What are the major factors affecting population size?

The correct answer highlights the comprehensive range of ecological interactions and environmental factors that influence population size. Predation affects the number of individuals in a population by controlling species numbers through hunting and consumption. Competition arises when organisms vie for limited resources such as food, space, and mates, which can limit population growth. The availability of resources is crucial since inadequate resources can lead to starvation and decreased reproductive rates. Pollution can degrade habitats and affect the health and survival of individuals within a population, while diseases can spread rapidly and reduce population size by increasing mortality rates.

This multifaceted approach underscores that population dynamics are not dictated by a single factor but rather result from the interplay of various biological and environmental elements. In contrast, the other options, while relevant, do not encompass the broad spectrum of influences on population size as effectively. For instance, energy availability primarily impacts primary producers and does not directly account for interactions within populations. Climate change and habitat destruction signify important environmental changes but are more specific than the direct interactions considered in the correct answer. Similarly, human impacts and natural disasters are significant factors, but they represent external influences rather than the ecological interactions that typically govern population dynamics.