Transcript Population Ecology

Population
Ecology
Chapter 4.1
Population Dynamics
Objectives

Describe characteristics of populations.

Understand the concepts of carrying
capacity and limiting factors.

Describe the ways in which populations are
distributed.
What are some observations
you can make about
populations of insects over
the course of a year?

More mosquitoes and flies in the spring and
summer.

More spiders in the fall.

Less visible insects in the winter.

Does this mean all the insects die over the
winter?

No, some just find places to live and
others migrate to warmer areas.
Characteristics used to classify all
populations of organisms

All species occur in groups. We call these
groups populations.

The characteristics used to classify all
populations are:



Population Density:
Dispersion
Populations Ranges
Population Density

What does the term “dense” mean?

Dense means how many things are in an
area. The more thing the more dense the
population is.
Low Density
High
Density
Spatial Distribution

Spatial Distribution is how organisms are
distributed. Where do they live.
How do we classify how
organisms are distributed?
•
Dispersion, or the pattern of
spacing of a population within an
area.
– Uniform dispersion: usually
dispersed in a neat equal
pattern.
– Clumped dispersion:
dispersed where herds live in
large packs or clumps in areas
within the area they live.
– Random dispersion: where it
is unpredictable where they
live.
Population Ranges
Where organisms live


No organism, including humans,
live in all habitats in the
biosphere.
Some species can not adapt to
the abiotic conditions of the
area.

For example, an alligator would
not live in the Great Lakes.

Can you guess what abiotic
factor the alligator could not
adapt to?
Population Limiting Factors

Limiting factors are things that keep a
population from continuing to increase
indefinitely.

Two categories of limiting factors:


Density-independent factor
Density-dependent factor
Density-independent factor
•
Usually are abiotic (non-living) and include
natural phenomena.
– The Tsunami in Japan is an example of a
abiotic density-independent factor.
– The drought in Africa is another example.
•
It also includes human modification to
landscapes and areas.
– The destruction of the rain forest has
limited and even wiped out organisms.
Density-dependent factor

Any factor in the environment that depends
on the number of members in a population
per unit area.

These are often biotic (living) factors.

Examples are predation, disease parasite,
and competition.
Population growth rate

How fast a given population grows.

Emigration: number of individuals moving
away from an area. Not just people.

Immigration: individuals moving into a
population. Again, not just people.
What would happen if nothing
restricted a population from
growing?

Exponential growth model: Shows how a
population would grow if there were no limits
placed on it by the environment.
How do populations usually
grow?

Logistic growth model: most populations
experience times of growth and times on
maintaining population. The logistic growth
model demonstrates this type of growth.
Carrying capacity
•
What is the largest number of organisms a
population can support?
•
Carrying capacity is the largest number of
organisms a population can support.
•
When resources are plentiful there are more
births than deaths.
•
When resources are limited there are more
deaths than births. If this happens the
population has exceeded its carrying
capacity.
Reproductive Patterns
•
Not all organisms reproduce at the same rate.
•
Ever hear the term “reproduce like bunnies?”
– Bunnies produce more offspring than some species.
– People reproduce at a rate slower than bunnies, but
faster than elephants.
•
R-Strategies are organisms that reproduce at a faster
rate. Their goal is to produce as many offspring as
possible in a short time period in order to take advantage
of some environmental factor.
•
K-Strategies are organisms that reproduce fairly
predictably. Elephants reproduce at a predictable rate.
Their goal is to produce fewer offspring that will live to be
at an age that can reproduce themselves.