Final answer:
The actual reproductive rate related to selective pressures in organisms is called fecundity. High selective pressure leads to high fecundity with many offspring, while low pressure results in a lower fecundity with fewer, well-cared-for offspring. These strategies evolve through natural selection and are part of an organism's life history strategy.
Step-by-step explanation:
The actual reproductive rate of an organism, particularly in relation to the selective pressures it faces, is known as its fecundity. Fecundity is the potential reproductive capacity of an individual within a population. In environments with high selective pressures, such as high predation risk, organisms tend to have high fecundity, producing many offspring to ensure that some survive.
Examples include guppies which reproduce in large numbers due to the high risk of predation. Conversely, in areas with low selective pressures, organisms tend to exhibit lower fecundity with fewer offspring and greater parental investment, such as the case of elephants.
Life history strategies, such as the timing of reproduction and the energy budgeting between growth and reproduction, evolve through natural selection. Organisms with many small offspring have an r-selected strategy, thriving in unpredictable environments by maturing quickly and reproducing early.
On the other hand, organisms that reproduce later in life and invest heavily in a few offspring have a K-selected strategy, which is more common in stable environments where they can grow larger and provide significant parental care.