  Despite the general acknowledgment of the role of niche and fitness
differences in community dynamics, species abundance has been coined as a
relevant feature not just regarding niche perspectives, but also according to
neutral perspectives. Here we explore a minimum probabilistic stochastic model
to evaluate the role of populations relative initial and total abundances on
species chances to outcompete each other and their persistence in time (i.e.,
unstable coexistence). The present results show that taking into account the
stochasticity in demographic properties and conservation of individuals in
closed communities (zero-sum assumption), population initial abundance can
strongly influence species chances to outcompete each other, and also influence
the period of coexistence of these species in a particular time interval.
Systems carrying capacity can have an important role in species coexistence by
exacerbating fitness inequalities and affecting the size of the period of
coexistence. This study also shows that populations initial abundances can act
as an equalizing mechanism, reducing fitness inequalities, which can favor
species coexistence and even make less fitted species to be more likely to
outcompete better fitted species, and thus to dominate ecological communities
in the absence of niche mechanisms.
