In order to make room for the increasing population, new cities and towns are formed. A side effect of the construction of these

cities and towns is that

The side effects of increasing population is increased pollution and competition for survival.

Explanation:

As the resource in nature is limited. It do not increase with the increase in population. So same amount of resource must be utilized by the species if they are in less number or large (the amount consumed per head decreases). This creates the increase in competition and only fewer people will be able to live comfortably. Increasing pollution is also a major side effect of increasing population.