Post on 09-Mar-2018
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Chapter 34 Nature of
Ecosystems
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34.1 The Biotic Components of
Ecosystems
• Ecosystems
– Abiotic components include sunlight,
inorganic nutrients, soil type, water,
temperature and wind
– Biotic components are the various populations
of species that form a community
34.1 The Biotic Components of
Ecosystems
• Populations Within an Ecosystem
– Autotrophs (producers)
• Require an energy source and inorganic nutrients
to produce organic food molecules
• Manufacture organic nutrients for all organisms
• Green plants and algae carry on photosynthesis
• Some bacteria are chemoautotrophs
34.1 The Biotic Components of
Ecosystems
• Populations of an Ecosystem
– Heterotrophs (consumers)
• Need a preformed source of organic nutrients
• Herbivores: graze directly on plants or algae
• Carnivores: feed on other animals
• Omnivores: feed on both plants and animals
34.1 The Biotic Components of
Ecosystems
• Populations of an Ecosystem
– Decomposers
• Heterotrophic bacteria and fungi
• Break down nonliving organic matter
– They release inorganic matter to be used by producers
• Detritus: partially decomposed matter
– Earthworms and some beetles, termites, and maggots
34.1 The Biotic Components of
Ecosystems
• Energy flow and chemical cycling
characterizes every ecosystem
– Energy enters ecosystem in the form of sunlight
absorbed by producers
– Chemicals enter when producers take in inorganic
nutrients
34.1 The Biotic Components of
Ecosystems
• Energy Flow and Chemical Cycling
– Producers then make organic nutrients for
themselves and all other organisms in the ecosystem
• Consumers (herbivores and omnivores) gain nutrients and
energy from eating producers
• Higher level consumers (carnivores) then gain nutrients and
energy from eating herbivores and omnivores
– Some energy is released at each level to the
environment in the form of heat and waste products
Energy Flow and Nutrient Cycling Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
heat
heat
heat
producers
consumers
decomposers
energy
nutrients
solar
energy
inorganic
nutrient pool
Energy Balances Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© George D. Lepp/Photo Researchers, Inc.
growth and reproduction Energy to
carnivores
Heat to
environment
Energy
to detritus
feeders
34.2 Energy Flow
• The interconnecting paths of energy flow are
represented by diagramming food webs
– Grazing food webs begin with producers
– Detrital food webs begin with detritus
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a. Grazing food web
b. Detrital food web
Autotrophs Herbivores/Omnivores Carnivores
deer
rabbits
mice
chipmunks
birds
foxes
skunks
owls
snakes
hawks
detritus
fungi and bacteria invertebrates carnivorous invertebrates salamanders shrews
leaves
mice
fruits and
nuts
leaf-eating
insects
34.2 Energy Flow
• Trophic Level
– Composed of all the organisms that feed at a
particular link in a food chain.
– Grazing food chain
• Leaves → caterpillars → tree birds → hawks
– Detrital food chain
• Detritus → earthworms → shrews
– Primary producers, primary consumers,
secondary consumers
34.2 Energy Flow
• Ecological Pyramids
– Shortness of food chains can be attributed to
the loss of energy between trophic levels
– In general, only about 10% of the energy of
one trophic level is available to the next
trophic level
– Large energy losses depicted as an
ecological pyramid
Ecological Pyramid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
producers
herbivores
carnivores
top carnivores
34.2 Energy Flow
• Ecological Pyramids
– Biomass: the number of organisms at each
level multiplied by their weight
– Biomass of autotrophs much greater than
herbivores
– Biomass of herbivores greater than carnivores
34.2 Energy Flow
• Ecological Pyramids
– Inverted pyramids may be found in aquatic
ecosystems
• Herbivores may have a greater biomass than the
producers
• Over time, algae reproduces and are consumed
rapidly Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
herbivores
producers (algae)
relative
dry weight
34.3 Global Biogeochemical Cycles
• Biogeochemical Cycles
– Pathways by which chemicals circulate
through ecosystems involve both biotic and
abiotic components
• Reservoir: source unavailable to producers
• Exchange pool: source from which organisms take
chemicals
• Biotic community: chemicals move through
community along food chains
Reservoir
• fossil fuels
• mineral
in rocks
• sediment
in oceans Exchange
Pool
• atmosphere
• soil
• water Community
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
34.3 Global Biogeochemical Cycles
• Biogeochemical Cycles
– Two Main Types of Cycles
• Gaseous cycle: chemical element is drawn from
and returns to the atmosphere
• Sedimentary cycle: chemical element is drawn
from soil by plant roots, eaten by consumers,
returned to soil by decomposers
– Exception of water which exists in gas, liquid
and solid forms
34.3 Global Biogeochemical Cycles
• The Water or Hydrologic Cycle
– Freshwater evaporates from bodies of water
– Condensation – gas back to liquid - rain
– Eventually returns to oceans over time via
precipitation
– Human Impact
• In arid West and southern Florida, groundwater
mining is occurring
– Aquifers are being drained faster than they can be
naturally replenished
freshwater runoff
net transport of water vapor by wind
Ocean
Ice
Groundwaters
aquifer
precipitation
over land
transpiration from plants
and evaporation from soil
lake
H2O in Atmosphere
evaporation
from ocean
precipitation
to ocean
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34.3 Global Biogeochemical Cycles
• The Phosphorus Cycle
– Phosphorus moves from rocks on land to the
oceans
– Gets trapped in sediments
– Phosphorus moves back onto land following a
geological upheaval
– Phosphate is usually a limiting inorganic
nutrient for plants
34.3 Global Biogeochemical Cycles
• The Phosphorus Cycle
– Human Activities
• Phosphates are used in fertilizers, animal feeds,
and detergents
• Excess phosphates in water supplies can lead to
cultural eutrophication (over-enrichment)
– Algal blooms that can lead to massive fish kills
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biota
sedimentation
plants
decomposers
geological uplift
mineable rock
fertilizer
runoff
phosphate
in soil
animals and
animal wastes Biotic
Community
sewage treatment
plants
phosphate
in solution
detritus
phosphate mining weathering
34.3 Global Biogeochemical Cycles
• The Nitrogen Cycle
– Nitrogen gas makes up about 78% of the
atmosphere
– Plants cannot use nitrogen gas, so nitrogen is
a limiting inorganic nutrient for plants
– Nitrogen Fixation
• Carried out by some cyanobacteria and bacteria
• Conversion of nitrogen gas (N2) to ammonium ions
(NH4+)
– Plants can use ammonium ions
34.3 Global Biogeochemical Cycles
• The Nitrogen Cycle
– Nitrification: production of nitrates (NO3-)
which plants can also use
• Nitrogen gas converted to nitrate in atmosphere by
lightning, meteor trails, cosmic radiation which
provide the high energy needed for N to react with
O
• Ammonium in soil converted to nitrate by nitrifying
bacteria (chemoautotrophs)
– Denitrification: conversion of nitrate back to
nitrogen gas by denitrifying bacteria
34.3 Global Biogeochemical Cycles
• The Nitrogen Cycle
– Human Activities
• Nitrogen is added to fertilizers
– Runoff that contains nitrogen also contributes
to eutrophication
– Fertilizer use also results in the release of
nitrous oxide (N2O), a greenhouse gas
ozone shield depletion
plants
decomposers
NO3
NH4+
NH4+
(ammonium)
decomposers
N2 (nitrogengas) in
Atmosphere
N2 fixation
nitrogen-fixing
bacteria in nodules
and soil
dead organisms
and animal waste
nitrifying
bacteria
NO2
(nitrite) denitrifying
bacteria sedimentation
denitrification
Biotic
Community
NO3
(nitrate)
Biotic
Community
phytoplankton
runoff
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nitrification
human
activities
cyanobacteria
denitrifying bacteria
denitrification N2 fixation
34.3 Global Biogeochemical Cycles
• The Carbon Cycle • Photosynthesis takes up carbon dioxide from the
atmosphere
• Cell respiration returns it to the atmosphere
– Reservoirs of Carbon
• Dead organisms, fossil fuels, shells, limestone
34.3 Global Biogeochemical Cycles
• The Carbon Cycle
– Human Activities
• More carbon dioxide is being deposited in
atmosphere than is being removed
– Due to deforestation and burning of fossil fuels
• Increased carbon dioxide in atmosphere
contributes to global warming
– Carbon dioxide and other gases absorb and
radiate heat back to Earth – greenhouse effect
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Land plants
Soils
Ocean
combustion
photosynthesis
respiration
decay
runoff
diffusion
sedimentation
coal
oil
natural gas
destruction
of vegetation
CO2 in Atmosphere
bicarbonate (HCO3)
dead
organisms
and animal
waste