Answer: a. the entire population of the species spends winter in Oyamel.
Monarch butterfly cannot survive in extreme climatic conditions. These butterflies spend winter months in Oyamel fir forest of Mexico. Oyamel forest situated in mountain hills provides an ideal climate for their survival. Here, the temperature ranges from 0 to 15 degree Celsius. If the temperature is low, the monarch butterflies uses their fat reserves. The dense canopy of trees in Oyamel fir forest drives heat from the ground at night and protect these butterflies from rain, wind and snow. The supply of excess of water as in the case of water logging condition can make trees susceptible to diseases and pests. In winter majority of monarch butterfly concentrate over the same region of Oyamel fir forest. Such water logging conditions will make the forest unsuitable for survival and further may lead to extinction of these butterflies.
