Transcript sdhsjdhs

Environmental Science
Chapter 8:
Understanding Populations
Understanding Populations Big Ideas
• Population sizes change according to changes
in the environment.
• The size and growth rate of human
population has changed drastically over the
last 200 years. Those changes have led to
profound changes to almost every place on
Earth.
Section 8.1:
How Populations Change in Size
GOALS
• Describe the 3 main properties of a population
• Describe exponential population growth
• Relate how the reproductive behavior of
individuals can affect the growth rate of their
population
• Explain how nature regulates population size
The Decline of the Passenger Pigeon
• How does a species go
from having billions to
extinct in just one
century…The Passenger
Pigeon Story.
• Extinct in the wild since
1900 and last died in the
Cincinnati Zoo 1914.
Review: What is a population?
Population: all the members
of the same species that
live in the same place at
the same time
• Field mice living in a corn
field, grizzly bears of
Yellowstone Park area
Wolves in Yellowstone NP
Population Size
• Why care about the
size of the
population?
• How can scientists
estimate the
population (say of
Elephant Seals on a
beach in CA)?
Population Size
• The number of individuals in
a population at a given time
• Sudden and dramatic
decreases in population size
can indicate an unhealthy
population headed toward
extinction
• Ecologists often use sampling
techniques to estimate
population size.
Did You Know? The passenger
pigeon was once North America’s
most abundant bird. Hunting
drove them to extinction in less
than 100 years.
Estimating Population
How can you
estimate the
population of
trees in this
valley?
WHY NOT
COUNT THEM
ALL?
WHY IS
SAMPLING
NEEDED?
Mark and Recapture
• Common way of
estimating population
size
Population Density
What is
population
density?
What are
advantages
and
disadvantages
of high and
low density?
Population Density
•Measure of how crowded a population is
•Larger organisms
generally have lower
population densities.
•Low population density:
More space, resources;
finding mates can be difficult
•High population density:
Finding mates is easier; tends to be more competition;
more infectious disease; more vulnerability to predators
Population Distribution
How organisms are arranged within an area:
UNIFORM
RANDOM
CLUMPED
Occurs when
individuals hold
territory or compete
for space
Plants in a desert
Occurs where resources
needed are found
throughout
Most Common. Occurs
where resources are
together
Wildflowers in a meadow
Water hole in desert,
humans in cities
Many bird species are territorial. In
territorial birds species, what kind of
population structure would you
expect?
UNIFORM
Population Distribution
•Random distribution:
Organisms arranged in
no particular pattern
•Uniform distribution:
Organisms evenly spaced
•Clumped distribution:
Organisms grouped near resources; most
common distribution in nature
What type of distribution?
CLUMPED
WHY?
Population Growth?
• Why are there so few whales, but so many
bacteria?
Growth Rate
• Change in the size of a population over a given
time period
AND
Immigration
MINUS
Emigration
Factors the Determine Population
Growth
• A population’s relative birth
and death rates (mortality
and natality) affect how it
grows
• births > deaths = population
increase
• deaths > births = population
decrease
• Immigration
• Emigration
Immigration/Emigration
• In addition to births and deaths, population growth
is affected by immigration and emigration—
individuals moving into and out of a population.
• Migration, seasonal movement into and out of an
area, can temporarily
change population size.
Population Calculations
Net population Change =
(births + immigration) – (deaths + emigration)
There are 300 people living in a village, 50
children are born, 20 people die, 10 immigrate
and 2 emigrate. What is the new population?
Calculating Growth Rate
• Determined by the following equation:
(birthrate + immigration rate) – (death rate +
emigration rate)
• Growing populations have a positive growth rate;
shrinking populations have a negative growth rate.
• Usually expressed in terms of individuals per 1000
Current human growth rate 1.25% down from
2.2% in 1963
Every spring, many species of bird
travel north to the Arctic to breed, and
in the fall travel south again for the
winter. This is an example of _____
MIGRATION
How Populations Grow
• What
resources
are available
to the
population?
Patterns of Growth
EXPONENTIAL GROWTH
• Population increases by
a fixed percentage
every year.
• Normally occurs only when
small populations are
introduced to an
area with ideal
environmental conditions
• Rarely lasts long
WHAT SHAPE
DOES
EXPONENTIAL
GROWTH LOOK
LIKE?
Starts slowly, then
takes off – “JShaped Curve”
Why doesn’t exponential growth last
long?
Limiting Factors
Limiting Factor Principle:
too much or too little of
any abiotic factor can
limit or prevent growth of
a population, even if all
other factors are near or
above optimum
• Why are there no citrus
fruit growing in NJ?
• Why do trees grow
toward the sky?
What Might Be Some Limiting Factors
in the Ocean?
• Limiting factors
• may include:
• Salinity
• pH
• Sunlight
• Dissolved oxygen
• Temperature
Carrying Capacity
Limiting Factors lead to
Carrying Capacity: the
largest population an
environment can
sustain
What is the maximum
amount of wolves that
can be sustained in
Yellowstone?
Carrying Capacity
• Limiting resources –
used as quickly as
provided
• Competition within
population
• Competition for
territory
Carrying Capacity
Logistic Growth
Carrying Capacities
are NOT fixed
Exponential Growth – not controlled,
occurs when there are no limiting factors, and little
competition
Population
(Thousands)
Black Bear Population in Northern NJ
Logistic Growth – controlled
Population
(Thousands)
Pelican Population off the Western Coast of Florida
Population Growth of Wolves and Moose Living in the Isles Royale of Lake Superior
A population of wolves is reintroduced into
Yellowstone National Park. For the first
decade, the wolf population grows
exponentially. Then, the population growth
slows. The new pattern is known as ___
LOGISTIC GROWTH
In the example above, where wolves are
reintroduced to Yellowstone National Park, the
number of elk and other prey species within
the park are _____ Limiting Factors
Biotic Potential
•A species’ maximum rate at which its
population can grow
•Many factors influence biotic
potential, including gestation
time and generation time
•Species with high biotic potential can
recover more quickly from population
declines than species with low biotic
potential
Reproductive Potential
•The maximum number of
offspring that each member of
the population can produce in
ideal conditions
Biotic Potential
Scorpion Fish
• Mature 3-5 years
• Release 50,000 to
100,000 eggs
• Once fertilized take
12-16 days to hatch
• HIGH BIOTIC
POTENTIAL
Orangutans
• Females Mature 10
years
• Birth to single babies
once every eight years
• LOW BIOTIC
POTENTIAL
Population Regulation
• Population size may be density dependent or
density independent.
Density Dependent
• Deaths occur more quickly in a crowded
population than in a sparse population
• When individuals of a population are densely
packed together
• Limited resources, predation and disease
result in higher rates of death in dense
populations than in sparse populations
Density Independent
• Certain proportion of a population may die
regardless of the population’s density
• Affects all populations in a general or uniform
way
• Severe weather and natural disasters are often
density independent causes of death
Section 8.1
Population Growth Review
• Describe the factors that influence
population’s growth rate
• Explain exponential and logistic growth
• Explain how limiting factors and biotic
potential affect population growth
• Crash Course - Ecology