How are speciation and microevolution different?
One of the best known examples of speciation and microevolution are the Darwin Finches of the Galapagos Island.
There is good empirical evidence that a few finches from the mainland pioneered on the Island. These few finches adapted to the new environment in many ways. Some grew large beaks for breaking hard seeds. Some smaller beaks for breaking small seeds. Other narrow beaks for getting nectar.
It now considered that there are 13 different species of finches that have evolved from the few early pioneers. Clearly this can be consider to be speciation. However these different species can still mate and hybridize. This can be considered to be microevolution.
Microevolution because there has been no major changes in the DNA of the finches just different adaptations of existing DNA.
So empirically there is no difference in the finches between speciation and microevolution. ( See the Beak of the Finch Jonathan Weiner 1994.)
However according to the theory of Darwinian Evolution these small changes (microevolution) will not only result in new forms or species of finches but in the creation of whole new forms of life. Hence it is believed that through speciation dinosaurs turned into birds.
Scientists that do not question Darwinian Evolution believe that the small changes ( microevolution) will only result in new forms of the species such as can be seen in the evolution of dogs from the gray wolf.