Final answer:
Acclimation is a characteristic observed at the individual level where animals adjust to environmental changes, such as increase in red blood cells at higher altitudes. It is a reversible process that does not pass on to offspring, unlike adaptations which are genetic changes at the population level. The correct option is a-individual level.
Step-by-step explanation:
Acclimation is observed at the individual level, and it is a process by which an individual animal adjusts to changes in its environment, thereby improving function in a new environment.
For instance, when an animal migrates to a higher altitude, acclimatization involves the increase in the number of red blood cells to ensure adequate oxygen delivery to the body tissues in response to lower oxygen levels at the new altitude. Conversely, adaptation is a characteristic at the population level, where genetic changes occur over generations through natural selection, influencing the allele frequencies within the population.
Acclimatization allows animals to reestablish a homeostatic set point, but it is not a trait passed on to offspring. The changes are reversible and specific to the individual that experiences the new environment, such as seasonal changes in an animal's coat for temperature regulation.