Competition
Competition happens simply when there is more demand for a resource than that is available. This can come in many different forms. In a forest, the trees might be in competition for sunlight. In this case, the taller trees would have the advantage, while the shorter ones might not get as much sunlight. Polar bears might compete for a mate. There might even be competition for water. If there are too many animals in one area and not enough water, some might survive better than others depending on how much competition there is.
Image Sources:
1. http://fany.savina.net/wp-content/uploads/2010/03/
deerfight.jpg
2. http://www.bsos.umd.edu/psyc/Herberholz/crayfish_two1N.jpg
3. http://img.ezinemark.com/imagemanager2/files/30004252/2010/12/2010-12-31-12-02-38-1-this-is-the-most-incredible-food-fight-of-wild-ani.jpeg
4. http://2.bp.blogspot.com/_vP99DlcHAIk/TDfK3sP2IFI/AAAAAAAAABA/otE9_bHpPs0/s1600/autumn_
trees_p.jpg
5. http://www.bbc.co.uk/bitesize/standard/biology/images/animal_fight.jpg
6. http://static.ddmcdn.com/gif/polar-bear-4.jpg
1. http://fany.savina.net/wp-content/uploads/2010/03/
deerfight.jpg
2. http://www.bsos.umd.edu/psyc/Herberholz/crayfish_two1N.jpg
3. http://img.ezinemark.com/imagemanager2/files/30004252/2010/12/2010-12-31-12-02-38-1-this-is-the-most-incredible-food-fight-of-wild-ani.jpeg
4. http://2.bp.blogspot.com/_vP99DlcHAIk/TDfK3sP2IFI/AAAAAAAAABA/otE9_bHpPs0/s1600/autumn_
trees_p.jpg
5. http://www.bbc.co.uk/bitesize/standard/biology/images/animal_fight.jpg
6. http://static.ddmcdn.com/gif/polar-bear-4.jpg