Transcript 5.3 Populations

5.3 Populations
Exponential growth
 Population growth in which the rate of
growth in each generation is a multiple of the
previous generation. This occurs when
resources and conditions are not limiting.
Leads to overpopulation.
Populations
Exponential growth
*Any population has the potential to increase
exponentially but conditions are never
perfect. Food resources are limited, predation
occurs, and abiotic conditions are factors.
This limits population growth.
Exponential Growth
 Consider a country with
100 people, growing at
7% per year. In 10
years, the population will
double to 200 people, in
another 10 years it will
double again to 400
people, and ten years
after that it will double
again to 800 people. The
following graph shows
this exponential
population growth.
Carrying Capacity
*The number of
individuals of a species
that can be supported by an
ecosystem. In a balanced
ecosystem, the carrying
capacity of a species is
stable.
*When an ecosystem
reaches the carrying
capacity, the population
quits growing. This is
when the number of deaths
equals the number of
 This is represented in a
graph called an S-shaped
curve.
*Early populations grow
exponentially, as system
reaches its carrying
capacity, population
growth starts to slow.
Finally population growth
stops when carrying
capacity is reached.
Carrying Capacity
Limiting Factors
 The forces that stop a
population’s growth as
they reach their carrying
capacity.
 2 types of limiting factors
1. Density-Dependent Limiting
Factors
 Affect a population more strongly as the
population grows larger
 Dependent on population size
 3 factors
*food and water supply
*predation
*disease
 These populations show an S-shaped growth curve
2. Density-Independent
Limiting Factor
ffect a population
regardless of size
xample is a hurricane
 Affects the same
percentage of a population
regardless of its size
 3 factors
*climate
*human disturbance
*natural disasters
 These populations
show a boom-and-bust
curve. These
populations grow
exponentially when
conditions are
favorable and collapse
when conditions are
bad. Many insect
populations follow this
pattern.
Human Population
 Usually exponential, but not for
ever
 Due to advances in agriculture,
technology, energy development,
transportation, and medicine.