Transcript Understanding Populations

Environmental Science
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 1.13% down from
2.1% in 1968 (2015 was 1.15 %)
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
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
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Crash Course - Ecology