# 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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