Final answer:
A microbe infecting the whale population would likely decrease the carrying capacity of the whales, which could affect their relationship with seals and killer whales. This impact may lead to fluctuations in population growth that don't fit a sigmoid growth model.
Step-by-step explanation:
The microbe infecting the whale population in the Arctic ecosystem would likely lower the carrying capacity of the whales due to increased mortality or decreased birth rates. This alteration in whale dynamics could potentially affect the predator-prey relationship between seals and killer whales. If the availability of whales as a food source for the killer whales changes, it might alter the predation pressure on seals, and possibly affect the seal population as well. The resulting dynamics between these populations might not neatly fit into a sigmoid (S-shaped logistic) growth model due to the potential introduction of irregular ecological factors causing real-world fluctuations in population sizes.