Some birds have recently modified their migratory behavior. Instead of flying to warmer climates during the winter months, the birds are remaining in northern areas where they can consume discarded food that is abundant in landfills. As a result of this change in migratory behavior, many insect populations that the birds normally feed on in the warmer climate areas are now increasing. This is an example of human activity

The correct answer is "altering the equilibrium of ecosystems".

Explanation:

Ecosystem have a very complex and sometimes intricate equilibrium. Each species in an ecosystem have a role in the food chain, therefore, if humans affect the behavior of one species, undoubtedly, another species will be affected. In this case, insect populations are increasing as a result of birds modifiying they migratory behavior due to the presence of discarded food in the landfills. Most likely the increased insect populations will affect the plants population as well, creating a series of events that alter the equilibrium of the ecosystems.