food chains

• A food chain shows what gets eaten by what in an ecosystem
• It is a simplified version of a food web, showing only one chain of interactions
• All food chains start with a producer, which is a photosynthetic organism like a green plant or alga
• Photosynthetic organisms can produce glucose by photosynthesis, using the sun's energy to make biological molecules
• After producers, the next step in the chain are the primary consumers, which eat the producers
• Primary consumers can include rabbits, mice, aphids, etc., but only one is shown in the food chain
• Following primary consumers are the secondary consumers, which feed on the primary consumers
• Tertiary consumers come next, feeding on the secondary consumers
• As energy is passed up the different levels of the food chain, most of it gets lost
• If there were 1,000 joules of energy in the grass, only around 100 joules might be passed on to the mice, and around 20 joules to the owl
• The arrows in a food chain represent the flow of energy up the chain
• Predator-prey cycles
• Population of field mice and owls vary together over time in a predator-prey cycle
• The populations cycle up and down, with the predator population lagging slightly behind the prey population
• When the owl population is low, the mouse population increases
• When there are many mice, the owl population starts to increase due to more food availability
• High owl population leads to a decline in the mouse population, causing a decline in the owl population as well
• This decline in owl population allows the mouse population to rise again, restarting the cycle
• The cycle repeats due to the time it takes for entire populations to increase or decrease