Which of the following pairs are examples of limiting factors for population growth?

• A. Oxygen and nitrogen
• B. Food availability and space
• C. Weather and climate
• D. Evaporation and condensation

Answer: (B)

In ecology, a limiting factor is something that prevents a population from growing beyond a certain size in a given environment. The most direct limiting factors are resources the population relies on to survive and reproduce, and the space available to live and find those resources. Food availability determines how much energy organisms have to grow, reproduce, and survive, while space (habitat) limits how many individuals can live and access those resources without excessive competition. Together, they constrain population size to the carrying capacity of the environment.

The other options aren’t as clear-cut as limiting factors for population growth. Oxygen and nitrogen are essential for life, but their availability isn’t typically the primary factor that caps population size across most ecosystems. Weather and climate describe broad environmental conditions that influence survival, but they’re not the direct resources being consumed. Evaporation and condensation are processes in the water cycle, not factors that directly limit how large a population can grow.

So the pair that directly embodies limiting factors—resource and space limiting population size—is the one describing food availability and space.