What does carrying capacity refer to?

The correct answer is Option (1) → The capacity of a habitat to sustain a certain number of individuals due to available resources.

No population has unlimited food and space. As a population grows, its members compete for the limited resources. A habitat can support only a maximum number of a species, beyond which the population cannot grow. This limit is the carrying capacity (K). In logistic growth, the population rises and then levels off when it reaches K.

Option (1) The capacity of a habitat to sustain a certain number of individuals due to available resources. — Correct. Carrying capacity is the largest number of individuals that the resources of a habitat can support.

Option (2) The reproductive and competitive abilities of a population. — Incorrect. The reproductive and competitive abilities belong to the population itself. Carrying capacity is a limit set by the habitat’s resources.

Option (3) The reproductive capacity of a population. — Incorrect. The capacity of a population to reproduce is measured by r, the intrinsic rate of natural increase, not by K.

NCERT Extract:
Population Growth – “… No population of any species in nature has at its disposal unlimited resources to permit exponential growth. This leads to competition between individuals for limited resources. … In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. Let us call this limit as nature’s carrying capacity (K) for that species in that habitat.”