Food Webs

• Types of Species

• Autotrophs

• Autotrophs produce all the food that heterotrophs use
• Also called producers
• Without autotrophs, there would be no life on this planet
• Ex: Plants and Algae

• Heterotrophs

• Organisms that do not make their own food
• Consume other organisms in order to live
• Also called consumers
• Ex: Fish, Coral, Whales

• Heterotroph Types

• Scavengers/Detritivores

• Feed on the tissue of dead organisms (both plants and animals)
• Ex: Crayfish

• Herbivores

• Eat ONLY plants
• Ex: Green Sea Turtles, Manatees

• Carnivores

• Eat ONLY meat
• Ex: Sharks, Sea Stars

• Omnivores

• Eat BOTH plants and animals
• Ex: Horseshoe Crabs, Lobsters

• Decomposers

• Absorb any dead material and break it down into simple nutrients or fertilizers
• Ex: Bacteria and Fungi

• Transfer of Energy

• When a sea turtle eats the seagrass, it does not obtain all of the energy the seagrass has (much of it is not eaten)
• When a shark eats a sea turtle, it does not get all of the energy from the sea turtle (much of it is lost as heat)
• No organism EVER receives all of the energy from the organism they just ate
• Only 10% of the energy from one trophic level is transferred to the next
• This is called the 10% Law

• Trophic Levels

• Energy moves from one organism to another when it is eaten
• Each step in this transfer of energy is known as a trophic level

• The main trophic levels are

• producers
• consumers (primary, secondary, tertiary)
• decomposers

• Food Chain

• The energy flow from one trophic level to the other is known as a food chain
• A food chain is simple and direct
• It involves one organism at each trophic level
• Progression

• Primary Consumers – eat autotrophs (producers)
• Secondary Consumers – eat primary consumers
• Tertiary Consumers – eat secondary consumers
• Decomposers – bacteria and fungi that break down dead organisms and recycle the material back into the environment

• Food Webs

• Most organisms eat more the JUST one organism
• When more organisms are involved, it is known as a FOOD WEB
• Food webs are more complex and involve lots of organisms
• Diagram arrows

• Notice the direction the arrow points 🡪
• The arrow points in the direction of the transfer of energy, NOT “what eats what”

• Biomass

• The total mass of the organic matter at each trophic level is called biomass
• Biomass is just another term for potential energy
• Energy that is to be eaten and used
• The transfer of energy from one level to another is very inefficient (10% Law)

• Ecological Pyramid

• An ecological pyramid shows the relationship between consumers and producers at different trophic levels in an ecosystem
• Shows the relative amounts of energy or matter contained at each trophic level
• The pyramid shows which level has the most energy and the highest number of organisms

• Symbiosis

• A close and permanent association between organisms of different species
• Commensalism

• A relationship in which one organism benefits and the other is not affected
• Example: Barnacles on a whale

• Mutualism

• A relationship in which both organisms benefit from each other
• Example: Sea anemone and clownfish

• Parasitism

• A relationship in which one organism benefits and the other is harmed
• Example: Sea urchins and coral