3.1.2 Natural Selection
Variation
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Overproduction
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Competition for limited resources
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Differential survival and reproduction
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(16)Sexual reproduction in great tits produces unique gene combinations, creating genetic diversity
Great tits vary in bill depth, body mass, clutch size and egg-laying timing
Some female great tits carry genes for early April nesting; others nest in late April
Wood mice vary in body size, fur colour, metabolic rate and burrowing behaviour
A single oak produces over 70,000 acorns in a mast year
Blue tits lay 7-13 eggs yet the population stays roughly stable year to year
A bluebell produces hundreds of seeds, but only a tiny fraction survive to flower
More offspring are produced than the environment can support; most will not reproduce
Canopy caterpillar abundance peaks for just two to three weeks in spring
Great tits and blue tits compete intensely for caterpillars to feed nestlings
Light on the woodland floor is a critical limiting resource after late April
Oak seedlings beneath a closed canopy compete for light with the parent tree
Great tits timing egg-laying with peak caterpillars raise more surviving chicks
Oak seedlings in canopy gaps receive more light and are more likely to survive
Variation is heritable, so great tits with advantageous timing pass genes to offspring
Over generations the frequency of advantageous genes increases: this is evolution
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