The members of a particular species all need these same things from their habitat. They compete with each other to get enough of them. Organisms in a population adapt to daily and seasonal changes by responding to factors such as day-length, light intensity and temperature. Population Availability of things such as food, light, water and space limits the number of species that can survive in a particular habitat. Any increase in any of these may see a rise in population and a decrease may produce a corresponding fall.
Weeds are an example of plants that grow quickly and competitively.
We shall now consider predator prey relationships. These exist where animals have particular food sources. If there is only one main food source or prey for a predator, an increase or decrease in the food source will see an eventual corresponding rise or fall in the predator population. When tadpoles change into frogs they move on to land and eat slugs. The slug population falls and then recovers as frogs provide food for other animals.