C. Realized niche - actual niche where they are found if we do look for them. Competition Interaction between individuals of the same or different species, in which growth and survival of individuals of one or both species adversely affected. Interference competition - active competition between individuals. Exploitative competition - consumption of similar resources. Individuals need not come into contact to affect one another.
Bats eat pollen at night, beetles eat pollen during the day.
Two resource limited species cannot co-exist if their niches are identical. It follows that if their niches differ by some factor, they may co-exist. A limited resource is one of which there is not enough to go around. Alone each grows well in the identical niches of the laboratory experiment. Put together in the same niche in the lab, one goes extinct by competition with the other.