Symbiosis is the interaction between two living organisms. In most cases neither is harmed but benefited. This has been a part of the animal kingdom, as far as we know, since the beginning of time.
Mutualism: When both organisms benefit from the relationship. A good example of this are humans and dogs or bees and flowers. Both can benefit in a variety of ways. Maybe one animal needs protection or food and the other is benefited by the catering of the animal.
These ants are eating seeds on the sides of this plant. The ant's will get food while the plants seeds will be transported inside of the ants until the excrete it.
Commensailism: This is where one organism may benefit while the other is not benefited nor harmed. Examples of this would be when clown fish will use anemones as shelter. The clown fish gets a safe place to rest while the anemone is not affected.
Parasitism: A relationship where one organism benefits but the other is harmed. An example of this are ticks or leeches when they suck your blood. You are being hurt, while they are benefiting.
Population density is the amount of organisms in a given area. Say that there are 24 deer per square mile. That would be the population density.
Dispersion is the given area between each organism. There are three types.
The first is clumped. This is where the organisms roam in pacts like wolves. The second is uniform. The organisms will keep equal space between them and all others. An example of this is penguins. Then there is random where it is either constantly changing or the organisms don't care about spacing.
Four factors can determine the population size. Although it is constantly changing, the size of a population can be determined. The four factors are immigration, birth, emigration, and death.
Immigration is where organisms will move in to that certain area, increasing the population.
Births are the greatest but slowest way to increase a population. It carries on where the past generations left off.
The next one is emigration. This is where organisms leave the designated area to go somewhere else for whatever reason.
The final one is death. It is something that will happen to all of us eventually. This can slowly decrease the size of a population.
There are two different factors that play in keeping down the population. They are density dependent and density independent.
Density dependent is affected by the number of individuals in a given area. By there being less prey then predators, most of the predators will die off with the lack of food.
Density independent growth is anything that could be happen naturally like natural disasters such as hurricanes or tornadoes.