Ecosystems
Chapter 30
Ecosystem
• Definition: An array of organisms
together with their physical environment.
• Interconnected through:
– one-way flow of energy
– cycling of raw materials
• Needs continual energy inputs
Simple Energy
input from
Ecosystem sun
Model
Producers
Autotrophs (plants and other
self-feeding organisms)
Nutrient
Cycling
Consumers
Heterotrophs (animals, most fungi,
many protists, many bacteria)
Energy output (mainly metabolic heat)
Consumers
fruits SPRING
• Herbivores rodents,
insects
rabbits
• Carnivores birds
• Parasites
• Omnivores fruits SUMMER
• Decomposers and rodents,
rabbits insects
Detritivores birds
seasonal variation in the diet of an
omnivore (red fox)
fifth trophic level
top carnivore
marsh hawk (fourth-level consumer)
fourth trophic level
carnivore
crow (third-level consumer)
third trophic level
carnivore
garter snake (second-level consumer)
second trophic level
herbivore
(primary consumer)
cutworm
first trophic level
autotroph
flowering plants (primary producer)
Fig. 30-3, p.528
marsh hawk
Higher
Trophic crow Connections in a
Levels tallgrass prairie food web
upland
sandpiper
garter snake
frog
weasel badger coyote
spider
Second
Trophic
sparrow
Level
earthworms, insects prairie vole pocket gopher ground squirrel
First
Trophic grasses, composites
Level
Fig. 30-4, p.529
Pyramid of Energy
Biological Magnification
Nondegradable or slowly degradable
substances become more and more
concentrated in tissues of organisms at
higher trophic levels of a food web
DDT in Food Webs
• Synthetic pesticide banned in
United States since 1970s
• Carnivorous birds accumulate
DDT in their tissues, produce
brittle egg shells
Primary Productivity
• Gross primary productivity is
ecosystem’s total rate of photosynthesis
• Net primary productivity is rate at which
producers store energy in tissues in
excess of their aerobic respiration
Biogeochemical Cycle
• Flow of an essential substance from the
environment to living organisms and back
to the environment
• Main reservoir is in the environment
• Geologic processes and decomposition
continues the cycle
atmosphere
wind-driven water vapor precipitation
40,000 onto land
111,000
evaporation precipitation evaporation from land
from ocean into ocean plants (evapotranspiration)
425,000 385,000 71,000
surface and
groundwater
flow 40,000
ocean land
Water and Climate
Watershed
• A region where
precipitation is
funneled into a
single stream or
river
Ogallala aquifer
First used for irrigation
in 1911.
Widely used after
1930’s.
Now produces
irrigation for 20% of
Midwest crops.
Water table has
dropped as much as 5
feet in some places.
Global Water Crisis
• Limited amount of fresh water
• Desalinization is expensive and requires large
amounts of energy
• Aquifers are being depleted
• Groundwater is contaminated
• Sewage, agricultural runoff, and industrial chemicals
pollute rivers
Carbon Cycle
• Carbon moves in gaseous form
• Main source in sediments and rocks.
• Ocean water, soil, atmosphere, and
biomass also produce carbon.
diffusion between
atmosphere and ocean
bicarbonate and combustion of fossil fuels
carbonate in
ocean water
photosynthesis aerobic
respiration
marine food
webs
death,
incorporation sedimentation
into sediments uplifting
sedimentation
marine sediments
atmosphere
volcanic action combustion of
fossil fuels
photosynthesis aerobic combustion
terrestrial respiration of wood
rocks
deforestation
weathering land food
webs
soil water
peat,
death, burial, fossil
leaching, compaction over fuels
runoff geologic time
Fossil Fuels
Greenhouse Effect
• Greenhouse gases impede escape of
heat from Earth’s surface
Global Warming
Long-term increase in temperature of
Earth’s lower atmosphere
Greenhouse Gases Increasing
CO2 Methane
CFCs
N 2O
Table 30-1, p.537
Nitrogen Cycle
• Nitrogen is used in amino acids and nucleic
acids
• Main reservoir is nitrogen gas in the
atmosphere
• Nitrogen gas can’t enter food web
• Nitrogen fixation – bacteria convert nitrogen to
useable forms like ammonia; further converted
to ammonium and nitrate
Fig. 30-16, p.538
Phosphorus Cycle
• Phosphorus is part of phospholipids,
nucleotides, NADH, ATP
• Main limiting factor in ecosystems
• Reservoir is Earth’s crust; no gaseous
phase
mining FERTILIZER
excretion GUANO
agriculture
uptake weathering uptake
by by
autotrophs autotrophs
weathering
MARINE DISSOLVED DISSOLVED IN LAND
FOOD IN OCEAN SOIL WATER, FOOD
WEBS WATER LAKES, RIVERS WEBS
death, death,
decomposition decomposition
settling
sedimentation out leaching, runoff
uplifting
MARINE SEDIMENTS TERRESTRIAL ROCKS
over geologic time
Eutrophication
• Runoff from
phosphate fertilizers
accelerates algal
growth in waterways
• Resulting dense algal
blooms cause system
overload and death