Answer:
The most severe consequences would occur if there is a change in the population of the primary producers (grasses). Therefore, none of the options listed would have more severe consequences than a significant reduction in the grass population.
However, if we assume that the grass population remains stable, the introduction of a second predator that eats field mice (option 3) would have the most severe consequences. This change would lead to a decrease in the population of field mice, which in turn would decrease the population of the predator (hawk) that feeds on them. This disruption could potentially cause a cascade of effects throughout the food chain, ultimately affecting the population of grasses as well