Download Ecosystems

Ecosystems
Ecosystems
THE REALM OF
ECOLOGY
◀ An island
ecosystem
▼ A desert spring
ecosystem
Biosphere
• Biosphere
• Ecosystem Ecology:
Ecosystems
Interactions between the
species in a given habitat
and their physical
environment.
Communities
• Community
• Population
• Organism
Populations
Organisms
Figure 55.2
Factors that Limit Communities
•  Abiotic (nonliving) Limiting Factors
–  Temperature
–  Water
–  Soil type
–  Sunlight
–  Salinity
–  Wind stress
–  Altitude, depth
The two main ecosystem processes:
Energy flow and Chemical cycling
•  Biotic (living) Limiting Factors
–  Food source
–  Competition
–  Predators
–  Social factors, mates
–  Pathogens, parasites
–  Vegetation
Energy flow is one-way
SIMPLE TERRESTRIAL ECOSYSTEM
• 
Oxygen (O2)
Sun
Producer
Carbon dioxide (rabbit)
Primary consumer
(rabbit)
Precipitation
Falling leaves
and twigs
Secondary consumer
(fox)
1st
Law of thermodynamics: energy is not created,
nor destroyed. But transformed.
•  Energy enters ecosystems through photosynthesis
or chemosynthesis.
•  Some energy is transformed as used by producers;
some is passed through
food chain
•  All energy eventually
dissipates as heat.
Thus must always be
replenished.
Chemical cycling
Tertiary
consumers
Microorganisms
and other
detritivores
Producers
Detritus
Soil decomposers
Secondary
consumers
Primary consumers
Primary producers
Heat
Key
Water
Heyer
Soluble mineral nutrients
Sun
Energy flow
Figure 55.4
1
Ecosystems
Chemical matter is recycled
Solar Energy
•  Law of conservation of mass: Actual
atoms are constantly rearranged into
new molecules
•  Energy needed to form new bonds, but
atoms are reused
•  Different ecosystems have dissimilar solar
illumination
– Latitude
– Topography
– Depth (aquatic)
– Reflectance
Tertiary
consumers
Microorganisms
and other
detritivores
– Carbon cycle
– Nitrogen cycle
Detritus
Secondary
consumers
Primary consumers
Primary producers
Heat
Key
Chemical cycling
Energy flow
Sun
Figure 55.4
Reflectance vs. Available Solar Energy
Percent reflectance
80
60
Snow
•  Energy from lower trophic levels is
transferred to higher trophic levels
Clouds
Vegetation
•  5% - 20% of energy consumed is
available to next trophic level
40
Soil
20
•  Energy returns to the physical
environment as heat
Liquid water
0
400
600
800
Visible
Energy flows through the food web
1,000
– Remember thermodynamics!
“Energy is neither created nor destroyed!”
1,200
Near-infrared
Wavelength (nm)
Hardwood forest
Figure 55.5
Energy pyramid reflects loss of
energy at each trophic level
•  Only 1% of solar energy reaching Earth is
used by living systems
•  Only ~10% of energy consumed is available
to next trophic level
– “Energy Pyramid”
Plant material
eaten by caterpillar
200 J
67 J
Feces
•  Oak trees, caterpillars, birds
Heyer
100 J
Cellular
respiration
33 J
Not assimilated
Growth (new biomass;
secondary production)
Assimilated
Figure 55.10
2
Ecosystems
Pyramid of net production
Tertiary
consumers
Energy pyramid reflects loss of
energy at each trophic level
10 J
Secondary
consumers
Caterpillar —
• Feeding efficiency
= growth/consumed = 17%
• Production efficiency
= growth/assimilated = 33%
100 J
Primary
consumers
1,000 J
Primary
producers
10,000 J
Feces
Plant material
eaten by caterpillar
200 J
67 J
100 J
Not assimilated Growth (new biomass;
secondary production)
1,000,000 J of sunlight
Figure 55.11
Cellular
respiration
33 J
•  Production Efficiency:
–  Endothermic vertebrates: 1–3%
–  Ectothermic vertebrates: ~10%
–  Inverts: 20–40%
Assimilated
Figure 55.10
Pyramid of net production
Eating high on the
food chain is expensive!
Tertiary
consumers
Most chains limited
to 4–5 steps
Secondary
consumers
Primary
consumers
Primary
producers
10 J
Figure 55.11
100 J
1,000 J
10,000 J
1,000,000 J of sunlight
• Energetic hypothesis
•  Too little energy passed through steps to support another step.
•  Less than 10% passed on to next trophic level
Biogeochemical cycles:
"life-earth-chemical"
• Materials enter producers from atmosphere
or soil.
• Dynamic stability hypothesis
•  Even if average 1° primary production is sufficient,
oscillations/deviations in 1° production cause fluctuations in
higher steps below minimum viable population
Pools or Reservoirs of Materials
•  Pools available:
– Abiotic: atmosphere, soil, water, geological
• Return to abiotic world through respiration
and decomposition.
•  Materials cycle between pools
• Biologically important materials:
•  Size of pools constant only if entry equals exit
– Biotic: living or dead organic matter
–  Water (H2O)
–  Carbon (CO2)
–  Nitrogen (N2, NO3-, NO2-, NH4)
Heyer
3
Ecosystems
Global Water Cycle
Global Water Cycle
•  Humidity: water in atmosphere
•  Precipitation: rain, snow
•  Surface transport:
–  puddles, groundwater, rivers, oceans
•  Groundwater transport
–  aquifers
•  Evaporation:
–  transpiration: water loss from plants; helps maintain
local humidity
–  from organisms: sweat, urine, respiration
Watershed
Water cycle & NPP
•  Actual evapotranspiration
Net primary production (g/m2/yr)
=  annual amount of water evaporated from a landscape
and transpired by plants
3,000
Tropical forest
2,000
Temperate forest
1,000
Mountain coniferous forest
Desert
shrubland
0
Temperate grassland
Arctic tundra
0
500
1,000
1,500
Actual evapotranspiration (mm H2O/yr)
Impacted
watersheds
Natural/Forested Ecosystem
•  ↑permeability
•  → ↑percolation
•  ↓surface runoff
•  ↑interflow & retention
•  → ↑evapotranspiration
•  → ↑primary productivity
•  ↑groundwater
•  → ↑aquifer pool
•  → “gaining stream”
Developed/Impacted Ecosystem
•  ↓permeability
•  → ↓percolation
•  ↑surface runoff
•  → ↑erosion
•  → ↑flooding
•  → ↑sedimentation
•  ↓interflow& retention
•  → ↓evapotranspiration
•  → ↓primary productivity
•  ↓groundwater
•  → ↓aquifer pool
•  → “losing stream”
Heyer
Human activity disrupts
local water cycles
•  Diversion of surface transport
–  Irrigation
–  Dams
•  Disruption of soil water retention
(watershed disturbance)
–  Clear cutting of forests
–  Overgrazing
–  Permeability — compaction & loss of organic content
–  Also causes loss of minerals through runoff
•  Further losses of vegetation
–  Desertification
4
Ecosystems
Desertification
DESERTIFICATION
Africa
Moderate
Severe
Very Severe
U.S. 1930’s Dust Bowl
Heyer
5