What is the key distinction between speciation and macroevolution?
The key distinction is the origin of new or novel information.
speciations results from the natural selection of preexisting variation within the DNA of an organism. Macroevolution requires the formation of new information.
An example of speciation would be the variation of Finches on the Galapagos Islands. A small population of one type of finch arrived on the volcanic islands where the finches faced a new environment with many unfilled niches. The finches evolved into 13 different types of finches occupying different niches. These different species of finches can and do hybridize interbreeding with each other. There is no new genetic information required for this type of speciation.
An example of macroevolution is the transition from flying reptiles to birds. Scales need to be changed into feathers, cold blooded metabolism to hot blooded metabolism. Radically different proteins and physical structures need to be produced. New and unique types of information need to be produced.
Darwinian evolution extrapolates from the observations of speciation to the theory of common descent and macroevolution.