Regular distribution is observed for many organisms due to
a. the need to maximize exposure to sunlight
b. the need to avoid predators
c. interactions between individuals
d. the plentiful availability of water

c. interactions between individuals

An ecosystem involves both the biological (plants, animals, human beings) and non-biological (land, water, soil, and atmosphere) community which interacts as a system. More importantly, the living things are very dependent on the abiotic community since it cannot survive by itself. Every animal, plant and human needs the primary physiological needs of water, food and shelter provided by the abiotic system.   

Stimulates weight gain, so you put on excess weight