The highest number of individuals of a particular population that an ecosystem can support is called as the carrying capacity. The population depends on the environment for the basic necessities like the food, water, habitat, etc. the maximum population that can be sufficiently supported by all these factors by the ecosystem is called the carrying capacity.
If a population increases beyond the carrying capacity of the environment, there will be very less available resources to support the life hence, there will increase in the death rate. Therefore, option (a) is correct.
As there is limited supply of nutrients, there will be no more increase in the birth rate. Therefore, option (b) is incorrect.
As there is limited supply of nutrients, the organisms that can get through the competition can survive and those that cannot will die. Therefore, there will be an increase in the death rate. Therefore, option (c) is incorrect.
Immigrants will have huge competition if they enter into this environment that has already crossed its carrying capacity. Immigration favors only when there is an availability of favorable conditions. Hence, when the carrying capacity is maximum, immigration rate diminishes. Therefore, option (d) is incorrect.
Thus, if a population grows larger than the carrying capacity of its environment, the (a) death rate may rise.