Many north american animal species migrated to the south during pleistocene ice ages and returned to the north during interglacial periods. these observations are consistent with
a. expanded physiological tolerance.
b. distribution shift and habitat tracking.
c. migration barriers.
d. range expansion by adaptation.
e. declining habitat size.

The correct answer is option b. "distribution shift and habitat tracking".

Explanation:

Distribution shift is a common adaptation, at which species migrate to a different location looking for better living conditions. Habitat tracking is a very similar concept, but it refers to species either adapting or migrating in response to an environment detrimental. These two phenomenons explain why many North American animal species migrated to the south during Pleistocene ice ages and returned to the north during interglacial period. Pleistocene ice ages were a very challenging time for the species for being a period of repeated glaciations, therefore species had to adapted by distribution shift and habitat tracking.