Transcript Document

Unit 3 Human Population
and Carrying Capacity
Population Dynamics
is the study of how populations change in size, density
and age distribution.
Size- total number of individuals
Density- number of individuals in a certain space(
spatial distribution)
Age distribution- the proportion of individuals of
each age in a population
Four Factors affecting
Population size?
How do populations increase or
decrease?
Immigration:
movement of individuals
of a species into a
country or an area
Emigration:
movement of individuals
of a species out of a
country or area
Natality – birthrate
Mortality- deathrate
Population Change=
(Natality+Immigration)(Mortality+Emigration
Exponential Growth
A population with few or no resource
limitations grows exponentially.
Rate 1% - 2%
Examine the data: starts slowly and gradually
increases
Invasive species
Whooping crane p.169
However, this is not true for most populations.
Together biotic potential (essentially how fast
they can reproduce without the environment
having an impact) and environmental resistance
(environmental limits that affect population
growth) determine a carrying capacity for a
population.
Carrying capacity (K) - the maximum population of
a particular species that a given habitat can
support.
Fig. 9-4
Logistic Growth
involves rapid exponential growth followed by
a steady decline in population growth until
the population size levels off.
This occurs because the population
encounters environmental resistance and its
rate of growth decreases as it approaches the
carrying capacity.
After leveling off, the population fluctuates
slightly above and below the carrying capacity.
Overshoot- when organisms use up their resources
and temporarily exceed their carrying capacity
This happens because of a reproductive time lag: the
period needed for the birthrate to drop and the
deathrate to rise as a result of resource
overconsumption.
Fig. 9-5
A dieback or crash occurs unless a switch to an
alternate resources or leaves the area.
Reindeer introduced on an island in Alaska had no
alternate resource and the death of the herd.
Fig. 9-6
What limits population growth?
Limiting Factor -when a particular
condition or factor can be identified as a
key component that limits the size of a
population.
Air, water, nutrients, food, shelter, etc.
There are four categories of limiting
factors:
1. Availability of Raw Materials
Plants need nitrogen and
magnesium from the soil as
raw materials to manufacture
chlorophyll.
Adding fertilizer to the soil is a
way of preventing nitrogen
from being a limiting factor.
2. Availability of Energy
Plants require energy from sunlight.
Animals require food energy.
Food webs can be changed.
3. Accumulation of Waste Products
commonly a
limiting factor for
bacteria and
organisms that live
in small ecosystems
such as puddles,
pools and petri
dishes.
not a limiting factor
for most organisms
4. Interactions among Organisms
Since cottontail rabbits and white
tailed deer eat the twigs of many
species of small trees, they have a
limiting effect on the size of some
tree populations.
Parasites and predators cause the
premature death of individuals thus
limiting the size of the populations.
Factors Affecting Population Size
Fig. 9-3
Types of Population Change curves
stable- fluctuates above and below the carrying
capacity
irruptive- a stable population which on occasion
will explode or irrupt
cyclic- cyclical fluctuations over a defined period of
time
irregular- no order the fluctuations- chaos
Natural Population Curves
Fig. 9-7
Where Might the human population
be on this growth curve?
Human population
Video clip :
http://www.youtube.com/watch?v=4BbkQiQy
aYc
See worksheet: Applying Human Populations