Final answer:
The 'r' in population studies denotes the per capita rate of increase, (option 5) which can be calculated using the formula r = (b + i) - (d + e). It indicates the growth dynamics and potential of a population about birth rates, death rates, immigration, and emigration.
Step-by-step explanation:
When referring to the capacity of a population to grow, r equals the per capita rate of increase. This growth rate is fundamentally tied to the dynamics of the population's birth rate (b), death rate (d), immigration (i), and emigration (e). Its value indicates whether the population is increasing in size (positive r), decreasing in size (negative r), or remains stable (zero growth). The calculation of population growth rate (r) can be expressed by the formula r = (b + i) - (d + e). It's essential to recognize that r not only reflects the current status of a population's size but also embodies the potential for future changes, factoring in natural selection and resource availability.
Furthermore, r-selected species tend to have a high growth rate, which allows for rapid population increase but is often allied with harsh environments where the population size is generally below the carrying capacity. In contrast, K-selected species are typically associated with stable environments and populations near their carrying capacity.