Ecology
I. What Is Ecology?
A. Interactions and Interdependence
1. Ecology is the scientific study of interactions among organisms
and between organisms and their environment, or surroundings.
2. The biosphere contains the combined portions of planet in which
all of life exists, including land, water, and air, or atmosphere.
It extends from about 8 km above Earth’s surface to as far as
11 km below the surface of the ocean.
a)
3. Interactions within the biosphere produce a web of
interdependence between organisms and the environment in which
they live.
B. Levels of Organization
1. To understand relationships within the biosphere, ecologists ask
questions about events and organisms that range in complexity from
a single individual to the entire biosphere.
A species is a group of organisms so similar to one another that
they can breed and produce fertile offspring.
a)
Populations are groups of individuals that belong to the same
species and live in the same area.
b)
Communities are assemblages of different populations that live
together in a defined area.
c)
An ecosystem is a collection of all the organisms that live in a
particular place, together with their nonliving, or physical,
environment.
d)
A biome is a group of ecosystems that have the same climate
and similar dominant communities.
e)
C. Ecological Methods
1. Ecologists use a wide range of tools and techniques to study the
living world.
2. Regardless of the tools they use, scientists conduct modern
ecological research using three basic approaches: observing,
experimenting, and modeling.
a)
Observing is often the first step in asking ecological questions.
b)
Experimenting can be used to test hypotheses.
Many ecological phenomena occur over long periods of time or
on such large spatial scales that they are difficult to study.
Ecologists make models to gain insight into complex phenomena
such as the effects of global warming on ecosystems.
c)
3. All of these approaches rely on the application of scientific
methods to guide ecological inquiry.
II. Energy Flow
A. Producers
1. Without a constant input of energy, living systems cannot
function.
2. Sunlight is the main energy source for life on Earth.
3. Of all the sun’s energy that reaches Earth’s surface only a small
amount—less than 1%—is used by living things.
4. In a few ecosystems, some organisms obtain energy from a
source other than sunlight. Some types of organisms rely on the
energy stored in inorganic chemical compounds.
5. Only plants, some algae, and certain bacteria can capture energy
from sunlight or chemicals and use that energy to produce food.
6. Autotrophs use energy from the environment to fuel the assembly
of simple inorganic compounds into complex organic molecules.
7. Because they make their own food, autotrophs, like the kelp are
also called producers.
8. Producers are essential to the flow of energy through the
biosphere.
9. Photosynthesis
The best-known autotrophs are those that harness solar energy
through a process known as photosynthesis.
a)
During photosynthesis, these autotrophs use light energy to
power chemical reactions that convert carbon dioxide and water
into oxygen and energy-rich carbohydrates such as sugars and
starches.
b)
c)
On land, plants are the main autotrophs.
In freshwater ecosystems and in the sunlit upper layers of the
ocean, algae are the main autotrophs.
d)
10. Chemosynthesis
Although plants are the most visible and best-known
autotrophs, some autotrophs can produce food in the absence of
light.
a)
When organisms use chemical energy to produce
carbohydrates, the process is called chemosynthesis.
b)
B. Consumers
1. Many organisms—including animals, fungi, and many bacteria—
cannot harness energy directly from the physical environment as
autotrophs do.
2. The only way these organisms can acquire energy is from other
organisms.
3. Organisms that rely on other organisms for their energy and food
supply are called heterotrophs also known as consumers.
4. There are many different types of heterotrophs.
a)
Herbivores
b)
Carnivores
c)
Omnivores
d)
Detritivores
e)
Decomposers
C. Feeding Relationships
1. Energy flows through an ecosystem in one direction, from the sun
or inorganic compounds to autotrophs (producers) and then to
various heterotrophs (consumers).
2. The energy stored by producers can be passed through an
ecosystem along a food chain, a series of steps in which organism
transfer energy by eating and being eaten.
3. When the feeding relationships among the various organisms in
an ecosystem form a network of complex interactions, ecologists
describe these relationships as a food web.
4. Each step in a food chain or food web is called a trophic level.
a)
Producers make up the first trophic level.
b)
Consumers make up the second, third, or higher trophic levels.
c)
Each consumer depends on the trophic level below for energy.
D. Ecological Pyramids
1. The amount of energy or matter in an ecosystem can be
represented by an ecological pyramid.
2. An ecological pyramid is a diagram that shows the relative
amounts of energy or matter contained within each trophic level in a
food chain or food web.
3. Ecologists recognize three different types of ecological pyramids.
a)
Energy Pyramids
Only about 10% of the energy available within one trophic level
is transferred to organisms at the next trophic level.
(1)
b)
Biomass Pyramids
The total amount of living tissue within a given trophic level is
called biomass.
(1)
c)
Pyramids of Numbers.
Ecological pyramids can also be based on the numbers of
individual organisms at each trophic level.
(1)
III. Cycles of Matter
A. Recycling in the Biosphere
1. Unlike the one-way flow of energy, matter is recycles within and
between ecosystems.
2. Elements, chemical compounds, and other forms of matter are
passed from one organism to another and from one part of the
biosphere to another through biogeochemical cycles.
As the word suggests biogeochemical cycles connect biological,
geological, and chemical aspects of the biosphere.
a)
3. Matter can cycle through the biosphere because biological
systems do not use up matter, they transform it.
4. The matter is assembled into living tissue or passed out of the
body as waste products.
5. Biogeochemical cycles pass the same molecules around again
and again within the biosphere.
B. The Water Cycle
1. All living thing require water to survive.
2. Water moves between the ocean, atmosphere, and land.
3. As Figure 3-11 shows, water molecules enter the atmosphere as
water vapor, a gas, when they evaporate from the ocean or other
bodies of water.
4. The process by which water changes from liquid to an
atmospheric gas is called evaporation.
5. Water can also enter the atmosphere by evaporating from the
leaves of plants in the process of transpiration.
6. During the day, the sun heats the atmosphere. As the warm, moist
air rises, it cools eventually condensing into tine droplets that form
clouds.
7. When the droplets become large enough, the water returns to
Earth’s surface in the form of precipitation—rain, snow, sleet, or hail.
C. Nutrient Cycles
1. The food you eat provides energy and chemicals that keep you
alive.
2. All the chemical substances that an organism needs to sustain life
are its nutrients.
3. Primary producers, such as plants, usually obtain nutrients in
simple inorganic forms from their environment.
4. Consumers obtain nutrients by eating other organisms.
5. Every living organism needs nutrients to build tissues and carry
out essential life functions.
6. Like water, nutrients are passed between organisms and the
environment through biogeochemical cycles.
7. Carbon Cycle
a)
Carbon plays main roles.
(1)
Carbon is a key ingredient of living tissue.
Calcium carbonate is an important component of animal
skeletons.
(2)
(3)
b)
Carbon and oxygen form carbon dioxide gas.
Four main types of processes move carbon through its cycle:
Biological processes, such as photosynthesis, respiration, and
decomposition, take up and release carbon and oxygen.
(1)
Geochemical processes, such as erosion and volcanic activity,
release carbon dioxide to the atmosphere and oceans.
(2)
Mixed biogeochemical processes, such as the burial and
decomposition of dead organisms and their conversion under
pressure into coal and petroleum, store carbon underground.
(3)
Human activities, such as mining, cutting and burning forests,
and burning fossil fuels, release carbon dioxide into the
atmosphere.
(4)
(5)
Figure 3-13 helps to illustrate the carbon cycle.
8. Nitrogen Cycle
All organisms require nitrogen to make amino acids, which in
turn are used to build proteins.
a)
Many different forms of nitrogen occur naturally in the
biosphere.
b)
(1)
Nitrogen gas makes up 78% of Earth’s atmosphere.
Nitrogen-containing substances such as ammonia are found in
the wastes produced by many organisms and in dead and decaying
organic matter.
(2)
Some bacteria, which live in the soil and on the roots of plants,
convert nitrogen gas into ammonia in a process known as nitrogen
fixation.
c)
When organisms die, decomposers return nitrogen to the soil
as ammonia which is then picked up by producers.
d)
Other soil bacteria convert nitrates into nitrogen gas in a
process called denitrification. This process releases nitrogen into
the atmosphere again.
e)
f)
Figure 3-14 shows the nitrogen cycle.
9. Phosphorus Cycle
Phosphorus is essential to living organisms because it forms
part of important life-sustaining molecules such as DNA and
RNA.
a)
Although it is of great biological importance, it is not very
common in the biosphere.
b)
Unlike carbon, oxygen, and nitrogen, phosphorus does not
enter the atmosphere. Instead, it remains mostly on land in rock
and soil minerals, and in ocean sediments.
c)
d)
Figure 3-15 illustrates the phosphorus cycle.
D. Nutrient Limitation
1. Ecologists are often interested in the primary productivity of an
ecosystem, which is the rate at which organic matter is created by
producers.
2. One factor that controls the primary productivity of an ecosystem
is the amount of available nutrients.
3. When an ecosystem is limited by a single nutrient that is scarce or
cycles very slowly, this substance is called a limiting nutrient.
IV. The Role of Climate
A. What is Climate?
1. In the atmosphere, temperature, precipitation, and other
environmental factors combine to produce weather and climate.
2. Weather is the day-to-day condition of Earth’s atmosphere at a
particular time and place.
3. Climate refers to the average, year-after-year conditions of
temperature and precipitation in a particular region.
4. Climate is caused by the interplay of many factors, including the
trapping of heat by the atmosphere, the latitude, the transport of heat
by winds and ocean currents, and the amount of precipitation that
results.
B. The Greenhouse Effect
1. Carbon dioxide, methane, water vapor, and a few other
atmospheric gases trap heat energy and maintain Earth’s
temperature range.
2. These gases function life the glass windows of a greenhouse.
3. The natural situation in which heat is retained by this layer of
greenhouse gases is called the greenhouse effect.
C. The Effects of Latitude on Climate
1. As a result of differences in latitude and thus the angle of heating,
Earth has three main climate zones:
Polar zones are cold areas where the sun’s rays strike Earth at
a very low angle.
a)
Temperate zones range from hot to cold, depending on the
season.
b)
Tropical zones, or tropics revive direct or nearly direct
sunlight year-round, making the climate almost always warm.
c)
V. What Shapes an Ecosystem
A. Biotic and Abiotic Factors
1. Ecosystems are influenced by a combination of biological and
physical factors.
2. The biological influences on organisms within an ecosystem are
called biotic factors.
a)
These include the entire living cast of characters.
3. Physical, or nonliving, factors that shape ecosystems are called
abiotic factors.
For example, the climate of an area includes abiotic factors
such as temperature, precipitation, and humidity.
a)
4. Together, biotic and abiotic factors determine the survival and
growth of an organism and the productivity of the ecosystem in
which the organism lives.
5. The area where an organism lives is called its habitat.
a)
A habitat includes both biotic and abiotic factors.
B. The Niche
1. If an organism’s habitat is its address, its niche is its occupation.
2. A niche is the full range of physical and biological conditions in
which an organism lives and the way in which the organism used
those conditions.
3. A niche includes the type of food the organism eats, how it obtains
this food, and which other species use the organism as food.
4. The physical conditions that an organism requires to survive are
also part of its niche.
C. Community Interactions
1. Community interactions, such as competition, predation, and
various form of symbiosis, can powerfully affect an ecosystem.
2. Competition
Competition occurs when organisms of the same or different
species attempt to use an ecological resource in the same place at
the same time.
a)
The term resource refers to any necessity of life, such as water,
nutrients, light, food, or space.
b)
A fundamental rule in ecology, the competitive exclusion
principle, states that no two species can occupy the same niche in
the same habitat at the same time.
c)
3. Predation
An interaction in which one organism captures and feeds on
another organism is called predation.
a)
4. Symbiosis
Any relationship in which two species live closely together is
called symbiosis, which means “living together”
a)
Biologists recognize three main classes of symbiotic
relationships in nature: mutualism, commensalisms, and
parasitism.
b)
(1)
In mutualism, both species benefit from the relationship.
In commensalisms, one member of the association benefits and
the other is neither helped nor harmed.
(2)
In parasitism, one organism lives on or inside another
organism and harms it.
(3)
D. Ecological Succession
1. Ecosystems are constantly changing in response to natural and
human disturbances.
2. As an ecosystem changes, older inhabitants gradually die out and
new organisms move in, causing further changes in the community.
3. This series of predictable changes that occurs in a community
over time is called ecological succession.
4. Primary Succession
On land, succession that occurs on surfaces where no soil exists
is called primary succession.
a)
b)
The first species to populate the area are called pioneer species.
5. Secondary Succession
After a disturbance, such as a fire or human activity,
community interactions tend to restore the ecosystem to its
original condition through secondary succession.
a)
VI. Aquatic Ecosystems
A. Aquatic ecosystems are determined primarily by the depth, flow,
temperature, and chemistry of the overlying water.
B. Freshwater Ecosystems
1. Freshwater ecosystems can be divided into two main types:
flowing-water ecosystems and standing-water ecosystems.
2. Flowing-Water Ecosystems
Rivers, streams, creeks, and brooks are all freshwater
ecosystems that flow over the land.
a)
b)
Organisms that live there are well adapted to the rate of flow.
Some insect larvae have hooks that allow them to take hold of
aquatic plants.
(1)
(2)
Certain catfish have suckers that anchor them to rocks.
Trout and many other fishes have streamlines bodies that help
them move with or against the current.
(3)
3. Standing-Water Ecosystems
Lakes and ponds are the most common standing-water
ecosystems.
a)
There is usually a circulation within the system to help
distribute head, oxygen, and nutrients throughout.
b)
Plankton is a general term for the tiny, free-floating organisms
that live in both freshwater and saltwater environments.
c)
Unicellular algae, or phytoplankton, are supported by
nutrients in the water and form the base of many aquatic food
webs.
d)
Planktonic animals, or zooplankton, feed on the
phytoplankton.
e)
4. Freshwater Wetlands
A wetland is an ecosystem in which water either covers the soil
or is present at or near the surface of the soil for at least part of
the year.
a)
C. Estuaries
1. Estuaries are wetland formed where rivers meet the sea.
2. Estuaries thus contain a mixture of fresh water and salt water.
3. Many are shallow, so sufficient sunlight reaches the bottom to
power photosynthesis.
4. Most of the primary production of organic matter is not consumed
by herbivores. Instead, much of it enters the food web as detritus.
5. Detritus is made up of tiny pieces of organic material that provide
food for organisms at the base of the estuary’s food web.
6. Organisms that feed on detritus include clams, worms, and
sponges.
7. Salt marshes are temperate-zone estuaries dominated by salt-
tolerant grasses above the low-tide line, and by seagrasses under
water.
8. Mangrove swamps are coastal wetlands that are widespread
across tropical regions.
D. Marine Ecosystems
1. Unless you are an avid diver or snorkeler, it takes some
imagination to picture what life is life in the vast, three-dimensional
ocean.
2. Sunlight penetrates only a relatively short distance through the
surface of the water.
3. Photosynthesis is limited to this well-lit upper layer known as the
photic zone, typically down 200 m.
4. Below the photic zone is the aphotic zone, which is permanently
dark.
5. In addition to the division between the photic zones, marine
biologist divide the ocean into zones based on the depth and
distance from shore: the intertidal zone, the coastal ocean, and the
open ocean.
6. Intertidal Zone
Organisms that live in the intertidal zone are exposed to
regular and extreme changes in their surroundings.
a)
Once or twice a day, they are submerges in sea water. The
remainder of the time, they are exposed to air, sunlight, and
temperature changes.
b)
7. Costal Ocean
The costal ocean extends from the low-tide mark to the outer
edge of the continental shelf, the relatively shallow border that
surrounds the continents.
a)
One of the most productive coastal ocean communities is the
kelp forest. Kelp forests are named for their dominant organism:
a giant brown algae that can grow at extraordinary rates—as
much as 50 cm a day.
b)
8. Coral Reefs
In the warm, shallow water of tropical costal oceans are coral
reefs, among the most diverse and productive environments on
Earth.
a)
Coral reefs are names for the coral animals whose hard,
calcium carbonate skeletons make up their primary structure.
b)
9. Open Ocean
10. Benthic Zone
The ocean floor contains organism that live attached to or near
the bottom, such as sea stars, anemones, and marine worms.
a)
b)
VII.
Scientists refer to these organisms as the benthos.
How Populations Grow
A. Characteristics of Population
1. Three important characteristics of a population are its geographic
distribution, density, and growth rate.
2. Population density is the number of individuals per unit area. This
number can vary tremendously depending on the species and its
ecosystem.
B. Population Growth
1. Three factors can affect population size: the number of births, the
number of deaths, and the number of individuals that enter or leave
the population.
2. Immigration, the movement of individuals into an area, is another
factor that can cause a population to grow.
3. Emigration, the movement of individuals out of an area, can cause
a population to decrease in size.
C. Exponential Growth
1. Exponential growth occurs when the individuals in a population
reproduce at a constant rate.
2. Under ideal conditions with unlimited resources, a population will
grow exponentially.
D. Logistic Growth
1. As resources become less available, the growth of a population
slows or stops.
2. Logistic growth occurs when a population’s growth slows or stops
following a period of exponential growth.
3. The number of individuals an ecosystem can support is a carrying
capacity.
VIII. Limits to Growth
A. Limiting Factors
1. A limiting factor is a factor that causes population growth to
decrease.
2. Some of the limiting factors that can affect a population are shown
in Figure 5-5.
B. Density-Dependent Factors
1. A limiting factor that depends on population size is called a
density-dependent limiting factor.
2. Density-dependent limiting factors include competition, predation,
parasitism, and disease.
The regulation of a population by predation takes place within
a predator-prey relationship, one of the best-known mechanisms
of population control.
a)
b)
Parasites can also limit the growth of a population.
Like predators, parasites take nourishment at the expense of
their hosts, often weakening them and causing disease or death.
c)
C. Density-Independent Factors
1. Density-independent limiting factors affect all populations in
similar ways, regardless of the population size.
2. Unusual weather, natural disasters, seasonal cycles, and certain
human activities—such as damming rivers and clear-cutting
forests—are all examples of density-independent limiting factors.
IX. Human Population Growth
A. Historical Overview
1. Like the populations of many other living organisms, the size of
the human population tends to increase with time.
2. For most of human existence, the population grew slowly.
a)
Life was harsh, and limiting factors kept population sizes low.
b)
Food was scarce.
c)
Incurable diseases were rampant.
3. About 500 years ago, the human population began growing more
rapidly.
a)
Agriculture and industry made life easier and safer.
The world’s food supply became more reliable, and essential
goods could be shipped around the globe.
b)
Improved sanitation, medicine, and health care dramatically
reduced the death rate and increased longevity.
c)
With these advances, the human population experienced
exponential growth, as shown in Figure 5-10.
d)
B. Patterns of Population Growth
1. The human population cannot keep growing exponentially forever,
because Earth and its resources are limited.
2. Two centuries ago, English economist Thomas Malthus observed
that human populations were growing rapidly.
Malthus predicted that such growth would not continue
indefinitely.
a)
According to Malthus, war, famine, and disease would limit
human population growth.
b)
3. Today, scientists have identified a variety of social and economic
factors that can affect human populations.
4. The scientific study of human populations is called demography.
Demography examines the characteristics of human
populations and attempts to explain how those populations will
change over time.
a)
Birthrates, death rates, and the age structure of a population
help predict why some countries have high growth rates while
other countries grow more slowly.
b)
5. The Demographic Transition
Over the past century, population growth in the US, Japan,
and much of Europe has slowed dramatically.
a)
Demographers have developed a hypothesis to explain this
shift.
b)
According to this hypothesis, these countries have completed
the demographic transition, a dramatic change in birth and death
rates.
c)
So far, the demographic transition has been completed in only
a few countries.
d)
Despite the trend in the US, Europe, and Japan, the worldwide
human population is still growing exponentially.
e)
Much of the population growth today us contributed by only
10 countries, with India and China in the lead, where birthrates
remain high.
f)
6. Age Structure
Population growth depends, in part, on how many people of
different ages make up a given population.
a)
Demographers can predict future growth using models called
age-structure diagrams, or population profiles.
b)
Age-structure diagrams show the population of a country
broken down my gender and age group.
c)
C. Future Population Growth
1. To predict how the world’s human population will grow,
demographers must consider many factors, including the age
structure of each country and the prevalence of life-threatening
diseases, such as AIDS, malaria, and cholera.