Abstract
What is the underlying mechanism behind the fat-tailed statistics observed for species abundance distributions? The two main hypotheses in the field are the adaptive (niche) theories, where species abundance reflects its fitness, and the neutral theory that assumes demographic stochasticity as the main factor determining community structure. Both explanations suggest quite similar species-abundance distributions, but very different histories: niche scenarios assume that a species population in the past was similar to the observed one, while neutral scenarios are characterized by strongly fluctuating populations. Since the genetic variations within a population depend on its abundance in the past, we present here a way to discriminate between the theories using the genetic diversity of noncoding DNA. A statistical test, based on the Fu-Li method, has been developed and enables such a differentiation. We have analyzed the results gathered from individual-based simulation of both types of histories and obtained clear distinction between the Fu-Li statistics of the neutral scenario and that of the niche scenario. Our results suggest that data for 10–50 species, with approximately 30 sequenced individuals for each species, may allow one to distinguish between these two theories.
Highlights
One of the most interesting peculiarities of mother nature is the large variance in abundance of otherwise similar species
The abundance distribution admits a fat tail, which may be described by power-law or log-normal statistics
Adaptive theories suggest that the frequent species are the fittest, while the neutral theory explains the observed frequencies as a result of demographic stochasticity, assuming all species to have the same fitness
Summary
One of the most interesting peculiarities of mother nature is the large variance in abundance of otherwise similar species. The abundance distribution admits a fat tail, which may be described by power-law or log-normal statistics This observation is somewhat puzzling, as on the basis of evolutionary mechanisms and the competitive exclusion principle one expects the survival of only a few, most fit, species. The simplest explanations for this phenomenon are based on ‘‘niche theory’’ [5,6,7] This theory suggests that the abundance differences reflect fitness, or competitive ability variations. The observed frequency at present reflects the intrinsic fitness of that species, and one conjectures a similar community structure in past generations Another theory that gained much popularity in the last decade is the neutral theory of species abundance.
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