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
Lepisosteus osseus
http://fcn.state.fl.us/fwc/fishing/Fishes/gar.html
Rover: Actively search for food. Constant motion.
Bass, yellow perch
Attack:
 forward (most fish) or sideways (gar) lunge
 special grasping organs
Odonate
larvae
mentum
extends to
grasp prey
Capture:
 prey have adaptation
to avoid capture
 piscivores have lots
of teeth
http://insects.ummz.lsa.umich.edu/michodo/test/index.htm
predator – prey sizes
~ 1mm
http://bio-images.bgsu.edu
Blue Whale 100 ft, up to 220 tons
http://www.calpoly.edu/~jiturrir/ED480/whales/baleen.html
Other factors effect population levels; ex. parasitism, weather
predation
Time
population size
population size
parasitism
Time
Mechanisms of Population
Equilibrium: Plant-Herbivore
Livestock grazing in western US
-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)
=
Selective feeders
Migratory
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
population size
resources scarce,
competition
K= # that
resources
can support
Time
interspecific competition: occurs between members of
different species
 negative effect on both populations
 depends on adaptations of each population
realized
niche
spp 1 niche
spp 2 niche
competition
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/Biology
Pages/A/AustralianRabbits.jpg
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.
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.
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
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