When primary consumers disappear from an ecosystem, the dynamics are affected as follows:
- Producers (plants) would likely increase in population because there would be fewer herbivores to consume them.
- Secondary consumers (carnivores) would likely decrease in population because they rely on primary consumers as a food source. With the primary consumers gone, their food supply is also diminished.
Therefore, the correct response is: The producer population increases, while the secondary consumer population decreases.