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Environmental Science: Chapter 4. Ecosystems: How they change. Biotic Potential Vs. Environmental Resistance. Predator-prey Balance:Wolves and Moose. Steps in predation . Encounter. Attack. Capture. Ingestion. Encounter.

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Environmental Science: Chapter 4

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Environmental science chapter 4 l.jpg

Environmental Science: Chapter 4

Ecosystems: How they change

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Biotic Potential Vs. Environmental Resistance

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Predator-prey Balance:Wolves and Moose

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Steps in predation





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Ambush: Wait for prey to come to you. Burst speed. Pike, muskie, barracuda, gar

Lepisosteus osseus


Rover: Actively search for food. Constant motion. Bass, yellow perch

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Odonate larvae mentum extends to grasp prey



 forward (most fish) or sideways (gar) lunge

 special grasping organs


 prey have adaptation to avoid capture

 piscivores have lots of teeth

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predator – prey sizes

~ 1mm

Blue Whale 100 ft, up to 220 tons


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population size

population size



Other factors effect population levels; ex. parasitism, weather

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Mechanisms of Population Equilibrium: Plant-Herbivore

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-Livestock grazing occurs on more federal public lands than any other commercial use

-Affects more than 260 million acres – an area the size of Texas and California combined

-Water diversions, predator control, vegetation manipulation and fencing

-In the US, livestock grazing has contributed to the listing of 22 percent of federal threatened and endangered species (almost equal to logging (12 percent) and mining (11 percent) combined)

Livestock grazing in western US

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Selective feeders




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Interactions between species: competition vs predation












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K= # that resources can support

intraspecificcompetition: between members of same spp

 density dependent population regulation

 evolutionary change

resources scarce, competition

population size


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interspecific competition: occurs between members of different species

 negative effect on both populations

 depends on adaptations of each population

spp 2 niche

spp 1 niche

realized niche


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Dry habitat, trees can’t compete w/ grass

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  • Territoriality: defense of a resource against individuals of the same species

    • -Examples: wolves, songbirds, bluegill

    • -Means habitat supports fewer individuals and less competition is result

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Tipping the Balance: Introduced Species



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Chestnut Blight

-Fungus which entered US on Asian nursery stock imported to New York ~ 1900

-Spread by wind, rain, birds etc…, enters through cracks or wounds, multiplies rapidly, making sunken cankers which expand and kill everything above the canker

-American chestnut was devastated throughout the natural range, the Appalachian hills and highlands from Maine to Georgia

-By 1940, three and a half billion American chestnuts had perished.

-American chestnut stock advertised as "blight free", means it was grown in an area where no blight is present, outside the natural range or inside a greenhouse.

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Introduced Species

  • Why have these introductions resulted in a degradation of the ecosystems? (Think in terms of environmental resistance and biotic potential.)

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Disturbance and Succession

Equilibrium = No change

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  • 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

  • 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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Dramatic examples: HI lava flows

Relies on adjacent ecosystems

Rain of organic material, seeds, and spores accumulates in cracks

Some pockets moist enough to support scattered `ohi`a seedlings and a few hardy ferns and shrubs

Accumulation leaves, bark… converted by soil organisms into a thin but rich organic soil

A forest can develop in wet

regions in less than 150 years

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Aquatic Succession

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  • Ecosystems can show resilience during a disturbance


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  • Removes organisms, favors tolerant spp.

  • Reduces populations

  • Creates opportunities for other species to colonize

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Fire and Succession

  • Fire climax ecosystems: maintained by fire; e.g., grasslands, pine and redwood forests

  • What significance does this have for humans and where they live?

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Nutrient release to soil

Re-growth by remnant roots and seeds

Invasions from neighboring ecosystems

Rapid restoration of energy flow and nutrient cycling

Resilience Mechanisms After A Forest Fire

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Ecosystem management: thinking about the entire system rather than trying to maximize harvest of few populations

Adaptive management: 1) be prepared to chance policy 2) bring in stakeholders 3) do experiments

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