Ecological competition occurs when living organisms, including animals, plants, bacteria and fungi, need the same limited resources to thrive in their shared environment. An ecosystem could collapse if several species needed the same scarce resources to complete their life cycle. Competition will occur between organisms in an ecosystem when their niches overlap, they both try to use the same resource and the resource is in short supply. Animals compete for food, water and space to live. Plants compete for light, water, minerals and root space.