the difference between succession is diversity, density,maturity of plant species and animal adapt that area characterize succession into different class.

Fauna particularly depends on flora, in aspects of flora diversity, density, age (e.g. maturity, presence of dead / decaying parts) etc.

Intraspecific competition is something that goes on everywhere, where lifeforms are competing for limited resources. Just a humans are separated into infants, children, adolescents, young adults, middle aged adults and old adults, ecosystems, too, go through various stages; if one has a term to refer to them, it makes discussions about them easier. The major factor, of course, is time; besides that Boja and Dmitry above have enumerated the basic factors..