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Author Topic:   Overkill, Overchill, Overill? Megafaunal extinction causes
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 10 of 64 (60996)
10-15-2003 11:07 AM
Reply to: Message 1 by Mammuthus
10-15-2003 6:35 AM


I think it's likely that it was a combination of factors. And yeah, I know there's no way to test the idea because there's no way to account for the interaction of all the variables. However, combination looks like the only possible solution. All three of the hypotheses have problems when taken in isolation. Neither overkill or overill have smoking-gun evidence, and in neither case does the pattern look promising. Overchill doesn't work because it simply doesn't make sense - there have been a number of extinction pulses over the last few million years, none of which match up with documented large-scale climate change (i.e. again the pattern is wrong). What does make sense is a combination.
One possible scenario would look something like this:
Climate change becomes a framework. Based on what we've seen happen in modern cases on a smaller scale, populations of organisms facing environmental disruption have the choice of either exploiting the newly available resources, moving (habitat tracking), or dying out. In the Late Pleistocene, we see evidence that the entire continental biome was shifting northward (grasslands expanding, conifer forest moving north and upslope, etc). Since this was a (relatively) gradual change - we're not talking an Alvarez event here - it would be relatively easy for at least a fair selection of each of the now-extinct species to track with it. Local populations might disappear, but the fairly widely distributed species we're talking about wouldn't suffer much more than a population decline in overall numbers - and probably not enough to cause a crash. Eventually, all other things being equal, a new equilibrium would be established further north.
However, during a transition period like this, metapopulation dynamics are in flux. The old source-sink equilibrium is disrupted. Source population distributions are shifting, and normal dispersal patterns no longer hold. Dependent sink populations - rather than being replenished over time - simply disappear. Again, all other things being equal, the dynamics would ultimately be re-established elsewhere.
What happens when (an) additional, large-scale disruptive factor(s) is/are introduced into a dynamic system which is already precariously balanced? This could cause the entire edifice to come crashing down. Overkill may not have been necessary. Simply the introduction of a new major selection pressure into this system capable of culling a sampling - whether through disease, hunting or both - of those northward-tracking, already-reduced populations could cause a ripple effect that escalates over a fairly brief period into a large-scale metapopulation extinction vortex. And just like any other extinction pulse, the secondary and tertiary effects ripple up, down and horizontally through the food web. In an already stressed ecosystem, the ripple effects could be highly magnified. I think this does account for the extinction pattern in North America, anyway.
Humans may have been the proximate cause - but not in the way the overkill or even overill hypotheses propose. They were simply an additional strain on a disequilibrium system that sent it over the edge. A form of natural disaster like a flood or volcanic eruption.

This message is a reply to:
 Message 1 by Mammuthus, posted 10-15-2003 6:35 AM Mammuthus has not replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 11 of 64 (60997)
10-15-2003 11:11 AM
Reply to: Message 9 by Mammuthus
10-15-2003 10:35 AM


Or, what Mammuthus said.

This message is a reply to:
 Message 9 by Mammuthus, posted 10-15-2003 10:35 AM Mammuthus has replied

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 Message 12 by Mammuthus, posted 10-15-2003 11:42 AM Quetzal has not replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 24 of 64 (61323)
10-17-2003 4:27 AM
Reply to: Message 22 by Rei
10-17-2003 1:57 AM


Hi Rei,
Although I concur that the hyperdisease hypothesis is not tremendously well-supported - there's no "smoking gun" - the reasoning you gave for rejecting it is not valid.
Ok. Then name a series of lethal diseases which can cover the wide variety of species that we see go extinct.
It might surprise you to know that there are quite a few panzootic diseases that jump a wide variety of species. The one that springs immediately to mind is the Paramyxoviridae family morbillivirus that causes rinderpest. This pathogen effects cattle, sheep, goats, pigs, cape buffalo, giraffes, wildebeest, gazelle, kudu, hippos, etc. Basically anything with a cloven hoof (except camelids, for some reason). It has high mortality (80-90% depending on species) if untreated and the type of wildfire transmission rate postulated for the hyperdisease hypothesis. It is also a relatively fragile virus - meaning it burns out fairly quickly and can tolerate only a narrow range of temperature, etc. However, it has had significant impacts on populations wherever it is inadvertently introduced - from Indonesia (where it nearly wiped out the swayback pig population), to the Masai's domestic cattle herds of Kenya or the wildebeest of the Ngorogoro. Although the Pleistocene extinction was probably not rinderpest (after all, the buffalo survived), some type of similar pathogen is believed to be the cause.
In any case, there is a wide variety of pathogens - including such non-viral factors like mites (e.g. Sarcoptes scabiei, which is threatening foxes in Sweden and wombats in Australia), or protozoans (e.g. the Plasmodium species that causes avian malaria), and fungus (e.g., Batrachochytrium dendrobatides that is causing global dieoffs in amphibian populations - everything from anurans to salamanders), etc - that quite easily not only jump between species, but between families and even classes. For a rather good discussion of the panzootic and epizootic threat, see Daszak P, Cunningham AA, Hyatt AD, 2000, "Emerging Infectious Diseases of Wildlife Threats to Biodiversity and Human Health", Science 287: 443-449.
It's just not feasable. We've seen plenty of hunting to extinction, and plenty of habitat-destruction-to-extinction, etc, but never before witnessed a disease-to-extinction, especially not across such a wide variety of species.
Actually, that's a bit misleading. We've seen widely dispersed populations of single species eliminated globally by disease (ex, the global extinction of the snail Partula turgida by the protozoan parasite Stenhausia), and we're currently seeing the global reduction of amphibians by the Batrachochytrium fungus. Also, I'd suspect in the absence of vaccine, even rinderpest could cause global extinctions of the widely variable hosts, assuming it could get from point A to point B on its own somehow. So it IS feasible that some pathogen accompanied humans and their critters across the land bridge, and either directly or after mutation was able to cause the Pleistocene dieoff. As to whether it actually occurred, well, there isn't a lot of evidence. As I noted in my previous post on this thread, I'm not sure it makes a great deal of difference, since the cascade effect would be the same, regardless of proximate cause.
[This message has been edited by Quetzal, 10-17-2003]

This message is a reply to:
 Message 22 by Rei, posted 10-17-2003 1:57 AM Rei has replied

Replies to this message:
 Message 27 by Rei, posted 10-17-2003 2:30 PM Quetzal has replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 29 of 64 (61726)
10-20-2003 4:07 AM
Reply to: Message 27 by Rei
10-17-2003 2:30 PM


As I stated, I don’t support the hyperdisease model. Why are you insisting that anyone who doesn’t directly support overkill is by definition supporting hyperdisease in this thread? My point was that your disagreement with hyperdisease was based on invalid criticisms. There are a number of quite good arguments against and/or weaknesses in the model. Briefly:
1. There are no known pathogens which can propagate through dozens of different species in a continental metapopulation (emphasis on continental). It would require a highly variable organism — one capable not only of an extreme rate of infection (AR~1.0), but also an extremely high mortality (MR~1.0) with an aerosol transmission and high mutability. The only current pathogen that comes close is rinderpest. No one is suggesting that rinderpest is the culprit in this case — it was an example of a pathogen that countered your assertion that no such pathogen exists, and its propagation through multiple species, decimating the effected populations in a wave front from initial point of introduction throughout West Africa is a reasonable model for the hyperdisease idea. Your argument, that rinderpest hasn’t been established in NA or New Zealand is specious — IOW, so what?
2. Again relating to the nature of the pathogen, the existence of a highly virulent/high mortality bug implies that there is an intermediate host that provides a reservoir (i.e., that the pathogen doesn’t effect, or at least doesn’t kill). This would be required because of the rapid burn-out of this type of infection (wildfire effect). Something has to be wandering around re-introducing the bug. It has not been demonstrated that human specific-diseases of this virulence can be transmitted wholesale to multiple other species — it’s usually the reverse, making the suggestion that humans or their commensuals were the reservoir problematic.
3. In a continental biosphere, the disease would have to depress/disrupt populations of species so rapidly that they have no possibility of recovery anywhere in their original range. In the case of the Late Pleistocene event, even in areas which were unsuitable for human habitation, isolated or relictual populations were ALSO decimated. IOW, the humans-as-infectious-reservoir may not have been able to reach them. Something would have survived — if not mammoth, then any one of the other large herbivores OR one of the generalist carnivores (smilodon might have had a problem, but what about Arctodus or Canis dirus?). When climate change occurs, populations don’t just habitat track latitudinally, they also track altitudinally (Rappaport’s Rule). Your pine forest is shifting north? No problem, you either go north, or you can go up and keep a very similar niche open. Of course, this argument goes doubly for the overkill idea.
In my opinion, the overkill hypothesis is even weaker, if that’s possible. Not only do you have point three to contend with, you have the limitations imposed by technology and space. I’m sorry, but no matter effectively a group of humans managed to extirpate multiple species in the constrained space of an island using primitive, essentially hand tools (and there’s little question that the Maori accomplished that feat in a couple of centuries on New Zealand), you cannot logically extrapolate from that to a continent. Although it’s pretty fruitless to speculate on effective population size in a large migratory species like Mamuthus primogenus, overall we’re talking about (on two continents) at a minimum 10^7 to 10^9 individual animals eliminated in around 1-2000 years when you take all the different species into consideration. That’s a hell of a lot of killing. Unless the Clovis hunters were using automatic weapons and hunting from helicopters, it strikes me that the blitzkrieg hypothesis is asking more from human hunters than they are capable of. How many humans are we talking about? We’re looking at a front that is ever-expanding as these hunters moved further and further across the continent — IOW, their population density is getting smaller and smaller the further they travel into the continental landmass — the old force/space ratio dilemma faced by military planners. And they didn’t miss a single population? Please tell me how this was supposed to work.
Worse, the overkill hypothesis ignores the fact that numerous species DIDN’T disappear that would be as easy or easier to kill than mammoths, for example. Why didn’t the American bison disappear? Too many of them? What about caribou, elk, mule deer, etc etc. These were harder to hunt than mammoth or ground sloth? And if they were, for some as-yet-to-be-identified behavioral quirk, where are all the bones? The few identified kill sites associated with Clovis archeologically are indistinguishable from any other cause of mass die-off — including hyperdisease. Those few undisputed tool-marked bones could just as easily have been worked AFTER death: Clovis-as-scavenger vice Clovis-as-hunter. None of the remains show undisputed evidence of hunting — which is not a negative in-and-of itself. They COULD have been killed by hunting. The marks are equivocal and don’t prove hunting.
Finally, the correlation between the expanding human wave front and the last seen is unclear. Admittedly, this is due to the lack of fine grain in the fossil record, and holds for the hyperdisease as well as blitzkrieg hypotheses. What is clear is that first contact marked the beginning of the end. Whether humans were the ultimate or proximate causes remains to be determined. However, your belief that humans abruptly behaviorally adapted to a radically different lifestyle — in spite of the fact that there remained a wide variety of prey species they could have continued to massively over-exploit — requires even more assumptions than hyperdisease. After all, the pattern of the extinctions — massive numbers at first contact (some 40 genera) as nave species are effected by a new pathogen, followed by a lack of extinction after the surviving species become less susceptible — is as easily attributed to normal disease reaction as it is to over-hunting.
Finally, some specific points from your reply:
Funny. I'd say that the biggest cause of the death of Partula turgida was the introduction of a florida snail, to control the population of an escaped African snail. Only the last 5 snails died of the Stenhausia, and that was in captivity - the species was all but extinct anyway. That's nothing at all like this situation Mammothus advocates.
Depends on how you define it. The species was preserved in a lab as an effort to replenish it and save it from extinction. The species actually crashed from 260 individuals to zero in just under 21 months (1994-96). However, it was an counterexample to your assertion that no species had ever gone extinct through disease — not that this was a hyperdisease.
But nothing close to extinction. Even threatened populations seem to be holding out ok against it.
Unfortunately, your assertion does not a rebuttal make. Your turn to provide references, as my sources contradict yours. Not only the Daszak et al, 2000 I cited above, but also specifically relating to the amphibians see Daszak, Berger L, Cunningham AA, Hyatt AD, Green DE, Speare R, 1999, Emerging Infectious Diseases and Amphibian Population Declines, Journal of Emerging Infectious Diseases, 5:735-748. This latter reference discusses not only global population decline as I noted, but specifically the extinction of Bufo periglenes, possible extinction of several other rainforest species not related to habitat destruction, and massive declines in other species. And your reference is?
[This message has been edited by Quetzal, 10-20-2003]

This message is a reply to:
 Message 27 by Rei, posted 10-17-2003 2:30 PM Rei has replied

Replies to this message:
 Message 34 by Rei, posted 10-20-2003 3:55 PM Quetzal has replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 32 of 64 (61736)
10-20-2003 5:46 AM
Reply to: Message 30 by Mammuthus
10-20-2003 4:42 AM


Hey, O Hairy One,
Some of your reply was cross-posted with stuff I had.
On this bit, however:
So the other cyclical changes since the Pliocene where humans were not involved but extinction did occur could not have involved climate change? And I don't know that the extinctions at the end of the last ice age dwarfed previous die offs...the curious aspect of the end Pleistocene die offs was that they so specifically involved megafauna.
Especially the Late Miocene extinction pulse (the Hamphellian event) ~5 mya. Around 60 genera went extinct in North America, of which 35 IIRC were classed as megafauna (compared to 40 genera all told in the Pleistocene event). Globally, 10 of 18 equids, the Indricotheriidae, etc, all bit the dust. Some of it might be climatic (expansion of grasslands obliterating the habitat for browsers). Some of it was due to competition with newly evolved organisms. This latter is what did in the indricotheres, for example - competition with mastodonts and mammoths (bloody elephants ). Although vaguely correlated with large scale climate change (this is the one all the overchill folks point constantly to), there were obviously other factors than just climate change involved.
However, it supports your reference to non-human factors.

This message is a reply to:
 Message 30 by Mammuthus, posted 10-20-2003 4:42 AM Mammuthus has not replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 39 of 64 (61902)
10-21-2003 6:09 AM
Reply to: Message 34 by Rei
10-20-2003 3:55 PM


That wasn't my argument at all. Read again. I quote:
That doesn't mean that some other disease could have been the culrpit, but I would expect that we would see at least some New World reminant of whatever disease it was.
I don't disagree with this portion of your statement, which of course was why I didn't address it. Curiously, in your reply you neglected to include the sentence I was actually responding to:
quote:
Thank you, Quetzal, I was not familiar with the morbillivirus. However, it is worth nothing that the virus has never established itself in North America or New Zealand. That doesn't mean that some other disease could have been the culrpit, but I would expect that we would see at least some New World reminant of whatever disease it was.
Now who's arguing like a creationist?
I would be curious as to what sort of regions you are thinking of here, in which evidence of megafauna exists.
The canyon lands of Colorado weren't apparently occupied until the Folsom Period - post extinction - which were occupied by M. columbi, for one. The Channel Islands off California (M. exilis) also show no signs of human occupancy, although the "last seen" of the species is dated around 10.8 kya (remember, I said it was a problem with both overkill and overill). Etc - basically, there are a number of areas, large or small, which would be unsuitable or unlikely for ease of human passage wherein small populations of at least one of the extinct genera could have survived. We're talking continental landmass here - anything south of the retreating ice. Even at Martin's "best speed" estimate of 20 km per year, that's a heck of a lot of territory for hunters to cover - and they would perforce be following the path of least resistance to maintain this year after year.
Or faster. And note that New Zealand is the size of Arizona. I don't have range plots for the various megafauna, and I know that many were widespread, but I wouldn't be surprised if there were at least a couple who had a range that size.
Except that simple land surface comparisons are silly without taking into consideration exactly how that land is arranged. No place on New Zealand is further than 100 km from the ocean. IOW, this is a big area, but it is constrained. A group of humans sweeping across Arizona like a panzer division would just as likely cause the animals they were attacking to retreat to New Mexico or Colorado. There was no place for the moa to retreat to. Habitat destruction coupled with over-hunting are what did in the moa - just like the elephant birds of Madagascar, or for that matter, almost everything on Easter Island. The extreme sensitivity of island populations to ecosystem disruption and extinction cannot be compared to the resiliance of continent-wide populations. Although some of the basic population dynamics concepts can transfer (c.f., the "island effect" of habitat disruption), a too-close extrapolation is misleading, especially in the case of a continent-wide extinction event.
I'll accept those numbers, although it should be noted that, if mammoths spread in a manner similar to elephants in Africa, I would expect much closer to the 10^7 number for them. Also, one expects the lower ranges on carnivores which, while not as large, need to eat from a much larger prey base.
However, I wasn't talking just mammoths (and I'd find 10^7 mammoths an unrealistically big number, even on a continent). Also, carnivore populations could be expected to decline after a lag in correlation to their prey species, so are hunters wouldn't need to necessarily kill them. The point being that it is unclear that a selective megafaunal hecatomb of this magnitude could be caused by humans armed with a stone toolkit - no matter how well designed it was for killing large game. That it WAS so designed is not in question. That it was capable of this level of mass slaughter is what we are arguing.
And yet, how many moa would you expect in such a lush environment as New Zealand, the size of Arizona? They're a tiny fraction of the size of mammoths. I think the only reasonable argument that you could make against them is that there was geographically less area for humans to fill, but that argument only lasts so long in a continental situation.
Exactly my point. Thank you for making it for me - it is entirely conceivable (and in fact fairly well-documented) that the Maori were able to practically stand shoulder-to-shoulder and sweep the entire island (when they weren't slaughtering each other, that is) in the few centuries in which they were decimating the moa. The opposite occurs on a continent.
Again, also, keep in mind that many populations are unstable once they get damaged (such as passenger pigeons proved to be).
Keep it in mind? LOL! Read my first post on this thread - that is precisely the disequilibrium model I proposed.
They missed Wrangel Island until about 6,000 years ago - I mean, that was the time of the Pharaohs. The fact is, they had tons of time to find all of the remaining populations. And again, I don't advocate overkill as being the only reason; just one reason.
Err, yeah. Except Wrangel is an isolated island in the Chuktchi Sea off Siberia. It took the paleoindians until around 8-9000 ya to cause the extinction of the megafauna on Cuba as well (had to wait until they'd figured out how to make boats.) Btw - this mitigates as well against the cultural change idea you put forward. If the local paleoindians had evolved such a marvelous cultural adaptation after they realized they'd obliterated their food sources, why did they turn around and commit the same act in Cuba 1500-2000 years later? Reversion to type? Or possibly there might be some other factor than overkill involved in the first place...?
Assuming a population growth rate of 4 births that make it to adulthood (in this environment without as many human diseases, with plentiful game) per woman, from a source of 10,000 people they could reach about 1e34 in 2000 years. Clearly birth rate isn't a problem - the issue is how much resources are there for people to survive on. Initially, there are vast resources. Consequently, one expects, in the absense of social memes preventing it, a population boom.
Is this how you derived your 16 million population in North America during the extinctions? Do you have a population estimate for the pre-Clovis inhabitants of Beringia (the Nanana culture)? Are you aware that the Lesser Dryas is correlated with severe drought in many areas (c.f. the paleoindian wells at the Blackwell Draw site) which would have reduced population growth? I hope the smiley face is an indication that you don't take this type of geometric growth pattern too seriously. And remember, these folks are not only supposed to be doubling their population roughly every generation (according to Martin), but traveling across two continents in less than 1000 years AND simultaneously wiping out multiple species of megafauna without leaving a single relict population. Pretty tall order.
Smaller animals in general survived the Pliestocene better than large ones. For many reasons, humans have historically prefered to hunt large animals when they are capable of it, whether for food, for ritual, or for sport. Also, needing to be explained by people who do not consider overkill as part of the cause of the extinction, is why the extinction was so heavily focused on large animals.
Smaller? Well, only in comparison to the mammoths, mastodonts and ground sloths. There were also a much greater number of the other, more "traditional" prey species that I mentioned - and which would be easier to hunt than mammoths. Humans are opportunistic hunters, they don't simply go after the biggest simply because they are the biggest, unless you're proposing sport or ritual as a piece of the puzzle. There ARE buffalo jumps, etc, associated with Clovis where the terrain allowed, indicating to me that they were more interested in food than anything else.
I'm familiar with the theory, but that wouldn't explain the massive spear points designed to be mounted on massive spears that have been found. Perhaps one might argue that they went after the young or sick, but they clearly were killing these massive animals.
You're misinterpreting what I said. I never argued that Clovis didn't hunt mammoth or other large game. In fact, there was an interesting experiment done a few years back by an archeologist/anthropologist that duplicated Clovis technology and used it successfully during the conservation culling of an elephant herd in Africa. I have merely maintained that overkill is not supported - the scale doesn't work, not that Clovis didn't hunt. OTOH, several sites that are suggested as mass kill sites have evidence of worked bones that are not consistent with hunting - more on the order of butchering already dead animals.
Again, for the last time, I do *not* believe that it was an abrupt change - that's Mammothus's suggestion. I believe that it was steady natural selection. It sometimes feels like I'm debating with creationists here, and their "So why do these species changes just appear in the fossil record? Did the animals just suddenly decide to evolve?"
I think "abrupt" in this context refers to the timeline of the extinctions - they started roughly around the time of first contact, continued for couple thousand years across two continents, then stopped, in spite of the fact that there remained a myriad of prey species - some of which had been readily exploited by our paleoindians at the same time they were obliterating the other megafauna. This appears to be an "abrupt" change in attitude. An attitudinal change which you have not succeeded in documenting in any way, btw. After all, as soon as our friends were able to reach other areas, they picked up their old habits (e.g., Cuba). Moreover, the extinction event, although mostly megafaunal, ALSO included rodents, giant rabbits, etc, which by no stretch can be considered megafauna.
That seems like a rather unfair argument. If the last Steller's Sea Cow had died of pneumonia, would we claim that pneumonia wiped out the species?
Oh, good grief. In the context of your one-line objection to the point - yes, it was an example. Is it compelling? Arguable. It's not an area that has received a great deal of attention at all until fairly recently (less than five years or so). So that was an example I could lay my hands on easily. You don't like it, fine. Lay out your criteria for what you want to see - with the understanding that systematic study of EID is a nearly new field overall.
Bufo periglenes once occupied a region only 4km^2 - hardly a stable species. To make matters worse, they had a very rain-sensitive breeding cycle. Their population crashed in 1987 due to unusual rainfall - only 29 toads were known to have survived out of 30,000.
Oh bloody hell. Now you're really arguing like a creationist. You want to quibble over the examples? Fine: here's a reproduction of the table from the article I cited on amphibians. Argue at will:
Chytridiomycosis
E. & S. Australia (1993-1999) Multiple montane rain forest and temperate species. Mass deaths, local extinctions, population declines. Near-extinction of Taudactylus acutirostris. Hypothesized link with global extinction of two species of gastric brooding frog (Rheobatrachus spp.).
W. Australia (1998-1999) Multiple species, predominantly the western green (or motorbike) frog (Litoria moorei) Mass deaths, population declines.
Costa Rica (1994-99) Multiple montane rain forest species and Panama. Mass deaths, local extinctions, population declines. Hypothesized link with global extinction of golden toad, Bufo periglenes.
Ecuador (1999) Montane rain forest Atelopus species, Telmatobius niger, and Gastrothecus pseustes. Unknown impact.
Arizona (1996-1997) Leopard frog (Rana yavapiensis & R. chiricahuensis). Mass deaths.
S. Arizona (1999) Leopard frog (Rana sp.). Mass deaths.
Colorado (1999) Boreal toad (Bufo boreas). Mass deaths.
Colorado (1970s) Leopard frog (Rana pipiens). Mass deaths.
Sierra Nevada, California (1970s) Yosemite toad (Bufo canorus). Mass deaths.
Ranaviral disease
United Kingdom (1992-1999) Common frog (Rana temporaria). Mass deaths, possibly population declines.
Arizona (1995) Sonoran tiger salamander (Ambystoma tigrinum stebbinsi). Mass deaths in this endangered species.
N. Dakota (1998) Tiger salamander (A. tigrinum). Mass deaths.
Maine (1998) Tiger salamander (A. maculatum). Mass deaths.
Utah (1998) Tiger salamander (A. tigrinum). Mass deaths.
Saskatchewan, Canada (1997) Tiger salamander (A. tigrinum diaboli). Mass deaths.
[This message has been edited by Quetzal, 10-21-2003]

This message is a reply to:
 Message 34 by Rei, posted 10-20-2003 3:55 PM Rei has replied

Replies to this message:
 Message 47 by Rei, posted 10-21-2003 4:19 PM Quetzal has replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 40 of 64 (61905)
10-21-2003 6:55 AM
Reply to: Message 38 by Mammuthus
10-21-2003 5:36 AM


Just one correction here, O Extinct One:
15 sites with 50 bones that cannot even be distinguished from scavaging? A kill site cannot even be confirmed. Why do the tens of thousands of mammoth finds (mostly dating around the relevant time period due to preservation constraints) show natural death causes and not hunting? The ratio you ask for is overwhelmingly against overkill.
This isn't exactly accurate. At least four of the Arizona sites (Naco, Murray Springs, Escapule and Lehner) show pretty unequivocal evidence of mammoth kills. Naco had a mammoth with five Clovis points embedded in the chest. Lehner has a bison kill site, and Murray Springs shows both bison and a mammoth with several Clovis points inside. There's also another site (which I can't remember) that has a swamp version of a buffalo jump - apparently Clovis paleoindians herded a mixed bag of herbivores into a swamp, then slaughtered the group. It included mammoth and bison. Interestingly, the Lehner (9 remains) and Escapule (1 remain) site appears to be mostly juvenile mammoths rather than adults. Looks like they were pretty opportunistic.

This message is a reply to:
 Message 38 by Mammuthus, posted 10-21-2003 5:36 AM Mammuthus has replied

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 Message 41 by Mammuthus, posted 10-21-2003 7:08 AM Quetzal has not replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 49 of 64 (62082)
10-22-2003 4:35 AM
Reply to: Message 47 by Rei
10-21-2003 4:19 PM


You know, Quetzal, I'm not sure why we're debating here - we actually seem to agree on most issues related to this. My view is that many issues, of which hunting was one, led to changes in the flora and fauna in various regions, which in turn caused other species to decline. Some species weren't lucky enough to be able to recover. I assume that this is what you mean by your "disequilibrium" hypothesis.
Well, I'd say we're debating because of your insistence that human hunting - while perhaps not the ultimate cause - was in fact a major proximate cause of the extinctions. I disagree. It's similar to the debate over the relative importance of natural selection, etc, in evolution. Your assertions concerning the ability of paleoindians to effect mass destruction of continent-wide populations of megaherbivores and (indirectly) their predators is unsupported, and I think unsupportable. You're also using an inappropriate analogy of island extinctions (or the destructive practices of restricted populations such as the "Anasazi") to extrapolate to the wider continents-wide hecatomb of literally millions of organisms in a very brief period which is contraindicated by the available evidence. Finally, your argument concerning behavioral/cultural (meme) evolution in paleoindians has not been well-developed (in this case, you need to provide more detail on the argument, including what evidence might lead one to suspect that this occurred). That is why we are debating.
The disequilibrium model is an ecosystem-level approach deriving from the concept of ecosystems as complex adaptive systems, and owes more to the "overchill" hypothesis than anything else. Admittedly, it is also based on extrapolation from small-scale observation to continent-wide effect (as I accused you of doing in error), but rests on the foundation of the known severe changes in the continental biome and floral turnover at the end of the last glacial maxima, which makes it different than your extrapolation because it rests on verified evidence. Nobody apparently is interested in discussing it.
I don't disagree that disease can have a strong impact. What I disagree with is the notion that a disease or family of diseases have followed every major human migration into areas that haven't seen humans before in history, in different time periods and geographical areas, and taken a diverse, large group of otherwise healthy animals, from completely different orders, and brought them to extinction each time. That really seems like a preposterous concept to me, not something that has been observed in the world. Can diseases weaken a population? Yes. Can diseases kill off an already severely weakened population? Yes. Can diseases alone cause what is witnessed at the end of the Pliestocene? Very doubtful.
I don't think anyone other than MacPhee and his group is arguing that "overill" is the sole cause. Mammuthus certainly isn't. Even MacPhee, to be fair, is only concentrating on it exclusively because, according to him, "in many instances the adoption of a multifactorial explanation is really an admission of defeat rather than a breakthrough in understanding" (from MacPhee 1997, cited by Mammuthus above, pg 209). Along with the role of EID in wildlife population declines studied by Daszak's group and a very few others, IMO understanding the potential of disease to effect widespread diverse populations has significant implication for modern biodiversity conservation - and even for human pandemics. We ignore that at our peril. The only potential example for this is the highly selective extinction event that occurred in the Late Pleistocene. So I think it's worth exploring. Dismiss it if you will - but provide more comprehensive argument against than you have so far.
My main gripe with Mammothus on this front is that he seems insistant that killing had nothing to do with it. I disagree. The weapons used by the clovis culture weren't those of scavengers - they were those of hunters of large game. They had an entire continent to expand into, and plentiful food. It is only reasonable to expect a population boom. Is hunting the only reason? Of course not - the extinctions are too diverse for that. But hunting clearly is going to play a major impact on the environment itself. I also think it's preposterous to expect major amounts of preservation from such a brief time period 10kya.
Actually, I tend to agree with him on this overall. For example, in all of the southwestern sites associated with Clovis, there is only ONE that I can remember (and I forget which, specifically) that has any remains of sloths like Megatherium and Mylodon. Since the former's preferred habitat was the juniper scrublands of the American southwest and Mexico, I find the lack of remains associated with the known kill sites in the area to be problematic. Additionally, the hunting idea begs the question of the disappearance during this extinction pulse of all of the various bird species - which nearly number as many species as the megafauna - that ALSO disappeared. And not flightless rails like the ones that went extinct on islands. These birds include raptors, scavengers, etc. Also, the minifaunal extinctions that happened at the same time are unexplainable by hunting pressure. It might - and in fact has been - argued that these are secondary or tertiary effects of the megafaunal extinctions (given how proboscideans in Africa substantially alter ecosystems), but that is highly speculative and as yet unsupported.
I don't consider it preposterous to expect more evidence. Only Martin's blitzkreig takes it as a given that no evidence will be found because of the speed of the process. Given the number of well preserved mammoth hunter sites in Eastern Europe and Eurasia, I find it odd, as does Mammuthus apparently, that there are so few unequivocal sites in America - where substantially more and varied critters were supposedly destroyed.
I hate the unreasonable belief that native cultures were somehow all in touch with the environment, and only modern humans have become destructive. It's not evidenced by history.
As do I. However, that doesn't mean I'm going to seize on the opposite extreme without evidence. Which, in this case, is lacking. I'll gleefully cite early Polynesian, Malagasy, Maori and even "Anasazi" destructive habits whenever the subject comes up. But only in cases where there is evidence to support it.
P.S. - I still think it was unfair of you to pull out the second sentence of my first paragraph and hold it up alone, even though the sentence right after qualifies it. But that's beside the point.
Whatever.

This message is a reply to:
 Message 47 by Rei, posted 10-21-2003 4:19 PM Rei has replied

Replies to this message:
 Message 54 by Rei, posted 10-22-2003 3:01 PM Quetzal has replied

  
Quetzal
Member (Idle past 5872 days)
Posts: 3228
Joined: 01-09-2002


Message 56 of 64 (62268)
10-23-2003 1:44 AM
Reply to: Message 54 by Rei
10-22-2003 3:01 PM


If you want me to quantify it, I'd put it at about 20-30% relevance.
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Not just killing of herbavores, and indrectly causing their predators to die off. Killing of both predators and herbavores, in addition to altering the flora; this indirectly causing instabilility which leads to more die-offs, and this in turn leading to more instability... etc, until a new steady state can be reached.
I'm not clear how you derived this figure (off the top of your head?). In any event, the key difference between our positions is in the second paragraph: I don't consider the paleoindians to have figured very prominently at all in the extinctions. At worst, they were an additional factor - whether through disease or hunting - rather than anything remotely causative. The point being there is no evidence that they killed large numbers of megafauna. Local family groups probably. Extinction of localized population remnants possibly. Small numbers thither and yon, definitely. Tens of millions of organisms to the point of continent-altering ecosystem damage? Unlikely, and unsupported by the available evidence. In spite of finding thousands of dead mammoth scattered about, the record is a text of "random" death with little artifactual association, rather than non-random (as would be the case with human hunting being a factor. Martin explains this anomaly away by claiming that the speed of the slaughter was too fast - which I don't consider compelling in the absence of corroborating evidence.
Basically, you need to a) explain what evidence you would expect to find if your idea was correct; and b) provide specific examples that support your point.
1) I'd hardly call around a hundred kilometer radius "restricted".
2) I'm not saying that the entire continent was deforested. It was just an example of continental populations causing local environmental destruction.
1. You're not serious? Martin's blitzkreig requires a minimum population starting at 100 individuals (sound familiar in reference to the Maori?), migrating across the continent at a rate of 20 miles per year (I misquoted before, I'd said km - I just re-read his paper, and it was miles, not kms), with a population doubling every generation due to over-abundant game. 100 kms is NOTHING compared to what you are suggesting for the paleoindians. It is totally not beyond even my comprehension to believe that the Maori were capable of decimating every single population of naive organisms as rapidly as they did in such a tiny space. No refugia, a central mountainous area that was inhospitable to most of the moa (from my understanding), a restricted geographical area with no place to go. This is waaay different from a continental landmass with its myriad of possible refugia, etc.
2. Good thing. And I'm aware that they caused severe degradation/desertification in their zone. However, the point is it WAS restricted, it WAS localized, and we have NO examples from paleoecology where a continent was effected at the same level by humans. Your extrapolation is invalid, as there is no foundation for the assertion of equivalency.
Well, in the case of the Anasazi (an easily documented example), wouldn't you say that they were selected against, while the Pueblo were selected for? Also, what model would you propose for memes not having an effect?
Sounds suspiciously like you're shifting the burden of proof here. You tell ME what YOU would expect to find, and then provide examples. It's your hypothesis. Why should I develop a model for something I don't agree with? Try this: what leads you to think it's valid? Just 'cause it sounds good and you read something about memetic evolution somewhere? C'mon, Rei, you usually do better than this.
Highly selective? Unless your selection criteria is "large", I don't know how you come to this conclusion. On a quick search, 95% of large herbivores (>2 tons), and 73% of genera of animals weighing 44kg or more, went extinct in North America.
Yes, selective. The event took out the top, a few bits from the middle, and substantial bits from the bottom. Yet it left a huge chunk of the middle untouched. This pattern is totally inconsistent with hunting pressure being a significant factor. That means something else happened.
While some dates are still up in the air, it *does* appear to have been a very fast process, whatever killed them; in Europe, and Asia, it doesn't. And the key issue concerning whether the amount of evidence is what is expected or not is the speed; all debate on this topic hinges on that.
Speed is certainly one of the main factors. However, I'd say the extinction pattern itself is a more critical factor that needs to be addressed by any of the three leading models. None of which have done so very well, at this point.
P.S. - why do you keep putting "Anasazi" in quotes? Would you rather I refer to them as "ancestral Puebloans"?
I put "Anasazi" in quotes because I am unconvinced they represent a distinct and separate culture from the other southwestern tribes extant at the time. Puebloan is probably more accurate. IT's an affectation - don't sweat it.

This message is a reply to:
 Message 54 by Rei, posted 10-22-2003 3:01 PM Rei has not replied

  
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