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

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

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

http://fcn.state.fl.us/fwc/fishing/Fishes/gar.html

Lepisosteus osseus

Attack: forward (most fish) or sideways (gar) lunge special grasping organs

http://insects.ummz.lsa.umich.edu/michodo/test/index.htm

Odonate larvae mentum extends to grasp prey

Capture:

prey have adaptation to avoid capture piscivores have lots of teeth

Blue Whale 100 ft, up to 220 tons

http://www.calpoly.edu/~jiturrir/ED480/whales/baleen.html

predator – prey sizes

http://bio-images.bgsu.edu

~ 1mm

Other factors effect population levels; ex. parasitism, weather

Time po

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predation

parasitism

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Mechanisms of Population Equilibrium: Plant-Herbivore

-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

=

Selective feedersMigratory

Non-selective Non-migratory

Interactions between species: competition vs predation

resource consumer

+

-

predation

+

+

competition-

--

intraspecific competition: between members of same spp

density dependent population regulation evolutionary change

Time

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K= # that resources can support

resources scarce, competition

interspecific competition: occurs between members of different species

negative effect on both populations depends on adaptations of each population

spp 1 niche spp 2 niche

competition

realized niche

Dry habitat, trees can’t compete w/ grass

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

Tipping the Balance: Introduced Species

http://www.gdaywa.com/g5.php

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/AustralianRabbits.jpg

-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.

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

Introduced Species

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

Disturbance and Succession

Equilibrium = No change

• 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

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.

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

Dramatic examples: HI lava flows

Aquatic Succession

•Ecosystems can show resilience during a disturbance

Fire

Disturbance

• Removes organisms, favors tolerant spp.

• Reduces populations

• Creates opportunities for other species to colonize

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?

Resilience Mechanisms After A Forest Fire

• Nutrient release to soil• Re-growth by remnant roots and seeds• Invasions from neighboring ecosystems• Rapid restoration of energy flow and nutrient

cycling

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