By saying that one believes in microevolution, they are acknowledging that evolution happens, and that the primary mechanisms by which this happens is natural selection (or perhaps artificial selection, in the case of selective breeding). This is what Darwin showed. Macroevolution is a logical extension of this. There has been no evidence to show that there is some sort of barrier or limit to microevolution which would prevents species from transitioning to another. This is a recent idea which has been invented due to an idealogical opposition to the theory, which has no scientific support. Further, I have shown numerous instances where such a species transition has indeed occured. The examples I have presented occur in organisms where their life cycle is very short (e.g. bacteria) so that the effects can be observed in our lifetime. In animals, the life cycles are much longer, and the evolutionary process takes much longer to observe (thousands/millions of years). Nevertheless, this prcoess has been clearly shown to have occurred throughout the animal kingdom based on fossil and genetic evidence, among others.