What is the major difference between adaptive radiation and punctuated equilibrium?

Answer 1

They aren't exactly comparable as punctuated equilibrium is concerned with the evolutionary course of a species while an adaptive radiation generally involves speciation and so is concerned with the evolutionary course of a genus or family. That aside, the major difference is the variation in the rate of evolution: whether evolution is constant or occurring in bursts.

Punctuated equilibrium - A species has a constant phenotype for many generation (stabilizing selection; no evolution) followed by a rapid burst of evolution (directional selection) which is then followed by another long period of stability and so on. Using its name: the equilibrium (no evolution) is punctuated by short but strong bursts of evolution.

Adaptive radiation - A starting species expands into a new environment and begins to adapt to the new conditions, changing relative to the population still in the old habitat. These populations then colonize further habitats, each becoming different from the others, and so on... The "species" continually expands into new habitats, evolves, and eventually speciates producing a radiation of differently adapted species from a single ancestor. For your question, this means that selection is continually acting to make the populations more different from one and other rather than only happening in bursts