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Environmental Science: Toward a Sustainable Future Richard T. Wright

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Environmental Science: Toward a Sustainable Future Richard T. Wright Chapter 4 Ecosystems: How They Change PPT by Clark E. Adams Factors That Contribute to Ecosystem ... – PowerPoint PPT presentation

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Title: Environmental Science: Toward a Sustainable Future Richard T. Wright


1
Environmental Science Toward a Sustainable
Future Richard T. Wright
Chapter 4
  • Ecosystems How They Change
  • PPT by Clark E. Adams

2
Factors That Contribute to Ecosystem Change
  • Dynamics of natural populations
  • Mechanisms of population equilibrium
  • Mechanisms of species adaptation
  • Ecosystem response to disturbance
  • Lessons to learn

3
Dynamics of Natural Populations
  • Population growth curves
  • Biotic potential versus environmental resistance
  • Density dependence and critical number

4
Biotic Potential and Environmental Resistance
5
Population Equilibrium
A dynamic balance between births and deaths.
  • Births

Deaths
6
Population Growth Curves
7
Population Growth Curves
  • Reproductive strategies

Many offspring with low parental care
Few offspring with high parental care
J-shaped growth curve
S-shaped growth curve
8
Population Dynamics
  • Environmental resistance combination of biotic
    and abiotic factors that may limit population
    increase
  • Predators, competitors, disease
  • Adverse weather, limited food/nutrients

9
Biotic Potential and Environmental Resistance
10
Density Dependence and Critical Numbers
  • Factors of environmental resistance are either
  • density-independent effect does not vary with
    population density e.g., adverse weather
  • density-dependent effect varies with population
    density e.g., infectious disease
  • Critical number the lowest population level for
    survival and recovery

11
Mechanisms of Population Equilibrium
  • Predatorprey dynamics
  • Competition
  • Interspecific
  • Intraspecific
  • Introduced species

12
PredatorPrey Balance Wolves and Moose
13
Lessons to Be Learned about PredatorPrey Balance
  • Absence of natural enemies allows a herbivore
    population to exceed carrying capacity, which
    results in overgrazing of the habitat.
  • The herbivore population subsequently crashes.
  • The size of the herbivore population is
    maintained so that overgrazing or other overuse
    does not occur.

14
PlantHerbivore Dynamics
Reindeer on St. Matthew Island
  • No regulatory control (predation) on herbivores
  • Went into exponential growth pattern
  • Overgrazed habitat
  • Massive die-off of herbivores

15
Mechanisms of Population Equilibrium
PlantHerbivore
  • Compare the predatorprey with plantherbivore
    methods of controlling the size of the herbivore
    population.
  • How would the herbivore population growth curve
    look if diseases or predators were used as the
    control mechanism?

16
Keystone Species
  • A single species that maintains biotic structure
    of the ecosystem
  • Pisaster ochraceus a starfish that feeds on
    mussels, keeping them from blanketing the rocks

http//www.marine.gov/
17
Competition Intraspecific
  • Territoriality defense of a resource against
    individuals of the same species
  • Examples of wolves and songbirds
  • Results in priority access and use of resources
  • How do wolves and songbirds establish territory?

18
Competition Interspecific
  • Grasslands contain plants with both fibrous roots
    and taproots
  • Coexist by accessing resources from different
    soil levels

19
Introduced Species
  • Rabbits in Australia (next slide)
  • Chestnut blight in United States
  • Japanese beetles, fire ants, gypsy moths in
    United States
  • Water hyacinth, kudzu, spotted knapweed, purple
    loosestrife (see Fig. 4-13 in text) in United
    States

20
Rabbits Overgrazing in Australia
21
Introduced Species
  • Why have introductions of nonnative and exotic
    species resulted in a degradation of ecosystems?
    (Think in terms of environmental resistance and
    biotic potential.)
  • An example of the answer to this question is
    given in the next slide.

22
Introduced Species Rabbits in Australia
  • Introduced into Australia from England in 1859
  • No natural enemies rabbit population exploded
  • Overabundant herbivore population devastated
    natural vegetation (see Fig. 4-11 in text).
  • Using disease as control measure why will this
    procedure fail in the long term?

23
Mechanisms of Species Adaptation
  • Change through natural selection
  • Selective pressure determines which organisms
    survive and reproduce and which are eliminated.

24
Recipe for Change
25
Adaptations to the Environment
26
The Limits of Change
  • Adapt
  • Move (migrate)
  • Die (extinction)

27
Vulnerability of different organisms to
environmental changes
28
Prerequisites for Speciation
  • Original population must separate into smaller
    populations that do not interbreed with one
    another.
  • List some ways this might happen.
  • Separated populations must be exposed to
    different selective pressures.
  • Example arctic and gray fox (next slide)

29
Speciation Foxes
30
Speciation Galápagos Finches
31
Ecosystem Responses to Disturbance
  • Ecological succession
  • Disturbance and resilience
  • Evolving ecosystems

32
Equilibrium Theory
  • Ecosystems are stable environments in which the
    biotic interactions among species determine the
    structure of the communities present.

33
Succession and Disturbance
  • Ecological succession transition between biotic
    communities
  • Primary no previous biotic community
  • Secondary previously occupied by a community
  • Aquatic transition from pond or lake to
    terrestrial community

34
Primary Succession
35
Primary Succession
  • Mosses invade an area and provide a place for
    soil to accumulate.
  • Larger plants germinate in the new soil layer,
    resulting in additional soil formation.
  • Eventually shrubs and trees will invade the area.

36
Secondary Succession
37
Aquatic Succession
38
Disturbance and Resilience
  • Removes organisms
  • Reduces populations
  • Creates opportunities for other species to
    colonize

39
Fire and Succession
http//www.fs.fed.us/photovideo/
40
Ground Fire
41
Fire and Succession
  • Fire climax ecosystems dependent upon fire for
    maintenance of existing balance e.g.,
    grasslands, pine and redwood forests
  • What significance does this have for humans and
    where they live?

42
Resilience in Ecosystems
43
Resilience Mechanisms after a Forest Fire
  • Nutrient release to soil
  • Regrowth by remnant roots and seeds
  • Invasions from neighboring ecosystems
  • Rapid restoration of energy flow and nutrient
    cycling

44
Lessons to Learn
  • Managing ecosystems
  • The pressure of population

45
Managing Ecosystems
  • Protecting and managing the natural environment
    to maintain the goods and services vital to human
    economy and survival.

46
The Pressures of Population
  • What is the carrying capacity for the human
    population on Earth?
  • How will the human ecological footprint impact on
    natures goods and services?

47
Carrying Capacity and Overshoot
48
End of Chapter 4
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