  A central issue in ecology today is that of the factors determining the
relative abundance of species within a natural community. The proper
application of the principles of statistical physics to the problem of species
abundance distributions (SADs) has enabled us to identify the fundamental
ecological principles responsible for the near universal features observed.
These principles are (i) a limit on the number of individuals in an ecological
guild and (ii) per capita birth and death rates. We thus unify the neutral
theory of Hubbell [1], the master equation approach of Volkov et al [2, 3] and
a recent attempt at deploying statistical mechanics to deal with this problem,
the idiosyncratic [extreme niche] theory of Pueyo et al [4]; we have identified
the true origin of the prior in [4]. We also find in our results clear
indications that niches must be very flexible and that temporal fluctuations on
all sorts of scales are of considerable importance in community structure.
