9: Mortality, Survivorship, & Natality

Define natality.

rate of production of new individuals in a population

dynamic life table

fate of a group of individuals all born in the same year

time-specific table

fate of each age class in a population is recorded over a year

survivorship (1x)

probability of surviving to age x

age-specific death rate (qx)

probability of dying at age X

in what aspects of human society would a life table be used?

life insurance policies

characteristics of mortality curves

often have 1 or 2 U-shaped curves

What are the periods of high mortality?

1) early pre-productive phase

-predation & competition

2) early reproductive phase

-territory issues & acquiring mate

3) post-reproductive phase

-end of lifespan

Type I Survivorship Curve

examples?

mortality is highest after birth & during old age

ex// large birds, mammals, humans

Type II Survivorship Curve

examples?

mortality rate constant at all ages

ex// small birds & mammals, reptiles/amphibians, perennial plants

Type III Survivorship Curve

examples?

high mortality rate early in life→few survive to reproduce

ex// invertebrates, marine turtles, many plants

what does fecundity refer to?

number of offspring produced

age specific fecundity( mx)

mean number of female offspring produced by individual at age x

mean realized fecundity at age x (lxmx)

mean number of female offspring surviving at age x

net reproductive rate (R0)

mean number of female offspring produced by an individual during its lifetime

what does R0=1, R0>1, and R0<1 mean?

R0=1 means each female replaces itself & population is stable

R0>1 means population will increase

R0<1 means population will decrease

How do you find R0?

R0=sum of mean realized fecundity at age x (lxmx)