Transcript Chapter 16
Section 2 Energy Flow in Ecosystems CHAPTER 16 Grade 10 Biology Spring 2011 BELL RINGER A robin, snake, hawk, frog, grasshopper, mouse, and rabbit can all be found in an open field. Draw arrows to show what eats what in this field ecosystem. OBJECTIVES Distinguish between producers and consumers Compare food webs with food chains Describe why food chains are rarely longer than three or four links PRIMARY ENERGY SOURCES Primary Productivity: the rate at which organic material is produced by photosynthetic organisms in an ecosystem CHANGE OF ECOSYSTEMS OVER TIME Producers: organisms that first capture energy Plants, some bacteria, algae Make energy storing molecules CHANGE OF ECOSYSTEMS OVER TIME Consumers: organisms that consume plants or other organisms to obtain energy necessary to build their molecules TROPHIC LEVELS Trophic Level: an energy level that is used to study how energy is moved through an ecosystem Organisms are assigned to trophic levels Energy moves from one trophic level to another SUN PRODUCER CONSUMER CONSUMER TROPHIC LEVELS Food Chain: path of energy through the trophic levels of an ecosystem TROPHIC LEVELS First Level: occupied by producers Plants, algae, bacteria Producers use energy of the sun to build energy-rich carbohydrates Many also incorporate key nutrients (nitrogen) from the environment into their biological molecules TROPHIC LEVELS Second Level: herbivores eat the primary producers from the first trophic level Primary consumers Herbivores: animals that eat plants or other primary producers TROPHIC LEVELS Third Level: carnivores eat the primary consumers (herbivores) from the second trophic level Carnivore: animals that eat other animals Omnivore: both herbivores and carnivores TROPHIC LEVELS Detritivores: consumer, obtain their energy from the organic wastes and dead bodies that are produced at all trophic levels Bacteria, fungi, worms Decomposers: cause decay Bacteria, fungi This releases nutrients back into the environment TROPHIC LEVELS Fourth Level: carnivores that consume other carnivores Tertiary consumers, top carnivores TROPHIC LEVELS Food web: complicated, interconnected group of food chains In most ecosystems, energy does not follow simple straight paths Individual animals often fed at several trophic levels LOSS OF ENERGY IN A FOOD CHAIN Energy transfer: during every transfer of energy within an ecosystem, energy is lost as heat Amount of useful energy available to do work decreases as energy passes through an ecosystem Loss of energy limits number of trophic levels THE PYRAMID OF ENERGY Energy Pyramid: diagram in which each trophic level is represented by a block, and the blocks are stacked on top of each other, with the lowest trophic level on the bottom Pyramid shaped because each level represents the amount of energy stored in the organisms at that level LOSS OF ENERGY IN A FOOD CHAIN At each trophic level, the energy stored by the organisms in a level is about one-tenth of that stored by the organisms in the level below Fourth Trophic Level: 1J energy Third Trophic Level: 10J energy Second Trophic Level: 100J energy First Trophic Level: 1,000J energy LIMITATIONS OF TROPHIC LEVELS Most ecosystems involve three or four levels Too much energy is lost at each level to allow more Why can’t a large human population survive from eating lions? HUMANS EATING BREAD: HUMANS EATING BEEF: it takes a certain amount of grain…… It takes 10 times more grain……. To produce enough bread…… To feed one cow…… To make enough beef….. To provide one person with the same amount of energy. To provide one person with a certain amount of energy. LIMITATIONS OF TROPHIC LEVELS LIMITATIONS OF TROPHIC LEVELS Biomass: dry weight of tissue and other organic matter found in a specific ecosystem Each higher level on the pyramid contains only 10% of biomass found in the trophic level below it Used to determine the amount of energy present in trophic levels Used because the number of individuals in a trophic level may not be an accurate indicator of the amount of energy in that level Due to size of organisms REVIEW 1. 2. 3. How much energy is lost as you move up a trophic level? List the reasons why food chains do not tend to exceed four links? How are producers different from consumers. ANSWERS 1. 2. 3. 90% of energy is lost at each trophic level Food chains do not tend to exceed four links because so much energy is lost at each trophic level. Producers use energy (usually from the sun) to assemble food molecules, hence “producing food”. Consumers must take in (or consume) these food molecules to obtain their energy.