Life History Strategy




BIO326 : Population : Life Histories and Evolution : Life History Strategy

Exercise: Life History Strategy

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DUE: 25-Feb-2000. Work sent after this date will receive a grade of zero.

A species has a limited amount of evolutionary resources with which to respond to natural selection. Some populations grow rapidly and postpone reproduction until they reach a certain size. Other populations reach reproductive maturity rapidly, and put most of their resources into new offspring.

Consider two hypothetical fish populations in different habitats. The fish in both populations weigh 20g at one year of age and can forage enough to reproduce their own weight in further growth or in eggs. The individuals in the first population allocate 30% of their resources ( = their body weight) to growth and 70% to reproduction while the second population allocates 70 % of their resources to growth and 30% to reproduction.

Years

Characteristic 1 2 3 4 5 6

Slow growth/high fecundity

  Body weight   20      26     _____     _____     _____     _____

  Growth increment   6      7.8     _____     _____     _____     _____

  Weight of eggs   14      18.2     _____     _____     _____     _____

  Cumul egg weight   14      32.2     _____     _____     _____     _____

Rapid growth/low fecundity

  Body weight   20      34     _____     _____     _____     _____

  Growth increment   14      23.8     _____     _____     _____     _____

  Weight of eggs   6      10.2     _____     _____     _____     _____

  Cumul egg weight   6      16.2     _____     _____     _____     _____

	Years
Characteristic	1	2	3	4	5	6

Slow growth/high fecundity
Body weight	20	26	_____	_____	_____	_____
Growth increment	6	7.8	_____	_____	_____	_____
Weight of eggs	14	18.2	_____	_____	_____	_____
Cumul egg weight	14	32.2	_____	_____	_____	_____
Rapid growth/low fecundity
Body weight	20	34	_____	_____	_____	_____
Growth increment	14	23.8	_____	_____	_____	_____
Weight of eggs	6	10.2	_____	_____	_____	_____
Cumul egg weight	6	16.2	_____	_____	_____	_____

1. Following the relationships in Table 11.4 on pg 246, complete the rows for the two populations and enter your results in the textbox below.

2. Suggest (hypothesize) a schedule of life table survivorship (s_x for each age, x) for each population, which would be consistent with the growth and reproduction values you have in your table.

3. Your hypothesized survivorship values can be considered "a model" of this fish population, i.e., providing a description of how the population is expected to grow and predicting its behavior in the future. How would you test your model as a useful ecological tool for management of this population?

4. Suppose that these life history features are genetically controlled, and that "habitat improvement" by a government agency removes the barrier between the two fish habitats. Under what conditions would each of these life histories tend to eliminate the other by natural selection?

5. If reproduction in the rapid growth/low fecundity population were delayed for two years (all resources into growth in the first two years, then reproduce first in year 3), how would this delay in reproduction affect the relative contributions to future generations of the two populations? Enter in the textbox below the values you calculated to determine your answer.

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