How do living things in a community depend on each other?To study the realtionship betweenpopulations in a food chain, wecount the organisms and draw adiagram called a pyramid ofnumbers.This pyramid shows a typicalshape, with lots of producersbelow and just a few carnivores atthe top.
Drawing pyramidsThis pyramid is differentbecause there is only oneoak tree with lots ofcaterpillars living off it. The oak tree is one organism, but it is very large. To give a more realistic idea of the feeding relationship we use another pyramid called a pyramid of biomass.
Pyramid of biomassEcologists draw apyramid of biomass byweighing all theorganisms at each stageof the food chain.The mass of producers islarger than the mass ofconsumers to give atypical pyramid shape
Predators and preyPredators are organisms high up the food chain.They are good hunters, well adapted to finding,catching and killing their prey.Prey animals are well adapted for detecting andavoiding predators.
The poison dart frog has a brightly coloured toxic skin which putsoff predators.
The leaf frog is camouflaged to blend into the background.
• The golden eagle is well adapted as a predator.• Large forward facing eyes make it easier to spot potential prey.• The beak is hooked and sharp so easily tears flesh from the body of its prey.• Gliding flight is silent.• Talons kill by piercing vital organs or snapping bones.
Predator-prey relationshipIn any environment the relative number of predatorand prey are constantly changing, depending onenvironmental factors such as the availability ofgreen plants (producers).
Predator-prey relationshipGrouse are birds that live in moorland environment suchas in Scotland. Grouse eat mainly heather, and are preyfor eagles. heather → grouse → eagle
Predator-prey relationshipIf there is lots of heather and therefore plenty ofgrouse, the eagle population will thrive.More eagle predators will catch lots of grouse soafter a while the grouse population will fall.Then there are fewer grouse for the eagles toeat, so after a while the number of eagles fallstoo. This allows the number of grouse toincrease again, and so the cycle continues.