Final answer:
The approximate equilibrium population sizes for the pathogen and probiotic populations depend on the initial population sizes.
Step-by-step explanation:
The approximate equilibrium population sizes for the pathogen and probiotic populations depend on the initial population sizes, so option 4 is correct. The growth rate and population size of these populations can't be determined based on the given information without knowing the initial population sizes. The concept of exponential growth suggests that the population size will increase at a greater and greater rate over time.