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SkepticLance

Habitat loss = extinctions??

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All you're really saying is that there are two levels to protection: protecting the animals themselves from what kills them and protecting populations from what weakens them.

 

Nicely put. I'll have to remember that.

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In Bjorn Lomborg's book : "The Skeptical Environmentalist", he makes the statement that loss of natural habitat is a minor cause of extinctions. Two examples are given of places where massive natural habitat loss occurred with very little in the ways of extinction of species.

1. Puerto Rico.

2. Atlantic coast of Brazil.

 

Yet in environmentalist literature, habitat loss is almost invariably described as a major cause of extinctions.

 

Does anyone have any unambiguous examples of cases where habitat loss has caused substantial extinctions? Please try to use examples where other causes are unlikely.

 

Bjorn Lomborg is either very stupid, or he has been misinterpreted. Habitat loss is the most major threat to species, apart from maybe introduced species. Perhaps he means total extinctions from Earth as opposed to local extinctions? But many a mickle makes a muckle, and we've only been around for 40,000 years which is a blink of an eye in geological time. Once habitat is lost species reliant on it go extinct. We haven't yet lost certain species because of huge conservation efforts, not because habitat loss is not much of factor!

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bombus,

 

You may or may not be correct. Are you able to give clear cut examples to prove your point?

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To POM

 

There is no debate about the fact that humans cause widespread loss of natural habitat. The debate is about whether that is a major cause of extinctions.

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A quote by the World Resources Institute:

"Bjørn Lomborg is an Associate Professor of Statistics in the Department of Political Science, University of Aarhus, Denmark. His prior publications are in game theory and computer simulations. He has no professional training -- and has done no professional research..."

 

To read more:

 

http://pubs.wri.org/pubs_content_text.cfm?ContentID=697

 

http://www.grist.org/advice/books/2001/12/12/point/

 

http://www.americanscientist.org/template/BookReviewTypeDetail

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To gator.

 

Clearly you have not read Lomborg's book. If you had, you would know how much research went into it. An enormous amount.

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bombus,

 

You may or may not be correct. Are you able to give clear cut examples to prove your point?

 

OK.

 

The following species have become extinct in Wales primarily due to habitat loss (although once depleted hunting may have had an impact in some cases)

 

Wolf

Brown Bear

Wild Boar

Corncrake

lynx

 

 

I could go on and on about species currently threatened by habitat loss in the UK e.g. lapwing, barn owl, water vole, dormouse, silver studded blue butterflys, sandhill rustic moth, there are hundreds!

 

Now most of these species are still present somewhere on Earth, but if habitat loss occured everywhere they could go globally extinct - and this is now their greatest threat.

 

The Panda is only still around because massive conservation effort saved their habitat and put breeding programmes into action - else it would have gone by now. The same could be said for Gorillas, Chimpanzees, Orang-utans, and soooo many more.

 

It is true that hunting can wipe out a species e.g. the passenger pigeon, dodo, beaver from most European countries, certain whale species etc, and more known species have gone extinct from Earth as a result of hunting by man, but nowadays, the biggest threat is habitat loss - which I suppose could also include the effects of non-native introduced species.

 

Once a habitat is lost, how can a species designed to live in that habitat possibly survive?

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To bombus.

 

With all due respect to your good self, your examples have not changed Lomborg's arguments. He admits that there are many cases where habitat loss contributes to reduction in population size. He even admits there are times when habitat loss contributes to an extinction. However, there are numerous examples where hunting or introduction of alien species have very clearly destroyed whole species, without any other contributing factors that we can measure.

 

Such examples - where habitat loss is the sole cause of an extinction - appear to be very rare. I have not seen even one clear cut such case mentioned on this whole thread.

 

To gator..

You have not even mentioned the grandaddy of all attacks on Lomborg's book. That found in Scientific American, where the editor did the extraordinary, and devoted an entire chapter to denouncing Lomborg. The fact that people get offended by his approach and attack his work does not obviate his work. There are heaps of people, including some quite famous, who hate what Lomborg has done and will attack his work without mercy. All that shows is that he is writing something very controversial.

 

The book "Skeptical Environmentalist" is meticulously researched and referenced in minute detail. His facts remain facts, in spite of the attacks. I seriously suggest you go to your library and get a copy. Until you actually read it, you are not qualified to critique it.

 

Lomborg is a professor of statistics, and understands that most vital of all mathematical disciplines as applied to science. Using his detailed, mathematical approach means his book is backed up by factual data that is hard to criticise. However, the sheer volume of data means that, if someone looks hard enough, they will find a few bits and pieces that are no longer 100% accurate. That provides ammo for his opponents. The fact that any and every book of equal volume of data can be criticised in that way does not stop the critics.

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With all due respect to your good self, your examples have not changed Lomborg's arguments. He admits that there are many cases where habitat loss contributes to reduction in population size. He even admits there are times when habitat loss contributes to an extinction. However, there are numerous examples where hunting or introduction of alien species have very clearly destroyed whole species, without any other contributing factors that we can measure.

 

Yes I'd agree with that. To date most recorded extinctions have probably been caused by hunting.

 

Such examples - where habitat loss is the sole cause of an extinction - appear to be very rare. I have not seen even one clear cut such case mentioned on this whole thread.

 

I'd agree with that too, but the missing word is 'yet'. And it is a big word to leave out!

 

To gator..

You have not even mentioned the grandaddy of all attacks on Lomborg's book. That found in Scientific American, where the editor did the extraordinary, and devoted an entire chapter to denouncing Lomborg. The fact that people get offended by his approach and attack his work does not obviate his work. There are heaps of people, including some quite famous, who hate what Lomborg has done and will attack his work without mercy. All that shows is that he is writing something very controversial.

 

The book "Skeptical Environmentalist" is meticulously researched and referenced in minute detail. His facts remain facts, in spite of the attacks. I seriously suggest you go to your library and get a copy. Until you actually read it, you are not qualified to critique it.

 

Lomborg is a professor of statistics, and understands that most vital of all mathematical disciplines as applied to science. Using his detailed, mathematical approach means his book is backed up by factual data that is hard to criticise. However, the sheer volume of data means that, if someone looks hard enough, they will find a few bits and pieces that are no longer 100% accurate. That provides ammo for his opponents. The fact that any and every book of equal volume of data can be criticised in that way does not stop the critics.

 

Lomburg misinterprets the meaning of his statistical analysis because he knows bugger all about the subject matter. He's an idiot, and so is anyone who thinks that habitat loss is not a major threat to species (no offence unintended:-))

 

He was not a Professor either, he was an Associate Professor, which is actually a term used to mean a form of temporary lecturer, not a real Professor at all.

 

Let it go SkepticLance, you're on a loser here mate.

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This thread can go on and on forever, but we have already established the essential ingredient that Lomburg's interpretations vary from everyone else's because his criteria for "habitat loss" also vary.

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bombus said :

 

Let it go SkepticLance, you're on a loser here mate.

 

I am open to persuasion, and a big part of the reason I began this thread was to see if anyone could come up with any solid data to show this idea to be wrong. So far, no-one has. If I am on a loser, the big killing punch is yet to come.

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I am open to persuasion, and a big part of the reason I began this thread was to see if anyone could come up with any solid data to show this idea to be wrong. So far, no-one has. If I am on a loser, the big killing punch is yet to come.

 

Nobody has provided conflicting data because the data is the same. It is the interpretations that differ, and there are many reasons (some discussed here at length) why Lomborg is the one standing alone.

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Sayonara

I do not think Lomborg is standing alone. As I reported earlier, a New Scientist article covers the subject, including a lot of scientists who agree with Lomborg.

New Scientist (Australian printed edition) 22 May 2007 page 43

 

I also think it would be a very good thing for you to get hold of a copy of Lomborg's book, and read it. It is a great remedy for a closed mind.

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Sayonara

I do not think Lomborg is standing alone. As I reported earlier, a New Scientist article covers the subject, including a lot of scientists who agree with Lomborg.

New Scientist (Australian printed edition) 22 May 2007 page 43

I don't mean alone in the literal sense, obviously. But it seems to be a minority view.

 

I also think it would be a very good thing for you to get hold of a copy of Lomborg's book, and read it. It is a great remedy for a closed mind.

If you think I am being closed-minded about this, then clearly you have not paid close enough attention to my posts. I do not state that Lomborg is wrong, or that I believe him to be wrong. I consistently state that in this thread the discussions of his interpretations lack crucial information about his use of particular terms.

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In Bjorn Lomborg's book : "The Skeptical Environmentalist", he makes the statement that loss of natural habitat is a minor cause of extinctions. Two examples are given of places where massive natural habitat loss occurred with very little in the ways of extinction of species.

1. Puerto Rico.

2. Atlantic coast of Brazil.

 

Remember, you can ALWAYS find support for a theory, if that is what you are looking for. It looks like Lomborg did just that.

 

I would start here:

1: Kareiva P.

Ecology: compensating for extinction.

Curr Biol. 2004 Aug 10;14(15):R627-8. Review.

PMID: 15296781 [PubMed - indexed for MEDLINE]

 

2: Borrvall C, Ebenman B.

Early onset of secondary extinctions in ecological communities following the loss

of top predators.

Ecol Lett. 2006 Apr;9(4):435-42.

PMID: 16623729 [PubMed - indexed for MEDLINE]

 

3: Eklof A, Ebenman B.

Species loss and secondary extinctions in simple and complex model communities.

J Anim Ecol. 2006 Jan;75(1):239-46.

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This discussion reminds me of a case that we investigated last year.

 

An elderly lady was knocked to the floor during a robbery and suffered minor injuries. In hospital she developed secondary problems as a result of those injuries, and died.

 

At court, the prosecution argued that the robbery was aggravated by manslaughter because the actions of the offender led to the death of the woman. The defence argued that she was old, infirm, and on the way out anyway, and that she could have died from the same problems without having been injured.

 

One detective summed it up quite succinctly by asking the prosecution "had she been old, infirm, and on the way out anyway, and was hit by a bus, what would you say the cause of death was?"

 

 

Now I hate explaining things with analogies, as a general rule, but I think we have a similar situation here. Loss of habitat (which bear in mind does not necessarily mean complete loss, or even removal of biomass) is frequently the factor that weakens populations and systems, allowing other negative factors to drive them under.

 

So an obvious question is, do we consider that to be the root cause (or the indirect aggravating factor), as in "we would have gotten away with it too if it weren't for that darned habitat loss", or do we consider it to have no more (or even less) importance than any factors which follow it?

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I am open to persuasion, and a big part of the reason I began this thread was to see if anyone could come up with any solid data to show this idea to be wrong. So far, no-one has. If I am on a loser, the big killing punch is yet to come.

 

SkepticLance, I have to wonder why YOU didn't do any research on specific examples of extinction due to habitat loss. You keep talking about "anyone could come up with". Why are you putting the responsibility on us? It's also YOUR responsibility to look for contrary data.

 

Now, I immediately went to PubMed and entered the search "habitat, loss, cause, extinction" and got several papers. I am posting a few of them. Be sure to look at the reference list for the scientific articles to due the track back to specific examples. One thing to also consider: Lomborg may have created a strawman by saying "only" due to loss of habitat. Most extinctions involve a number of factors, of which loss of habitat is one. Hunting is also a major one. I picked only contemporary examples, but paleontology is full of examples where there was massive lost of habitat -- such as the desertification at the end of the Permian.

 

1. http://171.66.122.165/cgi/content/full/99/17/11229

 

This one you must go to. It is a PNAS article. Gives mathematical treatment of species exinction due to loss of habitat.

 

2. http://www.pnas.org/cgi/content/abstract/92/20/9343 4 species of bird lost thru habitat destruction of forests.

 

3. SCIENTIFIC AMERICAN 266 (5): 98-104 MAY 1992

 

4. http://www.wolfmoonpress.com/Books/lordgodbird.htm

 

5: J Anim Ecol. 2007 May;76(3):568-79.

 

Changes in landscape composition influence the decline of a threatened woodland

caribou population.

 

Wittmer HU, McLellan BN, Serrouya R, Apps CD.

 

Agroecology, Faculty of Land and Food Systems, University of British Columbia,

2357 Main Mall, Vancouver, British Columbia, Canada. huwittmer@ucdavis.edu

 

1. Large-scale habitat loss is frequently identified with loss of biodiversity,

but examples of the direct effect of habitat alterations on changes in vital

rates remain rare. Quantifying and understanding the relationship between habitat composition and changes in vital rates, however, is essential for the development of effective conservation strategies. 2. It has been suggested that the decline of woodland caribou Rangifer tarandus caribou populations in North America is precipitated by timber harvesting that creates landscapes of early seral forests.

Such habitat changes have altered the predator-prey system resulting in

asymmetric predation, where predators are maintained by alternative prey (i.e. apparent competition). However, a direct link between habitat condition and caribou population declines has not been documented. 3. We estimated survival probabilities for the threatened arboreal lichen-feeding ecotype of woodland

caribou in British Columbia, Canada, at two different spatial scales. At the

broader scale, observed variation in adult female survival rates among 10

distinct populations (range = 0.67-0.93) was best explained by variation in the amount of early seral stands within population ranges and population density. At the finer scale, home ranges of caribou killed by predators had lower proportions of old forest and more mid-aged forest as compared with multi-annual home ranges where caribou were alive. 4. These results are consistent with predictions from the apparent competition hypothesis and quantify direct fitness consequences for caribou following habitat alterations. We conclude that apparent competition can cause rapid population declines and even extinction where changes in species composition occur following large scale habitat change.

 

6: J. Theor. Biol. 2004 Oct 7;230(3):351-8.

 

Who dominates whom in the ecosystem? Energy flow bottlenecks and cascading

extinctions.

 

Allesina S, Bodini A.

 

Department of Environmental Sciences, University of Parma, Viale delle Scienze,

11/A, 43100, Italy. sallesina@nemo.unipr.it

 

In this paper, we investigate the problem of secondary extinction in food webs through the use of dominator trees, network topological structures that reduce food webs to linear pathways that are essential for energy delivery. Each species along these chains is responsible for passing energy to the taxa that follow it, and, as such, it is indispensable for their survival; because of this it is said to dominate them. The higher the number of species a node dominates, the greater the impact resulting from its removal. By computing dominator trees for 13 well-studied food webs we obtained for each of them the number of nodes dominated by a single species and the number of nodes that dominate each species. We illustrate the procedure for the Grassland Ecosystem showing the potential of this method for identifying species that play a major role in energy delivery and are likely to cause the greatest damage if removed. Finally, by means of two indices that measure error and attack sensitivity, we confirm a previous hypothesis that food webs are very robust to random loss of species but very fragile to the selective loss of the hubs.

 

1: Sun. 1992 Apr 28;:11A.

 

The mushroom message.

 

Zimmerman M.

 

A basic law of ecology is that living things are tightly dependent on one

another, often in ways that are not easy to imagine. Who, for example, would have predicted that when the last dodo was killed in 1675, that death would lead to the slow extermination of the tambalocoque tree, whose fruits germinate only after passing through the dodo's digestive system? Now no natural strands of tambalocoque younger than 300 years can be found. Or who would have predicted that clear-cutting tropical rainforests would so significantly alter local weather patterns that the tropical rainforest biome itself and its vast diversity of life might not survive?

 

I put this one up because, for the tree, there is a "loss of habitat". Not, in this case specific room to grow, but an essential part of the ecosystem.

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http://www.fws.gov/news/newsreleases/r1/D7DABD7B-442E-4C09-834A61126A5C25F4.html

 

""These species are especially vulnerable to extinction due to loss of habitat, their limited range, and the small populations that currently exist," said Steve Thompson, manager of the Service’s California/Nevada Operations Office. ... Habitat loss, invasive nonnative plant species, and residential and commercial developments are major factors contributing to the decline of these species. "

 

http://www.hear.org/pier/pdf/nrcs_plant_guide__triadica_sebifera.pdf

"Attwater’s prairie chicken (Tympanuchus cupido attwateri), once

abundant in the coastal prairie of Texas and

Louisiana, is near extinction due to loss of habitat."

 

http://www.cincikillies.org/Archive_Cons.htm

"According to Wolfgang Eberl, Aphyosemion elberti (bualanum) N'tui is extinct due to land clearing, although it is being maintained within the hobby. The same is true of several of the Cynolebias species from Uruguay (Valizas), which are no longer found in the wild, including C. cheradophilius, C. viarius, C. melanotaenia and C. luteoflammumlatus."

 

http://content.class.com/ewew_content/bio1b_v2/02pla/0202/0202_0403.htm

"Horsetails belong to the subphylum Sphenopsida. They are much tougher and harsher plants than ferns, yet only about 40 species remain because many varieties have become extinct due to loss of habitat."

 

http://quakeinfo.ucsd.edu/~gabi/erth15-05/Lecture27.html

"most birds probably go extinct due to loss of habitat (e.g. Calfornia Gnatcatcher, Kauai O'o) "

 

http://www.stors.tas.gov.au/item/stors/7b1a99a1-b1c5-3568-3d36... http://www.stors.tas.gov.au/item/stors/7b1a99a1-b1c5-3568-3d36-1ace96793eeb/1/ferns006.html

"Populations of B. cartilagineum at Georges Bay, Glengarry and at Tin Hut Creek are now presumed extinct due to loss of habitat through logging"

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One of the reasons I don't like "here is my example, now show me yours" discussions, is that it is an unconstrained battle which usually encourages a shift in the burden of proof.

 

How many examples should we provide? Should we counter with one for each of Lomborg's? Maybe we should have twice as many? How many examples will be acceptable or convincing? Alas, that has not been stated.

 

Although having said that, Go Lucaspa Go!

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One of the reasons I don't like "here is my example, now show me yours" discussions, is that it is an unconstrained battle which usually encourages a shift in the burden of proof.

 

How many examples should we provide? Should we counter with one for each of Lomborg's? Maybe we should have twice as many? How many examples will be acceptable or convincing? Alas, that has not been stated.

 

Although having said that, Go Lucaspa Go!

 

Thank you.

 

To answer your questions, it depends on what the hypothesis is. Remember, the idea is to falsify a hypothesis, and for that you don't need many examples. So you have to figure out what the hypothesis is.

 

One of my problems with the thread is that SkepticLance's statement of Lomborg's hypothesis changes in order to avoid falsification. He starts off with:

"In Bjorn Lomborg's book : "The Skeptical Environmentalist", he makes the statement that loss of natural habitat is a minor cause of extinctions. ... Does anyone have any unambiguous examples of cases where habitat loss has caused substantial extinctions?"

 

You can see the wriggle room here in "minor" and "substantial".

 

The hypothesis from SkepticLance's statement would be: loss of habitat ALONE does not cause any extinctions.

 

After all, if the hypothesis were "habitat loss causes some but not many extinctions" then the request for "unambiguous examples" would not make sense.

 

My examples falsify that hypothesis.

 

The hypothesis might be: loss of habitat ALONE does not cause "substantial" [as in a large number of species] extinctions.

 

If that is the hypothesis, then the paleontological data falsifies it. There have been extinctions of entire ecosystems brought on by loss of habitat by cooling (Ice Age), warming, or desertification.

 

But SkepticLance changes the hypothesis here:

With all due respect to your good self, your examples have not changed Lomborg's arguments. He admits that there are many cases where habitat loss contributes to reduction in population size. He even admits there are times when habitat loss contributes to an extinction. However, there are numerous examples where hunting or introduction of alien species have very clearly destroyed whole species, without any other contributing factors that we can measure.

 

In order for this paragraph to make sense, the hypothesis has to be: habitat loss is the ONLY cause of ALL extinctions.

 

Of course, that hypothesis can be, and has been, falsified. No ecologist I know defends that hypothesis (because it has been falsified). Lomborg has made a strawman hypothesis. The data says that habitat loss due to human activity usually directly causes the extinction of a few species. The loss of those species then causes the extinction of others as 1) the ecosystem collapses and 2) populations decline and become vulnerable to other causes such as predation or disease.

 

I think it is this shift of hypotheses -- and to a strawman hypothesis -- that triggered your comment about "burden of proof". It's not that the burden of proof has shifted, but that Lomborg has gone from a reasonable hypothesis to a hypothesis that has already been falsified and, therefore, no one is defending.

 

Why did Lomborg do this?

 

The difficulty comes when hypotheses have consequences outside science in policy and economics. Such is the case here with conservationism. With the supported hypothesis "habitat loss contributes to and sometimes is the sole cause of extinctions" comes the non-scientific policy of conservation of habitats. That has economic consequences -- such as restrictions on draining wetlands for (profitable) development.

 

So, one way to argue against the non-scientific policy is to challenge the science. Lomborg appears to be doing that: challenge that habitat loss causes extinctions. If the hypothesis is wrong, then there is no scientific basis for the non-scientific policy of preserving habitats. :) However, as SkepticLance has shown with that last quote, Lomberg is making a strawman hypothesis that habitat loss directly causes all extinctions.

 

Now, about that "shift in the burden of proof". That's a fallacy, you realize. There is no THE burden of proof. In any scientific argument, BOTH sides have a "burden of proof" and it NEVER resides on just one side. I realize your background is the law, and here humans have arbitrarily decided to make a "burden of proof". But you can't extrapolate that outside the law.

 

What science does is test hypotheses. In doing that, everyone has an obligation to do the testing in an attempt to show the hypothesis wrong. Science works best when the advocates of a hypothesis admit when the hypothesis has been falsified. However, sometimes advocates, often for emotional reasons, refuse to do this. There are several ways to try to avoid falsification. Lomborg (thru SkepticLance) is using one of them: in the face of falsification modify the hypothesis so that it is not falsifiable.

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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.

 

Some of the examples you and Sayonara have presented are good stuff. There are a few that indicate loss of habitat is a main cause of extinction. Although, when your references are looked at more closely, it appears that in any cases there are other major causes at work, as well.

 

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?

 

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?

 

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.

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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.

 

Unfortunately we are quite poor a deciding what to do to prevent extinctions. For example, currently on the Columbia River salmon are considered both threatened and endangered. Three causes have been identified.

 

1) Both the Columbia River and Snake River have been significantly dammed. This has changed the habitat.

 

2) Caspian Terns have been introduced. These birds nest on man made islands constructed from dredging debris. The Columbia River is dredged to open up water ways for barge traffic which extends to Lewiston Idaho on the Snake River. The birds eat young salmon during spring. Caspian Terns are an endangered species.

 

3) California sea lions is travel 145 miles up the Columbia River each year to prey on thousands of spring chinook salmon and steelhead that congregate below Bonneville Dam before moving up the dam's fish ladders. California sea lions are an endangered species.

 

Sensible people would correct this problem by submerging the man made islands and killing the sea lions at the Bonneville Dam fish ladders.

 

The emotional proposal is to remove the dams from the Columbia and Snake Rivers to protect the salmon. Now if they do that there won’t be much reason for dredging the Columbia for non existent barge traffic, so the Terns will go. Since the salmon won’t be easy prey at the fish ladders, the sea lions will go. This solution will however teach man not to mess with nature when the Northwest US economy collapses. Of course we could always build coal fired power plants to make up for the loss of power generation. Also, it’s good that trains can run on coal since we will have to ship all that inland grain by train over the Cascade Mountains instead of by much more efficient river barge. Won’t that be a plus for the environment.

 

A parting note. I appreciate the fact that you call for stopping poachers and not sport hunters. Legal sport hunting has always improved species recovery. Sport hunting places a monetary value on wild animals and therefore gives people a financial incentive to protect the species. Banning all hunting creates the opposite effect turning endangered animals into pests which encourages poaching. The over hunting mentioned often in this thread which has lead to species decline is market hunting (legal selling of the animals taken). Market hunting should always be prohibited in all forms.

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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.

 

I still think this is a tautology. if you take 'habitat' as 'place where you can live', then losing it obviously will lead to extinction (barring any other suitable habitatis in the vacinity you can move to).

 

now... what difference is it if your habitat becomes unlivable due to it's dissapearance (deforestation etc), it's toxification, introduction of predators (including humans), change in weather, dissapearance of food, etc etc etc?

 

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?

 

again taking 'habitat' to mean 'place where animal can live', 'not too many poachers' is kindof a pre-requisite for a location that tigers can use as a habitat, along with 'enough prey to sustain them', 'no toxins', 'correct weather', 'no really bad diseases', etc.

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Dak

 

That approach appears to consist of redefining your terms to make your argument true.

 

I do not think, in terms of this debate, we can define habitat loss to include the two main causes of extinction. That is : Over-hunting, and introduction of alien species.

 

Perhaps we should agree on habitat loss to mean removal of the main structure of the habitat. So if it is a forest, then removing the trees is what we talk about. If a coral reef, then removal of the hard corals.

 

This would exclude the two factors above, and exclude damage that happens without removing the main structures - such as pollution, which causes harm to a forest but does not remove the trees.

 

To waitforufo

 

A nice example. Perhaps a lesson in the need to think outside the square?

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