Food Chains

• Energy passes through an ecosystem using food chains and predator prey cycles.
• Food chains show what gets eaten by what in an ecosystem and are a simplified version of a food web because they don't show all of the interactions.
• A food chain starts with a producer which is some kind of photosynthetic organism like a green plant or alga.
• Photosynthetic means that the organism can produce glucose by photosynthesis, using the sun's energy to make biological molecules.
• The next step in the chain are the primary consumers which eat the producers.
• There must be some type of predator in a food chain, in this case it would probably be something like an owl.
• As the energy gets passed up the different levels in a food chain, most of it gets lost.
• The idea that organisms all interact and influence each other is a key concept in ecology.
• A predator prey cycle is a graph that shows how the population of field mice, a type of prey, and owls, a type of predator, vary together over time.
• In a predator prey cycle, the populations of both species cycle up and down but the change in the predator population always lags behind that of the prey.
• At the beginning of a predator prey cycle, the owl population is low and the mouse population is increasing because there are not many predators around.
• In the next section of a predator prey cycle, there are now loads of mice which means that there is lots of food for the owls and the pressure population starts to increase again.
• As the owl population gets too high, it starts to cause a decline in the mouse population because the mice are suddenly all being eaten because there are fewer mice and less food for the owls.
• The owl population starts to decline as well, allowing the mouse population to rise again, meaning that the cycle will just repeat again and again.
• The main reason that we get this cycle rather than everything reaching a steady equilibrium is that it takes a long time for entire populations to increase or decrease.
• Even if there is plenty of food around for the owls, it still takes multiple generations of breeding before there are lots more owls due to the good source of food.