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NOTE:
The following Powerpoint Presentation was originally created by Clark E Adams….
www.davenport.k12.ok.us/classes/jhhs/enviro/Chapter_04.ppt
Things have been changed from the original presentation for the purpose of this class.
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Environmental Science: Toward a Sustainable Future Richard T. Wright
Ecosystems: How They ChangePPT by Clark E. Adams
Chapter 4
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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
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Dynamics of Natural Populations
Population growth curves Biotic potential versus environmental
resistance Density dependence and critical number
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Biotic Potential and Environmental Resistance
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Population Equilibrium
Births Deaths
A dynamic balance between births and deaths.
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Population Growth Curves
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Population Growth Curves
Reproductive strategies:
Many offspring withlow parental care
Few offspring withhigh parental careJ-shaped growth curve
S-shaped growth curve
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Population Dynamics
Environmental resistance: combination of biotic and abiotic factors that may limit population increase Predators, competitors, disease Adverse weather, limited food/nutrients
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Biotic Potential and Environmental Resistance
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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
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Mechanisms of Population Equilibrium
Predator–prey dynamics Competition
Interspecific Intraspecific
Introduced species
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Predator–Prey Balance: Wolves and Moose
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Lessons to Be Learned about Predator–Prey 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.
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Plant–Herbivore Dynamics
No regulatory control (predation) on herbivores
Went into exponential growth pattern
Overgrazed habitat Massive die-off of
herbivores
Reindeer on St. Matthew Island
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Mechanisms of Population Equilibrium: Plant–Herbivore Compare the predator–prey with plant–herbivore
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?
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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/
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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?
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Competition: Interspecific
Grasslands contain plants with both fibrous roots and taproots
Coexist by accessing resources from different soil levels
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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
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Rabbits Overgrazing in Australia
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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.
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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?
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Mechanisms of Species Adaptation
Change through natural selection Selective pressure determines which organisms
survive and reproduce and which are eliminated.
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Recipe for Change
GENES ENVIRONMENT
ADAPTATIONSNATURAL SELECTION: For? or Against?
+
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Adaptations to the Environment
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The Limits of Change
Adapt Move (migrate) Die (extinction)
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Vulnerability of different organisms to environmental changes
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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)
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Speciation: Foxes
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Speciation: Galápagos Finches
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Ecosystem Responses to Disturbance
Ecological succession Disturbance and resilience Evolving ecosystems
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Equilibrium Theory
Ecosystems are stable environments in which the biotic interactions among species determine the structure of the communities present.
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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
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Primary Succession
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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.
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Secondary Succession
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Aquatic Succession
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Disturbance and Resilience
Removes organisms Reduces populations Creates opportunities for other species to
colonize
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Fire and Succession
http://www.fs.fed.us/photovideo/
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Ground Fire
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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?
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Resilience in Ecosystems
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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
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Lessons to Learn
Managing ecosystems The pressure of population
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Managing Ecosystems
Protecting and managing the natural environment to maintain the goods and services vital to human economy and survival.
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The Pressures of Population
What is the carrying capacity for the human population on Earth?
How will the human ecological footprint impact on nature’s goods and services?
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Carrying Capacity and Overshoot