Abundance distribution of common and rare plant species of Brazilian savannas along a seasonality gradient

Igor Aurélio Silva,Marcus Vinicius Cianciaruso,Marco Antônio Batalha

doi:10.1590/s0102-33062010000200011

Igor Aurélio Silva, Marcus Vinicius Cianciaruso + Show 1 more

Open Access

https://doi.org/10.1590/s0102-33062010000200011

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Abstract

We examined the species abundance distribution (SAD) of plant communities in: (1) a wet grassland, waterlogged throughout most of the year; (2) a seasonal savanna, with an annual dry season; and (3) a hyperseasonal savanna, with alternating drought and waterlogging over the year. We searched for differences in the abundance distributions of all species, as well as of the common and rare species. We tested whether the SADs fitted the lognormal, log-series, power fraction, and random assortment models. We found that environmental constraints may reduce the evenness of plant communities and change the SADs in savannas. We observed a lognormal abundance distribution in the wet grassland and a random abundance distribution in the hyperseasonal cerrado. The SAD of the seasonal savanna did not follow any model. The common species in the three communities were better fitted by the lognormal model. The rare species in the wet grassland and the hyperseasonal cerrado were better fitted by the random assortment model. The SAD of the rare species of the seasonal savanna did not follow any model. Seasonality seems to modify the lognormal distribution of the overall plant community, generating abundance distributions indistinguishable from random. However, differential community structuring between common and rare species may not be affected by seasonality. The different signatures of the abundance distributions of common and rare plants indicate that composite models are better predictors for SADs in savannas.

Highlights

Explaining differences in patterns of species abundance distribution (SAD) is an important stepping stone to understand how ecological communities are structured (McGill et al 2007)
We sampled 12,879 individuals belonging to 74 species in the wet grassland; 4,589 individuals belonging to 131 species in the seasonal cerrado; and 3,204 individuals belonging to 71 species in the hyperseasonal cerrado
We considered 54 species as rare ones in the wet grassland (1,019 individuals); 110, in the seasonal cerrado (956 individuals); and 51, in the hyperseasonal cerrado (217 individuals)

Summary

Introduction

Explaining differences in patterns of species abundance distribution (SAD) is an important stepping stone to understand how ecological communities are structured (McGill et al 2007). The universal J curve produced when a histogram of number of species on the y-axis vs abundance on the x-axis is plotted (Dewdney 2003) has motivated the development of many theoretical SAD models involving population dynamics (e.g., Hughes 1986; Hubbell 2001), niche partitioning (e.g., Tokeshi 1990; 1996), and spatial distributions (e.g., Harte et al 1999; Borda-de-Água et al 2002) Most of these models did not establish any empirical pattern beyond the expected J-curve itself and, as a result, few were ever rejected (McGill et al 2007). A promising approach for assessing SADs is comparing them under different environmental constraints

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