What controls how many eggs a species lays?

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Mark Hamlet

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What controls how many eggs a species lays?
« on: 02/12/2011 10:01:01 »
Mark Hamlet  asked the Naked Scientists:
Hey Chris and the Gang

Love your show and probably get more of a wow factor than your average bear. I get to go to the pub every weekend and say things like 'no way, you know they can breed a semi skimmed cow'

Anyhow, after reading Bill Brysons 'History of Nearly Everything' (that was worth 6 months at the pub) it spurred me on to read 'The Blind Watchmaker'

Which, to be honest, was a bit over my head... but it did make me think how an insect or fish that lays scores or hundreds of eggs, etc could know that it needed to do that in order to give its kin the best possible chance. (presuming that they learn things things over millions of years?) did they think that they ALL needed to do that first, then scale it down the bigger and more resource hungry they got)

or is this soooo of the mark that's the reason i got a D in Biology?

Mark (no way i am owning up to this if its a stupid question) Smith-Jones

What do you think?
« Last Edit: 02/12/2011 10:01:01 by _system »


Offline Don_1

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What controls how many eggs a species lays?
« Reply #1 on: 02/12/2011 13:50:55 »
The fecundity rate of species is not something which the animal (or plant) learns to control during its lifetime. For changes in the rate to be made it would take many generations and the experience of an individual cannot affect evolution in such a way. But you are right in the sense that fecundity is controlled by the natural habitat of the species, to some degree.
Most species will reproduce to achieve the maximum number of offspring possible for that species. How this equates to the fecundity rate is dependant on a number of factors. These include the age at which the individual becomes mature and the span of its reproductive capability. The size of the animal is also a factor, though this is not such a determining factor for plants. The time and effort invested on raising the young will also determine not only the number of eggs/young but also the frequency between and total number of times reproduction can take place.
The lifespan of the individual is another factor as is the mortality rate of the young. Fluctuating availability of resources, such as food, nesting space/materials, however, would only have an effect on that particular generation.
In all, fecundity rates of species is a fine balancing act which nature has evolved over 100s of millions of years.
A Blue Whale will have just one calf (twins are not common) and will not breed again for 2 3 years. Full grown it will weigh in at over 200 tons and may consume more than 4 tons of krill per day. Imagine how many krill must be spawned just to satisfy one Blue Whale. In fact it is estimated that there could be up to 6 billion tons of the two largest krill of the 80 odd known species in the Antarctic Ocean. So many, that at times the swarms are so big, they can be seen from space.
Some balancing act eh!
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