So please, be specific and do what Lomborg didn't: quantify your statement.

 

This is actually an important concept, since it relates to prioritising action in trying to save species from extinction. Should you put enormous effort into conserving habitat, or would we be better off putting that effort into stopping poaching?

 

It depends on the species. For species where poaching is a major problem, then you consider poaching. But for species that are NOT hunted, such as many of the fish species in the references I gave, stopping poaching isn't going to help is it? What you (and Lomborg) are trying to do is make a universal policy that says "always stop poaching and never save the habitat because habitat loss is a minor cause of extinction". That's just silly.

 

A good example is the Indian tiger. We know that habitat is being lost, and we know that tiger populations are dropping dramatically, and we know that poachers are killing tigers. Do we spend millions on habitat conservation, or do we put those resources into stopping poachers?

 

How about quantifying the number of tigers lost to poaching vs those who die due to habitat loss?

 

http://www.platinum-celebs.com/environment/news/013050.html says that about 50 Sumatran tigers are poached per year. That's about 10% of the remaining population.

 

I'm having a more difficult time determining the number of tigers lost to habitat loss. However, we do know that tigers depend on a range, so there is a fixed number of tigers (n) per unit of area.

 

"Our best approximation concludes that tiger habitats throughout India, Indochina, and Southeast Asia are now 40 percent less than what we estimated in 1995. As the Economic Tigers of Asia leap onto the world stage, wild tiger populations in those countries are in steep decline; today tigers occupy a mere 7 percent of their historical range and the threats are mounting, rather than diminishing." http://www.savethetigerfund.org/AM/Template.cfm?Section=Papers_and_Theses&TEMPLATE=/CM/ContentDisplay.cfm&CONTENTID=2715

 

Poaching, like other hunting, may simply be removing excess population over what the habitat can sustain. So a 10% loss per year is not necessarily a 10% loss of animals per year. Compare to losing 40% of TOTAL number of animals because you have a 40% reduction in habitat.

 

Let's do some numbers. Figure that the Sumatra tiger can sustain 500 individuals in the area it has. They lose 50 per year to poaching from 1995-2007 or a total of 600 tigers. However 500 is 40% of 1250, so in the same 12 year period we have lost at least 750 tigers to habitat loss.

 

My conclusion so far, is that we should concentrate on conserving habitat when the habitat is what is precious. However, we should concentrate on stopping poachers and controlling alien introductions, when preventing extinction is the goal.

 

That's not what the data we have in this thread says. If you only stop poaching and don't stop habitat loss for tigers, tigers are going extinct! Habitat loss is the greater threat.

[lucaspa]

If the goal is to prevent an extinction, where do we put our efforts?

 

As I see it, the biggest causes of extinctions, in order of importance, and approximately, are :

 

1. Over-hunting/over-fishing by humans.

2. Introduction of alien species into ecosystems that have not adapted to their presense.

3. Habitat loss.

4. Pollution.

5. Global warming.

 

1 and 2 are the biggest by far. This statement is based on the number of species we know have been made extinct by these two factors.

 

And where is YOUR data for that? You wanted data from us, but have failed to provide data of your own.

 

Habitat loss seems to be more important as a contributing factor than as a direct cause of extinctions, in most cases.

 

Again, where are your numbers? Also, you forget that there is a mininum number of individuals to maintain a viable gene pool. So habitat loss takes you to that minimum, and then the other causes are "contributing".

 

And no, quantifying should not be impossible. In fact, all you have to do is count up species from the papers where this has been documented. Why didn't Lomborg do that?

[SkepticLance]

lucaspa said

 

And where is YOUR data for that? You wanted data from us, but have failed to provide data of your own.

 

I began this thread with a question, based on an entry in Lomborg's book. I asked for clear examples of extinctions due to loss of habitat. The answer from yourself and others to day has been few such extinctions. I am already aware of any number of extinctions caused by over-hunting, or by alien introductions. For example : google Guam+"brown tree snake" to get a number of accounts how the introduction of the brown tree snake into Guam led to a number of extinctions.

 

In Australia, humans arrived 50,000 to 60,000 years ago. (The oldest skeleton is Mungo Man from a lake bed in New South Wales, dated at 50,000 years ago). The arrival of people 'coincided' with the loss of over 100 species of mega-fauna - exactly the kind of animals people like to hunt.

 

Polynesians crossed the Pacific over a period from 10,000 years ago to 1,000 years ago. Their movement coincided with a massive extinction event - about 2,000 species of endemic birds being lost. This was partly hunting, and partly the introduction of the polynesian rat. Here in New Zealand 36 species of birds went extinct within 200 years of the arrival of humans, while only a third of the rain forest was lost. Such extinctions with known causes were ascribed either to over hunting (11 species of moa) or to the polynesian rat.

 

There is no doubt at all that over-hunting and the introduction of alien species has caused, and continues to cause extinctions on the largest scale. The doubt lies with extinctions caused by habitat loss. Very few are the examples you, and others, can give of clear cut cases of species extinction due to habitat loss.

[Sayonara]

I began this thread with a question, based on an entry in Lomborg's book. I asked for clear examples of extinctions due to loss of habitat. The answer from yourself and others to day has been few such extinctions.

There is another element to this that we have yet to touch upon in this thread (even between the lot of us we have not managed it yet!)

 

The request "please provide clear examples of extinctions due to loss of habitat" is more appropriately provided as "please provide clear examples of extinctions due to loss of habitat that we know about".

 

I perceive the loss of habitat (in the physical sense you mentioned earlier) to be problematic here, because without a complete catalogue of everything that existed within a habitat before it was destroyed, we cannot very well be sure of knowing which species - if any - have been entirely lost during that destruction.

 

This is not so much of a problem for extensively studied ecosystems, but in relatively untouched and largely unknown systems such as deep Amazonian jungle, we have no idea what was there beforehand.

[SkepticLance]

Sayonara said :

 

The request "please provide clear examples of extinctions due to loss of habitat" is more appropriately provided as "please provide clear examples of extinctions due to loss of habitat that we know about".

 

But by comparison, if we ask the same about extinctions due to over-hunting, or introductions of alien species, we get literally hundreds of examples. I could quote at least 20 examples from memory. I could not quote even one extinction example due to loss of habitat.

[Sayonara]

But by comparison, if we ask the same about extinctions due to over-hunting, or introductions of alien species, we get literally hundreds of examples. I could quote at least 20 examples from memory. I could not quote even one extinction example due to loss of habitat.

 

And yet clearly they must have occurred, on account of all the incredibly devastating events that have hit this planet since life began. Comet strike, super volcanoes, ice ages, etc. They are hardly benign and they certainly destroy habitats.

 

I'm not really convinced, by the way, that you just "forgot" the K-T boundary mass extinction event.

[SkepticLance]

Sayonara

 

I do not think that events that occurred 60 million years ago can be quoted in this discussion. Humanity did not even exist then. And this debate is related to the current set of extinctions, which humanity is largely, one way or another, responsible for.

[Sayonara]

This thread makes a bit more sense now.

 

I think you may have lost your audience a little by not clarifying that Lomborg is only considering extinctions due to human action.

[bombus]

Sayonara

 

I do not think that events that occurred 60 million years ago can be quoted in this discussion. Humanity did not even exist then. And this debate is related to the current set of extinctions, which humanity is largely, one way or another, responsible for.

 

Most of the extinctions that have occurred in the past 10,000 years have in the main been a result of over-hunting by man. In that time we have not lost many species from Earth as a result of habitat loss but only because of massive conservation effort.

 

From what I can gather Lomburg is trying to say that habitat loss is not a major concern. This is complete nonsense, and it only takes the vaguest knowledge of biology, or ecology to figure this out.

 

So, Skeptic Lance, in all sincerity, what is the purpose of this post exactly? What are you trying to point out to us?

[SkepticLance]

bombus

 

I am not really trying to point anything out to you. I was interested in what Lomborg had to say. My own reading and observations seemed to bear out his point. I was trying to find out if other people were able to refute his point. So far, not really.

[bombus]

bombus

 

I am not really trying to point anything out to you. I was interested in what Lomborg had to say. My own reading and observations seemed to bear out his point. I was trying to find out if other people were able to refute his point. So far, not really.

 

Am I correct in thinking that Lomburg's point appears to be that habitat loss is not a major concern? If so, then I think his point has been well and truly refuted many times in this thread.

 

If this is NOT his point, and he is merely saying that most human related extinctions to date (that we know of!) have not been due to habitat loss (alone or otherwise) then he is not saying very much at all, as we know this already.

[SkepticLance]

to bombus

 

I agree that habitat loss is a tragedy. My wife and I own 1.85 hectares (4 acres) of land that we will be building our new home on soon. Most of that land is covered in regenerating rain forest. We are busy planting new 'forest giants' and rooting out alien weeds such as English gorse, and Argentine pampas. We trap and poison alien predators such as stoats, rats and possums so that the native birds can thrive. We are recreating natural habitat for native New Zealand plants and animals, and we consider this an important and worthwhile activity.

 

However, the point that Lomborg made was that loss of habitat was not a major cause of extinctions. He did not say it was unimportant in itself.

 

Lomborg is indeed saying that most human related extinctions are not due to habitat loss. I do not believe this can be said to be widely accepted. I have read numerous conservation articles, and have encountered the statement many times that habitat loss is a prime cause of extinctions in the world today. Since most current extinctions tend to be ascribed to human activity, that meets your definition.

[bombus]

However, the point that Lomborg made was that loss of habitat was not a major cause of extinctions. He did not say it was unimportant in itself.

 

Lomborg is indeed saying that most human related extinctions are not due to habitat loss. I do not believe this can be said to be widely accepted. I have read numerous conservation articles, and have encountered the statement many times that habitat loss is a prime cause of extinctions in the world today. Since most current extinctions tend to be ascribed to human activity, that meets your definition.

 

Habitat loss is certainly the prime cause of localised extinctions. Many localised extinctions lead eventually to global extinction, unless conservationists intervene. There also are thought to be many, many species going extinct now that have never even been recorded (such as in tropical rainforests). Habitat loss is probably the most major threat to species on Earth today, especially if you include invasive species as a form of habitat loss, and may actually be the main cause of extinction now.

 

Lomburg seems to be twisting the evidence, or even deliberately misuderstanding it if he is saying that "loss of habitat is not a major cause of extinctions".

 

He seems to be separating local extinctions and global extinctions, when actually they are usually the same thing in the long run.

 

Also, at what point does hunting become the reason for extinction in Lomburgs opinion? If habitat loss reduces a population of millions to a handful of individuals, which are then hunted to extinction, is it really fair/accurate to say that hunting caused the extinction just because it was the last nail in the coffin?

[SkepticLance]

bombus

 

We are talking about extinction of species. When the last individual of that species is dead, the species is extinct.

 

I am not sure how relevent localised extinctions are. Even in pristine environments where human impact is minimal, there are always a few species that are low in number. Some may survive as a species for millions of years, in spite of low numbers. Certainly, in the fossil record, there are organisms with hard shells or bones that fossilise well, which are nevertheless found in only very small numbers, but over long periods.

 

Thus, the significance of a species being low in number, in terms of extinction risk, is not clear cut.

[bombus]

bombus

 

We are talking about extinction of species. When the last individual of that species is dead, the species is extinct.

 

Yes, but global extinction of a species requires lots of localised extinctions

 

I am not sure how relevent localised extinctions are. Even in pristine environments where human impact is minimal, there are always a few species that are low in number.

 

Yes, but for a species to persist there are usually enough individuals to retain a healthy gene pool, unless the species is very resistant to inbreeding.

 

As an example, red squirrels are extinct throughout most of the UK.

 

In Wales we have a few scattered and isolated populations hanging on in coniferous woodlands. These are not viable in the long term, however, as they are small and in time will become too inbred and die off. Also, if these forests were felled the species would go extinct from Wales.

 

They are in the position they are due to habitat loss (essentially) as grey squirrels have stolen their former habitat.

[someguy]

If you consider all of the animals we don't know about that go extinct because of humans they must pretty much be all from destruction of habitat. Since we don't know about them then this number can't be documented. Only ones we know about can be hunted to extinction.. I can't imagine this would be a huge proportion especially if you count insects and stuff. I suppose also it depends on how you value it. do you count how many species die to what cause? how important the animal is to the ecosystem? how well known the animals that go extinct are? are you only considering the ones that actually go extinct? or does endangered qualify? It looks to me like loss of habitat is what will make US extinct and that to me i guess gives loss of habitat the win in the "most important extinction causes" category.

[SkepticLance]

bombus said :

 

They are in the position they are due to habitat loss (essentially) as grey squirrels have stolen their former habitat.

 

someguy said

 

If you consider all of the animals we don't know about that go extinct because of humans they must pretty much be all from destruction of habitat.

 

The above two quotes are argument by definition modification. If we go down that path, we might as well alter the definition to say that all human over hunting, alien introductions, pollution, etc are all just habitat destruction, and therefore all extinctions are due to habitat destruction by definition.

[Sayonara]

The above two quotes are argument by definition modification. If we go down that path, we might as well alter the definition to say that all human over hunting, alien introductions, pollution, etc are all just habitat destruction, and therefore all extinctions are due to habitat destruction by definition.

 

We have been telling you about this exact problem since the very first page of the thread.

 

It is our proposition that Lomborg is arguing from the point of view of a special definition of "habitat loss" which is not used or even recognised by other ecologists. He has chosen a definition which only produces the results he wants to see, which makes his arguments tautological.

[SkepticLance]

Sayonara

 

As I told you some time ago, Lomborg's examples were related primarily to forest habitat, and his text referred to habitat loss in this case as loss of forest. That is : when forest is cut down.

 

If you want to change the definition of habitat loss to include over hunting, or introduction of alien species, or pollution, or global warming or anything else, then we might as well end the discussion. It becomes meaningless by definition.

 

Habitat loss is when a particular habitat is destroyed. Full bloody stop.

 

It is not when something is added, such as another predator. or when a chemical spills into that habitat. Or all the other side issues you or others might want to introduce.

 

Habitat loss is loss of habitat. The habitat is destroyed. Is that simple enough?

[Sayonara]

As should be clear to you by now, because it came up posts and posts and posts ago, and has been discussed throughout the thread, it is Lomborg who is scaling back the definition of "habitat loss", to mean a removal or occlusion of physical features within a spatial domain.

 

The problem is, the "physical features" he is describing - especially in the case of forest habitats - are not simply inert background material. You are talking about trees and the plants, lichens, insects, birds etc that live on and in them. They are part of the system, not just "a thing which happens to be in the same space as one species we happen to be interested in".

 

Thus Lomborg cannot credibly consider his definition of "habitat loss" to be more satisfactory than any other definition ecologists use. What he is doing is substituting the meaning of habitat denial (which I pointed out with big flashing lights and honking klaxons on the first page of this thread) into a demonstration of massive network disruption, which grossly misrepresents the cause and effect within his examples.

 

There is a mildly disinterested but clear consensus in this thread that the only way Lomborg's point can be valid is if he is using his own tautological definitions.

 

I don't understand why you would get shirty about this. It's not like you are defending your own hypothesis, unless you are, in fact, Lomborg?

[Sayonara]

Actually, there is quite a subtle point in there which I want to make entirely clear so as not to encourage further misunderstanding:

 

Lomborg's examples of "habitat loss" in forest systems suffer from exactly the same problems of definition as each and every example you have discarded in this thread. Hence, no special case for ownership of the correct definition.

[bombus]

The above two quotes are argument by definition modification. If we go down that path, we might as well alter the definition to say that all human over hunting, alien introductions, pollution, etc are all just habitat destruction, and therefore all extinctions are due to habitat destruction by definition.

 

Indeed! Now maybe you are beginning to understand why Lomburg and his pointless ideas can be ignored.

[SkepticLance]

To Sayonara

 

No, I am not Lomborg. I am simply someone who bought Lomborg's book and read it. As far as definitions go, I doubt that "loss of habitat" is seriously disagreed with as a definition. When extinctions are discussed in scientific discussion, it generally means the loss of whatever it is that supports the life-form. That includes the plants around it, and various animal life. As I see it, the most common type of loss of habitat would be deforestation. The drying of the Aral Sea might be another example. Landslides a third. Drying of ponds. Desertification of previously fertile plains etc.

 

Lomborg uses several examples of loss of habitat, and all translate as deforestation.

 

I do not think you can, in all honesty, talk about the other main causes of extinctions, and call them loss of habitat. Not in the context of this discussion. That is, over-hunting, over-fishing by humans. Introductions of alien species. Pollution. etc.