I believe it is worth recommending the reading of this new review paper which discusses the various evolutionary theories en vogue, with emphasis in punctuated equilibrium, which is surely a very realistic model:
Jaroslav Fregg, Microevolutionary, macroevolutionary, ecological and taxonomical implications of punctuational theories of adaptive evolution. Biology Direct 2013. Open access → LINK [doi:10.1186/1745-6150-8-1]
Punctuational theories of evolution suggest that adaptive evolution proceeds mostly, or even entirely, in the distinct periods of existence of a particular species. The mechanisms of this punctuated nature of evolution suggested by the various theories differ. Therefore the predictions of particular theories concerning various evolutionary phenomena also differ.
Punctuational theories can be subdivided into five classes, which differ in their mechanism and their evolutionary and ecological implications. For example, the transilience model of Templeton (class III), genetic revolution model of Mayr (class IV) or the frozen plasticity theory of Flegr (class V), suggests that adaptive evolution in sexual species is operative shortly after the emergence of a species by peripatric speciation -- while it is evolutionary plastic. To a major degree, i.e. throughout 98-99% of their existence, sexual species are evolutionarily frozen (class III) or elastic (class IV and V) on a microevolutionary time scale and evolutionarily frozen on a macroevolutionary time scale and can only wait for extinction, or the highly improbable return of a population segment to the plastic state due to peripatric speciation.
The punctuational theories have many evolutionary and ecological implications. Most of these predictions could be tested empirically, and should be analyzed in greater depth theoretically. The punctuational theories offer many new predictions that need to be tested, but also provide explanations for a much broader spectrum of known biological phenomena than classical gradualistic evolutionary theories.
I don't dare to evaluate the paper but I do recommend reading it because it can help us to better understand what is going on when we talk of speciation, competition, evolution, dynamic equilibrium, etc. I picked up this quote:
Approximately 35% of the substitutions (20-70%, depending on the studied taxon) was shown to occur in brief periods of speciation. It is worth mentioning that we are not aware of how many speciation events actually occur in the studied, seemingly unbranched lineages. Therefore, the published estimates of speciation associated substitution rates represent only the lower margin of the real figures.
And the only figure, which illustrates how a highly diverse population/species can be stable and how evolution can happen and often does in bottlenecks instead:
The paper uses the "open review" format, including commentaries from the reviewers and the replies by the author - this I find an interesting novelty which adds some value to the paper by pointing possible avenues for discussion or further research.