During succession, in the successive seral stages, there is a/an:

During Ecologiccal Succession, the entire sequence of communities that successively change in a given area are called sere(s) and the individual transitional communities are termed seral stages or seral communities. In theses successive seral stages several features are changes continuously like change in the diversity of species of organisms, increase in the number of species and organisms, increase in the total biomass etc. Presently visible communities in the world have come to be because of succession that has occurred over millions of years since life started on earth.