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Population Ecology

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Discuss the 'sixth extinction' and measurement of extinction rates ... Ex: passenger pigeon, whooping crane, bald eagles, elephant seals ... – PowerPoint PPT presentation

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Title: Population Ecology


1
Population Ecology
  • Elizabeth Petrie
  • Jill Stittleburg
  • Sherry Wiedman

2
Todays objectives
  • Define carrying capacity
  • Describe how and why population growth rates
    change as the population approaches carrying
    capacity
  • Discuss the sixth extinction and measurement of
    extinction rates
  • Analyze human causes of extinction

3
Changes in Population Size
  • What causes populations to change in size?
  • What are some factors that may limit population
    growth?
  • Is there a point at which the population cannot
    grow anymore? Why or why not?

4
  • Population growth is a function of birth rate and
    death rate-

If birth rate gt death rate, population

increases
If death rate gt birth rate, population
decreases
If birth rate death rate, then the
population stablizes
5
Limiting Factors-
  • An environmental factor that prevents a
    population from increasing.

Lack of food water shelter space
6
  • There are 2 types of limiting factors
  • Density dependent factors
  • Density independent factors

7
Density- dependent factors
  • Limiting factors that increase in intensity as
    the population increases in size.
  • Will reduce birth rates or increase death rates

Ex. limited food supplies increased risk
of infectious disease toxins due to
increased waste levels
8
Density-independent factors
  • Influence population rates regardless of their
    density

Ex. weather events drought,
floods, extreme temperatures human
interventions
9
Carrying capacity
  • The maximum population that can be supported
    indefinitely in a given environment
  • Populations that are experiencing exponential
    growth eventually reach carrying capacity

10
Fruit Fly Population Growth
11
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12
Population Growth
  • When conditions are good, a population can grow
    exponentially
  • The effects of declining resources gradually slow
    growth rate
  • Growth rate declines to zero as it approaches
    carrying capacity
  • If a population grows beyond the carrying
    capacity, a population crash may occur

13
(No Transcript)
14
14.1 The Sixth Extinction
  • Vocabulary
  • Extinction complete loss of a species
  • Biodiversity entire variety of living organisms
  • Endangered Species Act law passed in 1973 with
    the purpose of protecting and encouraging the
    population growth of threatened and endangered
    species

15
Endangered Species Act (ESA)
  • Written and passed because humans seemed to be
    triggering the rapid rate at which species were
    being lost
  • Ex passenger pigeon, whooping crane, bald
    eagles, elephant seals
  • Critics of ESA say that saving all species is
    unrealistic goal because extinction is a natural
    process
  • The 10 million species living today represent
    only 1 of all species that have ever existed

16
Measuring Extinction Rates
  • Earths history highlighted by 5 mass extinctions
    thus far
  • Mass extinction period of a few thousand or few
    hundred years in which 50-90 of living species
    lost

From http//www.jkaneart.com/massextinctiongraph.h
tm
17
Causes of Mass Extinction
  • First five thought to be caused by natural global
    changes changes in sea level and climate
    fluctuations, changes in ocean and land
    formscontinental drift, asteroid impact
  • The sixth mass extinction (that scientists
    currently believe we are experiencing) is being
    caused by human activity

18
Human causes of extinction
  • Habitat Destruction
  • Habitat Fragmentation
  • Introduced Species
  • Overexploitation
  • Pollution
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