title: Analytical formulae for computing dominance from species-abundance distributions.
abstract: The evenness of an ecological community affects ecosystem structure, functioning and stability, and has implications for biodiversity conservation. In uneven communities, most species are rare while a few dominant species drive ecosystem-level properties. In even communities, dominance is lower, with possibly many species playing key ecological roles. The dominance aspect of evenness can be measured as a decreasing function of the proportion of species required to make up a fixed fraction (e.g., half) of individuals in a community. Here we sought general rules about dominance in ecological communities by linking dominance mathematically to the parameters of common theoretical species-abundance distributions (SADs). We found that if a community's SAD was log-series or lognormal, then dominance was almost inevitably high, with fewer than 40% of species required to account for 90% of all individuals. Dominance for communities with an exponential SAD was lower but still typically high, with fewer than 40% of species required to account for 70% of all individuals. In contrast, communities with a gamma SAD only exhibited high dominance when the average species abundance was below a threshold of approximately 100. Furthermore, we showed that exact values of dominance were highly scale-dependent, exhibiting non-linear trends with changing average species abundance. We also applied our formulae to SADs derived from a mechanistic community model to demonstrate how dominance can increase with environmental variance. Overall, our study provides a rigorous basis for theoretical explorations of the dynamics of dominance in ecological communities, and how this affects ecosystem functioning and stability.
authors.affiliation: National University of Singapore, Department of Biological Sciences, 14 Science Drive 4, 117543 Singapore. Electronic address: tfung2000@gmail.com.
authors.forename: Tak
authors.initials: T
authors.lastname: Fung
authors.affiliation: Institut National des Sciences Appliquées de Lyon, 20 Avenue Albert Einstein, Villeurbanne cedex, 69621 Lyon, France. Electronic address: villain.laura@gmail.com.
authors.forename: Laura
authors.initials: L
authors.lastname: Villain
authors.affiliation: National University of Singapore, Department of Biological Sciences, 14 Science Drive 4, 117543 Singapore; Smithsonian Tropical Research Institute, Balboa, Ancón, Republic of Panama. Electronic address: ryan.chis@gmail.com.
authors.forename: Ryan A
authors.initials: RA
authors.lastname: Chisholm
mesh_terms: D000818:Animals; D044822:Biodiversity; D058448:Biota; D008954:Models, Biological; D011157:Population Dynamics; D013045:Species Specificity; D014197:Trees / Q000254:growth & development
keywords: Biodiversity; Evenness; Gamma; Log-series; Lognormal