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Chapter 4
Key Concepts
 Basic ecological principles
 Major components of ecosystems
 Matter cycles and energy flow
 Ecosystem studies
 Principles of Sustainability
4-1 The Nature of Ecology
Ecology is the study of connections in nature.
Realm of Ecology
– Studies the levels of organization of living
things, from organism to biosphere, and all the
connections within.
Levels of Ecological Organization
The Earth’s Life-Support Systems
 Stratosphere
 Hydrosphere
 Lithosphere
 Biosphere
4-2 The Earth Life-Supporting Systems
• The Earth is an integrated system that consists of
rock, air, water, and living things that all interact
with each other.
• Scientists divided this system into four parts:
• The Geosphere (rock)
• The Atmosphere (air)
• The Hydrosphere (water)
• The Biosphere (living things)
The Earth as a System
• The Earth is divide into 3 layers:
1) The crust - thin and solid outermost layer of the
Earth above the mantle (<1% of Earth’s mass; 5-8 km
thick under ocean, 20-70 km under continents)
2) The mantle- layer of rock between the Earth’s
crust and core; medium density (about 64% of
Earth’s mass)
3) The core- central part of the Earth below the
mantle; composed of the densest elements
• These layers of material get progressively denser
as you move toward the center of the Earth.
Earth’s Layers
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The Earth as a System
• The lithosphere is the Earth’s crust and upper
mantle; contains our nonrenewable fossil fuels and
minerals.
• The atmosphere is the mixture of gases that makes
up the air we breathe; Mostly found in the first 30 km
above the Earth’s surface. (19 miles)
The Earth as a System
• The hydrosphere makes up all of the water on or
near the Earth’s surface; Much of this water is in the
oceans, which cover nearly ¾ of the globe.
• However, water is also found in the atmosphere, on
land, and in the soil.
The Earth as a System
• The biosphere is the part of the Earth where life
exists; a thin layer at the Earth’s surface that extends
from about 9 km (5.5 miles) above the Earth’s
surface down to the bottom of the ocean.
• The biosphere is therefore made up of parts of the
lithosphere, the atmosphere, and the hydrosphere.
Levels of Ecological Organization
Organisms
• Organisms are living things that can carry out life
processes independently.
• You are an organism, as is an ant, ivy plant, and
even each of the bacteria living in your intestines!
• Every organism is a member of a species.
• Species are groups of organisms that are closely
related and can mate to produce fertile offspring.
Populations and Communities
• Populations are groups of organisms of the same
species that live in a specific geographical area and
interbreed. (ie.all the field mice in a corn field make up a
population of field mice)
• Communities are groups of various species that live in the
same habitat and interact with each other. Every population is
part of a community.
• Land communities are often dominated by a few species of
plants. These plants then determine what other organisms can
live in that community.
Ecosystems
• Ecosystems are communities of organisms and their
abiotic environment.
• Examples are an oak forest or a coral reef.
• Ecosystems do not have clear boundaries.
• Things move from one ecosystem to another.
(Ex. Pollen can blow from a forest into a field, birds
migrate from state to state).
Biosphere
• All of the Earth’s ecosystems together.
• Part of the Earth where living organisms exist,
however, other layers of the Earth are needed to help
support life (abiotic factors)
Biotic and Abiotic Factors
• Biotic factors - environmental factors that are
associated with or results from the activities of living
organisms which includes plants, animals, dead
organisms, and the waste products of organisms.
• Abiotic factors - environmental factors that are not
associated with the activities of living organisms
which includes air, water, rocks, and temperature.
Natural Capital: Sustaining Life of Earth
 One-way flow
of energy from Sun
 Cycling of
Crucial Elements
 Gravity
Solar Capital: Flow of Energy to and from the
Earth
The Greenhouse Effect
• The greenhouse effect is the warming of the surface
and lower atmosphere of Earth that occurs when
carbon dioxide, water vapor, and other gases in the
air absorb and reradiated infrared radiation.
• Without the greenhouse effect, the Earth would be
too cold for life to exist.
The Greenhouse Effect
• The gases in the atmosphere that trap and radiate
heat are called greenhouse gases.
• The most abundant greenhouse gases are water
vapor, carbon dioxide, methane, and nitrous oxide,
although none exist in high concentrations.
How greenhouse gases lead to global warming: by Al Gore
The Greenhouse Effect
4-3 Ecosystem Components
• In order to survive, ecosystems need five basic components:
1) energy
2) mineral nutrients
3) water
4) oxygen
5) living organisms
• The main source of energy for an ecosystem comes
from the SUN.
• If one part of the ecosystem is destroyed or changes,
the entire system will be affected.
Life Depends on the Sun
• Energy from the sun enters an ecosystem through
photosynthesis. (plants, algae and some bacteria
use sunlight to make sugar molecules)
Energy Flow through the Biophere
• Closed systems are systems that cannot exchange
matter or energy with its surroundings.
• Open systems are systems that can exchange both
matter and energy with its surroundings.
• Today, the Earth is essentially a CLOSED system
with respect to matter, but an OPEN system for
energy as energy travels from plant to animal which
is eaten by other animals. In the process, some
energy is lost as heat to the environment.
Producers and Consumers
• Because plants make their own food, they are called
producers. (make organic molecules from
inorganic molecules) AKA autotrophs, or selffeeders.
• Organisms that get their energy by eating other
organisms are called consumer. (eats other
organisms or organic matter instead of producing its
own nutrients or obtaining nutrients from inorganic
sources) AKA heterotrophs, or other-feeders.
Energy Flow in Ecosystems
From Producers to Consumers
• Some producers get their energy directly from the sun by
absorbing it through their leaves.
• Consumers get their energy indirectly by eating producers or
other consumers.
* ANIMATION!
• Organisms can be classified by what they eat.
Types of Consumers:
• Herbivores
• Carnivores
• Omnivores
• Decomposers
• Each time an organism eats another organism, an
energy transfer occurs.
• This transfer of energy can be traced by studying
food chains, food webs, and trophic levels.
Trophic Levels
• Each time energy is transferred, some of the
energy is lost as heat.
• Therefore, less energy is available to organisms at
higher trophic levels.
4-4 Energy Flow through an Ecosystem
Primary consumer (herbivore)
Secondary consumer
(carnivore)
Tertiary consumer
Detritivores and scavengers
Trophic Levels/ Biomass
More living organisms at the base of the pyramid = more biomass
Showing energy loss from 1 trophic level to the next- grass stores
1,000 times more energy thank the hawk at the top level.
Food Chains
• A food chain is a sequence
in which energy is
transferred from one
organism to the next as each
organism eats another
organism.
• A food web shows many
feeding relationships that are
possible in an ecosystem.
Limits to Population Growth
• Zone of toleranceHomeostasis
• Limiting factor• Limiting factor principle – too
much or too little of any
abiotic factor can limit the
population growth, even if all
other factors are at optimum
conditions. (only as strong
as the weakest link!)
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Biomes
Biomes are based on climate
(average precipitation and temperature)
Biodiversity
 Genetic diversity
 Species diversity
 Ecological diversity
 Functional diversity
• Gross primary productivity (GPP) - the rate at which
an ecosystem's producers capture and store a given
amount of chemical energy as biomass in a given
length of time.
• Net primary production (NPP) - GPP that takes into
account plant cellular respiration .
NPP = GPP - respiration [by plants]
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Primary Productivity of Ecosystems
Terrestrial Ecosystems
Swamps and marshes
Tropical rain forest
Temperate forest
Savanna
Agricultural land
Woodland and shrubland
Temperate grassland
Tundra (arctic and alpine)
Desert scrub
Extreme desert
Aquatic Ecosystems
Estuaries
Lakes and streams
Continental shelf
Open ocean
800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800
Average net primary productivity (kcal/m2/yr)
Soils

Origins- parent material; mixtures of eroded rock,
mineral nutrients, decaying organic matter, and billons
of living organisms (mostly decomposers)

Soil Horizons based on the type of material the
horizons are composed of; these materials reflect the
duration of the specific processes used in soil
formation. They are described and classified by their
color, size, texture, structure, consistency, root quantity,
pH, voids, boundary characteristics, or concretions.
-
O horizon = leaf litter, crop/animal wastes
organic materials
A horizon = topsoil; humus (decomposed organic
matter with inorganic minerals); darker = more
nutrients
-
B horizon = subsoil; mostly inorganic, made of
broken down rock
-
C horizon = unweathered parent rock, bedrock
Variations with Climate and Biomes
• Soil formation greatly depends on the climate, and soils from
different biomes show distinctive characteristics.
• Temperature and moisture affect weathering and leaching. Wind
moves sand and other particles, especially in arid regions where
there is little plant cover. The type and amount of precipitation
influence soil formation by affecting the movement of ions and
particles through the soil, aiding in the development of different
soil profiles.
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Soil Profiles in Different Biomes
Mosaic
of closely
packed
pebbles,
boulders
Weak humusmineral mixture
Alkaline,
dark,
and rich
in humus
Dry, brown to
reddish-brown, with
variable accumulations
of clay, calcium
carbonate, and
soluble salts
Desert Soil
(hot, dry climate)
Clay,
calcium
compounds
Grassland Soil
(semiarid climate)
Forest litter
leaf mold
Acidic
lightcolored
humus
Humus-mineral
mixture
Light, grayishbrown, silt loam
Iron and
aluminum
compounds
mixed with
clay
Tropical Rain Forest Soil
(humid, tropical climate)
Dark brown
firm clay
Deciduous Forest Soil
(humid, mild climate)
Coniferous Forest Soil
(humid, cold climate)
Soil porosity
• Soil porosity refers to that part of a soil volume that is
not occupied by soil particles or organic matter. Pore
spaces are filled with either air, other gases, or water.
Large pores (macropores) allow the ready movement
of air and the drainage of water.
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Matter Cycling in Ecosystems
Biogeochemical cycles
 Hydrologic cycle (H2O)
 Carbon cycle
 Nitrogen cycle
 Phosphorus cycle
 Sulfur cycle
The Water Cycle (Hydrologic)
• Water cycle- continuous movement of water from the
ocean to the atmosphere to the land and back to the
ocean.
Consists of:
– Evaporation - change of a substance from a liquid
to a gas. Water continually evaporates from the
Earth’s oceans, lakes, streams, and soil.
– Condensation - change of state from a gas to a
liquid. Water vapor forms water droplets on dust
particles, to form clouds, where heavier drops then
fall from the clouds as rain.
– Precipitation - any form of water that falls to the
Earth’s surface from the clouds, and includes rain,
snow, sleet, and hail.
The Water Cycle
The Carbon Cycle
• Carbon - stored in the bodies of organisms as fat,
oils, carbohydrates, etc. ; Released into the soil or air
when the organisms dies.
• Carbon molecules form deposits of coal, oil, or
natural gas, which are known as fossil fuels.
• Fossil fuels store carbon left over from bodies of
organisms that dies millions of years ago.
The Carbon Cycle
• Carbon cycle - the movement of carbon from the
nonliving environment into living things and back
• Producers convert CO2 in the atmosphere into
carbohydrates during photosynthesis.
• Consumers obtain C from the carbohydrates in the
producers they eat. During cellular respiration,
carbon is released back into the atmosphere as
CO2.
• Some carbon is stored in limestone, forming one of
the largest “carbon sinks” on Earth.
The Carbon Cycle
The Carbon Cycle (Marine)
The Carbon Cycle (Terrestrial)
The Nitrogen Cycle
• Nitrogen cycle - the process in which nitrogen circulates
among the air, soil, water, plants, and animals in an
ecosystem.
– Nitrogen makes up 78 percent of the gases in the
atmosphere.
• All organisms need nitrogen to build proteins and DNA,
which are used to build new cells. However, it must be
altered, or fixed, before organisms can use it.
• Only some bacteria can fix atmospheric nitrogen into
chemical compounds that can be used by other
organisms. These bacteria are known as “nitrogenfixing” bacteria.
The Nitrogen Cycle
• Nitrogen-fixing bacteria - bacteria that convert
atmospheric nitrogen (N2) into ammonia (NH3)
• These bacteria live within the roots of plants and use
sugar provided by the plant to produce nitrogen
containing compounds such as nitrates (NO3)
• Nitrogen stored within the bodies of living things is
returned to the nitrogen cycle once those organisms
die through decomposers.
• After decomposers return nitrogen to the soil,
bacteria transform a small amount of the nitrogen into
nitrogen gas (N2) , which then returns to the
atmosphere to complete the nitrogen cycle.
Human Activities Affect the Nitrogen Cycle
• Burning fossil fuels = nitric oxide into the atmosphere
» Can convert to nitric acid = acid rain
• Nitrous oxide from livestock, wastes and inorganic
fertilizer is a greenhouse gas.
• Agricultural runoff and human sewage
• Farming removes nitrogen from topsoil
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The Nitrogen Cycle
• Nitrogen-fixing bacteria - bacteria that convert
atmospheric nitrogen (N2) into ammonia (NH3)
• These bacteria live within the roots of plants and use
sugar provided by the plant to produce nitrogen
containing compounds such as nitrates (NO3)
• Nitrogen stored within the bodies of living things is
returned to the nitrogen cycle once those organisms
die through decomposers.
• After decomposers return nitrogen to the soil,
bacteria transform a small amount of the nitrogen into
nitrogen gas (N2) , which then returns to the
atmosphere to complete the nitrogen cycle.
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The Nitrogen Cycle
The Nitrogen Cycle
The Phosphorus Cycle
• Phosphorus enters soil and water when rocks
erode. Small amounts of phosphorus dissolve as
phosphate (PO4-), which moves into the soil.
• Plants absorb phosphates in the soil through their
roots. Phosphorus is needed to build DNA.
• Many phosphate salts are not soluble in water, they
sink to the bottom and accumulate as sediment.
• Slower moving cycle so does not replenish itself
back in to the soil = for phosphorous based
fertilizers.
The Phosphorus Cycle
The Phosphorus Cycle
Nitrogen and Phosphorus Cycles
Fertilizers
• Fertilizers, used to stimulate and maximize plant
growth, contain both N and P.
• Excessive amounts of fertilizer can enter
terrestrial and aquatic ecosystems through runoff.
It can cause rapid growth of algae which can
deplete an aquatic ecosystem of important
nutrients such as oxygen.
The Sulfur Cycle
•
•
DMS (Dimethyl Sulfide)produced by
marine algae
Sulfuric acid= acid rain
How Do Ecologists Learn About Ecosystems?
• Field Research- observing/measuring ecosystem structure
and function
• Remote sensing and Geographic information
systems (GIS)- new technologies that gather data fed
through a computer for analysis. (ie. Computer generated maps
of forest cover, coastal changes,etc)
• Laboratory Research- controlled chambers such as tanks,
greenhouse; control CO2, temperature, light, humidity
• Mathematical models- simulations of ecosystems that are
large, complex, or difficult to study in the field/lab (ocean floor)