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Tortoise Tales
Biology - Unit IV
Students will:
Read a journal entry from a Galápagos field
Find examples of the five ecological
relationships (competition, predation,
parasitism, mutualism, and commensalism)
and take notes on the details they find in the
entry using a note-taking sheet.
This activity explores five important ecological relationships that make up a typical ecosystem:
1. Competition: Two or more organisms vying for the same food source or energy source.
Competition can be inter-specific (between individuals of different species) or intraspecific (between individuals of the same species).
2. Predation: One organism (the predator) kills and consumes another (the prey) for food
3. Parasitism: One organism (the parasite) takes food (energy) from another (the host)
without killing it.
4. Mutualism: A relationship involving two organisms in which both organisms benefit.
5. Commensalism: An ecological relationship between two organisms in which one
benefits and the other is not affected.
These community relationships help us to identify the niche that each organism occupies in its
habitat. They also help us identify and understand the interrelationships between and among
different organisms. The ecology of the Galápagos Islands has been affected by human
interference, both directly and through the non-native species that accompanied them to the
islands. The interrelationships of the native animals on the islands have been greatly influenced
by the introduction of dogs, goats, rats, pigs, as well as people.
Students will be asked to interpret the different types of ecological relationships that can be
identified with the giant tortoise. Apart from being a symbol of the islands, giant tortoises have
been hunted nearly to extinction and then salvaged from extinction by humans. Details of
human-tortoise interactions have been recorded for more than 300 years through letters and
journals of island visitors, and the tortoise has been the direct subject of study for many years by
scientists at the Charles Darwin Research Station.
1. Lead a class discussion about the five ecological relationships found in this
activity: competition, predation, parasitism, mutualism, and commensalism.
2. Divide students into teams of three of four and have them read Student
Printout 1 Dr. Betsy Jackson’s Journal. Although fictional, the activities and
observations described by Dr. Jackson are scientifically accurate, and her
Tortoise Tales
Biology - Unit IV
journal entry describes many examples of the relationships listed above. For
example, Dr. Jackson writes: “The sailors would take many animals and stack
them in the holds of their ships so they could have fresh food for
months.“ Here she is describing predation by humans on the tortoises.
3. Once students have read the journal, have the groups fill in Student Printout
2: Chart of Ecological Relationships. They should find examples of these
ecological relationships described in the journal entry.
1. Discuss examples of each type of ecological relationship found in Dr.
Jackson’s journal. For example:
Competition: Tortoises compete with one another as well as with the wild
goats for food.
Predation: The Galápagos tortoise was killed by sailors, pirates, and other
human visitors during the 19th century.
Parasitism: Mites and ticks suck blood from the tortoise.
Mutualism: The tortoise is "cleaned" of ticks and mites by the ground finches
that eat these parasites, and the tortoise benefits by not losing blood to the
parasitic insects.
Commensalism: The scientists at the Charles Darwin Research Station help
tortoises survive by raising the endangered young in specialized areas.
Humans receive no direct benefit from this action.
2.Describe the different factors that have contributed to the decreasing numbers of the giant
3.Ask students to give examples of ecological relationships found in their local habitats.
4.Review the food webs students created in the Galápagos Marine Food Webs activity.
Where do you find examples of these ecological relationships within the marine community?