  According to the competitive exclusion principle, in a finite ecosystem,
extinction occurs naturally when two or more species compete for the same
resources. An important question that arises is: when coexistence is not
possible, which mechanisms confer an advantage to a given species against the
other(s)? In general, it is expected that the species with the higher
reproductive/death ratio will win the competition, but other mechanisms, such
as asymmetry in interspecific competition or unequal diffusion rates, have been
found to change this scenario dramatically. In this work, we examine
competitive advantage in the context of quasi-neutral population models,
including stochastic models with spatial structure as well as macroscopic
(mean-field) descriptions. We employ a two-species contact process in which the
"biological clock" of one species is a factor of $\alpha$ slower than that of
the other species. Our results provide new insights into how stochasticity and
competition interact to determine extinction in finite spatial systems. We find
that a species with a slower biological clock has an advantage if resources are
limited, winning the competition against a species with a faster clock, in
relatively small systems. Periodic or stochastic environmental variations also
favor the slower species, even in much larger systems.
