Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 80 (8897 total)
Current session began: 
Page Loaded: 03-18-2019 3:55 PM
126 online now:
1.61803, AZPaul3, kjsimons, Meddle, PaulK, Phat (AdminPhat), ringo, Tangle (8 members, 118 visitors)
Chatting now:  Chat room empty
Newest Member: WookieeB
Post Volume:
Total: 848,434 Year: 3,471/19,786 Month: 466/1,087 Week: 56/212 Day: 17/39 Hour: 4/1


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
1
2345Next
Author Topic:   Overkill, Overchill, Overill? Megafaunal extinction causes
Mammuthus
Member (Idle past 4548 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 1 of 64 (60960)
10-15-2003 6:35 AM


What caused the end Pleistocene megafaunal extinctions?
This is a spin off topic from the Neanderthals thread in the Human Origins forum.
Replies to this message:
 Message 2 by Dr Jack, posted 10-15-2003 6:52 AM Mammuthus has responded
 Message 10 by Quetzal, posted 10-15-2003 11:07 AM Mammuthus has not yet responded
 Message 14 by Rei, posted 10-15-2003 2:33 PM Mammuthus has responded
 Message 60 by Brad McFall, posted 10-30-2003 8:11 PM Mammuthus has not yet responded
 Message 62 by Minnemooseus, posted 08-19-2007 10:04 PM Mammuthus has not yet responded

  
Dr Jack
Member (Idle past 178 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 2 of 64 (60961)
10-15-2003 6:52 AM
Reply to: Message 1 by Mammuthus
10-15-2003 6:35 AM


The systematic extermination of other major hunters by humans caused a population explosion in the mega-herbivores that destabilised the environment and led to a population crash.

Maybe.


This message is a reply to:
 Message 1 by Mammuthus, posted 10-15-2003 6:35 AM Mammuthus has responded

Replies to this message:
 Message 3 by Mammuthus, posted 10-15-2003 7:26 AM Dr Jack has responded

  
Mammuthus
Member (Idle past 4548 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 3 of 64 (60963)
10-15-2003 7:26 AM
Reply to: Message 2 by Dr Jack
10-15-2003 6:52 AM


Hi Mr. J

What were the hypothesized other hunters? Why are there so few sites supportable as kill sites?


This message is a reply to:
 Message 2 by Dr Jack, posted 10-15-2003 6:52 AM Dr Jack has responded

Replies to this message:
 Message 4 by Dr Jack, posted 10-15-2003 7:33 AM Mammuthus has responded

  
Dr Jack
Member (Idle past 178 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 4 of 64 (60965)
10-15-2003 7:33 AM
Reply to: Message 3 by Mammuthus
10-15-2003 7:26 AM


Hypothesised? No, hypothesised about it, M. We know of many megafauna hunters, sabre-tooth tigers being the most famous example.

I don't really see why kill-sites (meaning a site showing the remains of vast numbers of prey species, yes?) are expected. A Mammoth carries a lot of food, so I would expect killing individuals and moving to the corpse to be a sane strategy for nomadic tribes peoples.

I got this hyopthesis from an excellent web-site, unfortunately I can't find the thing now. I'll probably have another search later.


This message is a reply to:
 Message 3 by Mammuthus, posted 10-15-2003 7:26 AM Mammuthus has responded

Replies to this message:
 Message 5 by Mammuthus, posted 10-15-2003 8:06 AM Dr Jack has responded

  
Mammuthus
Member (Idle past 4548 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 5 of 64 (60967)
10-15-2003 8:06 AM
Reply to: Message 4 by Dr Jack
10-15-2003 7:33 AM


However, it is doubtful that sabre toothed cats would have had much of an impact on mammoth populations. They might get lucky and pick of a few juveniles separated from the herd or isolated males in a weakend state but much like modern elephants, it is doubtful mammoths had serious natural predators other than humans.

quote:
I don't really see why kill-sites (meaning a site showing the remains of vast numbers of prey species, yes?) are expected. A Mammoth carries a lot of food, so I would expect killing individuals and moving to the corpse to be a sane strategy for nomadic tribes peoples.

This would be a sane strategy but it is not what is proposed by overkill. If human hunters killed a couple of mammoths each season you would not expect kill sites..on the other hand you would not expect mammoths to be extinct either. If humans slaughtered all the mammoths across all of Asia and America you would expect to find kill sites because it would have required massive slaughter of a massive number of animals over a short period of time.

[This message has been edited by Mammuthus, 10-15-2003]


This message is a reply to:
 Message 4 by Dr Jack, posted 10-15-2003 7:33 AM Dr Jack has responded

Replies to this message:
 Message 6 by Dr Jack, posted 10-15-2003 9:35 AM Mammuthus has responded

  
Dr Jack
Member (Idle past 178 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 6 of 64 (60975)
10-15-2003 9:35 AM
Reply to: Message 5 by Mammuthus
10-15-2003 8:06 AM


They might get lucky and pick of a few juveniles separated from the herd or isolated males in a weakend state but much like modern elephants, it is doubtful mammoths had serious natural predators other than humans.

Mammoths are by no means the only mega fauna of the age. I think it's highly likely that the very large carnivores that lived in the same period as the very large herbivores ate said herbivores. Otherwise I can see no explanation for their also increased size. I was also under the impression that adult mammoth remains had been found with teeth marks consistent with those of sabre-tooth tiger, although this might have been after-death scavenging.

This would be a sane strategy but it is not what is proposed by overkill. If human hunters killed a couple of mammoths each season you would not expect kill sites..on the other hand you would not expect mammoths to be extinct either.

I'm not advocating the overkill hypothesis.


This message is a reply to:
 Message 5 by Mammuthus, posted 10-15-2003 8:06 AM Mammuthus has responded

Replies to this message:
 Message 7 by Mammuthus, posted 10-15-2003 9:59 AM Dr Jack has responded

  
Mammuthus
Member (Idle past 4548 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 7 of 64 (60982)
10-15-2003 9:59 AM
Reply to: Message 6 by Dr Jack
10-15-2003 9:35 AM


quote:
Mammoths are by no means the only mega fauna of the age. I think it's highly likely that the very large carnivores that lived in the same period as the very large herbivores ate said herbivores. Otherwise I can see no explanation for their also increased size. I was also under the impression that adult mammoth remains had been found with teeth marks consistent with those of sabre-tooth tiger, although this might have been after-death scavenging.

No, they were not the only megafauna. But they were a keystone species and there is precious little evidence that they had natural predators. The large size of elephantids, and tusk size in mammoths in particular, is better explained by sexual selection as opposed to predator avoidance. Elephantid size variation is rather pronounced and does not seem to correlate with presence or absence of predators.
There is evidence of sabre-tooth killing of mammoth babies. Like with both living genera of elephants males once they reach puberty get booted from the group (which consists of adult females and juveniles). They then go off and either form bachelor male groups or wander by themselves. (This was also likely the case for mammoths). Individual males in a weakened state might be susceptible to predation but elephants in groups would not. Taking an occassional juvenile or weak and injured male mammoth would not consitute full scale predation and there is no evidence for any predator that would specialize on mammoths. Hard to imagine predators of a highly intelligent, massive, group living herbivore other than humans.

quote:
I'm not advocating the overkill hypothesis.

I just try to bash overkill any chance I get


This message is a reply to:
 Message 6 by Dr Jack, posted 10-15-2003 9:35 AM Dr Jack has responded

Replies to this message:
 Message 8 by Dr Jack, posted 10-15-2003 10:02 AM Mammuthus has responded

  
Dr Jack
Member (Idle past 178 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 8 of 64 (60983)
10-15-2003 10:02 AM
Reply to: Message 7 by Mammuthus
10-15-2003 9:59 AM


What is your prefered hypothesis then? Do you see the correlation of mega-fauna extinction with the arrival of man as purely co-incidental?
This message is a reply to:
 Message 7 by Mammuthus, posted 10-15-2003 9:59 AM Mammuthus has responded

Replies to this message:
 Message 9 by Mammuthus, posted 10-15-2003 10:35 AM Dr Jack has not yet responded

  
Mammuthus
Member (Idle past 4548 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 9 of 64 (60992)
10-15-2003 10:35 AM
Reply to: Message 8 by Dr Jack
10-15-2003 10:02 AM


Nope. I prefer a combination of introduction of novel pathogens by the newly invading species (not just humans) affecting keystone species such as mammoths along with climate change allowing for faster breeding herbivores to outcompete keysoone species into extinction. Absence of the keystone species would have drastically changed the ecology in their former habitat which may have resulted in even more exinctions including sabre-tooth etc which also had competition from other carnivores who may have been better at switching prey.

The appeal to me of pathogens is not necessarily that it has to be correct but at least one can potentially collect evidence for introduction of novel pathogens that correlates with the arrival of humans. Positive supporting evidence does not seem to be available for overkill. Climate change as a singular cause of end Pleistocene mass extinction is also full of holes.


This message is a reply to:
 Message 8 by Dr Jack, posted 10-15-2003 10:02 AM Dr Jack has not yet responded

Replies to this message:
 Message 11 by Quetzal, posted 10-15-2003 11:11 AM Mammuthus has responded

  
Quetzal
Member (Idle past 3945 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 yet responded

  
Quetzal
Member (Idle past 3945 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 responded

Replies to this message:
 Message 12 by Mammuthus, posted 10-15-2003 11:42 AM Quetzal has not yet responded

  
Mammuthus
Member (Idle past 4548 days)
Posts: 3085
From: Munich, Germany
Joined: 08-09-2002


Message 12 of 64 (61000)
10-15-2003 11:42 AM
Reply to: Message 11 by Quetzal
10-15-2003 11:11 AM


I'm glad we cleared that up so quickly
This message is a reply to:
 Message 11 by Quetzal, posted 10-15-2003 11:11 AM Quetzal has not yet responded

Replies to this message:
 Message 13 by Speel-yi, posted 10-15-2003 2:14 PM Mammuthus has responded

  
Speel-yi
Inactive Member


Message 13 of 64 (61022)
10-15-2003 2:14 PM
Reply to: Message 12 by Mammuthus
10-15-2003 11:42 AM


A couple of questions for Mammuthus.

I'm wondering about why you are looking viruses or whether you have counted out bacteria for some reason I'm not picking up on. What about Anthrax? Has it been ruled out for any reason? Then what about diseases such as brucellosis, it may not kill the host, but may effectively render them sterile.

I also have a few more questions about primers, but will serve them up later.

Here is a link for anyone to consider the overkill hypothesis. It's only been around since the 1960s and the major proponent of it is Paul Martin at the U of Arizona. (Grayson and Martin are good friends incidently.)

http://www.outriderbooks.com/ot10.html

------------------
Bringer of fire, trickster, teacher.


This message is a reply to:
 Message 12 by Mammuthus, posted 10-15-2003 11:42 AM Mammuthus has responded

Replies to this message:
 Message 16 by Mammuthus, posted 10-16-2003 4:25 AM Speel-yi has not yet responded

  
Rei
Member (Idle past 5086 days)
Posts: 1546
From: Iowa City, IA
Joined: 09-03-2003


Message 14 of 64 (61026)
10-15-2003 2:33 PM
Reply to: Message 1 by Mammuthus
10-15-2003 6:35 AM


(Comments moved from the Neanderthal thread)

quote:
Also because of the thickness of the skin and the high muscle to fat ratio the meat of an elephant is not as good as other large herbavores

But what can't be eaten can be used for other quite useful purposes, from shelter to clothing.

quote:
This still does not address the extreme lack of kill sites

I find it surprising that you would expect to find even a significant percentage of total kill sites from a species hunted in such a vast range for such a (geologically) insignificant time. We don't hold anywhere close to such a standard for other fossils - why would we expect it for mammoths? A much more reasonable stance would be to compare the number of mamoth fossils found at kill sites during this time period to those not found at kill sites.

quote:
Aside from the fungi that live on Choloepus

And insects. Which live in the hair, not the skin (or more importantly, the muscle).

quote:
I can hardly imagine anyone subsisting on sloth meat

Why? Because of the size? If so, then Mylodon isn't addressed.

quote:
In any case, Mylodon, Northrotheriops to a lesser extent, was full of ossicles throughout the skin and probably not so easy to kill.

Humans are inventive. Depending on species, you may find mammoths that were upwards of 10 tons. Mylodon was only the size of an ox. Yes, it's better armored - but so? Humans have fought off far more fearsome armored creatures than that - for example, Megalania prisca. Throughout history, humans have killed crocodiles and alligators; small families of islanders alone have fought off komodo dragons, which have some pretty impressive armor; etc. I have little doubt that humans could have killed mylodon. Our chiefest hunting ability has been to learn the weak points of our prey.

quote:
This assumes that the immigrants practiced a more non-economical form of subsistance i.e. killing more than you need in the lands they came from. I don't know that there is any evidence for this.

There's tons of evidence that early natives to different areas employed incredibly ecologically destructive practices. When westerners first found Easter Island, there wasn't a tree on the island more than 10 feet tall, and a devastated people in constant warfare; this is why the presence of giant statues (which would have needed scaffoldings to make) was so surprising. Digs on the island have revealed that it used to be almost completely forested.

Likewise with the Anasazi. For a while, it was a puzzle how the Anasazi developed such a large civilization in the middle of a desert. However, archaeology has revealed that initially, Chaco Canyon wasn't a barren desert - arid, yes, but it was forested with pine and fir trees. As logging increased, they responded not by reducing consumption, but increasing the range that they brought in resources from. They built elaborate log-roads to get their wood in - from as far as 80 kilometers. Being a fairly delicate area, the region was inexorably altered.

I find it amazing that many people have trouble accepting that, given the track record of humans, that this would happen to the megafauna. What we're dealing with is a "land of plenty" situation. Humans move into an area where animals are not adapted to survive with humans hunting them or competing for their food supply, and where the flora is in rough equilibrium with its environment. Humans encounter what seems like a limitless hunting and harvesting paradise. A human population explosion occurs, and a native species population bust occurs, with some species going extinct. It has happened across the entire planet. If too many species go extinct in a region, the human populations there will decline or die out as well. As a consequence, over time the more balanced resource-utilizing societies are selected for.

And I agree with Speel-yi - there is far too wide of a range of species that go extinct to be explained by disease alone. I don't buy into the concept of a lethal disease that happens to jump species, but never made it over before we did, despite all of the migrations by other species of animals. Disease may be part, but wasn't the cause itself.

------------------
"Illuminant light,
illuminate me."


This message is a reply to:
 Message 1 by Mammuthus, posted 10-15-2003 6:35 AM Mammuthus has responded

Replies to this message:
 Message 15 by Speel-yi, posted 10-16-2003 4:16 AM Rei has not yet responded
 Message 17 by Mammuthus, posted 10-16-2003 4:44 AM Rei has responded

    
Speel-yi
Inactive Member


Message 15 of 64 (61141)
10-16-2003 4:16 AM
Reply to: Message 14 by Rei
10-15-2003 2:33 PM


I think you have to back up and consider that the examples that you are using are from agricultural settings. The use of optimal foraging technique would demand that a hunter be as opportunistic about getting kills, so if you have a species that is overhunted, the hunter switches to a more easily found prey simply because they go after things that are more easily found. In this way, you can see that a new equilibrium will be reached.

For fun, try out this link for a classic model of predator-prey relationships: http://www.gypsymoth.ento.vt.edu/~sharov/PopEcol/lec10/lotka.html

There is no doubt that humans modified the environment, but whether and how this modification led to the extinction of species is something we should figure out soon because it seems to be a continuing problem.

------------------
Bringer of fire, trickster, teacher.


This message is a reply to:
 Message 14 by Rei, posted 10-15-2003 2:33 PM Rei has not yet responded

  
1
2345Next
Newer Topic | Older Topic
Jump to:


Copyright 2001-2018 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2019