d. survivorship and selection type
DESCRIPTION
Survivorship curves: tell us how long individuals survive in a populationTRANSCRIPT
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D. Survivorship and Selection Type
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1. Survivorship curves:
tell us how long individuals survive in a population
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type I
species with a high survival rate of their young
most individuals are expected to die only when old
eg. humans
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type II:
- species in which individuals die at a constant rate from hunting, disease, etc.
- eg. squirrels, bees, most reptiles
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type III:
- species with most individuals die when young
- many babies are born, but few survive very long
eg. tobacco, salmon, oysters
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1000
100
10
0
Num
ber of survivors [log scale]
0 20 40 60 80 100 Percent of life span
Type I
Type II
Type III
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2. ‘r’ and ‘K’ selection
a. ‘r’ refers to species whose population is well below the carrying capacity and so can still grow exponentially with a rate ‘r’
b. ‘K’ refers to populations that are almost at the carrying capacity [K]
c. ‘r’ and ‘K’ refer to different strategies that will ensure the survival of the species
d. the environment, size of the organism, number & size of offspring, maturity, life expectancy and frequency of reproduction all influence this
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‘r’ strategy
unstable environment, density independent
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small size of organism
energy used to make each individual is low
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many offspring are produced
early maturity
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short life expectancy
each individual reproduces only once
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1000
100
10
0
Num
ber of survivors [log scale]
0 20 40 60 80 100 Percent of life span
Type III
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‘K’ strategy
stable environment, density dependent
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large size of organism
energy used to make each individual is high
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few offspring are produced
late maturity, often after a prolonged period of parental care
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1000
100
10
0
Num
ber of survivors [log scale]
0 20 40 60 80 100 Percent of life span
Type I
Type II
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handout;
work on parts B and C