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Ecosystems
(Ch 20; p. 374-375 in ch. 18)
Interactions of
organisms with each
other and their
environment:
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Driving force
behind much of
natural selection &
evolution.
Pivotal concept in
biology.
The Ecosystem Concept
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Ecosystem: An interacting system consisting of all
organisms plus the physical (abioltic) environment.
Community: all the organisms present; the living
component of an ecosystem.
Ecology: “Scientific study of interactions between
organisms and their environment” (p. 374).
–
Different from 'environmentalism' (p. 374)
–
But may help solve environmental problems.
Interactions Between Organisms (p. 429-432)
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Competition: Struggle for
resources (light, nutrients,
water, space, habitat, etc).
– Within & between
species.
– both partners inhibited
(p. 429)
Mutualism: both partners
benefit (p. 430).
– Mycorrhizae.
– Many plant-pollinator
interactions.
– Corals.
– Lichens.
Interactions Between Organisms (p. 429-432)
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Herbivory: heterotroph consumes
autotroph (p. 431).
– Plant-herbivore interactions:
– Defense mechanisms: thorns,
tough leaves, distasteful or toxic
substances.
Predation –A heterotroph kills & eats
another (p. 430).
Parasitism: (p. 432).
– Parasite: lives on, gets
nourishment from host organism
● Often small or microscopic.
– Pathogen: disease-causing
parasite.
– Autotrophs or heterotrophs may be
parasitized.
Structure of Ecosystems: Trophic
Structure (p. 422)
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“Trophic” = energy /feeding relationships.
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Energy enters ecosystem via photosynthesis.
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Flows through ecosystem as organisms consume each
other.
Trophic level = “feeding level” .
Food chain: Sequence of energy transfer (feeding)
from organism to organism (P. 432; Fig. 20.15).
Autotrophs or Producers (P.432):
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Photosynthetic autotrophs:
– Plants.
– Algae.
– Photosynthetic bacteria.
Chemo-autotrophs:
– Certain bacteria.
Energy Flow in Ecosystems: (p. 438)
– Primary Production (productivity):
● Energy captured by photosynthesis in
an ecosystem.
● Or organic material (Biomass)
accumulated as result of
photosynthesis.
● Globally, roughly 165 billion tons.
Consumers or Heterotrophs (p.433):
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Consume food (originally manufactured by
autotrophs)
–
Herbivores
–
Carnivores
–
Parasites
–
Omnivores
–
Detritivores
●
–
mainly animals: Scavenge non-living
organic matter.
Decomposers (especially fungi & bacteria)
●
consume non-living organic matter.
Food Web (p. 434):
Pattern of energy flow (feeding). Series of possible food
chains.
Consumers
Sunlight
Producers
Decomposers &
Detritivores
Energy Pyramids (p. 438):
Energy losses limit the number of possible trophic levels
Roughly 90% energy lost from one level of food
chain to another.
3rd-level consumers
Sunlight:
Roughly
1% captured
2nd-level consumers
1st-level consumers
Producers
Disturbances and Ecological: Succession
(p. 436).
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Change in community over time.
Ecological response to disturbance:
 Human-caused.
 Natural.
Denuded or disturbed area:
 Plants & animals colonize, & species change over time.
Disturbance & Succession occur in all ecosystems:
 Enhance diversity: more kinds of habitat.
 Primary Succession (p. 436): Succession begins in virtually
lifeless area with no soil.
 Secondary succession: (p. 437). Soil, other remnants of
former community remain. Usually faster than primary
succession.
Example of Secondary Succession:
Bare Ground after Logging in in East Texas
Recently Disturbed:
Bare Ground
Pioneer Stage:
weeds, annuals.
Early succession Stages:
Perennial herbs, Shrubs
Succession Example: After logging, East Texas
Early/ Mid-succession:
Trees (pines/ sweetgum)
invade.
Mid-succession: Pinedominated forest.
Late succession (Climax): broadleaf
“hardwood” trees (oak, beech).
Primary Succession: Tolbachik (Толбачик)
Volcano, Kamchatka, Russia
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Summer 2010: Succession following 1975 eruption.
Chemical Cycling in Ecosystems:
Biogeochemical (nutrient) Cycles: (P. 442)
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Energy flows through a system;
materials (essential elements) recycle.
Biogeochemical cycles:
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Water (p. 391)
Oxygen
Nitrogen (p. 442)
Carbon (p. 441)
Potassium
Phosphorus (p. 441)
Others
Hydrologic (water) cycle
The Carbon Cycle (p. 395; p. 441)
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Global distribution of carbon:
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Organic carbon
Living organisms (600 GT*).
– dead organisms & soil organic matter (1,600 GT).
Atmosphere (766 GT; mostly as CO2)
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Dissolved carbon-forms in oceans & other waters (40,000 GT).
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Long term carbon storage:
Fossil fuels (4,000 GT)
– Ocean sediments, limestone rocks, etc (100,000,000 GT).
● Main source:1-celled protists with calciumcarbonate-rich cell walls
* GT = “gigaton” =1 billion tons.
–
The Carbon Cycle (p. 395; p. 441)
Atmospheric CO2
Combustion
Photosynthesis
Respiration
Feeding
Decomposition
Rock
weathering
Dissolved C
Fossil fuels
Sedimentation; Limestone, etc.
Greenhouse Gases & Global Warming
(p 395)
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Human activity---disrupting respiration/
photosynthesis balance:
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Fossil fuel burning
–
Deforestation
CO2 buildup, increased heat trapping (Fig. 42.17.
Result: climate change, climate instability, rising
sea levels, & flooding.
Solutions??
Human threats to the Biosphere
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Problem: loss of biodiversity (p. 426)
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Extinctions
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Loss of ecosystem services (water/ air purification,
climate regulation, erosion control as ecosystems are
degraded.
Four main Causes of Declining Biodiversity:
1)Habitat destruction & fragmentation
2)Introduction of invasive species
In E. TX: pigs, privet, water hyacinth, hydrilla,
Chinese tallow tree, giant salvinia
3)Overexploitation
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4)Pollution
The Root Cause: Ever Expanding Size &
Dominance of Human Population (p. 426)
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Exponential human population growth since 1700's
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Urbanization (red): San Francisco area 1900-1990
1900
1940
1954
1962
1974
1990
How the Science of Ecology Can Help
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Conservation Biology
– Goal-oriented science seeking to understand & counter
biodiversity loss.
– Identify biodiversity “hot spots” to focus on.
– Research to determine Minimum /optimum preserve
sizes.
Restoration ecology: ecological principals to develop methods
of returning degraded areas to natural or functional state.
– Kissimmee river project, Fl, (p. 447).
Landscape Ecology: applying ecological principals to study of
land use patterns (p. 445).
– Goal: make ecosystem conservation part of land use
planning.
– Importance of corridors connecting otherwise
fragmented habitat patches (p. 445)
“Biophilia” & an Environmental ethic (p. 448)
The End
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