Organisms need resources from the habitat to survive and grow. Animals need resources of which are oxygen, space, shelter, food, water, and company. Plants require light, air, warmth and mineral salts and an area to grow. If any of these resources are missing, the population of organisms reduce.
Island Issues
Dutch explorer Jacob Roggeveen came across Easter Island, after discovering it on Easter Sunday 1722, describing it as a land with huge standing statues with no trees.
Scientists found evidence that trees were once striving on the island. During hundreds of years, people cut down trees for many reasons; building resources, to make fires & fishing. 1600 came around and trees were gone, and the people ran out of food. Birds also vanished from the island at the time.
Competition
We can see what eats what in a habitat by examining a food chain:
Grass -> Hare -> Lynx.
Organisms are competing each other for resources. The best adapted organisms have a higher chance of surviving and giving birth. The others may die or go away.
Food chains are combined to form food webs, which can show which animal eats this and so on.
Here, goshawks compete with lynxes for hares. If goshawks catch a disease and die, the population of hares will increase, which now means more food for lynxes, so there will now be more lynxes.
Population changes
Population changes depending on how much food is there to eat. A sparrow is the predator. The insects. When there are lots of insects, the sparrows have a lot to eat on. They then reproduce successfully, and the population numbers go up. When there are less insects, there isn’t much for sparrows to eat, ant therefore, they will starve (new-born offspring included), and others will move to a different place.
