Food Chains, Webs and Pyramids: Energy Flow and Energy Loss in Ecosystems Science 10
METHODS REPRESENTING ENERGY FLOW Scientists use different methods to represent energy moving through ecosystems. 1. Food chains 2. Food webs 3. Food pyramids
FOOD CHAINS Food chains show the flow of energy in an ecosystem (which generally starts from the SUN) Each step in a food chain is called a trophic level (used to show feeding & niche relationships among organisms). Producers = 1st trophic level Primary consumers = 2nd trophic level Secondary consumers = 3rd trophic level Tertiary consumers = 4th trophic level (at the top, has no predators!)
IMPORTANT NOTE The producers are the most populated, and as you go up in the trophic levels, the numbers of organisms in each level decreases. Therfore, the least number of organims are found in the 4th trophic level tertiary consumers, which are also known as HIGHER ORDER CONSUMERS.
Examples of terrestrial and aquatic food chains
CONSUMERS IN A FOOD CHAIN Consumers in a food chain can be classified as: 1.Detrivores – consumers that obtain energy and nutrients from dead organisms and waste matter Examples include earthworms, bacteria and fungi. Detrivores feed at every trophic level. Detrivores have their own, separate food chains and are very numerous. Example of a detritus food chain: Dead leavesbacteriamillipedeshrewraccoon
How do dead organisms contribute to energy flow? DECOMPOSITION describes the breakdown of organic wastes and dead organisms. This process releases energy used by DETRIVORES (ex. insects, bacteria, fungi) that eat dead matter and animal waste. DECOMPOSERS (ex. bacteria and fungi) also help to convert wastes/dead organims into nutrients that will again be used by plants and animals! Therefore, DETRIVORES/DECOMPOSERS eat EVERY trophic level.
2. Herbivores – primary consumers Herbivores eat plants (or producers) only.
3. Carnivores – secondary or tertiary consumers Secondary consumers eat non-producers, such as herbivores. Tertiary consumers eat secondary consumers. Also called top consumers or top carnivores.
4. Omnivores – consumers that eat both plants and animals Examples include humans and bears.
SUMMARY TROPHIC LEVEL TYPE OF ORGANISM ENERGY SOURCE EXAMPLE 1ST Primary producer Obtain energy from the sun Grass, algae (plants) 2ND Primary consumer Obtain energy from primary producers Grasshoppers (herbivores) 3RD Secondary consumer Obtain energy from primary consumers Frogs, crabs (carnivores) 4TH Tertiary consumer (has no predators, is at the top) Obtain energy from secondary consumers Hawks, killer whales (top carnivores)
FOOD WEBS Most organisms are part of many food chains. Food webs represent interconnected food chains. Food webs are models of the feeding relationships in an ecosystem. Arrows in a food web represent the flow of energy and nutrients. Following the arrows leads to the top carnivore(s).
This food web represents a terrestrial ecosystem that could be found in British Columbia.
Important Note About the Diagram The arrows represent the direction in which the “energy” is going or flowing. Label the following on the above diagram using the indicated abbreviations: Herbviore (H) Carnivore (C) Omnivore (O) Detrivore (D) Producers (P)
3. FOOD PYRAMIDS Food pyramids show the changes in available energy from one trophic level to another in a food chain. Energy enters at the first trophic level (producers), where there is a large amount of biomass and therefore much energy.
It takes large quantities of organisms in one trophic level to meet the energy needs of the next trophic level. Each level loses large amounts of the energy it gathers through basic processes of living. 80 – 90 percent of energy taken in by consumers is used in chemical reactions in the body and is lost as thermal energy. There is very little energy left over for growth or increase in biomass.
Food pyramids are also known as ecological pyramids. Ecological pyramids may show biomass, population, or energy numbers. The amount of life an ecosystem can contain is based on the bottom level of the ecological pyramid, where producers capture energy from the Sun.
Each level in the energy pyramid = a loss of 90 percent of total energy available. Lower trophic levels have much larger populations than upper levels. This shows the importance of maintaining large, biodiverse populations at the lowest levels of the food pyramid, the producers, since they store the most amount of energy.
QUESTION If producers produce 100% of the energy going through a food web and organisms use 90% at each trophic level, what percent of the initial energy does each trophic level receive? Level 1: Producers? Level 2:Primary consumers? Level 3:Secondary consumers? Level 4:tertiary higher order consumers?
HOMEWORK Reading Check page 59 #1-5 Reading Check page 64 #1-5 Two worksheets (each double-sided)