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Jon Abbatt (10)
Lecture 6

lecture 6 notes from prof. Thomson

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Jon Abbatt

Lecture 6: Age-structured populations and life histories  Age structure: the distribution of individuals among age classes within a population.  Geometric rate of population growth  the ratio of the population size after one year to that the beginning of the year: ( ) ( ) ( ) o Will eventually reach a stable age distribution; each age class grows or declines at the same rate  Fecundity: The number of offspring produced per reproductive episode. o Reproductive period usually preceded by resource-accumulation phase o Fecundity-survivorship trade-offs = cost of reproduction x: age specific variables nx: the number of individuals of age x in a population. bx: female offspring produced per reproductive season (b for birth) x : probability of being alive at age x dx: death rate, proportion of individuals of age x dying by age x+1 m x mortality rate; proportion of individuals of age x dying by age x+1 Shapes of survivorship curves  Type II survivorship curveconstant survival rate with age. Thus, survivorship declines exponentially with age.  Type I survivorship curve high survival rate at the beginning, falls off abruptly with age as the age-specific mortality rate increases (human; mortality is low early in life and then increases rapidly later in life) .  Type III survivorship curvehigh mortality rate in early life, survival rate increase later in life. (fishes; young individuals are extremely vulnerable to predation and other risk factors, which they escape as they grow larger and mature).  Net reproductive rate (R0): the expected total number of female offspring produced by an average female over the course of her life span. ∑ o ∑ would be the total # daughters produced by a mother who doesn’t die early; multiplying by discounts expected production by the probability that some mothers do die early  Generation time (T): the average period between the birth of an individual and the birth of its offspring; average age at which a female gives birth. ∑ ∑ o Th
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