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UNIT XI – ECOLOGY – (Chapter 3, 4-2, 4-3, 5-2)
Ecologists spend large amounts of time investigating interactions between _____________ and _________________ 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
__________________________.
I. LABORATORY INVESTIGATIONS
There are a variety of ways to conduct a laboratory investigation depending on the desired outcome.
A. Comparative – A _____________________________ of two or more things; for example, comparing plant cells with animal cells under the
microscope.
B. Descriptive – Observational lab in which quantitative (involve _____________ measurements, ___________________) and
qualititative (________________________________) information is obtained; for example, Eco-jars
C. Experimental – Designed experiment that follows the _______________________________. Clearly defined ______________________
and test group(s).
II. THE SCIENTIFIC METHOD (pp.3-15)
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 ___________________________ pattern of thinking to solve everyday
problems. In general, this problem-solving technique involves:
A. _____________________________________
B. Forming a __________________________
A hypothesis is a ______________________ explanation of the problem.
C. Setting Up a Controlled _____________________________
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 ___________________; a benchmark.
2. Experimental Group – Group in which all conditions are kept the same except for a __________________________. A variable is a
_factor changed by the experimenter__. Only _____ factor should be changed in each experimental group. This change is designed to
_test the hypothesis_.
a. manipulated (independent) variable – factor that is _______________ 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 ___________ are used as a visual representation
of the results. The types of graphs used most often to illustrate results are
1. ________________ Graph – Used to show relationship of a part to a whole
2. ____________ Graph – Used when independent variable isn’t continuous; for example, absorbency of different brands of paper towels
3. _____________ Graph – Used when ______________________ 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 ________ axis and the responding (dependent) variable is plotted on the ________ axis.
Manipulated (Independent) Variable:
_____________________________
Responding (Dependent) 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 _________________?
a. Was there a large enough _______________________?
b. Although no experimental set-up can be perfect, were the ___________________________ minimized?
c. Was there only __________________________ tested?
3. Is the experiment ____________________?
F. Constructing a Theory
A scientific theory is an explanation that has been tested ________________ times by many scientists.
A theory has been confirmed by repeated experiments, although it may eventually be _________________________.
III. What is Ecology? (pg 63 – 65)
A. ______________ is the study of the interaction among and between organisms and their environment. The term “ecology” was coined by
German biologist Ernst Haeckel. He based this term on the word oikos, meaning house. The combined portions of the planet in which all life
exists, including land, water, and air make up the biosphere (nature’s largest house). 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 __________________________.
Populations - Groups of organisms that belong to the same species and live in the same area (_________________).
Community – The assemblage of different _______________________ 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.
Biosphere – highest level of organization; includes all the living & non-living components.
IV. Energy Flow (pg 67 – 73)
All living things require energy. The ultimate source of energy for all living things on Earth is the _________________.
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 _____________________.
- Some producers capture light energy from the sun and transform it into the chemical energy of organic molecules in a process called
___________________________.
- Other producers are able to capture energy stored in the chemical bonds of molecules to make food in a process called ________________.
The amount of organic matter that the photosynthetic organisms of an ecosystem produce is called __________________________________.
Examples of autotrophs are plants, algae, kelp, plankton, and some bacteria.
B. Consumers – Organisms that rely on other organisms for their energy & food supply are called heterotrophs or _______________________.
There are several categories of consumers.
1. Herbivores – eat only plants or producers…. Ex. deer, cow, caterpillars
2. Carnivores – eat animals……..Ex. snakes, owls, coyotes
3. Omnivores – eat both plants and animals……Ex. humans, bears, crows
4. Detritivores – obtain 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. Bacteria & 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 determined by the organism’s source of energy.
- The lowest trophic level of any ecosystem is always occupied by the producers
- The 2nd trophic level is known as the ________________________ (1˚) consumer and is always an herbivore.
- At the 3rd trophic level are ___________________________ (2˚) consumers, animals that eat herbivores.
- 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 feed at several trophic
levels. This creates a complicated, interconnected path of energy called a food web.
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. Ecologists recognize three types of ecological pyramids….
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 ____%) 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 (____%) that they consume for life processes in order to maintain homeostasis (cell respiration,
movt, reproduction); and some is released or lost to the environment _________. 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)
2. Biomass Pyramid – the total amount of ___________________ within a given trophic level is called biomass. This is expressed in grams
of organic matter per unit area; it represents the amount of potential food available for each trophic level in an ecosystem. Ex. – if you start
off with 5000 grams of grain  500 grams of chicken 50 grams of human tissue.
3. Pyramid of Numbers – Represents the _____________________ of individual organisms at each trophic level. Typically, the pyramid
is the same shape as the energy and biomass pyramids – meaning that there are usually more organisms at the lower levels; however, that
is not always the case. Ex. In a forest – there are fewer producers than consumers…. A single tree has a large amount of energy &
biomass, but it is only 1 organism. Many insects live in the tree, but they have less energy and biomass.
V. Cycles of Matter (pg 74 – 80)
Nutrients In An Ecosystem – Unlike energy, nutrients are recycled within and between ecosystems. The paths of water, carbon, nitrogen, and
phosphorus, as they pass from the nonliving environment to living organisms and then back to the environment, form cycles called
biogeochemical cycles. Organisms require these nutrients to build tissues and carry out essential life functions.
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 underground.
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 N 2;
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 ___________________.
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 ________________________________. 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 ________________________________ 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? (pg 90-93)
A. Biotic & Abiotic Factors
Ecosystems are influenced by a combination of biological (biotic) and physical (abiotic) factors.
Biotic – all the ________________ factors; trees, mushrooms, bacteria, plants, animals, algae, predators, prey, etc
Abiotic – all the ______________________ factors; temperature, precipitation, humidity, wind, nutirent 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 (____________ 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 _________________. 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 .
b. Commensalism – only ____ 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 ___________ by the relationship. The organism that is harmed is
known as the host. Ex. – tapeworms, fleas, ticks, lice
D. Ecological Succession (pg 94-97)
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
a. First species to populate the area is called the _____________________________.
b. __________________ is the most common pioneer species after a volcano. Lichen = fungus and alga capable of growing on
bare rock. As lichen grows, it helps to break up the rocks. When lichen die they add organic material to help form soil to support
plants.
2. Secondary Succession – Occurs when a disturbance of some kind changes an existing community without removing the soil. Ex:
clearing land, plowing, wildfires.
a. Ecologists believe that succession in a given area proceeds in predictable stages ending with a mature, stable community,
referred to as a __________________________.
VII. Biomes (pg98 – 105)
Biome – terrestrial communities with certain soil & climate conditions, and particular plant & animal species. Plants & animals in each biome
have certain adaptations (inherited characteristics that increase chance of survival). Plants and animals also exhibit variations in tolerance
(ability to survive & reproduce in non-optimal conditions).
A. Biomes and Climate
Climate is an impt factor in determining which organisms can survive/flourish in each biome. Climate takes two things into consideration:
temperature & precipitation.
Microclimate – climate in a small area that differs from the climate around it. Ex. Fog in the streets of San Francisco
Climate Diagrams – tool used to illustrate the temp & precipitation at a given location during each month of the year.
B. The Major Biomes (see pg 100-104)
1. Tropical Rain Forest
2. Tropical Dry Forest –
3. Tropical Savanna –
4. Desert –
5. Temperate Grassland –
6. Temperate Woodland & Shrubland (Chaparral)–
7. Temperate Forest –
8. Northwestern Coniferous Forest –
9. Boreal Forest (Taiga)–
10. Tundra –
VIII. Limits to Population Growth (pg 124-127)
A. Limiting Factors – any factor that causes population growth to decrease.
1. 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
2. Density-Independent Factors – affects all populations, regardless of the population size. Ex. Unusual weather, natural disasters,
seasonal cycles, & certain human activities such as damming rivers & cutting down forests. Many species will display a crash in
population size as a result.