Cecie Starr Christine Evers Lisa Starr www.cengage.com/biology/starr Chapter 42 Ecosystems (Sections 42.1 - 42.6) Albia Dugger • Miami Dade College 42.1 Too Much of a Good Thing • Human activities can disrupt nutrient cycles that have been operating since long before humans existed • Phosphorus is often a limiting factor for aquatic producers, and sudden addition of phosphorus (eutrophication) causes algal blooms that cloud water and threaten aquatic species • eutrophication • Nutrient enrichment of an aquatic ecosystem Experiment: Phosphorus Enrichment Experiment: Phosphorus Enrichment nitrogen, carbon added nitrogen, carbon, phosphorus added Fig. 42.1, p. 709 42.2 The Nature of Ecosystems • In ecosystems, organisms and their environment interact through a one-way flow of energy and a cycling of nutrients • Ecosytems require ongoing inputs of energy (open systems) • Nutrients taken up by producers are returned to the environment by decomposers, then taken up again Energy Flows, Nutrients Cycle • Light energy that enters the system returns to the environment as heat • Nutrients are continually recycled Energy Flows, Nutrients Cycle light energy Producers plants; photosynthetic protists and bacteria energy in chemical bonds materials cycling Consumers animals; fungi; heterotrophic protists, bacteria, and archaeans heat energy Fig. 42.2, p. 710 Energy Flows, Nutrients Cycle light energy Producers plants; photosynthetic protists and bacteria energy in chemical bonds materials cycling Consumers animals; fungi; heterotrophic protists, bacteria, and archaeans heat energy Stepped Art Fig. 42.2, p. 710 ANIMATION: One-way energy flow and materials cycling To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Primary Producers and Production • An ecosystem runs on energy captured by primary producers • primary producer (autotroph) • An organism that obtains energy and nutrients from inorganic sources to build organic compounds • primary production • Rate at which producers capture and store energy • Varies by ecosystem, season, and nutrient availability The Roles of Consumers • Consumers are described by their diets: • Herbivores (plants) • Carnivores (animal flesh) • Parasites (tissues of a living host) • Omnivores (plants and animals) • Detritivores (detritus) • Decomposers (waste and remains) Key Terms • consumer • Organism that obtains energy and carbon by feeding on tissues, wastes, or remains of other organisms • detritivore • Consumer that feed on small bits of organic material • decomposer • Organism that feeds on biological remains and breaks organic material down into its inorganic subunits Energy Flow and Nutrient Cycling • Heat energy is not recycled: • Energy captured by producers is converted to bond energy in organic molecules, and released by metabolic reactions that give off heat • Nutrients are recycled: • Producers take up inorganic molecules (nutrients) from the environment to form organic molecules • Decomposers break down organic molecules and return nutrients to the environment ANIMATION: The role of organisms in an ecosystem To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE ANIMATION: Food chain To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 42.3 Food Chains • Food chains describe how energy and materials are transferred from one organism to another • food chain • Description of who eats whom in one path of energy in an ecosystem – transfer of energy to higher trophic levels • trophic level • Position of an organism in a food chain A Food Chain • First trophic level (primary producer): • Autotroph (grass) converts light to chemical energy • Second trophic level (primary consumer): • Grasshopper eats grass • Third trophic level (second-level consumer): • Bird eats grasshopper • Fourth trophic level (third-level consumer): • Coyote eats bird A Food Chain A Food Chain Fourth Trophic Level Third-level consumer coyote Third Trophic Level Second-level consumer sparrow Second Trophic Level Primary consumer grasshopper First Trophic Level Primary producer big bluestem grass Fig. 42.3, p. 711 A Food Chain Fig. 42.3.1, p. 711 A Food Chain Fig. 42.3.2, p. 711 A Food Chain Fig. 42.3.3, p. 711 A Food Chain Fig. 42.3.4, p. 711 Food Chain Limits • Energy captured by producers usually passes through no more than four or five trophic levels • The length of food chains is restricted by the inefficiency of energy transfers • Only 5-30% of energy in an organism at one trophic level ends up in tissues of an organism at the next trophic level 42.4 Food Webs • Food chains of an ecosystem cross-connect as a food web • Food web structure reflects environmental constraints and the inefficiency of energy transfers among trophic levels • food web • Set of cross-connecting food chains Types of Food Chains • Food webs include two types of interconnecting food chains: • grazing food chain • Energy transferred from producers to herbivores (grazers) • detrital food chain • Energy transferred directly from producers to detritivores (worms or insects) • Major food chain in land ecosystems Arctic Food Web Arctic Food Web Higher Trophic Levels human (Inuk) arctic wolf arctic fox A sampling of carnivores that feed on herbivores and one another gyrfalcon snowy owl ermine mosquito flea Second Trophic Level Parasitic consumers feed at more than one trophic level. Major parts of the buffet of primary consumers (herbivores) vole arctic hare lemming Detritivores and decomposers (nematodes, annelids, saprobic insects, protists, fungi, bacteria) First Trophic Level This is just part of the buffet of primary producers. grasses, sedges purple saxifrage arctic willow Fig. 42.4, p. 712 Arctic Food Web Fig. 42.4.1, p. 712 Arctic Food Web Fig. 42.4.2, p. 712 Arctic Food Web Fig. 42.4.3, p. 712 Arctic Food Web Fig. 42.4.4, p. 712 Arctic Food Web Fig. 42.4.5, p. 712 Arctic Food Web Fig. 42.4.6, p. 712 Arctic Food Web Fig. 42.4.7, p. 712 Arctic Food Web Fig. 42.4.8, p. 712 Arctic Food Web Fig. 42.4.9, p. 712 Arctic Food Web Fig. 42.4.10, p. 712 Arctic Food Web Fig. 42.4.11, p. 712 Arctic Food Web Fig. 42.4.12, p. 712 Arctic Food Web Fig. 42.4.13, p. 712 Arctic Food Web Fig. 42.4.14, p. 712 Arctic Food Web human (Inuk) arctic wolf Higher Trophic Levels A sampling of carnivores that feed on herbivores gyrfalcon snowy owl and one another Second Trophic Level Major parts of the buffet of primary consumers (herbivores) vole arctic hare lemming First Trophic Level This is just part of the buffet of primary grasses, sedges purple saxifrage arctic fox ermine mosquito flea Parasitic consumers feed at more than one trophic level. arctic willow Detritivores and decomposers (nematodes, annelids, Stepped Art saprobic insects, Fig. 42.4, p. 712 ANIMATION: Food webs To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Trophic Interactions in Ecosystems • Understanding links in food webs helps ecologists predict how ecosystems respond to change • Computer models show that all species in an ecosystem are closely linked by trophic interaction • Even in large communities with many species, 95% of species are within three links of one another A Land Food Web ANIMATION: Rainforest food web To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE BBC Video: Seed Banks Helping to Save Our Fragile Ecosystem BBC Video: The Vanishing Honeybee’s Impact on Our Food Supply BBC Video: What is the Environmental Cost for Your Food? 42.5 Ecological Pyramids • Ecological pyramid diagrams illustrate the inefficiency of transfers between trophic levels • A biomass pyramid shows amounts of organic material in bodies of organisms at each trophic level at a specific time • An energy pyramid shows energy flow through each trophic level in a given interval Florida Aquatic Ecosystem Florida Aquatic Ecosystem Fig. 42.6, p. 713 Florida Aquatic Ecosystem top carnivores (gar and bass) 1.5 carnivores (smaller fishes, invertebrates) 11 herbivores (plant-eating fishes, invertebrates, turtles) 37 producers (algae and aquatic plants) 5 809 detritivores (crayfish) and decomposers (bacteria) A Biomass pyramid (grams per square meter) Fig. 42.6a, p. 713 Florida Aquatic Ecosystem top carnivores (gar and bass) 1.5 carnivores (smaller fishes, invertebrates) 11 herbivores (plant-eating fishes, invertebrates, turtles) 37 producers (algae and aquatic plants) 5 809 detritivores (crayfish) and decomposers (bacteria) A Biomass pyramid (grams per square meter) Stepped Art Fig. 42.6a, p. 713 Florida Aquatic Ecosystem Fig. 42.6b, p. 713 Florida Aquatic Ecosystem top carnivores carnivores herbivores 21 detritivores + decomposers = 5,060 383 3,368 producers 20,810 B Energy flow pyramid (kilocalories per square meter per year) Fig. 42.6b, p. 713 Florida Aquatic Ecosystem top carnivores carnivores herbivores 21 detritivores + decomposers = 5,060 383 3,368 producers 20,810 B Energy flow pyramid (kilocalories per square meter per year) Stepped Art Fig. 42.6b, p. 713 Food and Energy • Feeding a population of meat-eaters requires far greater crop production than sustaining a population of vegetarians • A person who eats a plant food gets most of the calories in that food • When plant food is used to grow livestock, only a small percentage of the plant’s calories ends up in meat Key Concepts • Organization of Ecosystems • A one-way flow of energy and the cycling of raw materials among species maintain an ecosystem • Nutrients and energy are transferred in a stepwise fashion through food chains that interconnect as complex food webs ANIMATION: Energy flow at Silver Springs To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 42.6 Biogeochemical Cycles • Elements essential to life move between a community and its environment in a biogeochemical cycle • biogeochemical cycle • A nutrient moves between environmental reservoirs and in and out of food webs • Chemical and geologic processes move elements to, from, and among environmental reservoirs (rocks, sediments, water, atmosphere) Biogeochemical Cycles Biogeochemical Cycles Atmosphere Living organisms Rocks and sediments Seawater and fresh water Nonliving environmental reservoirs Fig. 42.7, p. 714 Key Concepts • Biogeochemical Cycles • In a biogeochemical cycle, a nutrient moves relatively slowly among its environmental reservoirs • The reservoirs may include air, water, and rocks • Nutrients moves more quickly into, through, and out of food webs