Ecosystems: What Are They and How Do They Work
Objectives
1.
Define ecology. List and distinguish among five levels of organization of matter that are the focus of the realm
of ecology.
2.
List the characteristics of life.
3.
Distinguish among lithosphere, hydrosphere, atmosphere, and ecosphere. Briefly describe how the sun,
gravity, and nutrient cycles sustain life on Earth. Compare the flow of matter and the flow of energy through
the biosphere.
4.
Distinguish between an open system and a closed system. Name and describe three types of biogeochemical
cycles.
5.
Define abiotic component of an ecosystem. List three important physical factors and three important chemical
factors that have large effects on ecosystems.
6.
Summarize the law of tolerance. Compare limiting factors in terrestrial and aquatic ecosystems.
7.
Define biotic component of an ecosystem. Distinguish between producers and consumers. List and distinguish
four types of consumers. Distinguish among scavengers, detritus feeders and decomposers. Distinguish
between photosynthesizers and chemosynthesizers; aerobic respiration and anaerobic respiration.
8..
Distinguish between food chains and food webs; grazing food web and detrital food web. Apply the second
law of energy to food chains and pyramids of energy, which describe energy flow in ecosystems. Explain how
there may be exceptions to pyramids of numbers and biomass, but not energy.
9.
Evaluate which ecosystems show the highest average net primary productivity and which contribute most to
global net primary productivity.
10. Briefly describe the historical development and distinguishing features of three approaches ecologists use to
learn about ecosystems: field research, laboratory research, and systems analysis.
11. Define ecosystem service. List five examples of ecosystem services. Distinguish among three types of
biodiversity. Briefly state two principles to sustain ecosystems.
Key Terms
abiotic
acid deposition
acid rain
aerobic respiration
aerobic respiration
ammonification
anaerobic respiration
aquatic life zones
aquifers
atmosphere
autotrophs
baseline data
bedrock
Biological community
biological community
biological diversity (biodiversity))
biomass
biomes
biosphere
biotic
carbon cycle
carnivores
chemosynthesis
community
consumers
consumers
core
crust
cycling of matter
decomposers
decomposers
denitrification
detritivores
dissolved oxygen (DO) content
distribution
ecological efficiency
ecology
ecosystem
fermentation
field research
flow of high-quality energy
food chain
food web
fossil fuels
freshwater life zones
Gaia hypothesis
genetic diversity
geographic information systems (GIS)
glaciers
global warming (p. 74)
gravity (p. 54)
greenhouse gases (p. 55)
gross primary productivity (GPP) (p. 66)
habitat (p. 53)
herbivores (p. 60)
humus (p. 68)
hydrologic (water) cycles (p. 70)
hydrosphere
hydrothermal vents
infiltration
laboratory research
leaching
limiting factor
limiting factor principle
liquid water
lithosphere
mantle
matter recycling
mature soils
microbes
natural greenhouse effect
natural greenhouse effect (p. 74)
net primary productivity (NPP) (p. 66)
nitrate ions (p. 74)
nitrification (p. 74)
Outline
The Nature of Ecology
nitrite ions (p. 74)
nitrogen cycle (p. 74)
nitrogen fixation (p. 74)
nitrogen-fixing bacteria (p. 74)
nutrient (biogeochemical) cycles (p. 70)
nutrients (p. 70)
ocean (marine) life zones (p. 56)
omnivores (p. 60)
one-way energy flow (p. 60)
one-way flow of matter and energy (p. 60)
optimum level (range) (p. 57)
organism (p. 52)
parent material (C horizon) (p. 69)
permafrost (p. 54)
Pests (p. 50)
phosphorous cycle (p. 76)
photosynthesis (p. 54)
photosynthesis (p. 58)
photosynthesis (p. 73)
phytoplankton (p. 58)
population (p. 53)
primary consumers (p. 60)
producers (p. 56)
producers (p. 58)
pyramid of energy flow (p. 64)
range (p. 53)
range of tolerance (p. 57)
remote sensing (p. 79)
salinity (p. 58)
sand (p. 70)
secondary consumers (p. 60)
silt (p. 70)
soil (p. 67)
soil horizons (p. 68)
soil profile (p. 68)
soil texture (p. 70)
species (p. 52)
stratosphere (p. 54)
subsoil (B horizon) (p. 69)
sulfur cycle (p. 77)
surface litter layer (O horizon) (p. 68)
surface runoff (p. 70)
systems analysis (p. 80)
third and higher level consumers (p. 60)
topsoil layer (A horizon) (p. 68)
trophic level (p. 63)
troposphere (p. 54)
water vapor (p. 54)
weathering
A. Ecology is the study of connections in the natural world. Ecologists try to understand interactions among
organisms, populations, communities, ecosystems and the biosphere.
1. An organism is any form of life. The cell is the basic unit of life in organisms.
2. Organisms are classified as either eukaryotic or prokaryotic based on the presence or absence of a
membrane-bound nucleus.
3. Organisms are classified into species, which groups organisms similar to each other together.
4. Sexually reproducing organisms are classified as a species if, under natural conditions, they can
potentially breed with one another and produce live, fertile offspring
5. The tiny microbes rule the world; they are unseen by the naked eye but keep the natural world
operating.
6. About 1.4 million species have been identified, but estimates of number of species range from 3.6
million to 100 million.
B. A population consists of a group of interacting individuals of the same species occupying a specific area.
Genetic diversity explains why these individuals may not behave nor look exactly alike. The habitat is the
place where a population or an individual usually lives. Its distribution or range is the area over which a
species may be found.
C. A community represents populations of different species living and interacting in a specific area. A
biological community consists of all the populations of different species interacting and living in a specific
area; this is a network of plants, animals, and microorganisms.
D. An ecosystem is a community of different species interacting with each other and with their nonliving
environment of matter and energy. All of the earth’s diverse ecosystems comprise the biosphere.
The Earth’s Life-support Systems
A. Various interconnected spherical layers make up the earth’s life-support system.
B. The atmosphere is the thin membrane of air around the planet.
C. The troposphere is the air layer about 11 miles above sea level.
D. The stratosphere lies above the troposphere between 11-30 miles; it filters out the sun’s harmful radiation.
E. The hydrosphere consists of earth’s water, found in liquid water, ice, and water vapor.
F. The lithosphere is the crust and upper mantle of the earth’s soil. It contains nonrenewable fossil fuels,
minerals, and soil, and renewable soil chemicals needed for plant life.
G. The biosphere includes most of the hydrosphere, parts of the lower atmosphere and upper lithosphere. All
parts of the biosphere are interconnected.
H. Ecology’s goal is to understand the interactions in the earth’s global skin of air, water, soil, and organisms.
I. Sun, cycles of matter and gravity sustain life on earth.
1. The one-way flow of high-quality solar energy through materials and living things (as they eat)
produces low-quality energy. Energy can’t be recycled.
2. Matter cycles through parts of the biosphere.
3. Gravity causes the downward movement of chemicals as matter cycles through the earth.
J. Solar energy just passes through the earth as electromagnetic waves; they warm the atmosphere, evaporate
and recycle water, generate wind, and support plant growth.
K. As solar radiation interacts with the earth, infrared radiation is produced. Greenhouse gases trap the heat
and warm the troposphere. This natural greenhouse effect makes the planet warm enough to support life.
Energy from the sun supports photosynthesis.
L. The Earth’s temperatures, distance from the sun and size all produce a livable planet. Its liquid water, orbit
from the sun, and its gravitational mass all contribute to sustaining life in this natural greenhouse.
Ecosystem Components
A. Terrestrial parts of the biosphere are classified as biomes, areas such as deserts, forests, and grasslands.
Aquatic life zones describe the many different areas found win a water environment such as freshwater, or
marine life zones (coral reefs, coastal estuaries, deep ocean).
B. The major components of ecosystems are abiotic (nonliving) water, air, nutrients, solar energy, and biotic
(living) plants, animals, and microbes.
C. Ecosystem characteristics include a range of tolerance to physical and chemical environments by the
ecosystem’s populations.
1. Law of tolerance: The distribution of a species in an ecosystem is determined by the levels of one or
more physical or chemical factors’ being within the range tolerated by that species.
a. The limiting factor principle states that too much or too little of any abiotic factor can limit or
prevent growth of a population, even if all other factors are at or near the optimum range of
tolerance. An abiotic factor such as lack of water or poor soil can be understood here.
b. Aquatic life zones can be limited by the dissolved oxygen (DO) content in the water or by the
salinity.
D. The major biological components of ecosystems are the producers/autotrophs that are self-feeders and the
consumers/heterotrophs.
1. Autotrophs make their own food from compounds in the environment (organisms such as green plants
and algae). A few specialized producers can convert simple compounds to more complex compounds
without sunlight, a process called chemosynthesis.
2. Consumers, or heterotrophs feed on other organisms or their remains.
a. Decomposers break down organic detritus (bacteria/fungi) into simpler inorganic compounds.
b. Omnivores feed on both plants and animals.
c. Carnivores feed on animals.
d. Detritivores feed on dead organic matter and break it down into smaller molecules
e. Herbivores feed on plants.
f. Natural ecosystems produce little waste or no waste. In nature, waste becomes food.
3. Glucose and other organic compounds are broken down and energy released by the process of aerobic
respiration, the use of oxygen to convert organic matter back to carbon dioxide and water. This process
is a net chemical change to that of photosynthesis.
4. Some decomposers are able to break down organic compounds without using oxygen. This process is
called anaerobic respiration, or fermentation. The end products are compounds such as methane gas,
ethyl alcohol, acetic acid, and hydrogen sulfide.
5. Matter is recycled; there is a one-way flow of energy.
Biodiversity
A. Biodiversity is the amazing variety of earth’s genes, species, ecosystems, and ecosystem processes.
1. The kinds of biodiversity are: genetic diversity, species diversity, ecological diversity and functional
diversity.
2. Human cultural diversity is included as part of earth’s biodiversity by some people.
3. Biodiversity keeps us alive and supports our economies.
4. Biodiversity is a renewable resource as long as humans live off the income, not destroy the capital.
Energy Flow in Ecosystems.
A. Food chains and food webs help us understand how eaters, the eaten, and the decomposed are
interconnected in an ecosystem.
B. The sequence of organisms as they are eaten is a food chain.
1. Trophic levels are feeding levels for organisms within an ecosystem.
a. Producers belong to the first tropic level.
b. Primary consumers belong to the second tropic level.
c. Secondary consumers belong to the third tropic level.
d. Detritivores and decomposers process detritus from all trophic levels.
2. Food webs are complex networks of interconnected food chains. They are maps of life’s
interdependence.
C. Energy flow in a food web/chain decreases at each succeeding organism in a chain or web.
D. The dry weight of all organic matter within the organisms of a food chain/web is called biomass.
Ecological efficiency is the term that describes the percentage of usable energy transferred as biomass from
one trophic level to another and ranges from 2%-40% with 10% being typical.
E. The greater number of trophic levels in a food chain, the greater loss of usable energy.
F. The pyramid of energy flow visualizes the loss of usable energy through a food chain. The lower levels of
the trophic pyramid support more organisms. If people eat at a lower trophic level (fruits, vegetables,
grains directly consumed) earth can support more people. There is a large loss of energy between
successive trophic levels.
G. Production of biomass takes place at different rates among different ecosystems.
1. The rate of an ecosystem’s producers converting energy as biomass is the gross primary productivity
(GPP).
2. Some of the biomass must be used for the producers’ own respiration. Net primary productivity (NPP)
is the rate which producers use photosynthesis to store biomass minus the rate which they use energy
for aerobic respiration. NPP measures how fast producers can provide biomass needed by consumers in
an ecosystem.
3. Ecosystems and life zones differ in their NPP. The three most productive systems are swamps and
marshes, tropical rain forest, and estuaries. The three least productive are tundra, desert scrub and
extreme desert.
H. The planet’s NPP limits the numbers of consumers who can survive on earth.
1. The highly productive tropical rain forest cannot support agriculture as practiced in developed
countries.
2. Marshes and swamps do not produce food that can be eaten directly by humans; they feed other aquatic
species that humans consume (fish, shrimp, clams).
I. Humans are using, wasting, and destroying biomass faster than producers can make it.
Matter Cycling in Ecosystems.
A. Nutrient cycles/biogeochemical cycles are global recycling systems that interconnect all organisms.
1. Nutrient atoms, ions, and molecules continuously cycle between air, water, rock, soil, and living
organisms.
2. These cycles include the carbon, oxygen, nitrogen, phosphorus, and water cycles. They are connected
to chemical cycles of the past and the future.
B. The water/hydrologic cycle collects, purifies, and distributes the earth’s water in a vast global cycle.
1. Solar energy evaporates water, the water returns as rain/snow, goes through organisms, goes into bodies
of water, and evaporates again.
2. Some water becomes surface runoff, returning to streams/rivers, causing soil erosion, and also being
purified, itself.
3. The water cycle is powered by energy from the sun. Winds and air masses transport water over the
earth’s surface.
4. Water is the primary sculptor of earth’s landscape.
5. Water is the major form of transporting nutrients within and between ecosystems.
C. The water cycle is altered by man’s activities:
1. We withdraw large quantities of fresh water.
2. We clear vegetation and increase runoff, reduce filtering, and increase flooding.
3. We add nutrients like fertilizers and modify the quality of the water.
4. The earth’s water cycle may be speeding up due to a warmer climate. This could change global
precipitation patterns and may intensify global warming (water vapor increases in the troposphere).
D. The carbon cycle circulates through the biosphere. Carbon moves through water and land systems, using
processes that change carbon from one form to another.
1. CO2 gas is an important temperature regulator on earth.
2. Photosynthesis in producers and aerobic respiration in consumers, producers, and decomposers
circulates carbon in the biosphere.
3. Fossil fuels contain carbon; in a few hundred years we have almost depleted such fuels that have taken
millions of years to form.
4. Carbon recycles through the oceans. Oceans act as a carbon sink, but when warming occurs they
release carbon dioxide.
E. Excess carbon dioxide’s addition to the atmosphere through our use of fossil fuels and our destruction of
the world’s photosynthesizing vegetation has contributed to global warming. The natural greenhouse effect
is being strengthened by increasing temperatures.
F. Nitrogen is recycled through the earth’s systems by different types of bacteria.
1. The nitrogen cycle converts nitrogen (N2) into compounds that are useful nutrients for plants and
animals.
2. The nitrogen cycle includes these steps:
a. Specialized bacteria convert gaseous nitrogen to ammonia in nitrogen fixation.
b. Special bacteria convert ammonia in the soil to nitrite ions and nitrate ions; the latter is used by
plants as a nutrient. This process is nitrification.
c. Decomposer bacteria convert detritus into ammonia and water-soluble salts in ammonification.
d. In denitrification, nitrogen leaves the soil. Anaerobic bacteria in soggy soil and bottom sediments of
water areas convert NH3 and NH4+ back into nitrite and nitrate ions, then nitrogen gas and nitrous
oxide gas are released into the atmosphere.
3. Human activities affect the nitrogen cycle.
a. In burning fuel, we add nitric oxide into the atmosphere; it can be converted to NO 2 gas and nitric
acid and it can return to the earth’s surface as acid rain.
b. Nitrous oxide that comes from livestock, wastes and inorganic fertilizers we use on the soil can
warm the atmosphere and deplete the ozone layer.
c. We destroy forest, grasslands and wetland and, thus, release large amounts of nitrogen into the
atmosphere.
d. We pollute aquatic ecosystems with agricultural runoff and human sewage.
e. We remove nitrogen from topsoil with our harvesting, irrigating and land-clearing practices.
f. Increased input of nitrogen into air, soil and water is affecting the biodiversity toward species that
can thrive on increased supplies of nitrogen nutrients.
G. We need to use phosphorus-based fertilizers because the phosphorus cycle is much slower in moving
through the earth’s water, soil, and organisms and is often the limiting factor for plant growth.
1. Phosphorous washes from the land, ending up in the ocean where it may stay for millions of years.
Phosphorus is used as a fertilizer to encourage plant growth.
2. Phosphorus also limits growth of producers in freshwater streams and lakes due to low solubility in
water.
H. Man interferes with the phosphorous cycle in harmful ways.
1. We mine phosphate rock to produce fertilizers and detergents.
2. We cut down tropical forests and, thereby, reduce the phosphorus in tropical soils.
3. We compromise aquatic systems with animal waste runoff and human sewage.
I. Sulfur cycles through the earth’s air, water, soil, and living organisms. Much is sorted in rocks and
minerals, buried deep under ocean sediments.
1. Natural sources of sulfur are hydrogen sulfide, released from volcanoes, swamps, bogs, and tidal flats
where anaerobic decomposition occurs.
2. Some marine algae produce dimethyl sulfide (DMS). DMS acts as nuclei for condensation of water
found in clouds. This can affect the cloud cover and climate.
3. Sulfur compounds can be converted to sulfuric acid that falls as acid deposition.
4. Burning coal and oil, refining oil and the production of some metals from ores all add sulfur to the
environment.
How Ecologists Learn About Ecosystems
A. Ecologists do field research, observing, measuring the ecosystem structure and function.
B. New technologies such as remote sensing, geographic information systems (GISs) gather data that is fed
into computers for analysis and manipulation of data. Computerized maps may be made of an area to
examine forest cover, water resources, air pollution emissions, coastal changes, and changes in global sea
temperatures.
C. Ecologist use tanks, greenhouses, and controlled indoor and outdoor chambers to study ecosystems
(laboratory research). This allows control of light, temperature, CO2, humidity and other variables.
D. Field and laboratory studies must be coupled together for a more complete picture of an ecosystem.
E. Systems analysis develops mathematical and other models that simulate ecosystems that are large and very
complex and can’t be adequately studied with field and laboratory research. This allows the analysis of the
effectiveness of various alternate solutions to environmental problems and can help anticipate
environmental surprises.
F. We need baseline data about components, physical and chemical conditions in order to determine how well
the ecosystem is functioning in order to anticipate and determine how best to prevent harmful
environmental changes.
G. Natural ecosystems achieve long-term sustainability by use of renewable solar energy and by recycling the
chemical nutrients.
These guidelines from nature need to be adopted by humans in order to live more sustainably on earth.
Summary
1.
Ecology is the study of connections in nature.
2.
Life on earth is sustained by the one-way flow of high-quality energy from the sun, by the cycling of matter,
and by gravity.
3.
Matter, energy, and life are the major components of an ecosystem.
4.
Energy in an ecosystem decreases in amount to each succeeding organism in a food chair or web.
5.
Soil is a complex mixture of eroded rock, mineral nutrients, water, air, decaying organic matter, and billions of
living organisms. It covers most of the earth and provides nutrients for plant growth. Soils are formed by a
break down of rock, decomposing surface litter and organic matter. Bacteria and other decomposer
microorganisms break down some of soil’s organic compounds into simpler inorganic compounds.
Matter is recycled through the earth’s ecosystem of air, land, water, and living organisms. This vast global
recycling system is composed of nutrient cycles.
6.
7.
Scientists study ecosystems through the use of aquarium tanks, greenhouses, and controlled indoor and outdoor
chambers. specific variables are carefully controlled, like temperature, light, carbon dioxide and humidity.
8.
Two principles of sustainability found from learning how nature works are the law of conservation of matter
and the two laws of thermodynamics.
Glossary
Chapter 3
abiotic
Nonliving. Compare biotic.
aerobic
respiration
Complex process that occurs in the cells of most living organisms, in which nutrient organic
molecules such as glucose (C6H12O6) combine with oxygen (O2) and produce carbon dioxide
(CO2), water (H2O), and energy. Compare photosynthesis.
albedo
Ability of a surface to reflect light.
anaerobic
respiration
Form of cellular respiration in which some decomposers get the energy they need through the
breakdown of glucose (or other nutrients) in the absence of oxygen. Compare aerobic respiration.
aquatic
Pertaining to water. Compare terrestrial.
aquatic life zone Marine and freshwater portions of the biosphere. Examples include freshwater life zones (such as
lakes and streams) and ocean or marine life zones (such as estuaries, coastlines, coral reefs, and
the deep ocean).
atmosphere
The whole mass of air surrounding the earth. See stratosphere, troposphere.
autotroph
See producer.
bacteria
Prokaryotic, one-celled organisms. Some transmit diseases. Most act as decomposers and get
the nutrients they need by breaking down complex organic compounds in the tissues of living or
dead organisms into simpler inorganic nutrient compounds.
biodiversity
Variety of different species (species diversity), genetic variability among individuals within each
species (genetic diversity), variety of ecosystems (ecological diversity), and functions such as
energy flow and matter cycling needed for the survival of species and biological communities
(functional diversity).
biogeochemical Natural processes that recycle nutrients in various chemical forms from the nonliving environment
cycle
to living organisms and then back to the nonliving environment. Examples are the carbon, oxygen,
nitrogen, phosphorus, sulfur, and hydrologic cycles.
biological
community
See community.
biological
diversity
See biodiversity.
biomass
Organic matter produced by plants and other photosynthetic producers; total dry weight of all
living organisms that can be supported at each trophic level in a food chain or web; dry weight of
all organic matter in plants and animals in an ecosystem; plant materials and animal wastes used
as fuel.
biome
Terrestrial regions inhabited by certain types of life, especially vegetation. Examples are various
types of deserts, grasslands, and forests.
biosphere
Zone of earth where life is found. It consists of parts of the atmosphere (the troposphere),
hydrosphere (mostly surface water and groundwater), and lithosphere (mostly soil and surface
rocks and sediments on the bottoms of oceans and other bodies of water) where life is found.
Sometimes called the ecosphere.
biotic
Living organisms. Compare abiotic.
calorie
Unit of energy; amount of energy needed to raise the temperature of 1 gram of water 1[[degree]]C
(unit on Celsius temperature scale). See also kilocalorie.
carbon cycle
Cyclic movement of carbon in different chemical forms from the environment to organisms and
then back to the environment.
carnivore
Animal that feeds on other animals. Compare herbivore, omnivore.
cell
Smallest living unit of an organism. Each cell is encased in an outer membrane or wall and
contains genetic material (DNA) and other parts to perform its life function. Organisms such as
bacteria consist of only one cell, but most of the organisms we are familiar with contain many
cells. See eukaryotic cell, prokaryotic cell.
chemosynthesis Process in which certain organisms (mostly specialized bacteria) extract inorganic compounds
from their environment and convert them into organic nutrient compounds without the presence of
sunlight. Compare photosynthesis.
community
Populations of all species living and interacting in an area at a particular time.
condensation
nuclei
Tiny particles on which droplets of water vapor can collect.
consumer
Organism that cannot synthesize the organic nutrients it needs and gets its organic nutrients by
feeding on the tissues of producers or of other consumers; generally divided into primary
consumers (herbivores), secondary consumers (carnivores), tertiary (higher-level) consumers,
omnivores, and detritivores (decomposers and detritus feeders). In economics, one who uses
economic goods.
decomposer
Organism that digests parts of dead organisms and cast-off fragments and wastes of living
organisms by breaking down the complex organic molecules in those materials into simpler
inorganic compounds and then absorbing the soluble nutrients. Producers return most of these
chemicals to the soil and water for reuse. Decomposers consist of various bacteria and fungi.
Compare consumer, detritivore, producer.
detritivore
Consumer organism that feeds on detritus, parts of dead organisms, and cast-off fragments and
wastes of living organisms. The two principal types are detritus feeders and decomposers.
detritus
Parts of dead organisms and cast-off fragments and wastes of living organisms.
detritus feeder
Organism that extracts nutrients from fragments of dead organisms and their cast-off parts and
organic wastes. Examples are earthworms, termites, and crabs. Compare decomposer.
dissolved
oxygen (DO)
content
Amount of oxygen gas (O2) dissolved in a given volume of water at a particular temperature and
pressure, often expressed as a concentration in parts of oxygen per million parts of water.
distribution
Area over which we can find a species. See range.
ecological
diversity
The variety of forests, deserts, grasslands, oceans, streams, lakes, and other biological
communities interacting with one another and with their nonliving environment. See biodiversity.
Compare functional diversity, genetic diversity, species diversity.
ecological
efficiency
Percentage of energy transferred from one trophic level to another in a food chain or web.
ecology
Study of the interactions of living organisms with one another and with their nonliving environment
of matter and energy; study of the structure and functions of nature.
ecosphere
See biosphere.
ecosystem
Community of different species interacting with one another and with the chemical and physical
factors making up its nonliving environment.
fermentation
See anaerobic respiration.
food chain
Series of organisms in which each eats or decomposes the preceding one. Compare food web.
food web
Complex network of many interconnected food chains and feeding relationships. Compare food
chain.
fossil fuel
Products of partial or complete decomposition of plants and animals that occur as crude oil, coal,
natural gas, or heavy oils as a result of exposure to heat and pressure in he earth's crust over
millions of years. See coal, crude oil, natural gas.
freshwater life
zones
Aquatic systems where water with a dissolved salt concentration of less than 1% by volume
accumulates on or flows through the surfaces of terrestrial biomes. Examples are standing (lentic)
bodies of fresh water such as lakes, ponds, and inland wetlands and flowing (lotic) systems such
as streams and rivers. Compare biome.
functional
diversity
Biological and chemical processes or functions such as energy flow and matter cycling needed for
the survival of species and biological communities. See biodiversity, ecological diversity, genetic
diversity, species diversity.
genetic
diversity
Variability in the genetic makeup among individuals within a single species. See biodiversity.
Compare ecological diversity, functional diversity, species 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. Compare net primary productivity.
habitat
Place or type of place where an organism or population of organisms lives. Compare ecological
niche.
herbivore
Plant-eating organism. Examples are deer, sheep, grasshoppers, and zooplankton. Compare
carnivore, omnivore.
heterotroph
See consumer.
HIPPO
Acronym for habitat destruction and fragmentation, invasive species, population growth, pollution,
and overharvesting.
humus
Slightly soluble residue of undigested or partially decomposed organic material in topsoil. This
material helps retain water and water-soluble nutrients, which can be taken up by plant roots.
hydrologic
cycle
Biogeochemical cycle that collects, purifies, and distributes the earth's fixed supply of water from
the environment to living organisms and then back to the environment.
hydrosphere
The earth's liquid water (oceans, lakes, other bodies of surface water, and underground water),
frozen water (polar ice caps, floating ice caps, and ice in soil, known as permafrost), and water
vapor in the atmosphere. See also hydrologic cycle.
infiltration
Downward movement of water through soil.
kilocalorie (kcal) Unit of energy equal to 1,000 calories. See calorie.
leaching
Process in which various chemicals in upper layers of soil are dissolved and carried to lower
layers and, in some cases, to groundwater.
limiting factor
Single factor that limits the growth, abundance, or distribution of the population of a species in an
ecosystem. See limiting factor principle.
limiting factor
principle
Too much or too little of any abiotic factor can limit or prevent growth of a population of a species
in an ecosystem, even if all other factors are at or near the optimum range of tolerance for the
species.
lithosphere
Outer shell of the earth, composed of the crust and the rigid, outermost part of the mantle outside
the asthenosphere; material found in earth's plates. See crust, mantle.
loams
Soils containing a mixture of clay, sand, silt, and humus. Good for growing most crops.
microorganisms Organisms such as bacteria that are so small that they can be seen only by using a microscope.
natural
greenhouse
effect
Heat buildup in the troposphere because of the presence of certain gases, called greenhouse
gases. Without this effect, the earth would be nearly as cold as Mars, and life as we know it could
not exist. Compare global warming.
net primary
productivity
(NPP)
Rate at which all the plants in an ecosystem produce net useful chemical energy; equal to the
difference between the rate at which the plants in an ecosystem produce useful chemical energy
(gross primary productivity) and the rate at which they use some of that energy through cellular
respiration. Compare gross primary productivity.
nitrogen cycle
Cyclic movement of nitrogen in different chemical forms from the environment to organisms and
then back to the environment.
nitrogen fixation Conversion of atmospheric nitrogen gas into forms useful to plants by lightning, bacteria, and
cyanobacteria; it is part of the nitrogen cycle.
nutrient
Any food or element an organism must take in to live, grow, or reproduce.
nutrient cycle
See biogeochemical cycle.
omnivore
Animal that can use both plants and other animals as food sources. Examples are pigs, rats,
cockroaches, and people. Compare carnivore, herbivore.
organism
Any form of life.
percolation
Passage of a liquid through the spaces of a porous material such as soil.
phosphorus
cycle
Cyclic movement of phosphorus in different chemical forms from the environment to organisms
and then back to the environment.
photosynthesis
Complex process that takes place in cells of green plants. Radiant energy from the sun is used to
combine carbon dioxide (CO2) and water (H2O) to produce oxygen (O2) and carbohydrates (such
as glucose, C6H12O6) and other nutrient molecules. Compare aerobic respiration,
chemosynthesis.
population
Group of individual organisms of the same species living in a particular area.
precipitation
Water in the form of rain, sleet, hail, and snow that falls from the atmosphere onto the land and
bodies of water.
primary
consumer
Organism that feeds on all or part of plants (herbivore) or on other producers. Compare detritivore,
omnivore, secondary consumer.
primary
productivity
See gross primary productivity, net primary productivity.
producer
Organism that uses solar energy (green plant) or chemical energy (some bacteria) to manufacture
the organic compounds it needs as nutrients from simple inorganic compounds obtained from its
environment. Compare consumer, decomposer.
pyramid of
energy flow
Diagram representing the flow of energy through each trophic level in a food chain or food web.
With each energy transfer, only a small part (typically 10%) of the usable energy entering one
trophic level is transferred to the organisms at the next trophic level. Compare pyramid of
biomass, pyramid of numbers.
range
See distribution.
range of
tolerance
Range of chemical and physical conditions that must be maintained for populations of a particular
species to stay alive and grow, develop, and function normally. See law of tolerance.
respiration
See aerobic respiration.
salinity
Amount of various salts dissolved in a given volume of water.
scavenger
Organism that feeds on dead organisms that were killed by other organisms or died naturally.
Examples are vultures, flies, and crows. Compare detritivore.
secondary
consumer
Organism that feeds only on primary consumers. Compare detritivore, omnivore, primary
consumer.
species
Group of organisms that resemble one another in appearance, behavior, chemical makeup and
processes, and genetic structure. Organisms that reproduce sexually are classified as members of
the same species only if they can actually or potentially interbreed with one another and produce
fertile offspring.
species
diversity
Number of different species and their relative abundances in a given area. See biodiversity.
Compare ecological diversity, genetic diversity.
stratosphere
Second layer of the atmosphere, extending about 17[[endash]]48 kilometers (11[[endash]]30
miles) above the earth's surface. It contains small amounts of gaseous ozone (O3), which filters
out about 95% of the incoming harmful ultraviolet (UV) radiation emitted by the sun. Compare
troposphere.
sulfur cycle
Cyclic movement of sulfur in different chemical forms from the environment to organisms and then
back to the environment.
terrestrial
Pertaining to land. Compare aquatic.
tertiary (higherlevel)
consumers
Animals that feed on animal-eating animals. They feed at high trophic levels in food chains and
webs. Examples are hawks, lions, bass, and sharks. Compare detritivore, primary consumer,
secondary consumer.
transpiration
Process in which water is absorbed by the root systems of plants, moves up through the plants,
passes through pores (stomata) in their leaves or other parts, and evaporates into the atmosphere
as water vapor.
trophic level
All organisms that are the same number of energy transfers away from the original source of
energy (for example, sunlight) that enters an ecosystem. For example, all producers belong to the
first trophic level, and all herbivores belong to the second trophic level in a food chain or a food
web.
troposphere
Innermost layer of the atmosphere. It contains about 75% of the mass of earth's air and extends
about 17 kilometers (11 miles) above sea level. Compare stratosphere.
water cycle
See hydrologic cycle.
weathering
Physical and chemical processes in which solid rock exposed at earth's surface is changed to
separate solid particles and dissolved material, which can then be moved to another place as
sediment. See erosion.