Download Galapagos Food Web Activity Part I

Name ___________________ Per # _______ Date ___________
Galapagos Food Webs
Background:
Every ecosystem has its own food web. This activity focuses on a food web for the marine
ecosystem in the coastal waters of the Galapagos Islands. The ecology of a marine food web is
influenced by environmental factors such as the climate, the salinity of the water, the ocean
currents, and the winds.
In most ecosystems, the first level of a food web is composed entirely of “producers” –
organisms such as plants that get their energy directly from the sun. In some others, there is
an outside energy source such as thermal vents in the deep oceans. Food webs are divided
into trophic levels; the organisms in a particular trophic level are all the same number of steps
away from the primary producers on the lowest, or first, level.
The higher levels of a food web, by contrast, are composed of “consumers” – organisms that
get their energy by eating other organisms. The second level is composed of herbivores,
which get their energy by eating producers; the third level is composed of carnivores, which
get their energy by eating herbivores; and the highest levels are composed of carnivores that
eat other carnivores.
Decomposers exist at every level of a food web. Decomposers are those organisms that get
their energy by devouring the dead organisms from every food web level. Whether breaking
down dead plants to the inorganic nutrients that make up the soils, or decomposing dead
animals, these organisms are as important in a food web as all of the others. Decomposers
help to replenish the nutrients that are essential to the producers and help to rid the
ecosystem of dead organisms that would quickly pile up.
Pre-activity Questions:
1. Read the background information and answer the following questions:
a. Where does this activity focus its food web on? ___________________________________
b. In most ecosystems, the first level of a food web is composed of _________________________.
c. The second level is composed of ______________________________.
d. The third level is composed of _______________________________.
e. The highest level is composed of __________________________________.
f. ____________________________ exist at every level in the food web.
g. Decomposers get their energy by ______________________________________________.
h. Decomposers help to replenish _____________________________________.
2. Read the information about each animal on the attached pages. You may use the following 2 charts to help
plan and organize your food web.
What
does the
animal
eat?
Ex: Killer
Whale
Fur seals, sea
lions,
dolphins,
humpback
whales, large
fish
What
does the
animal
eat?
3. You and your group will work on #3 and #4 together and turn in one food web. Color the animals based on
the following groups:
Energy source …Yellow
1 st level Carnivores (2nd order consumers)...Orange
Producers…Green
2 nd level Carnivores (3rd order consumers)…Red
Herbivores (1st order consumers)…Blue
Scavengers…Purple
Decomposers…Brown
4. Carefully cut them out.
5. Using tape or glue, attach the animals to your large piece of paper to make a food web. You must have a
MINIMUM of 13 animals in your food web (at least 2 from each trophic level and one decomposer). Be sure to
label every organism and each trophic level.
REMEMBER: The arrows go in the direction of ENERGY FLOW.
Analysis Questions:
1. At which levels of the food web would one expect to find:
A. The largest population? _____________________________
B. The smallest population? ___________________________
C. The largest adult organism? ________________________
D. The smallest adult organism? _______________________
2. Which organisms might be described as “top carnivores”? How would your ecosystem be affected if all top
carnivores were removed?
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3. Think about how changes in the environment could affect populations of organisms. Below are 2 examples
of how environmental changes can have severe consequences on life in the Galapagos. Come up with your
own example of how a change in a food web can affect the population of an organism. See below for
examples: ______________________________________________________________________________
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Example 1: El Niño. Marine iguanas primarily eat ulva, a type of green algae that looks like lettuce, which
grows on ricks in the cool, shallow waters around the islands. If, during an El Niño, the ocean temperatures
were to rise, the ulva could disappear. As other types of algae are not as nutritious for the iguanas, iguanas
would suffer from malnutrition and weaken from disease or predation before often before they die of hunger.
Example 2: Upwellings. As the wind moves surface water away from the coast cold subsurface waters are
brought up to the surface in a process known as “upwelling”. Upwellings bring cold, mineral- and nutrientrich water from the deeper sea levels close to shore. The algae population explodes! Herbivores that eat the
algae, such as marine iguanas, thrive. But they wear down the reefs upon which they feed and the large reefs
cannot survive. Then the other animals that need a large reef to survive would have to move elsewhere or die.