Final answer:
A dramatic increase in the penguin population would most likely lead to a decrease in the krill population, as krill are the primary food source for penguins in the food web. Other effects on the ecosystem might occur, but the direct impact would be on krill.
Step-by-step explanation:
If the penguin population were to dramatically increase in a food web, the most likely consequence is C. the population size of the krill would decrease. Penguins primarily feed on krill, and an increase in penguin numbers would lead to greater predation pressure on krill populations. This is a common occurrence in ecosystems where the predator populations increase, affecting the abundance of their prey.
While considerations like increased reproductive success in elephant seals or impacts on other species like squid and cod might be secondary effects, the direct impact of rising penguin numbers would most likely be seen on their main food source.
The concepts of carrying capacity and population dynamics are essential in understanding these ecosystem interactions. For example, if the major food source of another predator, such as seals, declines due to factors like pollution or overfishing, both the carrying capacity and the seal population would likely decrease as seals depend on their food source for survival and reproduction.