Answer:
Changes in the basal levels that are on the bottom of the food chain.
Step-by-step explanation:
Trophic levels are represented by steps in the food chain. In a simplified diagram, the first basal level is represented by primary producer organisms that include plants and algae. The herbivores are localized in the second place, while in the final levels it is possible to find carnivores and predatory species. It is well known that the changes in the basal trophic levels of this chain (i.e., changes in the first and the second levels) may alter the equilibrium of the food chain and consequently have effects on the stability of the ecosystem.