Living Environment Regents Practice Test

The significant decline in monarch butterfly populations can primarily be attributed to habitat destruction and loss. Over recent years, many natural habitats that monarchs rely on, such as milkweed plants (the exclusive host for monarch caterpillars), have been drastically reduced due to agricultural expansion, urban development, and the widespread use of pesticides. The elimination of these critical habitats not only diminishes breeding grounds, but it also affects their migratory routes and stops where butterflies pause during their long journeys.

In contrast, increased predator populations would generally not cause a drastic decline exclusively reliant on habitat conditions, while greater availability of food sources could potentially support butterfly populations rather than diminish them. Habitat preservation efforts, although beneficial for wildlife, do not explain the decline; in fact, they aim to counteract the effects of habitat loss.

The focus on habitat destruction highlights the urgency for conservation and restoration efforts to create and maintain environments that can support the lifecycle of monarch butterflies.