Answer: d)All of the above
Explanation: Competitive effect is defined as the interaction created between species or organism , which usually results in negative situation. There are certain condition for the competition such as supply of any resource in limited quantity, etc.So competition is also invoked by the density of the species present and in order to exist in an ecosystem and thus there is the high chances of the overlapping of species as well.
Therefore,option(d) is the correct option.
