
The Biosphere and Human Effects Chapter 18
18.3 Types of Land Ecosystems • Different climates support different types of plant life, which support different types of animals • Biome • Type of ecosystem that can be characterized by its climate and dominant vegetation
Deserts • Low rainfall produces deserts at latitudes around 30° north and south, where dry air descends • Desert • Biome where little rain falls, humidity is low, and the main plants store water in their tissues or tap into water sources deep underground
Grasslands • Grasslands form at midlatitudes in the interior of continents between deserts and temperate forests • Grasslands • Biome where grasses and other low-growing plants are adapted to warm summers, cold winters, periodic fires, and grazing animals • Example: shortgrass and tallgrass prairies
Chaparral • Dry shrublands (chaparral) are found in South Africa, California, and Mediterranean regions • Chaparral • Biome where cool, wet winters and hot, dry summers support shrubs adapted to periodic fires
Grassland, shrublands, and woodlands Fig. 18-5c, p. 365
Tropical Rain Forests • At the equator, high rainfall and temperature support tropical rain forests with broadleaf trees that remain green year-round • Tropical rain forest • Species-rich tropical biome in which continual warmth and rainfall allows dominant broadleaf trees to grow all year
Deciduous Broadleaf Forests • Deciduous broadleaf trees are adapted to regions that cannot sustain year-round growth • Deciduous tree • A tree that drops all its leaves annually just before a season that does not favor growth • Temperate deciduous forest • Biome dominated by trees that drop all their leaves and go dormant during a cold winter
Coniferous Forests • Conifer forests dominate high latitudes in the Northern Hemisphere and other regions where drought, poor soil, or periodic fires prevent broadleaf trees from taking hold • Taiga (boreal forest) • Extensive northern biome dominated by conifers • A cold, dry season alternates with a cool, rainy season
Tundra • Tundra forms at high latitudes and high altitudes • Arctic tundra • Youngest, most northerly biome, dominated by low plants adapted to a short growing season and a layer of permanently frozen soil (permafrost) • Alpine tundra • High-altitude biome dominated by low plants
18.4 Types of Aquatic Ecosystems • Composition of aquatic communities is influenced by gradients of sunlight penetration, water temperature, salinity, dissolved gases, rate of water movement, and depth
Freshwater Ecosystems • A lake is a standing body of water • Light decreases with depth; different communities live at different depths and distances from shore • Streams and rivers are flowing water ecosystems • Physical characteristics that vary along its length influence the types of organisms that live in it • Fast-flowing cooler water holds more oxygen than warmer, slower-moving water
Marine Ecosystems • Estuary • A semi-enclosed area where nutrient-rich water from a river mixes with seawater • Highly productive ecosystem • Seashores • Rocky shores have grazing food chains based on algae; sandy shores have detrital food chains
Marine Ecosystems • Benthic province • The ocean’s rocks and sediments • Pelagic province • The ocean’s open waters • In upper waters, photosynthetic organisms form the basis of grazing food chains • Deeper communities subsist on materials that drift down from above
Marine Ecosystems • Coral reefs • Formation composed of secretions of coral polyps, found in tropical, sunlit seas • Main producers are photosynthetic protists that live inside the coral’s tissues • Coral bleaching • Stress response in which a coral expels the photosynthetic protists in its issues
water of the open ocean water over continental shelf air at ocean surface continental shelf sunlit water Pelagic Province 0 “twilight” water 200 sunless water 1,000 2,000 Benthic Province 4,000 deep-sea trenches 11,000 depth (meters) Fig. 18-10a, p. 369
Marine Ecosystems • Seamount • An undersea mountain • Hydrothermal vent • Place where hot, mineral-rich water streams out from an underwater opening in the Earth’s crust • Producers are prokaryotes that strip energy from minerals
Comparing Aquatic Ecosystems • In well-lit upper waters, photosynthetic producers are the base for grazing food chains • Detritus drifting down from above sustains most deep-water communities in lakes and oceans • Hydrothermal vent communities on the ocean floor are sustained by energy that prokaryotes harvest from minerals
18.5 Human Effects on the Biosphere • The increasing size of the human population and its increasing industrialization have far-reaching effects on the biosphere • Effects range from extinction of individual species to global climate change
Increasing Species Extinctions • Humans are increasing the rate of species extinctions by degrading, destroying, and fragmenting natural habitats, by overharvesting species, and by introducing exotic species
Increasing Species Extinctions • Endangered species • Faces extinction in all or part of its range • Threatened species • Likely to become endangered in the near future • Endemic species • Evolved in one place and is found nowhere else
Living or Extinct? • Ivory-billed woodpecker
Threatened Species • Habitat destruction threatens the eastern prairie fringed orchid – aquifer depletion and pollution endanger Texas blind salamanders
The Global Impact of Human Activities • Human activities threaten entire ecosystems • Desertification • Deforestation • Air pollution and acid rain • Water pollution • Trash in aquatic ecosystems • Air pollution and the ozone hole • Greenhouse gases and global warming
Desertification • Poor agricultural practices turn grasslands or woodlands into deserts • US Great Plains (the Great Dustbowl) • Sahara Desert • Desertification • Conversion of grassland or woodlands to desertlike conditions
Desertification • Dust from the Sahara over the Atlantic Ocean
Deforestation • Human activities strip woodlands of trees • Flooding • Landslides • Increases atmospheric CO2 • Decreases atmospheric oxygen • Deforestation • Removal of all trees from a large tract of land
Deforestation • Clearing tropical forests in Brazil
Pollution • Human activities generate pollutants that kill animals and damage ecosystems • Pollutant • Natural or man-made substance released into the environment in greater than natural amounts, and that damages the health of organisms
Acid Rain • Acid rain • Rainfall contaminated by acidic pollutants • Burns trees, kills fish, leaches nutrients from soil • Caused by pollutants that combine with water vapor in the atmosphere to form acids • Sulfuric acid from sulfur dioxides from coal-burning power plants and factories • Nitric acid from nitrogen oxides from vehicles and power plants that burn gas and oil
Other Sources of Water Pollution • Pollution from point sources may be identified; dealing with pollution from nonpoint sources is more difficult • Industrial chemicals and heavy metals • Oil from vehicles • Runoff of fertilizers, pesticides, herbicides, and animal wastes • Sewage and excreted prescription drugs • Sediments