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The diverse environments of the Galápagos Islands, as well as their relative isolation from the rest of the world, helps promote the evolution of the unusual features of many Galápagos animals. The organisms of the Galápagos live in habitats that are harsh in many ways, but which also offer some advantages.
Because of the upwelling of cool, nutrient-rich waters, there is a greater abundance of marine food than is normally found in tropical waters. Temperatures on land, furthermore, tend to be cooler than elsewhere in the tropics because of the surrounding cool water. Until recently, the islands natural isolation prevented most large mammalian predators from establishing significant numbers. These elements had an impact on the first species that originally came to the islands. Over time, these species adapted through natural selection to survive in these unusual conditions.
Separate students into pairs and give each pair a copy of the Student Printout.
Ask each pair to view the Online Resource Galápagos Animal Gallery. In the gallery, paired photographs depict similar animals of the same size. Instruct your students to compare these images carefully and list any differences they notice, no matter how small, on the Student Printout. In addition, have them briefly describe each animals habitat and diet. Student descriptions for the pairs of images might look like this:
Lives in dry region
Lives in area of thick vegetation
Eats leaves high in trees
Eats grasses and leaves close to ground
Highly arched shell opening
Low, rounded shell opening
Lives near the water
Lives in dry regions on land
Long claws for gripping rocks
Found only in the Galápagos
Not found in the Galápagos
Small, vestigial wings
Long, well-developed wings
Streamlined body for swimming
Thick, strong legs for swimming
Once they have listed the differences between each pair of animals, have your students choose one animal from each pair and explain how its adaptations help the animal survive in its habitat.
Ask students to brainstorm a list of reasons why each of these closely related animals has evolved in different ways. How do these adaptations allow each organism to thrive in its particular habitat? Many Galápagos animals have adapted through natural selection and fit previously unoccupied habitats, so they may look very different from species found elsewhere in the worldor even in a different habitat right next door!
How have isolation and the unique conditions of the Galápagos Islands given rise to the unusual features of Galápagos animals? Ask students to give examples of features from the animals they compared. Once you have discussed the differences between each pair of animals, share the following information with the students:
Land Iguana A large relative of the South American and Caribbean terrestrial iguana, it has a round tail, a pointed nose and is brownish-red in color on top, yellow-orange underneath. It eats grass and other terrestrial plants, especially the large prickly-pear cactus.
Marine Iguana The only sea-going iguana in the world, it has a flat tail, a somewhat square nose, dark coloration, and partially webbed feet. The dark coloration allows young iguanas to be camouflaged by the dark lava on which they live and enables iguanas of all ages to absorb more heat from the sun.
Saddleback Tortoise One of the major groups of giant tortoises in the Galápagos Islands, it has an arched carapace (shell) in the front and has long legs, a long snout, and a long neck that allow it to reach for its food high above the ground. The saddleback type of Galápagos tortoise has been found on the dry areas of Española, Pinzon, Pinta, and Fernandina Islands.
Domed Tortoise Another of the major groups of giant tortoises in the Galápagos, it has a rounded shell, blunt snout, and a shorter neck. The dome-shaped tortoise is found on islands with rich vegetation like Santa Cruz and Isabela. The domed tortoise is larger and heavier, and the rounded shape of its shell allows it to move through the thick vegetation more easily than the saddleback tortoise.
Flightless Cormorant Found only in the Galapagos, it is dark with black coloration above and brown underneath. It has a streamlined body, strong legs, sparsely feathered vestigial wings (small and useless for flight), and webbed feet. The flightless cormorant uses its strong legs and webbed feet to swim and capture fish, eels, and octopuses.
Cormorant There are 28 other living species of cormorants, all of which use their wings for flight. Because these other cormorants have well-developed wing muscles, their bodies are not as streamlined as those of the flightless cormorant, but their legs, which are not used for swimming as much as with the flightless cormorant, are much more refined. Cormorants mainly eat fish.
How would existing Galápagos animals have to adapt to survive in other parts of the world or in different habitats? Would they survive if they were introduced into similar ecosystems elsewhere in the world? What kind of adaptations would allow existing Galápagos animals to survive in other habitats around the world? (Remember, organisms cant adapt because they want to or need to.)
This activity uses the following principles of the National Science Education Standards for grades 5-8:
Structure and Function in Living Systems
Living systems at all levels of organization demonstrate the complementary nature of structure and function. Important levels of organization for structure and function include cells, organs, tissues, organ systems, whole organisms, and ecosystems.
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.
Behavior is one kind of response an organism can make to an internal or environmental stimulus. A behavioral response requires coordination and communication at many levels, including cells, organ systems, and whole organisms. Behavioral response is a set of actions determined in part by heredity and in part from experience.
An organisms behavior evolves through adaptation to its environment. How a species moves, obtains food, reproduces, and responds to danger are based in the species evolutionary history.
Populations and Ecosystems
Populations of organisms can be categorized by the function they serve in an ecosystem. Plants and some microorganisms are producers--they 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.
Diversity and Adaptations of Organisms
Millions of species of animals, plants, and microorganisms are alive today. Although different species might look dissimilar, the unity among organisms becomes apparent from an analysis of internal structures, the similarity of their chemical processes, and the evidence of common ancestry.
Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment.
Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow its survival. Fossils indicate that many organisms that lived long ago are extinct. Extinction of species is common; most of the species that have lived on the earth no longer exist.