28 CHAPTER 5 BIOMES: GLOBAL PATTERNS OF LIFE Chapter Objectives
Recognize the characteristics of some major terrestrial biomes as well as the factors that determine their distribution. Understand how and why marine environments vary with depth and distance from shore. Compare the characteristics and biological importance of major freshwater ecosystems. Summarize the overall patterns of human disturbance of world biomes.
Key Terms Biomass Epilimnion Hypolimnion
Littoral zone Stratification Vulnerable
Concept Review 5.1
Terrestrial Biomes
Biomes are areas with similar climate conditions, growth patterns, and vegetation types. Temperature and precipitation are the most important determinants of biome distribution. Latitude and elevation play a key role in temperature and precipitation change. Vegetation change associated with latitude is referred to as vertical zonation. Humid tropical regions are the most complex and biologically rich. The soil in tropical areas tends to be thin and nutrient-poor. The nutrients in tropical biomes are contained in the living organisms. When the living organisms are removed from the biome, it is unable to repopulate due to loss of nutrients. Tropical seasonal forests are drought tolerant. Drought tolerant areas may be more agriculturally productive and a healthier place for humans to live than a tropical rainforest. Tropical seasonal forests are endangered due to human activity.
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5.2
Grasslands and savannas are areas with too little rainfall to support trees. Grazing pressure from livestock threatens the native animals and plants. Deserts are areas with less than 30 cm of rain per year. Plants and animals in deserts are specially adapted to these conditions. Temperate grasslands have rich soils and are now used extensively for agriculture and grazing. Temperate forests are of two types—deciduous and coniferous. Deciduous forests can regrow quickly because of climate conditions. Coniferous and deciduous forests face extensive human exploitation, causing loss of habitat for native animals. The boreal forest and taiga support forests tolerant of cold temperatures, mainly conifers. The tundra biome has very low productivity and low diversity due to the extremely short growing season and cold temperatures. Tundra environments are not directly threatened by human activity but instead are impacted by global climatic change.
Marine Ecosystems
Marine ecosystems are not as well understood as land-based ecosystems. Marine ecosystems depend upon photosynthetic organisms to support the food web. Vertical stratification is a key feature of aquatic ecosystems. Temperature and light penetration determine biodiversity and productivity. The amount of oxygen in the water is determined by temperature— cold water holds more oxygen than warm water. Reefs are the best known marine ecosystems. Reefs occur in shallow water and have high biological diversity. Reefs are the most endangered ecosystem due to human activity. Mangroves are trees that grow in salt water along coastlines. Mangrove forests and swamps stabilize shorelines and provide habitat for young aquatic organisms. Estuaries are bays consisting of fresh and salt water mixing together. Estuaries are nutrient-rich and provide habitat for young aquatic organisms. Barrier islands are important structures that protect coastal shorelines and estuaries.
30 5.3
Freshwater Ecosystems
5.4
Lakes are stratified by light, oxygen, and temperature. Freshwater ecosystems are centers of biodiversity because they are a reliable source of water for land animals. Aquatic communities are highly impacted by nutrient excess and availability. Wetlands are relatively small areas that are essential for migrating birds and breeding due to high levels of productivity. Wetlands filter runoff and prevent flooding.
Human Disturbance
Humans interfere with biological productivity and habitat throughout the world. Temperate deciduous forests are the most human dominated biomes. Grasslands and chaparral are also highly impacted by humans. Tundra and arctic biomes are least disturbed due to their harsh climate and low productivity. Many islands have lost much of their native habitat.
Class Time: The Acorn outline suggests you devote 10 to 15 percent of the course on ecosystems, energy flow, biodiversity, and biogeochemical cycles. Plan to spend 5 to 7 days on this chapter.
Approach and Tips Begin the chapter by reviewing basic geography. Make sure students can differentiate between latitude and longitude, know the continents, and have an awareness of population centers. A great satellite image of the population centers of the world from NASA is found at http://veimages.gsfc.nasa.gov/1438/earth_lights.gif. If you can display the picture on the computer or television it will show students where the majority of people live and the difference between developing and developed countries. It is a good introduction to the next two chapters on populations. Once you have established these basics, turn to the map at the back of the book titled “A Guide to Map Reading.” This map contains a wealth of information regarding the world’s ecological regions. In your discussion of biome distribution, be sure to include the role altitude plays with regard to habitat and productivity.
31 In the Introduction section, students were told that they needed to make themselves the “experts” for a given topic. When studying biomes, students should first become the expert on the area in which they live: temperature, precipitation, seasons, and so on. After they are armed with this knowledge, they can obtain knowledge on a different biome in order to be able to discuss and compare the similarities and differences between where they live and another area. Students should be able to discuss a native plant and animal in each, along with the effect humans have had on the area. While it is tempting to have students research individual biomes and write a paper on the topic, there probably isn’t time within the course for this activity. Figures 5.5 to 5.12 include climate graphs. Most students are not familiar with graphs giving more than one set of information at a time. Be sure you discuss the individual components of each graph. You will probably have to call their attention to the changing scales, so that if they are presented with two or more graphs to compare side by side they do not overlook this detail. Figures 5.5, 5.6 and 5.10
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The penetration and concentration of light plays a key role in biological activity in both terrestrial and aquatic ecosystems. Students can experience the impact of the concentration of light by performing a simple experiment. Be sure to have students develop the investigation themselves. First, the angle of the sunlight striking the earth plays a role in its intensity. Shine a light on a sphere (representing the earth) at different angles (from the same distance) to measure how concentrated the light is and how much area the light covers. Students may want to have a thermometer in order to measure the temperature over a period of time in each location. To investigate light penetration, students could shine the light on a horizontal surface from increasing heights. Again, measuring the temperature and size of the beam will give students an indication of what happens below the surface of the water. If you have one available, a light meter would be a nice addition to the experiment.
33 Wetlands are important ecosystems due to their ability to clean and filter water. You can demonstrate this using a tall beaker, a piece of screen across the top, and a section of sod sitting on the screen. Pour silty water on the sod and watch the water that percolates through into the beaker. You may want to have students perform this activity with household products added to the water needing to be cleaned. Estuaries are areas where fresh water from a river joins salt water in a bay. Plants living there have adapted to the presence of salt in the water. Tolerance of salt is another activity your students could investigate. Have students prepare salt water in different concentrations. Moisten a paper towel with the water sample and place it in a plastic bag with radish seeds. The seeds will germinate in a few days and students can observe how tolerant they are of the salt. The same experiment can be performed using fertilizer in correlation with a discussion on runoff. Upon completion of this chapter, students should be aware that human impact occurs globally and that it takes a very long time to repair damage that has been done. Many times it is impossible for the ecosystem to recover from the impact. This would be a good time to have students think about legislation that protects the environment, as well as how they as individuals can lessen their impact on the ecosystem. Chapter 25 provides information and ideas for students to begin with. Each student should be able to discuss a law or other legislation that deals with the protection of ecosystems.
Applications Although you probably do not want to spend too much time having students do extensive research on each biome type, a short lab to allow students practice their observation skills while researching biomes is a good one-day activity. The students may need access to the Internet or to books in order to answer some of the questions. Gather different plants, soil, or animal skins and place them at stations around the room. Have students rotate from station to station recording their observations and answering the questions. An example of the one I use with plants is below. Biome Lab Purpose:
Observe representative plants of the different biomes and answer questions about the various biomes.
Procedure: Go to each station. Observe and sketch the plants. Answer the questions about each type of plant.
34 Station 1: a. b. c. d. e. Station 2: a. b. c. d. e. Station 3: a. b. c. d. e. f. Station 4: a. b. c. d. e.
Observe and draw the pine branch. Answer the following questions. In which biome would you typically find this type of plant? How does the shape and texture of the leaves of this plant help it survive in this biome? What would be some characteristics of the soil that would be found in this biome? What are the temperature and precipitation averages of this biome? Name at least three animals that are typically found in this biome. Observe and draw the cactus and answer the following questions. In which biome would you typically find this type of plant? How does the shape and texture of the spines on this plant help it survive in this biome? What would be some characteristics of the soil that would be found in this biome? What are the temperature and precipitation averages of this biome? Name at least three animals that are typically found in this biome. Observe and draw the lichen and answer the following questions. In which biome would you typically find this type of plant? How are lichens important in the process of succession? What two organisms compose lichens and what is this relationship? What would be some characteristics of the soil that would be found in this biome? What are the temperature and precipitation averages of this biome? Name at least three animals that are typically found in this biome. Observe and draw the two different grass plants and answer the questions. In which two biomes are these plants most typical? How do their roots and leaves help them adapt to this biome? What would be some characteristics of the soil that would be found in this biome? What are the temperature and precipitation averages of this biome? Name at least three animals that are typically found in this biome.
Station 5: Observe and draw the ball moss and the Spanish moss and answer the following questions. a. In which biome are these types of plants most typical? b. What is an epiphyte? c. What would be some characteristics of the soil that would be found in this biome? d. What are the temperature and precipitation averages of this biome? e. Name at least three animals that are typically found in this biome.
35 Then, have students diagram the hydrologic cycle and relate the location of biomes to how the cycle impacts the climate.
Common Mistakes and Misconceptions A few common mistakes that students make in this chapter are • Believing that the soils in the rainforest are fertile when in fact they are extremely poor. • Thinking that the desert is devoid of life (in fact it is very diverse). • Comprehending the hierarchal relationship between populations, communities, ecosystems, and biomes. • Understanding the impact that humans have on each biome, including global climate change and its effect on each. • Identifying the areas between two biomes and the necessity of leaving these areas as undisturbed as possible.
Suggested Website: Once again, the Enviroliteracy website has a wonderful page on all of the biomes and it includes pictures and related links. The link is found at http://www.enviroliteracy.org/category.php/3.html. Over on the right hand side of the page, in green, you will find links to biodiversity, steps toward conservation, and value of biodiversity, classifying species, drivers of biodiversity loss, habitats, biomes and eco-regions and hotspots of biodiversity.
Questions 1. What is the relationship between biodiversity and altitude? Discuss the two most important abiotic factors. 2. In a temperate forest the nutrients are held in the soil. In a tropical rainforest the nutrients are held in the living organisms. How does deforestation impact each of these biomes immediately? After 5 years? After 10 years? 3. Compare climate graphs of grassland and deciduous forest. Name three similarities and three differences. 4. Coral reefs are made up of colonies of the coral animal and an algae that lives within it. Explain the relationship between the two organisms. 5. What characteristics of the plants that live in a grassland make the grasslands soil so rich and deep? What characteristics of the plants that live in a rainforest make the soil there so poor and shallow?
