Population Ecology
Chapter 4
GPS
•
•
SB4 Students will assess the
dependence of all organisms on one
another and the flow of energy and
matter within their ecosystems.
d. Assess and explain human activities
that influence and modify the
environment such as global warming,
population growth, pesticide use, and
water and power consumption.
 A biological
community is a
group of
interacting
populations that
occupy the
same area at
the same time.
A desert oasis
• Organisms within a community adapt
to the conditions in which they live.
• These conditions are often abiotic
factors
• Communities are often stable but may
evolve and change over time.
Keeps a population in check.
Doesn’t allow unlimited growth.
Limiting factors include:
Food, water, shelter/ habitat, mates
Organism compete for these limited
resources
Population Dynamics
Populations of species are
described by density,
spatial distribution, and
growth rate
Population Characteristics
Population Density
The number of individuals per unit area
Spatial Distribution
The pattern of spacing of a population
Visualizing Population
Characteristics
Interactive CD
Population Ranges
• Populations can not live in all
environments
• Abiotic conditions effect the range of
environments in which a population can
live
• A species might not be able to expand its
population range because it cannot
survive the abiotic conditions found in the
expanded region.
Population Limiting Factors
There are two categories of limiting factors
1. density-independent factors
Any factor in the environment that does not depend
on the number of members in a population per
unit area
2. density-dependent factors
Any factor in the environment that depends on the
number of members in a population per unit area
Disease
Temperature
Competition
Parasites
Storms
Food
Habitat disruption
Drought
Environmental limits to population
growth
Density-dependent factors
disease, competition, parasites, and food
Density-independent factors
temperature, storms, floods, drought,
habitat disruption
• An upper limit and lower limit that define
the conditions in which an organism can
survive
• The ability of any organism to survive
when subjected to abiotic factors or biotic
factors is called tolerance.
Population Growth Rates
Exponential growth
As the population gets large it also grows
faster
Reasons this occurs:
2. As individuals mature,
reproducing individuals increases.
Population size
1. Initial increase is slow because few
breeding individuals
Time
Exponential growth is not
realistic
Population size
Populations tend to grow until some
environmental condition stops growth
This is called
Logistic
Population
Growth!!
Time
Carrying capacity and Limiting
factors
Keeps a population in check.
Doesn’t allow unlimited growth.
Limiting factors include:
Food, water, shelter/ habitat, mates
Organism compete for these limited
resources
Reproductive patterns
Species of organisms vary in:
the number of births per reproduction
cycle
the age that reproduction begins,
the life span of the organism
What causes a population to grow
Number of births is greater than the
number of deaths
Immigration exceeds Emigration.
What causes a population’s
numbers to decrease?
Number of births is less than the
number of deaths
Emigration exceeds immigration.
2 Reproductive Patterns
• K-strategist
–
–
–
–
Little environmental change
Generally large organisms
Long life spans
Few offspring with extended parent care
• R-strategist
–
–
–
–
Fluctuating abiotic factor occur
Generally small organisms
Short life span
Many offspring
Elephants
Bacteria
Mice
Humans
Cows
Termites
Lions
Rabbits
• Demography- the study of human
population growth characteristics.
• Age structure-proportions of a
population that are at different age
levels.
Predator prey relationships