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Reason for adapting the clutch size to the food available

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Reason for adapting the clutch size to the food available

Postby Smig » Mon Mar 15, 2010 4:12 pm

I've just read that the Snowy Owl adjust the clutch size (from 5 to 14 eggs) depending on the amount of prey that is available.

Can this be explained as an adaptation to adjust the prey population and avoid its extinction? Its main food source are lemmings, which cyclically go through population booms and then drop to near extinction. It seems to me that reducing the clutch size as the prey population reduces would allow for a recovery of the prey population and avoid extinction.

I guess that other, more short-term explanations could exist like to allow for a more steady influx of resources for the fewer Snowy Owls that are born which might be very important due to the low temperatures where they live in.

Is the reason known? If not, what do you think?

Another question, are there more examples of this behavior in nature?
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Re: Reason for adapting the clutch size to the food available

Postby mel004 » Mon Mar 15, 2010 5:01 pm

Although I don't know for sure why Snowy Owls adjust their clutch size, evolution tends to be very selfish. Most individuals only care about their own survival. So I doubt Snowy Owls reduce their clutch size to benefit the lemming population's regrowth. I would guess it has to do more with the health of their own offspring. If there isn't very much food and they have a lot of offspring, the small amount of food would have to be "shared" among all the offspring which could negatively effect the baby owls. (Some birds will actually starve the smaller offspring when there is little food and only feed the big, healthy ones. I don't know if that is the case for Snowy Owls.) If the owls have a smaller clutch size then even when there is little food they can feed all of their offspring and hopefully have 5 healthy offspring instead of 14 weak offspring.
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Postby Smig » Wed Mar 17, 2010 7:17 pm

Yes, I had a bias towards my suggested explanation because I've tried to develop a simulation of an ecosystem but I could never achieve a steady state, I always had peaks and extinctions, and when I read about this clutch size adaptation caused by prey availability, it seemed like an easy way to make everything work.

I see now that it's a bit of a stretch to think that would be the cause of the adaptation but I still think that it may have the effect of lowering the risk prey extinction, whether or not that was the reason for the adaptation.
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Postby JackBean » Thu Mar 18, 2010 9:24 am

actually, in nature there is not steady state, but instead there are really peaks and extinctions in prey and hunt populations
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.
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Re: Reason for adapting the clutch size to the food available

Postby Smig » Thu Mar 18, 2010 4:18 pm

Yes but I didn't mean that in a literal sense, I mean, some ecosystems at least are so stable that they give the impression of being in a steady state, depending on the timescale that we are observing. Like orbits for example, the moon is escaping the earth but it's doing it so slowly that in our everyday lives, its as if its orbit is completely stable.
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Postby JackBean » Thu Mar 18, 2010 5:18 pm

but I meant big changes in only one decade. I don't know the exact numbers, but there can be big changes.
http://www.biolib.cz/en/main/

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Postby Smig » Thu Mar 18, 2010 5:55 pm

You said that there *can* be big changes so I don't think we're disagreeing. I acknowledge that big changes are possible in only a decade, population booms and extinctions are probably the norm, the lemmings example in my first post is one of those extreme cases, they get almost extinct cyclically and then there's a huge population boom every 4 years or so. No one knows exactly why.

All I said after that was that I attempted to create a simulation with a steady system and that what I meant was to emulate some ecosystems that appear steady because the oscillations are so much smaller.
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