Download trophic level

Name ______________________________________ Test Date___________
Unit XII Scientific Method & Ecology Notes
Ecologists spend large amounts of time investigating interactions between
_biotic____ and _abiotic___ factors. It is important that ecologists have an
understanding of experimental design. An experimental design that is flawed
does not produce valid results or justifiable _conclusions_______.
I. LABORATORY INVESTIGATIONS
There are a variety of ways to conduct a laboratory investigation depending
on the desired outcome.
A. Comparative – A _comparison______ of two or more things; for
example, comparing plant cells with animal cells under the microscope
B. Descriptive – Observational lab in which quantitative (involve numbers,
measurements, quantities__) and qualititative (_descriptions__)
information is obtained; for example, Eco-jars
C. Experimental – Designed experiment that follows the scientific method.
Clearly defined _control__ and test group(s).
II. THE SCIENTIFIC METHOD
The term, “scientific method” is misleading because it actually refers to a
process that is neither reserved for ecologists and other scientists, nor a
methodical set of steps to be followed in a specific order. Instead, it is an
_organized___ pattern of thinking to solve everyday problems. In general,
this problem-solving technique involves:
A. _Question or Problem_________
B. Forming a _hypothesis_____
A hypothesis is a _TESTABLE explanation of the problem.
C. Setting Up a Controlled _Experiment___
To test a hypothesis or find an answer to a question, a scientist will
usually set up a controlled experiment. A controlled experiment usually
consists of two groups:
1. Control – Set-up used as a standard for comparison; a benchmark.
2. Experimental Group – Group in which all conditions are kept the
same except for a _variable___. A variable is a _factor changed by
the experimenter__. Only _one__ factor should be changed in each
experimental group. This change is designed to _test the hypothesis_.
a. manipulated (independent) variable – factor that is _changed by
the experimenter.
b. responding (dependent) variable – condition that is measured or
observed as a result of that change.
D. Collecting Data
Data from an experiment should be presented in a concise and
organized manner. Often _graphs_ are used as a visual
representation of the results. The types of graphs used most often to
illustrate results are:
1. _Circle____ Graph – Used to show relationship of a part to a whole
2. _Bar___ Graph – Used when independent variable isn’t continuous; for
example, absorbency of different brands of paper towels
3. _Line______ Graph – Used when _independent_______ variable is
continuous; for example, time. A line graph most clearly shows the
relationship between the independent & dependent variables in an
experiment. In a line graph, the manipulated (independent) variable
is plotted on the _X____ axis and the responding (dependent)
variable is plotted on the _Y__ axis.
Manipulated (Indept) Variable:
________________________
Responding (Depent) Variable:
________________________
E. Analysis and Conclusion
After collecting data, a scientist must analyze the data and form
conclusions based on the following questions:
1. Do the results _support or refute the hypothesis?
2. Is the experimental set-up _valid_____?
a. Was there a large enough _sample size____?
b. Although no experimental set-up can be perfect, were the
_sources of error_ minimized?
c. Was there only _one variable___ tested?
3. Is the experiment _repeatable____?
F. Constructing a Theory
A scientific theory is an explanation that has been tested many times
by many scientists.
A theory has been confirmed by repeated experiments, although it may
eventually be _disproven_.
III. What is Ecology?
A. Ecology is the study of the interaction among and between organisms
and their environment. Interactions within the biosphere produce a web
of interdependence between organisms and the environment in which
they live. It is this interdependence of life on Earth that contributes to an
ever-changing, or dynamic, biosphere.
B. Levels of Organization
Species - A group of similar organisms so similar to one another that can
interbreed and produce fertile offspring.
Populations - Groups of organisms that belong to the same species and
live in the same area (habitat).
Community – The assemblage of different populations that live together
in a defined area.
Ecosystem – all the organisms that live in a particular place, together with
their nonliving, or physical, environment.
Biome - is a group of ecosystems that have the same climate and similar
dominant communities.
Tropical
Rainforest
Biosphere – highest level of organization; includes all the living & non-living
components.
IV. Energy Flow
All living things require energy. The ultimate source of energy for all living
things on Earth is the sun.
A. Producers– Organisms that are able to capture energy from sunlight or
chemicals and use it to produce food are known as autotrophs. They
use energy from the environment to fuel the assembly of simple inorganic
compounds into complex organic molecules. (Ex. carbs, lipids, proteins,
nucleic acids) Because these organisms make their own food, they are
also known as producers.
 Some producers capture light energy from the sun and transform it
into the chemical energy of organic molecules in a process called
photosynthesis.
Photosynthesis takes place in the _chloroplasts__ of plant cells. The
equation for photosynthesis is_CO2 + H2O + light energy  C6H12O6 + O2__.

Other producers are able to capture energy stored in the chemical
bonds of molecules to make food in a process called
chemosynthesis.
The amount of organic matter that the photosynthetic organisms of an
ecosystem produce is called primary productivity.
Examples of autotrophs: plants, algae, kelp, plankton, some bacteria.
B. Consumers – Organisms that rely on other organisms for their energy &
food supply are called heterotrophs or consumers. There are several
categories of consumers.
1. Herbivores – eat only plants or producers…. Ex. deer, cow, caterpillars
2. Carnivores – eat animals (other consumers).Ex. snakes, owls, coyotes
3. Omnivores – eat both plants and animals……Ex. humans, bears
4. Detritivores – obtain their energy from organic wastes and dead
bodies of plants and animals…. Ex. mites, earthworms, snails, crabs,
vultures
5. Decomposers - cause decay by the breakdown of organic matter &
releases the nutrients back to the environment to be used again by
other organisms. Ex. Kingdom Eubacteria & Fungi
C. Feeding Relationships – Energy flows through an ecosystem in one
direction; it cannot be recycled. Energy flow begins with the sun, is
captured by producers, then transferred to various consumers.
Ecologists assign every organism in an ecosystem to a trophic level,
which is a step in the pathway of energy flow and is determined by the
organism’s source of energy.




The 1st or lowest trophic level of any ecosystem is always occupied
by the producers
The 2nd trophic level is known as the primary (1◦) consumer and is
always an herbivore or an omnivore.
At the 3rd trophic level are secondary (2◦) consumers, animals that
eat other consumers (herbivores or omnivores).
Many ecosystems contain a 4th trophic level, consisting of carnivores
that consume other carnivores – these are called tertiary (3◦) consumers.
D. Illustrating Energy Flow – There are several illustrative techniques used
by ecologists to show energy flow in an ecosystem.
1. Food Chains – A food chain illustrates how energy is transferred by
showing a series of steps beginning with a producer; illustrating the
transfer of energy through organisms eating and being eaten. The
arrow in a food chain always means “is consumed by”. Food chains
are organized into trophic levels.
Example: sun  grass(producer)  grasshopper(1°consumer) 
lizard(2°consumer)  owl(3°consumer)
Example: sun  cattail(producer)  caterpillar(1°consumer) 
frog(2°consumer)
2. Food Webs – In most ecosystems, energy does not follow simple
linear paths because animals have a tendency to eat a variety of
organisms and are eaten by a variety of organisms. This creates a
complicated, interconnected path of energy called a food web.
Example:
According to this food web . . .







How many different producers
are there?
Is the grasshopper a producer,
primary, or secondary consumer?
Is the grasshopper an herbivore, carnivore, or omnivore?
What organism(s) acts as the decomposer?
Give an example of an organism in this food web that acts as secondary and tertiary consumer.
If all the squirrels in the community perished, would the hawk be able to survive? Explain.
If the grass was destroyed, which organism would be most directly affected? Explain.
E. Ecological Pyramids – diagrams that show the relative amounts of
energy or matter contained within each trophic level in a food chain or
food web.
1. Energy Pyramid – there is no limit to the # of trophic levels that a food
chain can support; however, there is a slight drawback. Only part of
the energy (approximately 10%) that is stored in one trophic level is
passed on to the organisms in the next trophic level. This is because
organisms have to USE much of the energy (90%) that they consume
for life processes in order to maintain homeostasis (cell respiration,
movt, reproduction); and some is released or lost to the environment
as heat. Therefore, at each trophic level, the energy stored by the
organism is about one-tenth of that stored by the organisms in the level
below. Because of this, most food chains typically consist of only 3 or 4
trophic levels. (more levels = less energy available)
V. Cycles of Matter
Nutrients In An Ecosystem – Unlike energy from the sun, nutrients are only
available to an ecosystem in specific quantities and must be _recycled__ within
and between ecosystems. Nutrients may become a _limiting factor____
when they are depleted. Organisms require nutrients to _produce energy,
build biomolecules, cells, etc_____. Although all nutrients, including
_water____, are re-cycled, there are a few nutrient cycles that are especially
important.
A. Water Cycle – Water enters the atmosphere in the form of water vapor.
Water vapor then condenses falls to ground in form of rain or snow.
Some of this precipitation becomes runoff from the ground and collects in
rivers, lakes, streams, oceans. The rest evaporates and condenses into
clouds in the atmosphere. Rainfall then sends water back to earth taken
up by the roots of plants to be used for photosynthesis. Water then moves
into the atmosphere by evaporating from the leaves (transpiration) through
openings called stomata)
B. Carbon Cycle – Organisms require carbon to make organic molecules like
carbs, lipids, proteins, & NA’s. Four main processes move carbon through
its cycle:
1. Biological processes like photosynthesis, cell resp, decomposition
2. Geochemical processes like erosion & volcanic activity (atmosphere &
oceans)
3. Mixed biogeochemical processes like burial and decomp of dead
organisms and their conversion under pressure into coal and petroleum
(fossil fuels) – these store C under ground.
4. Human activities – mining, cutting and burning forests, burning fossil
fuels (release CO2 into atmosphere)
C. Nitrogen Cycle – Organisms require nitrogen to build proteins and nucleic
acids. The atmosphere is very rich in nitrogen gas, or N2; however, most
organisms are unable to use that gas because the two nitrogen atoms in a
molecule of N2 are connected by a triple covalent bond. Only bacteria
produce the enzymes needed to convert nitrogen from the atmosphere to a
useable form. Bacterial enzymes break the triple covalent bonds and bind
the nitrogen atoms to hydrogen, forming ammonia (NH3). This process is
known as nitrogen fixation. After nitrogen fixation is carried out by
bacteria in soil, the nitrogen compound is then absorbed by plants and used
to make proteins. When organisms die, decomposers return the nitrogen to
the soil where it may be taken up by producers again or returned to the
atmosphere by other bacteria.
D. Phosphorus Cycle – It is an important component of ATP, RNA, and DNA.
Phosphorus is found in soil and rock as calcium phosphate, which dissolves
in water to form phosphate ions (PO4). This phosphate is absorbed by the
roots of plants and used to build ATP and DNA. Heterotrophs that eat the
plants reuse the organic phosphorus, and then when these animals die and
decay, the bacteria in the soil convert the phosphorus from the organic
molecules back into PO4.
E. Nutrient Limitation – when an ecosystem is limited by a single nutrient that
is scarce or cycles very slowly. This can limit an organisms growth & have
an impact on the primary productivity of an ecosystem. Ex. Open oceans
are normally nutrient-poor compared to the land – 1/10,000 the amount of N
found in soil. Runoff from heavily fertilized fields can result in an algal
bloom, which if there aren’t enough consumers to eat the algae, it can
disrupt the equilibrium of an ecosystem.
VI. What Shapes an Ecosystem?
A. Biotic & Abiotic Factors
Ecosystems are influenced by a combination of biological (biotic) and
physical (abiotic) factors.
Biotic – all the living factors; trees, mushrooms, bacteria, plants, animals,
algae, predators, prey, etc
Abiotic – all the non-living factors; temperature, precipitation, humidity,
wind, nutrient availability, soil type, sun
Together biotic and abiotic factors determine the health of an ecosystem
and its productivity.
B. The Niche
A niche is an organism’s way of making a living (role that it plays in its
community). It is comprised of physical and biological factors, like the type
of food it eats, how it obtains its food, the way it is food for other organisms,
how and when it reproduces, its physical living requirements to survive, etc.
No two species share the same niche in the same habitat…. Ex. – you can
have 3 species of North American warblers in the same spruce tree – but
they will feed at different elevations & in different parts of the tree.
C. Community Interactions
Community interactions, such as competition, predation, and various forms
of symbiosis, can have a powerful effect on an ecosystem.
1. Competition – competition occurs when organisms of the same or
different species attempt to use an
ecological resource (H2O, nutrients, light, food, or space) in the same
place at the same time. Direct competition often results in a winner and
a loser (who fails to survive). To prevent this, there is a rule in ecology
known as the competitive exclusion principle - no two species can
occupy the same niche in the same habitat at the same time Ex.
Different species of warblers in spruce tree
2. Predation – interaction in which one organism captures and feeds on
another organism. The organism that does the killing/eating is called the
predator, and the food organism is the prey. Predators have
specialized ways to go about capturing and killing their prey.
3. Symbiosis – relationship in which two species live closely together –
“living together” There are three
main types of symbiotic relationships:
a. Mutualism – both species benefit. Ex- flowers depend on insects for
pollination, and the insects depend on the flowers for food; Nitrogen
fixing bacteria and plants; E.coli in the large intestine .
Error!Error!
b. Commensalism – only one organism benefits, & the other organism
is neither helped nor harmed. Ex. barnacles on a whale’s skin
c. Parasitism – only one organism benefits, & the other organism is
harmed by the relationship. The organism that is harmed is known
as the host. Ex. – tapeworms, fleas, ticks, lice
D. Ecological Succession
Ecosystems are constantly changing in response to natural and human
disturbances. As an ecosystem changes, older inhabitants gradually
die out and new organisms move in, causing further changes in the
community.
Ecological succession – a series of predictable changes that occurs in
a community over time.
1. Primary Succession – Occurs on surfaces where no soil exists. Ex:
after volcanic eruption, glaciers melting
 First species to populate the area is called the pioneer species.
 Lichen is the most common pioneer species after a volcano
because they are capable of growing on bare rock. A lichen is a
fungus and a cyanobacterium living together. Cyanobacterium
are photosynthetic bacteria. In a lichen, the cyanobacteria
provides food for the fungus and the fungus provides water and
minerals for the cyanobacteria. As lichen grows, it helps to break
up the rocks. When lichen die they add organic material to help
form soil to support plants.
After a
volcano in
Hawaii
2. Secondary Succession – Occurs when a disturbance of some kind
changes an existing community without removing the soil. Ex: clearing
land, plowing, wildfires.
 Ecologists believe that succession in a given area proceeds in
predictable stages ending with a mature, stable community,
referred to as a climax community.
Error!
VII. POPULATIONS WITHIN AN ECOSYSTEM
Populations within an ecosystem cannot have unlimited growth. There are
conditions that have an impact on population size known as
_limiting factors__. Limiting factors may be
described as density-dependent or density-independent.
A. Density-Dependent Factors – a factor that depends on the population
size. These factors become limiting when the population density (#of
organisms per unit area) – reaches a certain level. These factors have a
greater effect on large, dense populations (do not have as a great an
impact on small, scattered populations). Ex. Competition, predation,
parasitism, disease
B. Density-Independent Factors – affects all populations, regardless of the
population size. Ex. Unusual weather, natural disasters, & certain human
activities such as damming rivers & cutting down forests.
C. Climax Community – A climax community is a __stable_ community
with very little population growth or decline. Each ecosystem has a
_carrying capacity_, a certain number of organisms that can exist
__successfully_. When the carrying capacity is exceeded, resources
become a _limiting factor_, and population numbers __decline_.