# BIOL150 Chapter Notes - Chapter 10: Density Dependence, Carrying Capacity, Logistic Function

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20 Jul 2016
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Chapter 10: Pages 136-141
Most important question asked involves growth or decline in numbers of
individuals
Population’s overall growth rate is a function of birth rates, death rates,
immigration rates and emigration rates
Growth rate is change of individuals in the population (∆N) per unit time (∆t)
oIf no immigration or emigration is occurring, then population’s
growth rate is equal to # of individuals in the population (N) times the
per capita rate of increase (r), which is difference between birth rate
per individual (b) and death rate per individual (d)
oIntrinsic rate of increase, rmax, refers to conditions are optimal and
the birth rate is at its highest and death rates are as low as possible.
Expressed as:
∆N/∆t = rmaxN
ormax is high for species that breed at a young age and produce many
offspring and low for species where it takes years to mature and
produce few offspring each year.
rmax is a function of a species’ life history traits
rmax is characteristic and does not change, whereas r is
instantaneous growth rate and constantly changes
r is normally much lower than rmax
Exponential population growth occurs when r does not change with
population size or density.
oLook at figure 10.6 at the bottom of notes
oGrowth rate does not depends on number of individuals in the
population  density independent
o# of individuals added to a population is a function of N even if r is
constant.
oRate of increase is the same, but the # of individuals added is not
oExponential growth is observed in two circumstances
A few individuals found a new population in a new habitat
A population has been devastated by a storm or some other
type of catastrophe and then begins to recover, starting with a
few surviving individuals
oCannot ever continue indefinitely
oWhen population density gets very high, populations per capita birth
rate will decrease and per capita death rate will increase, causing r to
decline  density dependent
Carrying capacity, K, is defined as the max number of individuals in a
population that can be supported in a particular habitat over a sustained
period of time
oFood, space, water, soil quality, resting or nesting sites all factors to
carrying capacity
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