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Energy Flow Through Ecosystems An Introduction to Energy and Laws of Thermodynamics Ecosystem Ecology • Examines interactions between the living and non-living world • Ecosystem- the sum of all the organisms living within its boundaries (biotic community) and all the abiotic factors with which they interact Levels of Organization Biosphere Biome Ecosystem Community Population Organism Thermodynamics • Physical Laws that govern energy relationships • Involves Two Processes: • Energy Flow – Energy cannot be recycled therefore there must be a constant supply • Chemical Recycling – Matter can be recycled and Nature does it with perfection. First Law of Thermodynamics Conservation of Energy • The study of energy transformation – In short, the law of conservation of energy states that energy can not be created or destroyed, it can only be changed from one form to another or transferred from one body to another, but the total amount of energy remains constant (the same). Chemical energy (a) First law of thermodynamics: Energy can be transferred or transformed but Neither created nor destroyed. For example, the chemical (potential) energy in food will be converted to the kinetic energy of the cheetah’s movement in (b). Second Law of Thermodynamics Law of Entropy • In any energy transformation, some energy is lost as unusable energy in the sense that work cannot be performed. This is usually in the form of heat. Heat co2 + H2O (b) Second law of thermodynamics: Every energy transfer or transformation increases the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s surroundings in the form of heat and the small molecules that are the by-products of metabolism. Two Important Questions • Where does the energy needed for living organisms originate? • How is energy used by these organisms? Flow of energy through life = Metabolism • The totality of an organism’s chemical reactions – driving life processes by transforming energy from one form to another organic molecules ATP & organic molecules sun solar energy ATP & organic molecules organic molecules ATP & organic molecules Metabolism Chemical reactions of life Oxidation – Reduction Anabolic reactions › Forming bonds between molecules › Consume energy Catabolic reactions › Breaking bonds between molecules › Release energy Living Organisms • Temporary storage units for useful energy, whereby one organism can be used by another as a source of energy. The Source of High Quality Energy • Most of the Energy arrives as electromagnetic radiation from the sun • Supports photosynthesis (less than 2%) • Powers the cycling of matter • Drives climate and weather that distribute heat and H2O Solar radiation Energy in = Energy out Reflected by atmosphere (34%) UV radiation Absorbed by ozone Lower Stratosphere Visible (ozone layer) Greenhouse light Troposphere effect Heat Absorbed by the earth Radiated by atmosphere as heat (66%) Heat radiated by the earth Earth Autotrophs are producers • They capture energy and • • • synthesize their own organic nutrients. They can do this by photosynthesis or chemosynthesis. Chemosynthetic bacteria get energy and raw materials from vents called "smokers" on the ocean floor. Tube worms rely upon the bacteria that coexist with them to make food at the bottom of the ocean. Photoautotrophs • Autotrophs (=self-nourishing) are called primary producers. • Photoautotrophs fix energy from the sun and store it in complex organic compounds • • • • green plants algae some bacteria some protists light simple inorganic compounds photoautotrophs complex organic compounds Chemoautotrophs • Chemosynthesis. • Chemosynthetic bacteria get energy and • raw materials from inorganic sources Oxidize reduced inorganic substances (typically sulfur and ammonia compounds) and produce complex organic compounds. • Nitrifing bacteria • Halophiles (found in highly concentrated salt lakes) • Thermophiles (found in hot springs and geysers) oxygen reduced inorganic compounds chemoautotrophs complex organic compounds Heterotrophs are Consumers • Heterotrophs are consumers, they must consume preformed organic nutrients synthesized by other organisms. Heterotrophs • Heterotrophs (=other-nourishing) cannot produce their • own food directly from sunlight+ inorganic compounds. They require energy previously stored in complex molecules. Examples of heterotrophs – – – – – complex organic compounds Herbivores – eat plants Carnivores – eat meat Omnivores – eat both plants and meat Scavengers – eat carrion Saprophytes – eat dead or decaying material heterotrophs heat simple inorganic compounds this may include several steps, with several different types of organisms Components of Ecosystems • Abiotic cycles • Producers (autotrophs) – Source of all food • Photosynthesis • Chemosynthesis Consumers (heterotrophs) Aerobic respiration Decomposers (bacteria, fungus) – Oxygen Anaerobic respiration – Methane, H2S Decomposers Heat – Matter recyclers… – Release organic compounds into soil and water where they can be used by producers Heat • • • • Abiotic chemicals (carbon dioxide, oxygen, nitrogen, minerals) Heat Heat Producers (plants) Consumers (herbivores, carnivores) Heat Solar energy PHOTOSYNTHESIS 6CO2 + Carbon Dioxide 6H2O + LIGHT Water C6H12O6 Glucose + 6O2 Oxygen CELLULAR RESPIRATION C6H12O6 Glucose + 6O2 Oxygen 6CO2 + Carbon Dioxide 6H2O Water + ENERGY ATP Primary Productivity • Primary productivity determines • • • the amount of energy available in an ecosystem Primary productivity is affected mostly by light in aquatic ecosystems • Limiting nutrient is phosphorus or nitrogen Temperature and moisture are key control factors in terrestrial ecosystems Evapotranspitation • Water transpiration Primary Productivity • Gross Primary production • Total primary production in an ecosystem • Not the amount of energy available to consumers! • NPP=GPP-R • R= energy used for respiration • Energy expended: Plants use the energy captured in photosynthesis for maintenance and growth. Trophic Levels – Energy Pyramids • An energy pyramid provides a means of describing the feeding and energy relationships within a food chain or web. • Each organism in an ecosystem is assigned to a feeding (Trophic) level based on source of energy • The greatest amount of energy is found at the base of the pyramid. • The least amount of energy is found at top of the pyramid Tertiary consumers Secondary consumers Primary consumers Producers Energy Flow Heat First Trophic Level Second Trophic Level Third Trophic Level Fourth Trophic Level Producers (plants) Primary consumers (herbivores) Secondary consumers (carnivores) Tertiary consumers (top carnivores) Heat Heat Heat Solar energy Heat Heat Detritvores Heat Energy Pyramid • Each step shows that some energy is stored or utilized in the organism which eats the preceding one. • Shows that much of the energy is lost when one organism in a food chain eats another. Most of this energy which is lost goes into the environment as heat energy. • It is estimated that only 10% of the energy at each trophic level is available to organisms at the next higher level. Energy is sometimes considered in terms of biomass = the dry weight of tissue of all the organisms and organic material in an area. Producer organisms represent the greatest amount of living tissue or biomass at the bottom of the pyramid. There are more plants on Earth than there are animals. Bio=life Mass=weight Bio + Mass = Weight of living things within an ecosystem. Biomass Why we transform each species into biomass instead of absolute numbers Numbers Pyramid Biomass Pyramid Implications of Pyramids…. • Why could the earth support more people if the eat at lower trophic levels? • Why are food chains and webs rarely more than four or five trophic levels? • Why are there so few top level carnivores? • Why are these species usually the first to suffer when the the ecosystems that support them are disrupted? Average number of links = 3.5 10 Streams Lakes Number of observations 8 Terrestrial 6 4 2 0 1 2 3 4 Number of links in food chain 5 6 Food Webs • A food web is a series of • • interrelated food chains which provides a more accurate picture of the feeding relationships in an ecosystem More than one thing will usually eat a particular species. A species will many times feed at multiple levels on the trophic pyramid Generalized Food Web of the Antarctic Humans Blue whale Sperm whale Killer whale Note: Arrows Go in direction Of energy flow… Elephant seal Crabeater seal Leopard seal Emperor penguin Adélie penguins Petrel Squid Fish Carnivorous plankton Herbivorous zooplankton Krill Phytoplankton