Environmental Science Chapter 8: Understanding Populations

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Environmental ScienceChapter 8Understanding
Populations
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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.

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Section 8.1How 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

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The Decline of the Passenger Pigeon

• How does a species go from having billions to
  extinct in just one centuryThe Passenger Pigeon
  Story.
• Extinct in the wild since 1900 and last died in
  the Cincinnati Zoo 1914.

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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
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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)?

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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
Americas most abundant bird. Hunting drove them
to extinction in less than 100 years.
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Mark and Recapture

• Common way of estimating population size

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Estimating Population
How can you estimate the population of trees in
this valley? WHY NOT COUNT THEM ALL? WHY IS
SAMPLING NEEDED?
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Population Density
What is population density? What are advantages
and disadvantages of high and low density?
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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

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Population Distribution
How organisms are arranged within an area
RANDOM
CLUMPED
UNIFORM
Occurs where resources needed are found
throughout Wildflowers in a meadow
Most Common. Occurs where resources are
together Water hole in desert, humans in cities
Occurs when individuals hold territory or compete
for space Plants in a desert
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Many bird species are territorial. In territorial
birds species, what kind of population structure
would you expect?
UNIFORM
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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

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What type of distribution?
CLUMPED WHY?
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Population Growth?

• Why are there so few whales, but so many bacteria?

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Growth Rate

• Change in the size of a population over a given
  time period

AND
Immigration
MINUS
Emigration
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Factors the Determine Population Growth

• A populations relative birth and death rates
  (mortality and natality) affect how it grows
• births gt deaths population increase
• deaths gt births population decrease
• Immigration
• Emigration

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Immigration/Emigration

• In addition to births and deaths, population
  growth is affected by immigration and
  emigrationindividuals moving into and out of a
  population.
• Migration, seasonal movement into and out of an
  area, can temporarily
  change population size.

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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?
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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
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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
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How Populations Grow

• What resources are available to the population?

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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 J-Shaped Curve
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Why doesnt exponential growth last long?
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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?

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What Might Be Some Limiting Factors in the Ocean?

• Limiting factors
• may include
• Salinity
• pH
• Sunlight
• Dissolved oxygen
• Temperature

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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?

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Carrying Capacity

• Limiting resources used as quickly as provided
• Competition within population
• Competition for territory

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Carrying Capacity
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Logistic Growth
Carrying Capacities are NOT fixed
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Exponential Growth not controlled, occurs when
there are no limiting factors, and little
competition
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Logistic Growth controlled
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Population Growth of Wolves and Moose Living in
the Isles Royale of Lake Superior
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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
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Biotic Potential

• An organisms maximum ability to produce
  offspring in ideal conditions
• Many factors influence biotic potential,
  including gestation time and generation time
• Organisms with high biotic potential can recover
  more quickly from population declines than
  organisms with low biotic potential

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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

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Population Regulation

• Population size may be density dependent or
  density independent.

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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

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Density Independent

• Certain proportion of a population may die
  regardless of the populations density
• Affects all populations in a general or uniform
  way
• Severe weather and natural disasters are often
  density independent causes of death

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Section 8.1 Population Growth Review

• Describe the factors that influence populations
  growth rate
• Explain exponential and logistic growth
• Explain how limiting factors and biotic potential
  affect population growth

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Section 8.2How Populations Change in Size

• GOALS
• Explain the difference between niche habitat
• Describe the 5 major types of interactions
  between species
• Describe the adaptations to competition and
  predation

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Niche
A species role in its ecosystem Ex. spiders eat
many smaller insects, bees help to pollinate
flowers. No two species occupy the same exact
niche in their environment (Habitat is the
environment in which they live)
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How do species interact?

• Competition different organisms attempt to use
  the same limited resources
• among or between species
• organisms fight for places to live, food to eat
  and organisms to mate with

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Adaptations to Competition

• Niche restriction divide the niche in time or
  space
• Use less of the niche than they are capable of
  using

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2. Predation organisms feed on other organisms
(predator) or are being eaten (prey)
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Adaptations to Predation

• Camouflage
• Excellent vision
• Warning coloration
• Mimicry
• Protective covering

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3. Symbiosis two species living closely
together
Types of Symbiosis Mutualism both species
benefit. (flowers bees) Commensalism one
member benefits the other is unaffected.
(barnacles whales) Parasitism one member
benefits and the other may be harmed. (Tapeworm)
Link!
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Section 8.2How Populations Change in Size

• Explain the difference between niche habitat
• Describe the 5 major types of interactions
  between species
• Describe the adaptations to competition and
  predation