Another stupid question from Raz!

[alfred russel]

We get a lot of talk about the effect climate change will have on the species diversity, and the effect habitat loss will have on the species diversity, and the effect over exploitation will have on species diversity.

But something that is talked about much more rarely is that humans are moving plants and animals around to new environments. Australia for instance has a very unique set of species because it evolved in isolation: but it is isolated no longer. 

[Malthus]

We get a lot of talk about the effect climate change will have on the species diversity, and the effect habitat loss will have on the species diversity, and the effect over exploitation will have on species diversity.

But something that is talked about much more rarely is that humans are moving plants and animals around to new environments. Australia for instance has a very unique set of species because it evolved in isolation: but it is isolated no longer.

Agreed - 'invasive species' caused by humans moving stuff around has, so far, had a truly enormous impact. I suspect it is the single most significant thing people have done to affect species diversity.

[Razgovory]

I had only used humans and ants as examples as they both infest my house.  I was noting that humans are radically different in morphology then dino-age ancestors while ants really aren't.  Hell, humans are radically different then their ancestors 5 million years ago.  Further examples could be crocodiles which look like crocodiles from 100 million years ago and whales that don't look anything like their ancestors from that time period. 

I suspect some of it is do to mass extinctions. For instance when the Permian era ended Dinosaurs took on all sorts of forms.  When the Cretaceous period came to a close mammals speciated into a whole bunch of forms ranging from flying animals like bats to aquatic animals like whales.  Still it doesn't explain why some animals seem to be "In a rut".  I use that figuratively.  Ants are of course some of the most successful animals on the planet. They just seem so unchanging compared to other animals.

Raz, I'd point out a few things...first I'd emphasize that you are discounting too quickly the difference between large and small land animals. There are a long list of small animals (like ants) that have similar looking animal ancestors that haven't seemed to change much through the ages.

But try naming the large ones. You did come up with crocodilians. But I'd question that. First, the order evolved just 83m years ago per wiki (http://en.wikipedia.org/wiki/Crocodilia), so their 100m year date you mentioned is probably inaccurate. Second, the larger ones died off with the dinosaurs, so it is possible that the similarities between modern and ancient crocodilians is due to convergent evolution rather than direct ancestory. It is interesting that you brought up whales--I was indirectly alluding to it earlier. The common ancestor of whales was a mammal that had the appearance of a crocodile (http://en.wikipedia.org/wiki/Ambulocetus_natans). I believe there earlier version of the crocodile body type before the crocodilians--it seems to simply be a stable body type that has evolved multiple times.

In any event, crocodilians may be the exception rather than the rule.

I was thinking of the ancestor of whales even further back, before they even semi-aquatic.  It looked like something that might raid your trash can at night.  There were some types of crocdilia that looked different, but they are long extinct.  The current ones look a lot like their direct ancestors. Other animals that look remarkably similar are some species of frog and fish.  A lot of these things are "cold blooded".  Perhaps there is some limitation in inherent in their cardiovascular system or nervous system. 

[alfred russel]

The current ones look a lot like their direct ancestors.

I'm not sure that they didn't pass through a phase where they looked different though. Virtually all land animals of a certain size went extinct at the end of the Cretaceous. Are you sure they didn't?

Other animals that look remarkably similar are some species of frog and fish.

Fish--yeah, I excluded them earlier. Larger fish species tend to be more durable. Amphibians--while there are larger specimens, I'm not sure any of the larger specimens have a continuous and consistent history going back so far.

[Sheilbh]

We get a lot of talk about the effect climate change will have on the species diversity, and the effect habitat loss will have on the species diversity, and the effect over exploitation will have on species diversity.

But something that is talked about much more rarely is that humans are moving plants and animals around to new environments. Australia for instance has a very unique set of species because it evolved in isolation: but it is isolated no longer.

Agreed - 'invasive species' caused by humans moving stuff around has, so far, had a truly enormous impact. I suspect it is the single most significant thing people have done to affect species diversity.

Bastard American squirrels and crayfish

[Razgovory]

The current ones look a lot like their direct ancestors.

I'm not sure that they didn't pass through a phase where they looked different though. Virtually all land animals of a certain size went extinct at the end of the Cretaceous. Are you sure they didn't?

Other animals that look remarkably similar are some species of frog and fish.

Fish--yeah, I excluded them earlier. Larger fish species tend to be more durable. Amphibians--while there are larger specimens, I'm not sure any of the larger specimens have a continuous and consistent history going back so far.

Of course I can't be sure.  When you talk about "large" animals, how large are you thinking.  In my mind I was thinking larger then a rat mostly to distinguish it from things like bugs.

[Admiral Yi]

Bastard American squirrels and crayfish

What have squirrels or crayfish ever done to you? 

[Sheilbh]

Bastard American squirrels and crayfish

What have squirrels or crayfish ever done to you? 

They're both invasive species. American Grey Squirrels kill prettier Red Squirrels.

American signal crayfish are more serious. As well as outcompeting the local crayfish population they fuck up the river banks which causes problems for all sorts of other species. We're encouraged to trap and eat the oversexed bastards

[alfred russel]

Of course I can't be sure.  When you talk about "large" animals, how large are you thinking.  In my mind I was thinking larger then a rat mostly to distinguish it from things like bugs.

I didn't have a firm definition in mind, but a bit bigger than yours. More than ~3 ft tall? (or in the case of a crocodile, long)

[frunk]

Evolution isn't a steady progress for any population.  There's a variety of reasons for this:

Species that fit their niche well tend to stay in it.
Opportunities to exploit a new niche.
Sexual reproduction rate.  Ant's sexual reproduction rate isn't as fast as might be expected, as the majority of it is asexual.
Adaptability of current form.

The ant morphology/hive behavior seems to be one of the sweet spots in evolutionary development.  It's been developed independently at least twice (ants and termites) and both times have been very successful.

[Valmy]

They're both invasive species. American Grey Squirrels kill prettier Red Squirrels.

Even our squirrels are racists

[Maximus]

Evolution isn't a steady progress for any population.  There's a variety of reasons for this:

Species that fit their niche well tend to stay in it.
Opportunities to exploit a new niche.
Sexual reproduction rate.  Ant's sexual reproduction rate isn't as fast as might be expected, as the majority of it is asexual.
Adaptability of current form.

The ant morphology/hive behavior seems to be one of the sweet spots in evolutionary development.  It's been developed independently at least twice (ants and termites) and both times have been very successful.

I was not aware that some ants reproduce asexually.  How is evolution even possible in that case?

FWIW I just looked it up on wiki after your comment. It indicates that some species do not mate at all. That may not be 100% accurate of course.

[Razgovory]

Well, at one point all evolution was driven by asexual reproduction.

[frunk]

Evolution isn't a steady progress for any population.  There's a variety of reasons for this:

Species that fit their niche well tend to stay in it.
Opportunities to exploit a new niche.
Sexual reproduction rate.  Ant's sexual reproduction rate isn't as fast as might be expected, as the majority of it is asexual.
Adaptability of current form.

The ant morphology/hive behavior seems to be one of the sweet spots in evolutionary development.  It's been developed independently at least twice (ants and termites) and both times have been very successful.

I was not aware that some ants reproduce asexually.  How is evolution even possible in that case?

FWIW I just looked it up on wiki after your comment. It indicates that some species do not mate at all. That may not be 100% accurate of course.

From the wiki:

The life of an ant starts from an egg. If the egg is fertilised, the progeny will be female (diploid); if not, it will be male (haploid).

There's always a chance for some random mutation during reproduction even if it is asexual.  There isn't nearly as much genetic variety possible, but it is there.

[alfred russel]

Most of us probably know that bacteria reproduce by fission asexually. But you may not know that some bacteria have methods of gene transfer in their reproductive cycle, creating a sort of sexual mechanism of reproduction.

It has been a while since I was in school, so this theory may not be current anymore, but in college I was taught the theory that bacterial lines that can only reproduce by fission--true asexual reproduction--are all less than 10,000 years old. Apparently while asexual reproduction is more efficient in the short term, in the long term it slows evolution to the extent that it is a dead end. So asexual reproduction keeps reevolving, only to die out after some short term success.