Learning Targets
“I Can…”
• Discuss several factors that influence a
population’s growth rate.
• Distinguish between immigration and
emigration.
• Explain how a change in birth rate or death
rate can affect the population growth rate.
• Visualize exponential growth.
Populations
Interdependence in Nature
How Populations Grow
Hydrilla verticillata
• Native to Asia
• Aquarium plant that was
tossed into Florida waters
by a fish farmer in 1950
• Began to reproduce
quickly and take over
waterways
• Why did these plants get
so out of control?
How Populations Grow?
New England Cod
• Catch has dropped
dramatically in recent
years
• In 1982, the catch was
57,200 metric tons; in a
recent year it was only
3048 metric tons
• Where did all the fish
go?
Describing Populations
• Both the Hydrilla and the cod involve dramatic
changes in population size over a period of
time
• What is a population?
– A group of organisms of a single species that lives
in a given area
Describing Populations
• Geographic Range: The area inhabited by a
population
Describing Populations
• Population Density: the number of individuals
per unit area
Describing Populations
• Population Distribution: how individuals in a
population are spaced out across the range of
the population
Describing Populations
– Uniform Distribution
Describing Populations
• Age Structure: the number of males and
females of each age a population contains
Population Growth
• A population will increase or decrease in size
depending on how many individuals are
added to it or removed from it.
• The factors that affect population growth are
the birth rate, death rate, and the migration
rate
Population Growth
Number of Times Napkin is Folded
0
1
2
3
4
5
6
7
8
9
10
11
Number of Napkin Layers
Exponential Growth
• Under ideal conditions with unlimited
resources, a population will grow
exponentially, where the size of each
generation of offspring will be larger than the
generation before it
Exponential Growth
Learning Targets
“I Can…”
-Derive a formula for exponential growth
-Define “logistic growth.”
-Draw/Interpret a graph for a population that is
experiencing exponential growth.
-Name the three phases of logistic growth and
identify these three regions on a graph.
-Define “carrying capacity.”
-Explain what happens if a population reaches its
carrying capacity.
Exponential Growth
Calculating Exponential Growth
http://edweb.sdsu.edu/t2arp/quest/pop/Population_Growth.html
Answer the following five Questions!
1. Predict phase 5, phase 6, phase 7?
2. How many people are there in phase ten, fifteen, and
twenty?
3. Do you see a pattern? Explain.
4. At what phase does the growth seem large to you?
Why?
5. Draw a simulation model, like the one above, for each
mother having three babies.
6. Answer Questions 1-4 for the simulation in question 5.
Logistic Growth
• Naturally, populations do not grow
exponentially for long, otherwise they would
already cover the earth. There are actually
phases of growth within populations
– Phase 1: Exponential Growth
– Phase 2: Growth Slows Down
– Phase 3: Growth Stops and has reached its
Carrying Capacity
Logistic Growth
Logistic Growth
Learning Targets
“I Can…”
-Define “limiting factor” and give several
examples of limiting factors in a population.
-Distinguish between density-dependent and
density-independent limiting factors and give
several examples of each.
-Interpret population growth curves for several
different sample populations.
-Establish symbiotic relationships by comparing
the growth curves of two species.
Limits to Population Growth
• A limiting factor is a factor that controls the
growth of a population
• Limiting factors determine the carrying
capacity of an environment for a species
• Limiting factors keep most natural populations
somewhere between extinction and totally
overtaking the planet
Limits to Population Growth
• Density-Dependent Limiting Factors: factors
that affect populations when the population
density reaches a certain level; these factors
do not generally affect small, scattered
populations
– Competition for resources
– Predator/Prey relationships
– Parasites and disease
– Stress from overcrowding
Limits to Population Growth
• Density-Independent Limiting Factors: affect
all populations in similar ways, regardless of
population size and density
– Unusual weather (hurricanes, droughts, floods)
– Natural disasters (wildfires)