Final answer:
Erythropoiesis is stimulated by the release of erythropoietin from the kidneys when blood oxygen levels decrease. This leads to the production of more erythrocytes to compensate for the reduced oxygen availability.
Step-by-step explanation:
Erythropoiesis is the process through which red blood cells (erythrocytes) are produced. The hormone responsible for stimulating erythropoiesis is erythropoietin (EPO), primarily secreted by the kidneys. This process is triggered when there is a decrease in oxygen levels in the blood. The correct answer to which scenario stimulates the production of erythrocytes is that erythropoiesis is stimulated when oxygen levels in the blood decrease, not increase. Other conditions that can lead to increased EPO production include moving to a higher altitude where partial pressure of oxygen is lower, starting an aerobic exercise program, or losing erythrocytes due to bleeding or disease.