Ecology Review Sheet Answer Key
1. What branch of biology deals with interactions among organisms, between organisms, and their
environment? Ecology
2. If an ecologist sets up a greenhouse to study the effect of carbon dioxide on endangered plant species,
what aspect of the scientific method is he pursuing? Modeling. The scientists are attempting to create
the conditions currently affecting the earth, but on a small scale, where they can control all the
variables
3. Compare and contrast the nutrient content of land ecosystems versus open ocean ecosystems.
Open oceans tend to be very low in nutrients. By the time land nutrients have run off into the ocean,
the get very dilute by the time they make it far from shore.
4. Identify 3 basic ways ecologists study the living world.
Observing, modeling, experimenting
5. Describe the organization (hierarchy) of all the elements of the biosphere.
Individual (or
member of apopulationscommunitiesecosystemsbiomesbiosphere
species)
6. Name 3 primary producers. Plants, algae and some bacteria
7. What are the 2 ways primary producers convert energy. Photosynthesis and chemosynthesis
8. Compare and contrast herbivores and carnivores. NOTE: This is how a proper compare/contrast looks
(compare) Both are consumers of other organisms (contrast) Herbivores eat the primary producers
(plants, algae or photosynthetic bacteria). Carnivores eat herbivores or some other consumer
9. Describe how energy is transferred through an ecosystem, beginning with the sun. Be sure to include
the amount of energy that is retained and which is transferred.
The producers are considered to contain 100% of the available energy from the sun, even though they
use 90% of all incoming energy for themselves. When they are eaten by the second trophic level (the
primary consumers), the consumer is only getting 10% of all available energy. For example, if there
was 1000 kcals of energy taken in by producers, only 100 kcals are passed into the second trophic
level. They also use 90% of what they have consumed, so the third trophic level (the carnivore) is only
obtaining 10 kcals of energy. Each trophic level achieves the exact same result—10% of the energy
from the previous trophic level
10. Differentiate between the following: food web, food chain, trophic level and food pyramid.
A food chain is the simplest illustration of energy transfer—what eats what, in other words. It usually
contains a producer, primary consumer (herbivore), secondary consumer (carnivore), and one more
trophic level (top carnivore, scavenger, omnivore, etc.). A food web is a more realistic illustration of
energy transfer, because it shows more than one relationship between each of these organisms,
which is how it exists in nature. A food pyramid shows the various trophic levels that exist within a
given ecosystem.
11. The term for each step in the transfer of energy is a(n) ________trophic level____________________.
12. State the role each organism plays in an ecosystem:
Producer a photosynthetic or chemisynthetic
organisms that transfers energy from the sun
or from chemicals in the environment. Plants,
algae and some bacteria are producers
Herbivore directly consumes the producer
deer are herbivores, as are cows, horses, etc.
Carnivore “meat-eaters”. Usually consumes
Herbivores, but may also consume other
Carnivores
Scavenger not a “hunter” as we think of them.
generally takes advantage of meat left behind
by other organisms (carcasses). Vultures, eagles,
and ravens are common scavengers
Omnivore eats a variety of food stuffs. Meat
vegetation, carcasses, etc. Bears are a good
example of omnivores, as are humans
detritivore organisms that consume broken down
organic matter, such as crayfish and earthworms
Autotroph are producers. This is a general
term used for organisms that can absorb
energy and convert is for storage (plants)
heterotroph any organism that must consume something else to obtain energy
Decomposer organisms that absorb nutrients
From broken-down organic matter, like most
Fungi
chemoautotroph a rare class of organisms that use
inorganic chemicals to convert and store energy.
Usually bacteria that live in hostile environments
13. Describe all aspects of each of these:
Water Cycle There is a finite (limited) amount of water on earth, contained in oceans and freshwater biomes.
Water EVAPORATES from these, then CONDENSES in the form of mists or clouds. When the air becomes
saturated by water vapor, PRECIPITATION occurs as rain, snow, sleet or hail. When it hits the ground,
RUNOFF from high places brings the water back to SURFACE WATER reservoirs. Water that cannot flow down
hill LEECHES (infiltration) into the earth and forms GROUNDWATER reservoirs, such as aquifers. Water
exposed to the air once again evaporates and becomes part of the cycle. Ground water is taken up through
the roots of plants, and excess water exits the leaves as water vapor in the process of TRANSPIRATION.
Carbon-Oxygen cycle Carbon exists in the atmosphere as carbon dioxide, CO2, which is why this cycle is often
combined into one. Carbon dioxide from the atmosphere also mixes in with surface waters as dissolved
carbon dioxide (the same reason your soda is “fizzy). Plants use the carbon dioxide from the atmosphere in
the photosynthesis process, and put out oxygen as a “waste”gas. Life on earth is carbon-based, containing
many molecules that contain a huge amount of carbon. When they die and are decomposed, this carbon is
returned to the environment as hydrocarbons.
Nitrogen cycle Nitrogen gas, N2, makes up about 78% of the atmosphere. It is very necessary for life (for
amino acids in proteins, and in nucleic acids that make up our hereditary info), but because of the triple
bond, it is not useful to most organisms the way it is. Fortunately, some bacteria are capable of nitrogen
fixation when associated with the roots of some legumes (peas, beans, peanuts, alfalfa) and through
processes of ammonification and denitrofication, form useable ammonium, nitrite and nitrate ions, which the
plants absorb and are passed on to consumers when they are eaten.
14. What is the relationship between climate and weather? Climate is defined by the average, daily
weather conditions over a long period of time. Weather would be temporary and local conditions,
such as rainy, sunny, snowy, etc. The average of these conditions make up the climate of a given
biome.
15. How does longitude affect climate? It doesn’t. This is one of those “thinker” questions that you guys
call a “trick question.” 
16. Is the greenhouse effect a good thing or a bad thing for planet Earth? The greenhouse effect is a good
thing, in that without it, earth would be as uninhabitable as the other planets (so far as we have been
able to discover). It would be too cold to support life. On the other hand, human activity seems to
have increased to a LARGE extent the amount of carbon dioxide (which is what acts as a “blanket” to
keep all the sun’s heat from escaping back into space), we have turned it into a “heating blanket.”
Too much heat is being held within our atmosphere, causing global effects, such as the melting of the
polar ice. It seems to be a case of “too much of a good thing.”
17. Differentiate between niche and habitat. Habitat is simply the place an organisms lives in its
environment. Its niche is all the roles, jobs, or characteristics of an organism, so its habitat is PART of
its niche.
18. Why can several species of warblers (birds) share the same tree without competition forcing some of
them away? Specific adaptations of the warblers allow them to share the same environment (this is
called INTRAspecific competition, because they are the same species—if they were not, it would be
INTERspecific competition). Competitive exclusion takes place, and they use their adaptations to use
the resources in one small part of the tree. For example, some warblers only occupy the very top of
the tree, while others remain lower down, and near the trunk of the tree. This is the same principal as
what Gause observed with two competing species of paramecium.
19. What is the primary reason that Earth has 3 major climate zones? Because of the tilt of its axis, the
amount of sunlight falling on the earth varies. Also, as the earth travels around the sun, it does not
travel in a perfect circle. Its path is more oval, so at one point (perihelion), the sun is closest to the
earth. At the other side of its oval path (aphelion) the sun is furthest from the earth so less energetic
rays reach the earth.
20. List 5 disturbances that humans cause that affect ecosystems, often in a negative way.
Your own answers may vary based on experience. Some disturbances might include mining,
commercial logging, transfer of invasive species (Eurasian milfoil purple loosestrife, rusty crayfish).
21. Differentiate between primary and secondary ecological succession. Primary succession begins on
bare rock (the PIONEER SPECIES), and occurs after large-scale geologic events such as the retreat of a
glacier or volcanic activity. Secondary succession occurs after disturbances such as hurricanes and
fire, or even old farm lands that are no longer farmed. The primary difference is that living organisms
are already present, they just change as new species emerge or crowd out existing species.
22. Define and give at least 1 example of each of the following relationships; circle those that are symbiotic.
Mutualism a symbiotic relationship in which both species benefit from the relationship. One example
would be a honeybee and the flowers it feeds on. The bee gets food, and helps the flower species out by
transferring pollen that sticks to it to other flowers.
Herbivory Plant predation. The consuming of plants by an herbivore.
Commensalism a symbiotic relationship in which one organism benefits, and the other does not, but
neither is it harmed. Nemo is an example of commensalism! The clownfish gets protection from
predation because it is immune to the sting of the anemone, but the anemone doesn’t benefit from the
presence of the clownfish. However, neither is the anemone harmed.
Predation When one non-autotrophic organism consumes another.
Parasitism A symbiotic relationship in which one organism benefits (the parasite), and the other is harmed
(the host). As a rule, it is not in the parasite’s interest to harm the host, because if the host dies, so does
the parasite. Sometimes this happens, but more often than not, the host is simply damaged by the
parasite.
23. Identify the major biomes and the characteristics that define them Study chapter 4, section 4, for the gist.
There is no need to memorize the biomes and their characteristics. You will simply need to be able to
interpret graphic information regarding the biomes (pictures, tables, graphs, etc.)
24. Compare and contrast the two types of growth curves exhibited by populations as they grow. Include
an example of when each of these graphs might be created. A j-shaped (exponential) graph describes a
population that has unlimited resources, and thus, no carrying capacity to its environment. This is
unrealistic in nature, and occurs only over a short period of time, because resources are NEVER
unlimited. An S-shaped (logistic) curve describes the natural state of most populations. They may
grow quickly in the beginning, but they will begin to use up all the resources (reaching CARRYING
CAPACITY of the environment) and will begin to die off. After this, the population becomes stable.
25. What is a limiting factor? Give an example. Limiting factors are the resources that keep populations
from increasing exponentially. Food, space, shelter, nesting sites, are some examples. Limiting
factors will affect the DISPERSION and DENSITY of populations; if a resource becomes scarce due to
too many organisms in one location, they will be forced to emigrate or may die from lack of resources.
26. Differentiate between a pioneer species and a climax community. A pioneer species is THE first species
to occupy bare rock during primary succession. A climax community is a stable community of mostly
mature species.
27. What is emigration? The generally permanent moving of an organism or species from one
environment to the other. Not to be confused with MIGRATION, which is the temporary change of
habitat, often due to weather.
28. What are the “zones” of a marine ecosystem, as described by ecologists. The marine zones are defined
by the amount of light or depth. The APHOTIC zones are those that receive little to no sunlight; the
PHOTIC zones receive ample sunlight for the species that live there. The BENTHOS is the bottom of a
marine ecosystem, where organisms such as flounder and halibut live.
29. In a biomass pyramid, at which level would we expect to find the greatest mass? Why? Since only 10%
of the available energy is passed on, the base of the pyramid would be expected to have the greatest
biomass. As energy is transferred, it can support fewer organisms at each trophic level.
30. Looking at a graph of human population growth, describe the historical events that created this growth
curve. Looking at the human population in the past 2000 years (since scientists still argue over when
we became “human” as we know us), population growth was very slow in the beginning, showing a
graph that rises very slowly, if you graph numbers vs. time. This is due to poor living conditions, lack
of technology and “good” medicine and health care. Also to how spread out communities of people
were in the early days of human existence. With the onset of the industrial revolution, science and
technology improved, allowing people to live and reproduce longer than ever before. This cause an
exponential upswing in the population, and consequently, the graph. There was a brief downturn
during the middle ages when the plague swept across Europe, but it rebounded nicely, and is still
increasing exponentially.