What problems would you expect to observe in an ecosystem without primary consumers?

If the primary consumers are removed from an ecosystem, there would be no way for energy to get from the producer (plant) level to higher level consumers which eat only primary consumers. So the population increases in producer (and probably producer diversity) and decreases in secondary, tertiary and higher order consumer populations.

The correct answer is a. we know this because n (hap) + n (hap) = 2n (dip).