Energy Flow Through Ecosystems An Introduction to Energy and Laws of Thermodynamics

Ecosystem Ecology Levels of Organization Biosphere Biome Ecosystem 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 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). (a) Chemical 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).

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.   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. (b) Heat co2 H2O +

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 organic molecules  ATP & organic molecules solar energy  ATP & organic molecules

Metabolism Chemical reactions of life Oxidation – Reduction Anabolic reactions Catabolic reactions Forming bonds between molecules Consume energy 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 Solar radiation Energy in = Energy out Reflected by atmosphere (34%) UV radiation Absorbed by ozone by the earth Visible light Lower Stratosphere (ozone layer) Troposphere Heat Greenhouse effect Radiated by atmosphere as heat (66%) Earth Heat radiated 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

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 complex organic compounds photoautotrophs

Chemoautotrophs 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 complex organic compounds reduced inorganic compounds chemoautotrophs

Heterotrophs are Consumers Heterotrophs are consumers, they must consume preformed organic nutrients synthesized by other organisms.

Heterotrophs 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 Herbivores – eat plants Carnivores – eat meat Omnivores – eat both plants and meat Scavengers – eat carrion Saprophytes – eat dead or decaying material heat complex organic compounds simple inorganic compounds heterotrophs 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 Oxygen Anaerobic respiration Methane, H2S Decomposers Matter recyclers… Release organic compounds into soil and water where they can be used by producers Heat Abiotic chemicals (carbon dioxide, oxygen, nitrogen, minerals) Producers (plants) Decomposers (bacteria, fungus) Consumers (herbivores, carnivores) Solar energy

PHOTOSYNTHESIS CELLULAR RESPIRATION 6CO2 + 6H2O + LIGHT C6H12O6 + 6O2 Carbon Dioxide Water Glucose Oxygen CELLULAR RESPIRATION C6H12O6 + 6O2 6CO2 + 6H2O + ENERGY Glucose Oxygen Carbon Dioxide Water 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 Detritvores Heat First Trophic Level Second Trophic Third Trophic Fourth Trophic Solar energy Producers (plants) Primary consumers (herbivores) Tertiary (top carnivores) Secondary (carnivores) Detritvores

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.

Biomass 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.

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?

Number of observations 10 8 6 4 2 Average number of links = 3.5 Streams Lakes Terrestrial Number of observations 1 2 3 4 5 6 Number of links in food chain

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 Crabeater seal Killer whale Elephant seal Leopard Adélie penguins Petrel Fish Squid Carnivorous plankton Krill Phytoplankton Herbivorous zooplankton Emperor penguin Note: Arrows Go in direction Of energy flow…