A study published in the journal Science in October 1999 showed that a community's biological stability is based on its species' ability to withstand environmental changes, such as warmer climates and chemical changes in the atmosphere.

Based on a report published in the January 6, 2000 issue of Nature magazine, one species well suited to adapting itself to such environmental changes are the marine iguanas of the Galapagos Islands. The Galapagos Islands are greatly affected by El Niño, which makes the cold, nutrient-rich currents usually coming from the west and south disappear. The change in current affects the algae populations that grow along the tidal basins of the rocky island shores

The Galapagos marine iguanas prefer to eat green and red algae, which are abundant during La Niña years. During El Niño, these algae disappear and up to 90% of the iguana population can starve to death. The iguanas that survive do so by eating brown algae that are difficult for them to digest. In order to make themselves more efficient at eating the reduced amount of food available, the iguanas shrink in body size. They may shrink as much as 20% of their body length. By shrinking, they increase their chances of survival.

• Read a report about the Galapagos iguanas adapting to El Niño: Galapagos iguanas shrink to survive El Niño
  
  
• Read about the Galapagos iguanas in general: Diving Dragons of the Galapagos
  
  
• Read a report about the biodiversity study (published in Science, October 1999): Adapting to environment called key

Learning about the Problem

There are many environmental changes that require species to adapt in order to survive, e.g., global warming, loss of habitat due to human expansion, water and air pollution. In order to learn more about how species adapt, you can work this series of Biology Explorer activities. (Requires Logal Express. Get a free trial subscription now.):

• Eating Efficiently, in which you examine the effect of different anatomical and physiological adaptations on the population growth of two related species
  
  
• Survival Strategies, in which you examine two survival strategies, known as K-strategy and r-strategy
  
  
• Environmental Changes, in which you examine the different responses species have to environmental changes and catastrophes

Note one interesting point about the Galapagos iguanas. Usually adaptation happens over many generations, due to "survival of the fittest." In the case of the iguana, adaptation is occurring within the lifetime of individual iguanas, which can grow and shrink repeatedly.

Thinking about the Problem

Apply what you learned in the Biology Explorer activities to the Galapagos iguanas.

• What anatomical and physiological adaptations do the iguanas make?
• Do they use a K- or an r-strategy for survival?
• What other adaptation mechanisms might you "recommend" to the iguanas?

For the Teacher: Extending the Problem

• The following sites present a variety of animals and how they adapt to changes in their ecosystem in order to survive. It is interesting to compare closely related species to see the similarities and differences.
  • Plant and Animal Adaptations to the Cold
  • Virtual Antarctica: The information is not presented in a section neatly titled "Adaptations," but it is there for curious students to find.
  • Sea World: Click on a species, and then on the Special Adaptations link.
  
  
  
• The Galapagos Islands, brought to public attention by the works of Charles Darwin, have long been of interest to biologists. Students who want to learn more about the Islands' ecosystem can visit these sites. Note that they also address the issue of adaptation for survival.
  • "Voyage to the Galapagos," is the transcript from the acclaimed Scientific American Frontiers program on PBS.
    
    
  • Virtual Galapagos, a cyber field trip, this site includes extensive information on the history and wildlife of the Islands. It presents detailed maps. (Note: The Education Workbook is no longer functional.)
    
    
  • Charles Darwin Research Station: This research station is dedicated to the preservation of the wildlife on the Galapagos Islands.
    
    
  • Galapagos Islands Wildlife Refuge: This site emphasizes the Galapagos wildlife.
  
  
  
• Students may want to learn more about the weather phenomena El Niño and La Niña. The following sites all offer a wealth of information.
  
  
  • Tracking El Niño
    
    
  • El Niño Rules
    
    
  • NOAA's El Niño Theme Page
    
    

  Note: The Virtual Antarctica and Virtual Galapagos sites listed above are both based on actual TerraQuest expeditions. You can have groups of students study each ecosystem and then compare and contrast their findings.