There will be a great loss of diversity at first but will animals evolve and fill the diversity gaps i.e. if theres no predator of species X but its and species Y both hunt species Z will species Y evolve to hunt species X and redress the balance?
Estimates of species lifetimes are not based merely upon morphological divergence documented in the fossil record. Genetic divergence can also be used to estimate the average duration of species. (These divergence rates are in part calibrated by using the fossil record, but based on morphological differences greater than those found at the species level; they may also be calibrated based on biogeographical considerations.)
Research indicates in general that there is a 2% sequence divergence in mitochondrial DNA per million years. Also, more than 90% of sister-species (species that are one another’s closest relatives) show at least a 2% sequence divergence. This indicates that the majority of species are more than one million years old.
There are currently about 10,000 species of birds in existence. If rates of extinction and speciation were in balance, we would expect about one species to become extinct every 100 years. This would presumably be the normal “background” rate for the past million years or so.
More than 100 species of birds have been documented to have become extinct since 1800. (Many more are so severely threatened that they are almost certain to disappear in the very near future.) This gives a current extinction rate of at least 0.5 species per year, or 50 times the “normal” rate. Note that this only takes into account species lost in the recent past, not those that may have been killed off as Homo sapiens spread through most of the world, and that these are included as part of the mass extinction currently taking place.
50 times larger would certainly be on the “high side of average.”
My point was not that the rate for Britain could or should be extrapolated to the rest of the world, but that even if the rate for the rest of the world were very much smaller it would mean the extinction of a much higher absolute number of species.
I would agree that this particular study does not have the degree of significance that the article claims for it. However, it is an additional piece of evidence in the large body of research that indicates biodiversity is being lost at a much higher rate than is “normal,” and that the overwhelming cause of this loss is human activity.
Colibri I have seen this use of genetic divergence as a guide to species extinction before. It seemed terribly dodgy then and it seems even more dodgy now that you have explained it. Simply knowing that the majority of species diverged from their nearest relative more than 1 million years old tells us next to nothing about extinction rates.
From my understanding the process simply can not work.
Consider the massive deforestation experienced in Europe pre-1300. Somewhere between 50% and 75% of the forest cover was removed. That must have caused extinctions. But we will assume that the species that became extinct were evenly represented in all age classes. What that means is that 99% of the organisms found in Europe could have become extinct and the mean species residence time would remain exactly the same before and after the event – 1 million years.
Knowing that the survivors diverged 1 million years ago doesn’t tell us anything at all about what the extinction rate was. We could have had 10, 000 bird species in Europe alone prior to this event with a mean age of 1 million years and you would have been arguing that one European species should become extinct every hundred years. The day after the event we could have had 100 bird species in Europe, still with a mean age of 1 million years, and you would be arguing, as you are now, that only one species should become extinct every thousand years. The exact same method is producing figures that vary by a factor of 100. That tells me that it is sloppy science.
The whole concept is perfectly self contradictory. It relies on a uniform extinction rate with no mass extinction events in order to establish mean residence times, but it exists exclusively to establish that the current event is a mass extinction and well above the mean.
To put it another way the use of genetic divergence relies entirely on an a priori assumption that extinction events similar to the current one are abnormal. And yet you are attempting to use it to establish that the current extinction event is abnormal. That isn’t even logically valid, much less good science. Of course once we reject the assumption that the current mass extinction event is unusual then genetic divergence tells us nothing. If we use it in isolation it is quite possible that 90, 000 bird species could have become extinct last Thursday and the mean residence time for the surviving species would not change. Yet you would still be trying to get the expected extinction rate by dividing 1 million by 10, 000 instead of 90, 000 and arriving at the wrong figure completely.
Here is the article I first read on this. It was published in 1999. 5 years ago they said that in 100 years 50% of the worlds flora and fauna could be on the road to extinction. So 5% of the way through this extinction we are seeing some species on the decline.
Pretty wide brush, and alarmist, I think. There are natural die offs of populations that occur when necessity demands it. I am not 100% convinced that what we are seeing here is in fact the 6th extinction. I am not sure how natural selective thinning could be ruled out. Are we taking our toll on this planet? Positively. Is our effect exponential based on our continued industrialism? Yep, I think so.
But there are a number of things going right here, people, and as long as there is a base of consumers willing to spend their dollars in places that encourage bio-diversity, I think that we as a planet will be ok. Not great, but OK.
I am not saying that we shouldn’t all be stewards of this planet, but I do not believe that is an acheivable goal. There are way too many cultures, countries and political systems without much cohesion to make a world wide effort effective.
As long as people are starving in sub-saharan Africa, ecology and protecting endangered species will not be a driving economic force. Growing food will be more important than protecting elephants or lions or any other vanishing or endangered species. Since we are hardwired to ensure our survival, I can not imagine these priorities changing without major social, economic and political upheaval. I also can not imagine what would have to happen here in the US or Europe for us to say we will give up consumption to ensure a species of butterfly survives.
Hmmm, I don’t quite follow the connection between mtDNA and extinction rates either (sure, they’re great for identifying maternal ancestry but…) Could you explain this a bit more?
Now as to the “Science” of it (of the importance of the study):
You are right, however,
Extinction is a difficult topic to research. We have only circumstantial evidence, can’t experiment well, and have to estimate based on preconceptions, but…
If we take the evidence we do have (fossils, extant species…) we can calculate an average lifespan for a species at about 4 to 5 million years or so. (The average I am using is from David Raup and here.)
Estimates for total biodiversity come in at around 5 million species (on the low end) to over 10 million (how this is done).
We should therefore expect one species to become extinct every year or so on average (or slightly more), but like any such “averaging” data (river flooding is a good example), this probably won’t be uniform over the measured period - it will come in “lumps”.
Now if the current (observed) rate for extinction exceedes the expected rate we may have cause for concern. I say “may” because we still don’t know if we are experiencing one of those “lumps” or not. Humans obviously affect the ecosystem, but the severity is difficult to measure because of the uncertainty of what a “normal” extinction rate is. (Current extinction rate estimates are from 10 to 1,000 times :eek: higher than this expected amount - of course, it all depends on the estimates and the agenda.) Further, Raup has argued that mass extinctions are periodic. For example - The K-T extinction is a 100 million year event (but it still could happen twice in ten years as such).
Most studies (such as the OP’s) - though not decisive on their own, are helpful in gathering evidence on extinction rates and the effects of human activity, so we can both improve our estimates and (maybe) adjust our activity. Though you’re right Jane, there currently is no economic benefit in altering our actions, better estimates may change that.
That’s because your understanding of the process, and of the available evidence, is very limited.
Genetic divergence data is not the only evidence available. Analysis of the fossil record indicates an average species lifetime for vertebrates throughout the Cenozoic of approximately 1 million years, based on appearance and disappearance of different forms in the record. Speciation and extinction rates vary somewhat during specific periods, but a species lifetime of about 1 million years is a reasonable order-of-magnitude average figure for the last 65 million years. Note that this is a rate calculated by the analysis of individual lineages, and does not depend at all on the absolute number of species present at any one time.
You objected to using data from the fossil record, based on the fact that some species are sufficiently similar that they would not be detected as being different from fossils alone. Genetic data on presently existing species (for which behavioral and other data is available) provides corroboration of the speciation estimates derived from the fossil record. In both cases the estimates are on the order of magnitude of 1 million years. In certain limited circumstances, speciation rates may be higher, but this does not hold over large areas or over long time periods.
Actually, the predicted impact based on biogeographic theory is less than that. Based on the species-area curve, a 90% reduction in habitat area results in a 50% reduction in species diversity. However, this only holds on a local scale. On a regional scale, the effect of habitat loss can be either greater or less depending on how localized and specialized species are. In the case of Europe (and other temperate areas) most species are widespread and relatively resilient in terms of habitat, so that the actual species loss has probably been less. In the tropics, where species are more localized and more habitat-restricted, the impact of habitat loss could be greater on regional biodiversity.
That tells me that your math is sloppy, and you don’t really understand what it is we are calculating here.
In the first place, your arithmetic is wrong:
Assuming equilibrium between speciation and extinction, in the first case we have 1,000,000 years/10,000 species = one species extinction every 100 years per 10,000 species. In 10,000 years, we can expect 100 extinctions, or one percent of the total.
In the second case, we have 1,000,000 years/100 species = one species extinction every 10,000 years (not 1000, as you have it). In 10,000 years, we can expect 1 extinction out of 100 species, or one percent of the total.
This is exactly the same rate as in the first example.
As I pointed out earlier, the extinction rate is not just estimated from the genetic divergence data, it is also calculated directly from the fossil record. The fossil record tells us that the current extinction rate exceeds average rates over the past 65 million years.
There is a very strong consensus among scientists, based on peer-reviewed research appearing in scientific journals, that the current rate of extinction is very high and is overwhelmingly due to human-caused impacts on the environment. In 1998, a poll of scientists indicated that 70% believed that we were in a period of extinction comparable to that of the previous mass extinctions in Earth’s history. These are the people who are most familiar with and best able to evaluate the available data. On the other hand, most of the accusations of “bad science” leveled at these conclusions comes from non-scientists who find the results inconvenient from a political or economic point of view.
The mtDNA divergence data provides estimates of the rate of speciation. If the total number of species is to be stable over some length of time, then speciation must be balanced by extinction. If speciation exceeds extinction, then species numbers increase; if extinction exceeds speciation, then species numbers go down.
Since the rate of present species extinctions exceed by an orders of magnitude (or several orders of magnitude) the speciation rate as estimated by genetic data, one concludes that we are not presently in a period of equilbrium of species number, but one in which species number is rapidly declining.
If species lifetimes were more on the order of 10,000 years, than the current extinction rate might not be too far out of line.
Regarding your figure of 5 million years as a species lifetime vs the 1 million I gave, I would mention that Raup’s estimates are based mainly on marine invertebrates, which may have longer species lifetimes than vertebrates. In any case, the estimates are of the same order of magnitude, and a 5 million year species lifetime estimate would indicate that current extinction rates are even more extreme.
Interesting. The article cites some of the work of one of my own colleagues here.
This mass extinction hasn’t just started. Some scientists think that our ancestors were responsible for the extinction of the megafauna of Australia and the Americas 30,000-10,000 years ago. More certainly, expansion of humans into the Pacific Islands and to Madagascar between 1-1200 A.D. caused the extinction of hundreds (more likely thousands) of species. Another wave of extinction coincided with the Age of Discovery after 1500, with the introduction of non-native plants and animals around the world. We are now in the midst of the next wave, caused by an enormous increase in human population and its impact on the environment during the past century.
Human activity is implicated in the vast majority of extinctions for which a cause is known. These die-offs are certainly not “natural.”
And yet you are apparently unable to show examples of where it is limited.
But as already noted most species never leave any remains at all. That means the margin for error is huge.
This technique produces an inevitable sampling erro. Those species most likely to be fossilised will be the most widespread and/or the most abundant. Widespread and abundant species also tend to be the most robust since they are not restricted in range, diet or numbers. As a result any analysis of the fossl record will contain an overabundance of those species least likely to become extinct. Any age calsultaed will inevitably be on the high side.
And that of course is the entire problem isn’t it? You are calculating survival times from those fossils that have lineages, which are those lineages which have proven abundant enough or dispersed enough temporally or spatially tp provide multiple fossils.
How do these analyses deal with monotypic fossils? Do they assign a duration of 1 day to these species? I doubt it since it would be hard to produce a mean of 1 millio years if they did. Or do they just discoiunt them altogether?
That alone should ring alarm bells. You are saying that the average residence times of the finely divided extant species which are distinguished many times on the basis of genetic analysis is the same as the data obtained using fossil evidence which over-represtents abundant species.
Yes I’m well aware of that. You are evading the point. I didn’t say 99% of species did become extinct. I said that if they could have become extinct in the recent past you would not be able to tell using genetic evidence.
And that was precisely my point. The technique always produces the same rate of extinction. But rate is effected by initial state.
Knowing that the survivors diverged 1 million years ago doesn’t tell us anything at all about what the extinction rate was. We could have had 10, 000 bird species in Europe alone prior to this event with a mean age of 1 million years and you would have been arguing that one European species should become extinct every hundred years. The day after the event we could have had 100 bird species in Europe, still with a mean age of 1 million years, and you would be arguing, as you are now, that only one species should become extinct every 10 thousand years. The exact same method is producing figures(not rates) that vary by a factor of 100. That tells me that it is sloppy science.
That is my point Colibri, and one you chose to ignore to comment instead on a mathematical error that is in favour of my case.
This example demonstrates that your technique will not and can not detect even the most catastrophic extinction events in the last 500 years. That is my point. Very sloppy science to use a technique to calculate the occurrence of extinction events that is totally unable to detect extinction events.
But that normal rate, as I have proved, is calculated using atechnique that needs to assume that the current event is abnormally high. If we assume the current event is in fact abnormally low then, we would have the same technique predicting (in your own words) “one species extinction every 10,000 years” despite a real recent extinction event of 990 species per year. Clearly the technique is completely inadequate for predicting normal rates.
That is just ablatant argument from popularity coupled with an appeal to authority. In response I simply point out that there was a strong consensus amongst scientists that continental drift did not occur and that the universe was in a steady state. Prior to that there was consensuse that the sun orbited the Earth. Simply having consensus tells us nothing. Lots of scientists have believed lots of silly things. Even more will say they believe them if their funding depends on it, as we both know.
I would also point out that Paul Ehrlich said 20 years ago that 250, 000 species beome extinct every years 25 years ago, and that 50% of species would already be extinct by today. Shortly after Tom Lovejoy predicted that 25% pf all species would have vanished by this. Then Norman Myers said that 20% of all species pwuld be extinct by today. All respected scientists. All publsihed and cited in credible jpurnals. All comploetely wrong. Us scientists do make misttakes you know, especially when dealing with areas like this where there is os little data and so many problems.
The fact that only 70% believe the current situation is a mass extinction proves that there is muh room for debtae on this topic.
So let’s debate the facts we have right here, right now.
(1) The actual story behind continental drift is more complicated than the simplistic histories that are bandied about by people like Michael Crichton and you. Here is a link on that.
(2) There seems to be a profoundly anti-scientific attitude around that the process of science…e.g., science proceeding through publication in peer-reviewed journals…should be replaced (for example) by people, of dubious training, arguing on message boards. This seems to have become particularly pronounced as certain people have decided they don’t like what the scientific community is concluding in its peer-reviewed analyses and would prefer to believe what, say, Bjorn Lomborg has concluded on the subject. For example, the WSJ editorial page seems to believe that they can just cherry-pick the views of a few scientists even if they go against nearly all the work in the peer-reviewed literature on climate change. The current U.S. Administration is doing this sort of thing in regards to science and, as we now know, in regards to intelligence on Iraq. As someone astutely pointed out in a previous thread, it is basically the rise in “post-modernism” on the Right…You don’t like the conclusions that the scientific process is providing, well, these others conclusions that your buddy here provided have just as much validity.
Just for completeness, I will repost my thoughts on this continental drift thing and the issue of scientific consensus from this thread:
You admitted it yourself:
This implies that you were not familiar with the explanation until now. Your discussion so far does not indicate you have any familiarity with the primary literature. Instead your strategy is to attempt to poke holes in research you have not actually read, based on your own speculations about supposed flaws in it, without actually citing any research or data supporting your own position.
I did not say it was the same, I said it was of the same order of magnitude.
You are contending that the fossil record is systematically biased to the extent that it will give a false reading of several orders of magnitude. The genetic data, which are based on extant species, many of them very similar, and many of them relatively rare, refute this.
Then why didn’t you use some more realistic figures?
But we would be able to tell using the fossil record. We have both.
Actually, it is possible to predict both speciation and extinction rates from genetic data. One example is:
Ricklefs, Robert E. Global diversification rates of passerine birds
Based on cladistic analyses, Ricklefs concludes that extinction rates for passerines over the past 24 million years have been about 90% of speciation rates, with a gradual increase in diversity:
That is, speciation and extinction rates of the order of magnitude of about 1 million years.
Given that passerines make up about half of all birds, if the rates for non-passerines are similar, we expect roughly one extinction per all birds per century.
For birds, a very conservative estimate, based on 100 documented extinctions in the last 200 years (almost all of them due to the direct or indirect impact of human activity), is one extinction every 2 years.
Note that this is a very conservative estimate. Research on fossil birds in the Pacific by Steadman (Steadman, D.W., 1995a. Prehistoric extinctions of Pacific island birds: biodiversity meets zooarchaeology. Science 267: 1123– 1131) indicate that human colonization of the Pacific resulted in the extinction of c. 2000 bird species in the past few thousand years. The extinction rate is only likely to go up: A total of 182 species of birds are Critically Endangered as of today (meaning they will almost certainly become extinct within the next century without massive conservation intervention), and a total of 1,186, or 12% of all birds are Threatened. A significant number of the latter are also likely to become extinct in the next century. It is very likely that the extinction rate in the near future will exceed one per year.
For an extinction rate of one species every two years to yield a stable number of species, then the typical speciation rate must be on the order of 10,000 years. In addition to the genetic evidence, this is refuted by the fact few birds on “continental” islands (those that were connected to the adjacent continent when sea level was lower during the Ice Ages prior to about 10,000 years ago) have differentiated at the species level. Most of them are the same as the populations on the adjacent mainland, while a minority have differentiated at the subspecific level. And before you object that birds can fly and that this is what has prevented differentiation, the same holds true for non-flying vertebrates. If a speciation rate of 10,000 years was typical, then we would expect much more extensive speciation on continental islands.
The present extinction rate would lead to the extinction of all birds within 20,000 years, if not balanced by a similar rate of speciation. Blake, are you really contending that a large percentage of existing bird diversity was generated over a period of a few tens of thousands of years? Because that is what your assertion that the present extinction rate is “normal” nescessarily implies. You need to actually support your position that the current extinction rate is not abnormally high, rather than relying on unsupported speculation on why it might not be.
Nonsense. It would be an “appeal to authority” if I were merely citing the opinion of one or a few prominent scientists. Mentioning the consensus of expert opinion does not constitute an “appeal to authority.” And the fact that the idea is “popular,” as you put it, among those most familiar with the data is significant. It’s not like they were conducting a poll on Britney Spears.
I will refer you to jshore’s excellent answer on this one.
Now who’s “appealing to authority?” Because some individual scientists may have been wrong in their specific estimates of 20 years ago does not discredit the large body of current research on the topic.
(However, I believe that your specific figures are misstated. For example, Lovejoy, in the Global 2000 Report, stated that under some deforestation scenarios, 15-20 of species might be expected to go extinct by the year 2000. In any case, these estimates are probably not “completely wrong,” regarding the dimensions of the problem over the long term, only in contending that they would take place over a shorter period. According to biogeographic theory, which you claim to be familiar with, the rate of habitat loss in the recent past, and which still continuing, should cause this kind of species loss over a time frame that is comparatively short in evolutionary/ecological terms, though perhaps not decades.)
Us scientists? You are lumping yourself with Lovejoy, Ehrlich, and Myers?
The figure doesn’t indicate that the others didn’t believe there wasn’t a serious extinction problem going on, just that it had not yet reached the level of the K-T mass extinction just yet.
OK, as soon as you start producing some facts in support of your own position.
By the way, when I am confronted with a scientific issue in which I am not very familiar with the current state of the field, I always like to check and see what has been published by National Academies Press, the publishing arm of the National Academy of Sciences (and Engineering and Medicine). In this regard, here is a report published from an NAS colloquium called “The Future of Evolution” and here is a book “Biodiversity II” published by NAP [but with the disclaimer that “the views expressed in this book are solely those of the author(s) and do not necessarily reflect the views of the National Academies.”] Both of these are readable online.
[And, thanks, Colibri, for giving us a firsthand account of the current state of the science in the field. You are definitely taking the StraightDope motto of “fighting ignorance since 1973” to heart!]
I’m not a biologist but just from a common sense point of view I cannot see how the explosion in human populations over the last century combined with the associated conversion of most wild land to agricultural and industrial uses could not result in a mass extinction of some magnitude. Where will all those wild critters live? In wheat fields? I don’t think so.
Actually you said neither. You said that one corroborated the other. Whether it is the same or the same order of magnitude matters little.
The whole point is that you are saying that the average residence times of the finely divided extant species which are distinguished many times on the basis of genetic analysis is the same as the data obtained using fossil evidence which over-represents abundant species. That should ring some alarm bells.
I am contending, and have provided my logic to show, that the fossil record could be biased by several orders of magnitude. Do you really believe that many fossils are not monotypic? DO oyu really believe that abundant and widespread species are both more prone to fossiliation and less prone to extinction?
You have refused to even address these points. In particular you have not told me what these analyses do with monotypic fossils.
Because it is an example intended to show that your methodology will not even detect extraordinary changes. If it won’t detect extraordinary changes how can it possibly detect realistic changes?
But I have already pointed out that he fossil record will be flawed because those species least prone to extinction will be heavily over represented.
But I have already pointed out that this methodology can not even detect massive recent extinction rates. If it can’t detect massive recent events its predictions for future events will be extremely limited.
It does not imply any such thing. It implies that mass extinctions could have come and gone with astounding regularity and been largely undetectable to either of the methods you are relying on. If mass extinction events of similar magnitude to the current one occurred more often than you have concluded from the methods you are relying on then by extension the current mass extinction event is less abnormal than you believe.
Oh what absolute rubbish. Since when has science or logic required that a falsification be accompanied by an alternative? All that is required is that your methodology be shown to be base don false assumptions.
I don’t need to accept your theory that invisible unicorns cause gravity jus because I can’t prove what does cause gravity. I only need to falsify your hypothesis and then admit ignorance.
Mentioning the results of a survey OTOH.
If that’s the best you can manage then I will consider that I have taken this point. I fail to see any relevance to what JShore has posted. It’s fails entirely to address what I have said. In fact it seems to be entirely a strawman of what he thinks my opinion or sources might be. It has no bearing on the actual position I have presented.
Nor did I say or imply that it did. What it does show, when couped with the rest of my response, is that scientific consensus does not make something right.
Of course it doesn’t indicate the contrary either. It just leaves it blank. The point is tha1/3 of the scientists surveyed agree with me that the current extinction event is higher than average but not as severe as you claim.
A novel idea from a scientist. At least as novel as the idea that falsification requires alternative. Your facts can not be disputed except by more facts. I can’t just dispute the logic of your chain of reasoning or the flaws in your methodology. Convenient for you, but hardly in the spirit of science or fighting ignorance.
No dice, Blake. Since you have not addressed most of my arguments, I don’t feel it’s necessary to continue this discussion until you do. Your last post amounts to pure bullshitting. If you can’t or won’t provide any actual facts or evidence to support your position (which you have yet to do), then I sincerely don’t think it’s worth my time debating you. You have not “proved” anything, nor have you “falsified” anything. (If you think you have, you’re no scientist.) You have merely made some assertions which you have not backed up, while failing to address most of the key points in my posts. I don’t have any interest in engaging in a debate concerning the validity of a large body of peer-reviewed research, when your argument is based on nothing more than your own ill-informed opinions and speculations.
If you want to fight (your own) ignorance, go read the extensive literature on the subject. Come back when you can actually cite some references in support of your views. If you are too lazy to make that effort, it’s not my job to educate you. And before you claim victory by asserting that I am not able to answer your arguments, I am perfectly willing to continue the debate once you have adequately answered mine.