Emergence and maintenance of biodiversity is one of the most fundamental questions in evolutionary ecology. Although the ecological processes and consequences of the appearance and removal of species have been extensively analyzed, the underlying evolutionary dimensions of those ecological events have received less attention. The fluctuation of species richness in the evolutionary time-scale suggests the different extinction and speciation rate over time, and those different rates suggest different community structures. We developed and examined an individual-based model that represents the coevolutionary dynamics of quantitative traits driven by trophic and competitive interactions. Our model showed the existence of two different metastable states of communities, simple communities that consist of resource producer species (MS1) and communities with multiple trophic levels (MS2). The transitions between those two states, MS1 to MS2 and MS2 to MS1, were triggered by occasional resource switch to be a consumer species and extinction of an intermediate trophic species, respectively. Larger number of individual’s traits, i.e., dimension of the trait space, increased the specie richness at MS2 but simultaneously decreased the duration of MS2.