Correct option is B

Read the following passage and answer the questions:
The size of a population for any species is not a static parameter. It keeps changing with time, depending on various factors including food availability, predation pressure and adverse weather. In fact, it is these changes in population density that give us some idea of what is happening to the population – whether it is flourishing or declining. A population at any given time is composed of individuals of different ages. If the age distribution is plotted for the population, the resulting structure is called an age pyramid

food and space availability is obviously essential for the unimpeded growth of a population. Ideally, when resources in the habitat are unlimited, each species has the ability to realise fully its innate potential to grow in number, as Darwin observed while developing his theory of natural selection. Then the population grows in an exponential or geometric fashion.
In amensalism, one species is harmed whereas the other is unaffected.
Natality refers to the number of births during a given period in the population that are added to the initial density. Mortality is the number of deaths in the population during a given period. Immigration is the number of individuals of the same species that have come into the habitat from elsewhere during the time period under consideration. Emigration is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.

A true example of an organism and its ecological niche is: