What is the term for an organism's ability to survive and reproduce in its environment?

The term describing an organism's ability to survive and reproduce in its environment is referred to as fitness. This concept is central to the theory of natural selection and evolutionary biology. Fitness is not merely about physical strength; instead, it encompasses various traits that enhance an organism's chances of survival and successful reproduction within a specific environment.

For example, an organism might possess certain advantageous traits, such as the ability to find food efficiently, evade predators, or withstand environmental stresses. All of these factors contribute to greater reproductive success, meaning that the organism is more likely to pass on its genes to the next generation. Fitness is often measured not only by the number of offspring produced but also by the viability and reproductive capabilities of those offspring.

While adaptation, selection, and evolution are related concepts within this context, they do not define the specific ability to thrive and reproduce as accurately as fitness does. Adaptation refers to the process through which organisms evolve traits that improve their survival chances in response to environmental pressures, selection pertains more to the mechanisms driving changes in populations over time, and evolution describes the broader changes in species and populations across generations. Therefore, fitness is the most precise term to encapsulate the essence of survival and reproduction within a given environment.