Final answer:
In an ecosystem, the introduction of Orca whales would lead to top-down control, resulting in an increase in kelp populations as the whales would reduce otter populations. When seals' food sources decline, their population and the carrying capacity also decrease due to reduced resource availability.
Step-by-step explanation:
If Orca whales were introduced to the ecosystem and began to feed on the otters, it would exhibit top-down control, and kelp populations would increase. This scenario is based on the principle that predators control the population of their prey, which in turn affects the prey's prey population. In the case of Orca whales preying on otters, the otters would be less able to feed on their primary food source, which is sea urchins. With fewer otters, the sea urchin population would be less controlled, allowing the kelp forests they feed upon to thrive. Thus, the correct answer is a. Top-down, increase.
If the major food source of seals declines due to pollution or overfishing, the carrying capacity of the seals would decrease, as would the seal population. This is because the carrying capacity is determined by the availability of resources, such as food, which supports the size of a population. Without enough food, both the carrying capacity and the population decrease. Therefore, the correct answer is a. The carrying capacity of seals would decrease, as would the seal population.