Final answer:
Pandas primarily eat bamboo due to its abundance and accessibility in their natural habitat. Their physiological and behavioral adaptations allow them to digest this fibrous plant, which is low in nutrients but high in availability, helping fulfill their energy requirements.
Step-by-step explanation:
Pandas eat bamboo because it is the most readily available food source in their habitat. The giant panda's diet is nearly exclusively bamboo, as these bears have evolved both physically and behaviorally to consume this fibrous plant material. Bamboo plays a critical role in panda ecology, predominantly because these plants are perennial and have a unique life cycle, living for many years and flowering only once. Bamboo can grow extensively–up to 70 years or more–before blooming and then die after seeding, which presents challenges for panda survival as it disrupts their food supply.
While pandas can eat other types of vegetation and occasionally even consume meat, the vast stands of bamboo in certain regions of China provide a reliable and substantial amount of food. Bamboos' high vegetative growth allows pandas to maintain their substantial energy needs, despite the plant's low nutritional content. Thus, the reliance on bamboo as a primary food source is a result of their adaptation to their environment, the availability of the plant, and the ability of their digestive systems to process the cellulose and other components in the bamboo.