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Ch. 4 - Ecology, Ecosystems and Food Webs
Ecology - five levels of matter in nature (overhead)
Organisms > Populations > Communities > Ecosystems > Ecosphere
Parts of the Earth
Core - inner and outer (iron) Mantle - includes the asthenosphere Lithosphere - upper mantle and
crust
Atmosphere
thermosphere mesosphere stratosphere - ozone layer troposphere - lower atmosphere (climate)
Hydrosphere - water
Biosphere - ecosphere
What sustains life on earth?
one-way flow of energy cycling of matter and nutrients gravity
Open and closed systems:
Open: flow of energy and matter in and out of the system
Closed: only flow of energy into and out of the system. No flow of matter
Sun: Nuclear fusion
Natural Greenhouse Effect: greenhouse gases are water, carbon dioxide, methane, nitrous oxide and
ozone.
Ecosystems: land: Biomes (determined largely by the climate) - see Video: BIOMES water: Aquatic
Life Zones
Boundaries of an ecosystem - ECOTONES
Components of an Ecosystem:
Abiotic - nonliving (water, air, nutrients, solar energy)
Biotic - living -( plants and animals)
Range of Tolerance (Tolerance limits) Limiting Factor principle
Major Living components of an ecosystem
Producers (autotrophs)
photosynthesis
chemosynthesis
Consumers
Herbivores - plant eaters PRIMARY - feed directly on producers
Carnivores
secondary - feed only on primary consumers (herbivores)
tertiary - feed only on other carnivores
Omnivores - eat plants and animals
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Other consumers:
scavengers:
Detritivores
Decomposers
Respiration
Aerobic
Anaerobic
Food Webs and Energy Flow in Ecosystems
Food Chain: high quality energy (sunlight) is converted to nutrients by photosynthesis. This energy is
passed on to consumers and eventually decomposers. Low quality heat is emitted into the
environment
Trophic Level: feeding level
producers
1st trophic level
primary consumers
2nd trophic level
secondary consumers 3rd trophic level
etc.
Food Web is an interconnected food chains (complex)
1. grazing food webs
2. detrital food webs
Biomass
Ecological Efficiency - the percentage of energy transferred from one trophic level to another. a 10%
efficiency means that 90% of the energy is lost.
Pyramids of Energy Flow - illustrate energy loss in a food chain
help explain how the Earth can support more people if people would eat more grains, vegetables,
etc., and not eat consumers of those grains (steer, deer, etc.)
Top level carnivores (eagles, hawks, tigers, sharks) are few in number and are the first to suffer when
the ecosystems are disrupted. - making them especially vulnerable to extinction.
Storage of biomass at various trophic levels can be represented by a pyramid of biomass.
Pyramid of Numbers Gross Primary Productivity (GPP) - the rate at which an ecosystem's producers convert solar energy
into chemical energy as biomass
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Net Primary Productivity (NPP) - biomass that is left after producers use some for
their own use.
How do Ecologists learn about Ecosystems?
Field Research
Lab Research
Systems Analysis
Systems Measurement Data Analysis Systems Modeling Systems Simulation Systems Optimization –
Ecosystem Services and Sustainability
Why is Biodiversity such an important ecosystem service?
The two Basic Principles of Ecosystem Sustainability
1.
2.
Soils
Soil - mixture of eroded rock, minerals, organic matter, water, air, living
organisms (decomposers)
very slow to renew
Horizons
O - litter
A - topsoil
B - subsoil
Profiles
Soil Texture
Clay - silt -sand - gravel Relative amounts determine texture of the soil
porosity volume of the pores
permeability - determined by the average size of the pores in the soil
See soil triangle in text.
Soil texture, porosity and permeability determine a soil's 1) water-holding
capacity, 2) aeration or oxygen content, and 3) workability. (ease of cultivation)
Soil acidity (pH) - influences the uptake of nutrients
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Nutrient Cycling
Rainfall - can erode soil, dissolve soil nutrients
Wind - can blow away topsoil and deposits nutrients elsewhere
Nutrients lost from one ecosystem must enter another ecosystem
Nutrient Cycles and
What are Nutrient (biogeochemical) Cycles?
a process by which nutrients are recycled between living organisms and
nonliving environment.
The three general types of nutrient cycles:
Hydrologic Cycle
Atmospheric Cycle
Sedimentary Cycle
The Water Cycle
Role of Water - terrestrial: major factor that determines types of organisms that
can live there: rain forests and deserts.
Aquatic ecosystems: water flow influences temperature, salinity, and availability
of nutrients.
How is water cycled in the Ecosphere?
evaporation
transpiration
condensation
precipitation
infiltration
percolation
runoff
Humidity - the amount of water in the air - depends on the temperature of the air.
Absolute humidity (g/kg)
Relative humidity (%)
Precipitation - requires the presence of condensation nuclei (volcanic ash,
smoke, sea salts, any particulate matter)
Dew Point - the temperature at which condensation will occur
Aquifer
Water Table
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Circulation rate - underground water (300-4600 yrs), lakes (13 years), streams
(13 days), atmosphere (9 days), ocean (37,000 yrs) and glaciers (16,000 yrs).
Many of the natural processes act to purify the water (a natural
distillation/filtration process).
How people affect the water cycle:
1. we withdraw large quantities of fresh water from lakes, rivers, groundwater, ...
2. we clear vegetation from land for agriculture and other uses (increasing runoff
and reducing infiltration)
3. we modify water quality by adding nutrients (phosphates) and other pollutants
The Carbon Cycle
Carbon - the currency of energy exchange
the flow of energy follows the flow of carbon (temp. is proportional to the conc. of
CO2)
See pp.78-79 for conceptual model of the carbon cycle.
Average residence time: atmosphere (3 yrs), soils (25-30 yrs), oceans (1500 yrs).
How people affect the carbon cycle:
1. forest and brush removal - less vegetation to remove CO2 through
photosynthesis
2. burning fossil fuels
The Nitrogen Cycle
Role of nitrogen: used by organisms to make vital organic compounds - amino
acids, proteins, DNA and RNA.
Usually in short supply and limits the rte of primary production.
Nitrogen (N2) cannot be absorbed and used directly by plants or animals.
most complex of the nutrient cycles.
Nitrogen fixation - bacteria convert N2 into NH3 [N2 + 3 H2 ==> 2 NH3];
cyanobacteria in soil and water and by the Rhizobium bacteria living in small
nodules on the roots of legumes (soybeans, alfalfa, and clover).
-
-
Nitrification - NH3 is converted to NO2 (toxic to plants) and then to NO3 (readily
used by plants).
+
Assimilation - roots absorb NH3, NH4 and nitrate to make the nitrogen
containing compounds.
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Ammonification - specialized decomposed bacteria convert the nitrogen rich
organic compounds (waste, etc.) into simpler nitrogen containing inorganic
+
compounds (NH3 and NH4 ).
+
Denitrification - bacteria convert NH3 and NH4 back into nitrite and nitrate and
then into N2 and nitrous oxide (N2O).==> which is released into the atmosphere
and the process starts all over again.
How people affect the Nitrogen Cycle:
We react nitrogen with hydrogen to make ammonia (the Haber Process)revolutionizing agriculture.
1. Emit NO when we burn fuel. the NO produces HNO3 (acid rain); create O3 and
photochemical smog.
2. Emit heat-trapping nitrous oxide (N2O) into the atmosphere through the action
of anaerobic bacteria on livestock waste
3. remove nitrogen from the earth's crust when we mine nitrogen containing
mineral deposits for fertilizers.
4. remove nitrogen from topsoil when we burn grasslands and clear forests.
5. add excess nitrogen compounds to aquatic systems in agricultural runoff,
discharge of municipal sewage and deposition of nitrogen compounds from the
atmosphere.
6. add excess nitrogen compounds to terrestrial ecosystems through
atmospheric deposition involving HNO3 and NO2.
The Phosphorus Cycle
3-
2-
essential nutrient for plants and animals (as PO4 and HPO4 )
How is Phosphorus Cycled in the Ecosphere?
Water, crust and in living organisms.
In Sedimentary Cycle: phosphate deposits on land and shallow ocean deposits to
living organisms and then back to the land and ocean. Phosphorus is found as
phosphate salts in rock and is released by weathering of the rock, is dissolved in
soil water and taken up by plant roots.
Phosphorus and its compounds are not gaseous so P is not circulated in the
atmosphere.
Phosphorus cycle is very slow.
Most soils are low in phosphorus, so P is the limiting factor for plant growth (so
fertilizer is needed).
How people affect the Phosphorus Cycle (3):
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1. we mine large quantities of phosphate rock for fertilizers and detergents
2. cutting down the rain forests reduces available Phosphate. In rain forests, all
phosphate is found in the plants and animals, not the soil. P is washed away
when forests are cut and burned.
3. we add excessive phosphate to aquatic ecosystems in runoff of animal wastes
from livestock feedlots, runoff of commercial fertilizers
The Sulfur Cycle
Sulfur is a component of most proteins and some vitamins.
S enters atmosphere in several natural sources.
H2S from active volcanoes and breakdown of organic matter in swamps, bogs,
tidal flats.
SO2 (from volcanoes)
2-
SO4 salts from sea spray.
How people affect the Sulfur Cycle:
1. burning sulfur-containing coal and oil to produce electricity
2. refining petroleum
3. by using smelting to convert sulfur compounds of metallic minerals into free
metals (Cu, Pb, Zn),
4. other industrial processes.
Rock Cycle - How rocks change over time
Slowest of all Earth's cycles
Three types of rocks:
Igneous
Sedimentary
Metamorphic
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