Click on this icon to download free Adobe Acrobat Reader software. You will need this program to access materials in PDF format.
This activity explores five important ecological relationships that make up a typical ecosystem:
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 intra-specific (between individuals of the same species).
Predation: One organism (the predator) kills and consumes another (the prey) for food (energy).
Parasitism: One organism (the parasite) takes food (energy) from another (the host) without killing it.
Mutualism: A relationship involving two organisms in which both organisms benefit.
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.
Lead a class discussion about the five ecological relationships found in this activity: competition, predation, parasitism, mutualism, and commensalism.
Divide students into teams of three of four and have them read Student Printout 1 Dr. Betsy Jacksons Journal. Although fictional, the activities and observations described by Dr. Jackson are scientifically accurate, and her 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.
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.
Discuss examples of each type of ecological relationship found in Dr. Jacksons 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.
Describe the different factors that have contributed to the decreasing numbers of the giant tortoise.
Ask students to give examples of ecological relationships found in their local habitats.
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?
This activity uses the following principles of the National Science Education Standards for grades 5-8:
Understandings about Scientific Inquiry
Different kinds of questions suggest different kinds of scientific investigations. Some investigations involve observing and describing objects, organisms, or events; some involve collecting specimens; some involve experiments; some involve seeking more information; some involve discovery of new objects and phenomena; and some involve making models.
Regulation and Behavior
All organisms must be able to obtain and use resources, grow, reproduce, and maintain stable internal conditions while living in a constantly changing external environment.
Populations and Ecosystems
A population consists of all individuals of a species that occur together at a given place and time. All populations living together and the physical factors with which they interact compose an ecosystem.
Populations of organisms can be categorized by the function they serve in an ecosystem. Plants and some microorganisms are producersthey make their own food. All animals, including humans, are consumers, which obtain food by eating other organisms. Decomposers, primarily bacteria and fungi, are consumers that use waste materials and dead organisms for food. Food webs identify the relationships among producers, consumers, and decomposers in an ecosystem.
For ecosystems, the major source of energy is sunlight. Energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis. That energy then passes from organism to organism in food webs.
The number of organisms an ecosystem can support depends on the resources available and abiotic factors, such as quantity of light and water, range of temperatures, and soil composition. Given adequate biotic and abiotic resources and no disease or predators, populations (including humans) increase at rapid rates. Lack of resources and other factors, such as predation and climate, limit the growth of populations in specific niches in the ecosystem.
This activity is an online modification of a chapter from NSTAs publication Ecology and Evolution: Islands of Change. Visit the Ecology and Evolution Web page to learn more about the range of Galápagos-oriented activities that can be found in the full-length book.