Transcript CP-Ch4-PopulationDynamics

Do Now: Bird migration
What are some observations you can make of
bird populations during winter, spring, fall, &
summer?
Population, Dynamics, & Growth
What is a Population?
– A group of individuals of the same species living
in the same area at the same time
•
Characteristics of Populations
•
Birth Rate
•
Death Rate
•
Age Structure
•
Survivorship (predator-prey)
•
Immigration
•
Emigration
Chapter 4-1
Population Density
• Number of organisms per unit of area
How to measure population size?
– In most cases, it is impractical or impossible to count
all individuals in a population
• Mark Recapture (goldfish lab)
• Random Sampling (sunflowers)
Mark-recapture
– Animals are trapped, marked, and then
recaptured after a period of time
– Total Population Size: N=MC/R
Random sampling
• Collect data by taking “random” samples in
different areas
• Sunflower activity!
• Crab activity!
• Lab activity!
Why Use These Techniques?
• Because individuals within a population
are dispersed differently
• Three dispersion patterns
– Clumped
– Uniform
– Random
Clumped
Most common in nature
• There is physical protection
• There are a lot of nutrients
• The initial position is close to the parents
Clumped
Uniform
• equal space between individuals
– Trees in an orchard
– Seeds in a garden
Random
• patternless, unpredictable way
• Some populations exhibit both clumped and uniform
dispersion patterns, but on different scales
Dynamics & Growth
• Two growth curves
• Known as population Growth Curves
– J-shaped
– S-shaped
Do Now: Population Dynamics
1.
If some cattle wandered off, would they still
be considered part of the population?
2. If a new herd came by, would they be part
of the existing population?
Population, Dynamics, & Growth
Exponential Growth Model: Ideal Environment
• Unlimited resources
(J-shaped curve)
Population Growth Curves
Logistically
population growth levels off
at the carrying capacity (K)
logistic growth
(S-shaped curve)
The Logistic Growth Model:
Reality of a Limited Environment
• Populations grow exponentially for a while
• But the population-limiting factors restrict population
growth
– Lack of food
– Lack of Space
– Competition
– Disease
– Predation
Population, Dynamics, & Growth
• The logistic
growth model
– Population growth
is slowed by limiting
factors
These factors are known as…
• Density Dependent Factors
• Density Independent Factors
• Density-dependent factors
– Food, light, nutrients, water
– Increase a population’s death rate
– decrease a population’s birth rate
• Density-independent factors
– Includes events
• seasonal freezing
• Volcanic eruptions
• other natural disasters
• densityindependent
factors limit
population size
before densitydependent factors
become important
Exponential
growth
Sudden
decline
What is going on here…
Predator-Prey Cycles
•
•
•
•
Low # predators = high # prey
As # prey increase, # predators increases
High # predators = low # prey
As # prey decrease, # predators decrease
Do Now: Snowshoe Hare & Lynx
Prey
Predator
Discuss: What is happening to the
populations?
Do Now: Industrial Revolution
1800
• How/why did this lead to a population explosion?
Do Now: WWII
1939-1945
• How did this lead to a population decline?
Do Now: Medicine & Sanitation
• How did this lead to a population increase?
Demography
• Study of human population size, density,
distribution, movement, birth and death rates
Ch.4-2
Population Ecology
Human Population Growth Rate
 Human population
growth rate has
slowed.
 Why?
Population Ecology
 Human population growth is not the same in all
countries.
Population Ecology
 A population’s age structure is the number of males
and females in each of three age groups:
pre-reproductive, reproductive stage, & post-reproductive
Population Ecology
 Concerns about
exceeding the carrying
capacity
 Resources?
Survivorship Curves
• 1. Type I - mortality occurs among the elderly
– (e.g., humans in developed countries)
• 2. Type II - mortality is not dependent on age
– (e.g., many species of large birds, squirrels, and fish)
• 3. Type III - juvenile mortality is extremely high
– (e.g., plant and animal species producing many offspring of
which few survive, underdeveloped countries)
Survivorship
Age Structure and Population Dynamics
Rapid growth
Kenya
Male
Slow growth
United States
Female
Male
Female
Zero growth/decrease
Italy
Male
Female
Primary
reproductive
ages
Percentage of population
Percentage of population
Percentage of population
These age structure diagrams indicate that less developed countries such as Nigeria
have a much higher percentage of young people than highly developed countries.
As a result, less developed countries are projected to have greater population growth
than highly developed countries.