Transcript Ecology: 37-2 The Living Environment

Population Ecology
Mrs. Gamari
Ecology
 The study of the interaction between
organisms and their environment (living
and non-living).
 Biotic – living factors
 Example: living organisms in the environment and
their effects on other living things
 Abiotic – non-living factors
 Example: water, oxygen, light, temperature,
inorganic and organic nutrients
Organization in the Living
Environment
 Ecologists often study a group of organisms in a
particular environment.
 Population
 All individuals of a single species that live within a certain area
 EXAMPLE: All of the bullfrogs in a pond = population
 Community
 A group of different populations/organisms in a certain area.
 Example: The bullfrogs, fish, algae, plants, etc. in that same pond
 Ecosystem
 A community and its physical environment; made of abiotic and biotic
factors.
 Continual exchange between all parts (living and nonliving) of the
ecosystem
Population Size
 The number of individuals that a population
contains.
 Can be difficult to measure directly, especially
if there are too many organisms over a large
area, and they are very mobile.
 Therefore, an ecologist may need to ESTIMATE the
number of individuals in a population
CRITICAL THINKING
 An ecologist counts 25 oak trees in a
small patch of forest. S/he needs to
estimate how many oak trees would be in
an area that is 10x larger than the small
patch.
How many oak trees could be in that larger
area? Explain your reasoning.
Population Density
 Measures how crowded a population is.
 Number of individuals per unit of area
 Some areas are sparsely populated,
while others are very densely populated.
 Why do you think this may be?
Measuring the Number of
Individuals in a Population
 Random Sampling – count the number of
individuals in a small area. Extrapolate to find
the number of individuals in a larger area.
 Mark and Recapture – mark a sample of
individuals and return them to the wild. Come
back and capture another sample to see how
many have already been marked. Use a
formula to estimate population size
Dispersion
 The spatial distribution of individuals within
the population
http://www.uwyo.edu/dbmcd/popecol/feblects/lect06.html
• The distribution of a population may be impacted by
availability of resources, social behavior, or habitat
conditions.
Age Structure
Total number
of people
Males
Females
Age ranges
The Regional Institute © 2007
Western New York Age Pyramid, 2000
http://www.uwyo.edu/dbmcd/popecol/feblects/lect06.html
Percentage of individuals
within a particular age range
Population Dynamics
 A population will change in
size depending on how many
organisms are added to it and
how many organisms are
removed from it.
 If resources are not limited,
then the population will grow
when the number of new
individuals added to the
population (births) is greater
than the number of individuals
who leave the population
(deaths).
 Immigration vs. Emigration
J- Shape Curve
 The population keeps
growing over time.
Starts slowly, but then
rapidly increases.
 Number of individuals
coming into the
population exceeds the
number leaving the
population
The Biology Corner
http://www.biologycorner.com/bio4/notes/popgrowth.php
Carrying Capacity
 The maximum population that can be
supported by resources in the
environment.
In reality, resources are not “unlimited.”
S- Shape Curve
 Shows how a
population becomes
limited by
environmental factors
The Biology Corner
http://www.biologycorner.com/bio4/notes/popgrowth.php
 The “plateau” is the
carrying capacity for the
area – the maximum
number of individuals
that the environment
can support.
Factors That Limit
Population Growth
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Nutrients
Water
Disease
Competition
Predation
Space
Population Regulation
 Density-Independent Factors
 Weather, floods, fires
 Reduce the size of populations, regardless of the original
size or density of a particular population.
 Density-Dependent Factors
 Resource limitations, shortage of food, habitats
(competition, predation, disease, parasitism and disease)
 Triggered by increasing populations
 An individual’s chance of surviving depends on the number
of other individuals in that area.
Predation
Competition
 Intraspecific competition: competition
within a species for resources (food, light,
space, nutrients, habitats)
 Interspecific competition: competition
between members of different species.
HUGE impact on evolutionary change
because survival rates can be affected
over time.