The actual niche the organism is able to occupy in the presence of competitors is called its:. A) fundamental niche.
B) realized niche.
C) interference niche.
D) intraspecific niche.
E) exploitative niche.

B) realized niche

Explanation:  

The ecological niche refers to all the environmental factors that influence the growth, survival, and reproduction of species. These factors also include the interaction between species. The term ecological niche refers to the fundamental niche or the realized niche.    

When an inferior competitor is excluded by the superior competitor, this is known as competitive exclusion. This occurs when there is not habitat differentiation, and both species can not share the same niche. In this case, the effective or realized niche of the dominant species completely occupies the fundamental niche of the inferior competitor.        

 In the exposed example the organism is able to occupy a niche in the presence of competitors, which is the clue for us to classify this niche as a realized niche. The organism needs to interact in a certain way with its competitors. There is an interaction between taxonomic groups, or between individuals.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.