Author Topic: Episode #260  (Read 14908 times)

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Offline Moloch

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Re: Episode #260
« Reply #105 on: July 17, 2010, 11:46:26 PM »
I've a question-what did Bob and Steve mean by "bottleneck" in their discussion of evolution?

A genetic bottleneck is when a species is kept to a small population because of an outside influence. The mammal population exploded when the bottleneck caused by the dinosaurs was removed. Other bottlenecks would be caused by island formations, climate change, and  human influences.
ref.
http://www.mansfield.ohio-state.edu/~sabedon/biol1505.htm

Quote

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
Albert Einstein
I am skeptical that Einstein actually said this.  This doesn't sound like something he would say.
ref.
http://quoteinvestigator.com/2010/05/04/universe-einstein/
Your explanation of a genetic bottleneck is largely incorrect. A bottleneck is more accurately described as when a population undergoes a change which forces only a small number of individuals through the other side of the bottleneck. This results in a loss of genetic diversity and messes with allelic frequencies. An island population subjected to a volcano, a continental population subjected to rapid climate change or a population devastated by disease are good examples.

Your example of mammals pre Cretaceous extinction is incorrect because the mammal population was likely in relative equilibrium and then the extinction allowed for rapid adaptive radiation. This is different to a bottleneck.

It doesn't necessarily have to be the result of a disaster, though, nor does it have to encompass an entire species' population. It can simply be a subpopulation getting cut off from the main. See also my comment on the previous page.
It seems like you're saying that when a small part of a population drifts from the main and establishes a new colony this is also a bottleneck? This is somewhat untrue as small breakaways are usually referred to as founder effects, not bottlenecks. A bottleneck usually leads to a founder effect but not the other way around.

Offline werecow

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Re: Episode #260
« Reply #106 on: July 18, 2010, 10:34:55 AM »
It doesn't necessarily have to be the result of a disaster, though, nor does it have to encompass an entire species' population. It can simply be a subpopulation getting cut off from the main. See also my comment on the previous page.
It seems like you're saying that when a small part of a population drifts from the main and establishes a new colony this is also a bottleneck? This is somewhat untrue as small breakaways are usually referred to as founder effects, not bottlenecks. A bottleneck usually leads to a founder effect but not the other way around.

The way I see it, the founder effect is a possible result of a bottleneck (typically used in the context of migration of a small subpopulation). The way I've seen it used, a bottleneck is simply any event that severely reduces the effective breeding size of a population, whereas the founder effect is the resulting genetic diversity loss, increased drift, etc.
« Last Edit: July 18, 2010, 10:43:56 AM by werecow »
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Offline stands2reason

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Re: Episode #260
« Reply #107 on: July 18, 2010, 10:51:42 AM »
It seems like you're saying that when a small part of a population drifts from the main and establishes a new colony this is also a bottleneck? This is somewhat untrue as small breakaways are usually referred to as founder effects, not bottlenecks. A bottleneck usually leads to a founder effect but not the other way around.

You have it backwards. The founder effect is a specific case of a population bottleneck.  A founder effect only applies when a new population branches off; a population bottleneck can apply to any population.

Offline werecow

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Re: Episode #260
« Reply #108 on: July 18, 2010, 11:07:20 AM »
Founder effect:

Quote
The founder effect is an evolutionary phenomenon. Founder effects arise when a new and isolated environment is invaded by only a few members of a species, which then multiply rapidly. In the extreme case, a single fertilised female might arrive in a new environment. It is a type of population bottleneck. 

Population bottleneck

Quote
A population bottleneck (or genetic bottleneck) is an evolutionary event in which a significant percentage of a population or species is killed or otherwise prevented from reproducing, and the population is reduced by 50% or more, often by several orders of magnitude. A graph of this change resembles the neck of a bottle, from wide to narrow; hence the name.
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Offline Moloch

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Re: Episode #260
« Reply #109 on: July 18, 2010, 11:56:51 PM »
I'm satisfied  :D

Thanks for the clear up, I just hope I didn't have it that way in my Biogeography exam last semester  ???

Offline Slash

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Re: Episode #260
« Reply #110 on: July 19, 2010, 04:59:57 AM »


Thanks to all for quickly correcting me about population bottleneck. None of us SGU followers want to be the source of misinformation.  I have amended my original post. I included a retraction and this link http://en.wikipedia.org/wiki/Genetic_bottleneck  in my amended post.

See the graph at

http://upload.wikimedia.org/wikipedia/commons/thumb/0/0e/Population_bottleneck.svg/220px-Population_bottleneck.svg.png




Why is eyewitness testimony the lowest form of evidence in science and the highest form of evidence in the court?

Offline TheFallenLeaf

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Re: Episode #260
« Reply #111 on: July 20, 2010, 10:55:35 AM »
But seriously. Best SGU intro ever.
"If no heavy breath blew up these lungs while dirt and wet spit hung a ghost in the air, well, we’re still here." - David Bazan, "Heavy Breath"

Offline Jansob

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Re: Episode #260
« Reply #112 on: July 26, 2010, 02:27:12 AM »
On the subject of "sacred" symbols, here's an interesting tidbit: In Japan, where I live, you often see small wooden "torii" gates, (the gates that denote a shrine) placed at roadside rest stops. They are made of cheap thin wood, like you'd make a trellis out of. They are placed to keep people from dumping trash at the rest stop, because Japanese people would never litter at a shrine.

What's funny is that it's completely obvious that these are not real shrines...so they aren't trying to fool anyone. And it seems to work!
However beautiful the strategy, you should occasionally look at the results.
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Offline seaotter

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Re: Episode #260
« Reply #113 on: July 26, 2010, 01:13:57 PM »
How common are the wooden crosses set up at the sites of car wrecks in the rest of the country? Here in Alabama we have been advised that it is illegal and that periodically they will be removed for safety, but they are still ubiquitous.
"There is no use trying," said Alice; "one can't believe impossible things." Lewis Carroll

Offline Shivierie

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Re: Episode #260
« Reply #114 on: July 26, 2010, 02:45:53 PM »
How common are the wooden crosses set up at the sites of car wrecks in the rest of the country? Here in Alabama we have been advised that it is illegal and that periodically they will be removed for safety, but they are still ubiquitous.

On Long Island, NY, I don't think I've seen that many. Maybe 1, where a teen girl was killed, but I'm not so sure about there being a cross.
"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."
Albert Einstein

Offline Slash

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Re: Episode #260
« Reply #115 on: July 26, 2010, 06:24:07 PM »
How common are the wooden crosses set up at the sites of car wrecks in the rest of the country? Here in Alabama we have been advised that it is illegal and that periodically they will be removed for safety, but they are still ubiquitous.

There are several in Maine. One near my house goes up and down. I would like to replace it with broken liquor bottles to show my disrespect for the DUI driver.
Why is eyewitness testimony the lowest form of evidence in science and the highest form of evidence in the court?

Offline Jansob

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Re: Episode #260
« Reply #116 on: July 26, 2010, 11:34:51 PM »
Having lived in northern Arkansas with its frightening mountain roads, I kind of liked knowing where the dangerous spots were.  A small grove of crosses was a pretty good marker to slow down and watch for cars entering suddenly. Of course an official sign would be better, but the crosses were better than nothing!
However beautiful the strategy, you should occasionally look at the results.
— Winston Churchill —

Offline MountainManPan

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Re: Episode #260
« Reply #117 on: August 10, 2010, 07:10:34 PM »
How common are the wooden crosses set up at the sites of car wrecks in the rest of the country? Here in Alabama we have been advised that it is illegal and that periodically they will be removed for safety, but they are still ubiquitous.

There are several in Maine. One near my house goes up and down. I would like to replace it with broken liquor bottles to show my disrespect for the DUI driver.

Yeah, if it someone who got drunk and done got himself killed, then I have no sympathy for the victim.

 

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