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BIO153 Ch 50 SN.pdf

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Christoph Richter

Freeman, Biological Science, 4e, Chapter 50 Chapter 50 - An Introduction to Ecology Learning Objectives: Students should be able to … • Explain the goals of the branch of biology called ecology. • List the primary factors that limit the distribution and abundance of both aquatic species and terrestrial species. • Understand how climate varies and how it is changing. • Explain how a species distribution is affected by historical, biotic, and abiotic factors. Lecture Outline I. Areas of Ecological Study A. Ecologists study how organisms interact with their environment at different hierarchical levels. B. Organismal ecology 1. At the organismal level, researchers focus on how individual organisms interact with their environment. 2. Organismal ecologists study morphological, physiological, and behavioral adaptations that allow individuals to be successful in a particular habitat. 3. The sockeye salmon may be used to illustrate organismal ecology. (Fig. 50.1a) a. Sockeye salmon spend four or five years eating and growing in the ocean. b. They swim hundreds to thousands of miles to return to the stream where they hatched. c. After they breed in that streambed, the adults die. d. Scientists are interested in studying salmon breeding habits, traits that make them reproductively successful, and how they adapt to the changing environment as they migrate. C. Population ecology 1. A population is a group of individuals of the same species that live in the same area at the same time. 2. Population ecology seeksto understand how the numbers of individuals in a population change over time. a. These studies have helped predict the fate of endangered species. b. For example, population ecology studies have predicted that salmon populations are in danger based on their recent decline due to man-made changes to their environment. (Fig. 50.1b) D. Community ecology 1. A biological community consists of the species that interact with one another in a particular area. 2. Community ecologists study the nature and consequences of the interactions among species in a community. © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 50 3. Community ecologists are often called on to predict how human actions will affect ecological communities in the future. 4. Salmon as an example of a community ecology study a. Salmon eat smaller fish and are eaten by both bigger fish and marine and land mammals. (Fig. 50.1c) b. In both habitats, salmon are affected by disease and parasites as well as human disturbances such as damming and overfishing. E. Ecosystem ecology 1. An ecosystem consists of all the organisms that live in a certain area plus all nonliving, abiotic components such as air, water, and soil. 2. Ecosystem ecologists study how nutrients cycle and energy flows through an ecosystem. 3. Because humans are changing the way that nutrients cycle, ecosystem ecology is now particularly important. a. Global warming has become important to public policy. b. Ecosystem ecologists are called on to predict the impact of pollution on Earth and its inhabitants. 4. Sockeye salmon and their ecosystem a. Salmon form a link between marine and freshwater ecosystems as they carry nutrients and energy from one ecosystem to the other. (Fig. 50.1d) b. Human-induced changes in these ecosystems will profoundly affect salmon populations. F. How do ecology and conservation efforts interact? 1. Conservation biology is the effort to study, preserve, and restore threatened populations, communities, and ecosystems. 2. Ecologists study how interactions between organisms and their environments result in a particular species being found in a particular area at particular population size. Conservation biologists apply these data to preserve species and restore environments. II. Types of Aquatic Ecosystems A. An organism’s environment has both physical and biological components. 1. The abiotic or physical components include temperature, precipitation, sunlight, and wind. 2. The biotic (“living”) components consist of other members of the organism’s own species as well as individuals of other species. B. Nutrient availability 1. Levels of nutrients such as nitrogen and phosphorus limit growth rates in photosynthetic organisms. 2. Ocean upwellings bring nutrients to the surface. (Fig. 50.2) 3. Each year, lakes experience fall and spring turnovers, which redistribute freshwater nutrients as well as oxygen. (Fig. 50.3) © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 50 C. Water flow 1. Water movement presents a physical challenge; it can literally sweep organisms off their feet. 2. Marine intertidal organisms are exposed to air periodically. D. Water depth 1. Water depth dictates how much light reaches the organisms that live in a particular region. 2. Water removes light in the blue and red regions of the visible spectrum. (Fig. 50.4a) 3. In pure seawater, the total amount of light available at a depth of 10 m is less than 40% of the amount available at the surface, and virtually no light reaches depths greater than 40 m. (Fig. 50.4b) E. Freshwater environments: lakes and ponds 1. Ponds are small, while lakes are big enough that the water in them can be mixed by the wind. 2. Biologists describe the structure of lakes and ponds by naming five zones: (Fig. 50.5) a. The littoral zone consists of shallow waters near shore, where flowering plants are rooted. b. The limnetic zone is offshore and is composed of water that receives enough light to support photosynthesis. c. The benthic zone is made up of the substrate. d. Regions of the littoral, limnetic, and benthic zones that receive sunlight are part of the photic zone. e. Portions of a lake or pond that do not receive sunlight make up the aphotic zone. 3. As the temperature of the surface changes throughout the year, water from different temperatures can mix. This allows well- oxygenated water from the surface to reach the benthic zone and nutrient-rich water from the benthic zone to enter the littoral and limnetic zones. 4. Cyanobacteria, algae, and other microscopic organisms are collectively called plankton and live in the photic zone. Animals that consume detritus are common in the benthic zone. 5. Students should be able to predict which zone of lakes and ponds produces the most grams of organic material per square meter per year, and explain their logic. F. Freshwater environments: wetlands 1. Wetlands are shallow-water habitats where the soil is saturated with water for at least part of the year. 2. Wetlands are distinct from lakes and ponds for two reasons: a. They have only shallow water. b. They have emergent vegetation⎯that is, plants that grow above the surface of the water. 3. Marshes and swamps are wetland types characterized by a slow but steady flow of water. © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 50 4. Bogs develop depressions where water flow is low or nonexistent. Bog water is oxygen poor and acidic. (Fig. 50.6a) 5. Marshes lack trees and typically feature grasses. (Fig. 50.6b) 6. Swamps are dominated by trees and shrubs. (Fig. 50.6c) 7. Students should be able to explain why carnivorous plants, which capture and digest insects, are relatively common in bogs but rare in marshes and swamps. G. Freshwater environments: streams 1. Streams are bodies of water that move constantly in one direction. 2. Creeks are small and rivers are large. 3. The structure of a stream varies along its length. (Fig. 50.7) a. At its mountain origin, a stream is usually cold, narrow, and fast. b. As it reaches its ocean or lake destination, it becomes larger, warmer, and slower. 4. The organisms in a stream vary along its length. a. Small, fast-moving streams rarely have photosynthetic organisms. b. Wider, slower streams have algae and plants. 5. Students should be able to explain why fish species found in cold, fast-moving streams tend to be much more active than fish species found in warm, slow-moving streams. H. Freshwater/marine environments: estuaries 1. Estuaries are where rivers meet the ocean, which means that freshwater mixes with saltwater. (Fig. 50.8) 2. Because the water is shallow in estuaries and nutrients are constantly renewed by the incoming stream, estuaries are very productive environments. 3. Salinity has dramatic effects on osmosis and water balance, so species that live in estuaries have adaptations that allow them to cope with variations in salinity. 4. Students should be able to explain why estuaries and freshwater marshes contain few of the same species, even though they are both shallow-water habitats filled with rooted plants. I. Marine environments: the ocean 1. The world’s oceans form a continuous body of saltwater and are remarkably uniform in chemical composition. 2. Biologists describe the structure of an ocean by naming six regions: (Fig. 50.9) a. The intertidal zone (littoral zone) is along the shore. b. The neritic zone extends from the intertidal zone to an ocean depth of about 200 m (the edge of the continental shelf). c. The oceanic zone encompasses the remainder and largest of the ocean environments. d. The benthic zone is the area at the ocean bottom. © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 50 e. The photic zone receives sunlight to support photosynthesis. f. The aphotic zone is the area that is too dark to support photosynthesis. 3. Tides and wave action are major influences in the intertidal zone. 4. Large-scale currents circulate water in the oceanic zone in response to prevailing winds and Earth’s rotation. 5. Each zone is populated by distinct species. 6. In the tropics, shallow portions of the neritic zone may support coral reefs—among the most productive environments in the world. 7. Students should be able to predict whether animals that live in the aphotic zone have functioning eyes. III. Types of Terrestrial Ecosystems A. Each biome in the world is associated with a particular set of abiotic conditions. 1. Climate (temperature andprecipitation) affects the productivity of terrestrial biomes. (Fig. 50.10) 2. Weather consists of the specific short-term atmospheric conditions of temperature, moisture, sunlight, and wind. a. Temperature is critical because the enzymes that make life possible work most efficiently in only a narrow range of temperatures. b. Moisture is significant because it is required for life, and terrestrial organisms constantly lose water. c. Sunlight is essential because it is required for photosynthesis. d. Wind is important because it exacerbates the effects of temperature and moisture. 3. The nature of the biome that develops in a particular region is governed by the average annual precipitation and the annual variation in temperature and precipitation. Each biome contains species that are adapted to a particular temperature and moisture regime. 4. On land, photosynthesis and plant growth are maximized when temperatures are warm and conditions are wet; conversely, photosynthesis cannot occur efficiently at low temperatures or under drought stress. 5. Net primary productivity (NPP) is the total amount of carbon that is fixed per year minus the amount of fixed carbon oxidized during cellular respiration. a. NPP is often estimated by measuring aboveground biomass— the total mass of living plants, excluding roots. B. Terrestrial biomes: tropical wet forest 1. Also called rain forests, tropical wet forests are found in equatorial regions where the temperature and rainfall are high and variation is low. (Fig. 50.11) 2. These forests are not seasonal (aseasonal). © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 50 a. Plants grow all year long. b. There is no complete, seasonal loss of leaves. 3. Year-round growing conditions results in vigorous growth, high productivity, and large amounts of aboveground biomass. (Fig. 50.12) 4. Wet forests contain the highest amounts of biodiversity on Earth. a. More than 200 tree species may be found in one 10 m × 100 m plot. b. Wet forests may contain 30 million species of arthropods alone. 5. Wet forests contain extraordinary structural diversity. a. A multilayered tree canopy (the uppermost layers of branches) is intermingled with vines, epiphytes, shrubs, and herbs. (1) Epiphytes are plants that grow entirely on other plants. b. This diversity presents a vast array of habitat types for animals. 6. Students should be able to explain why the presence of vines and epiphytes increases the productivity of tropical wet forests. C. Terrestrial biomes: subtropical deserts 1. Subtropical deserts are found in bands about 30° latitude north and south of the equator. 2. Mean monthly temperatures vary but never fall below freezing. 3. The most striking feature is their low annual precipitation. (Fig. 50.13) a. Low precipitation in deserts results in very low productivity. b. Individual plants are widely spaced due to intense competition for water. (Fig. 50.14) 4. Desert species must cope with extreme temperatures and aridity. a. Adaptations are both morphological and physiological. Example: cacti. b. Traits that allow plants to escape drought include dormancy and short reproductive stages. 5. Students should be able to explain why most desert plant species have either no leaves or leaves with a small surface area. D. Terrestrial biomes: temperate grasslands 1. Temperature grasslands are found throughout central North America and the heartland of Eurasia. 2. Precipitation is still quite low, but annual precipitation is much greater than the amounts recorded in deserts. (Fig. 50.15) 3. Temperatures are moderate (temperate) but highly seasonal. a. Temperature variation dictates a well-defined growing season. b. Plant growth occurs only in months that have adequate moisture and warmth. 4. These areas are also called prairies or steppes. © 2011 Pearson Education, Inc. Freeman, Biological Science, 4e, Chapter 50 5. Grasses are the main life-form because conditions are too dry to support tree growth and too cold and seasonal to support drought- adapted desert species. (Fig. 50.16) 6. Grasslands can develop in forested regions if recurring fires burn out encroaching trees. a. Fires can occur naturally from lightening strikes. b. Fires may be set as a management tool. c. The plants that dominate grasslands are tolerant of fire and quickly resprout after burning. 7. Productivity is lower than in forests; however, grassland soil is highly fertile. a. The subsurface is packed with roots that add organic material to the soil as they decay. b. Soil retains nutrients because the rainfall is low enough to keep key
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