Contribution of rarity and commonness to patterns of species richness in biogeographic transitions regions: Woody plants of Uruguay

Abstract

There is a growing body of evidence suggesting that widespread (i.e. common) rather than geographically restricted species (i.e. rare) shape the overall distribution patterns of species richness. This is a non-intuitive fact, given that local and regional assemblages are normally composed by numerous rare species and few common ones. We evaluated here the primacy of common species in a biogeographic transition zone, where rarity has frequently a higher incidence. We analysed the geographical variability of trees and shrubs in Uruguay, located in a transitional zone between prairie and forest biomes, to assess the relative contribution of rare and common species to the generation of richness patterns. The distribution of 301 species of the native woody assemblage of Uruguay was mapped over the national grid system (302 quadrants of approximately 22 ¥ 30 km), using published data and herbarium records. The overall assemblage was segregated into four subassemblages in function of species distribution (quartiles). Species richness in the four quartiles was positively correlated with overall richness, but common species (quartile 3) showed the highest level of correlation. Then, we ranked species from the most widespread to the most restricted (common-to-rare) and from the most restricted to the most widespread (rare-to-common). Along each stage of the sequences we obtained a series of species richness patterns for increasing numbers of species. Correlating the species richness pattern for each subassemblage of both sequences with that of the full assemblage, we also found higher correlations in the common-to-rare sequence.We conclude the Uruguayan woody plants assemblage has a very large number of rare species as expected for a transitional biogeographical zone, but it was the common species that contributed most to the overall pattern of species richness. We propose the low contribution of rare species is explained by the most interspecific variability in ecological determinants within the assemblage of rare species.Therefore the spatial covariance among rare species is low, and so is the relationship with overall species richness.

Unequal Contribution of Widespread and Narrow-Ranged Species to Botanical Diversity Patterns

“…When prevalence was defined for tropical Africa, we found patterns of narrow-ranged species in Gabon to be more strongly correlated with the pattern of total species richness. This contradicts the results of previous studies which found patterns of widespread species being more strongly correlated with total species richness patterns [8–10,22,25,57]. In addition to the unique suite of species and habitats in each study area, four other matters need further consideration so as to put our results into perspective.…”

“…Our data set is strongly right-skewed and thus similar to the dataset of Uruguayan plants used by Perez-Quesada & Brazeiro [57], whose results are in line with ours. By contrast, Kreft et al .…”

“…Most studies order species based on their prevalence in the study area alone, which can be much smaller than the full range size of the species [10,22,23,25,50,57], with few positive exceptions [9]. For example, widespread African species are sometimes rare in Gabon and Gabonese endemics sometimes have a large prevalence within the country.…”

What determines plant species diversity in Central Africa?

“…When prevalence was defined for tropical Africa, we found patterns of narrow-ranged species in Gabon to be more strongly correlated with the pattern of total species richness. This contradicts the results of previous studies which found patterns of widespread species being more strongly correlated with total species richness patterns (Jetz & Rahbek, 2002, Kreft et al, 2006, Lennon et al, 2004, Mazaris et al, 2013, Perez-Quesada & Brazeiro, 2013, Vázquez & Gaston, 2004. In addition to the unique suite of species and habitats in each study area, four other matters need further consideration so as to put our results into perspective.…”

Commonness patterns and the size of the species pool along a tropical elevational gradient: insights using a new quantitative tool

“…Although common species are only a limited subset of the community, they account for the majority of individuals, biomass, and energy flows (Vázquez andGaston 2004, Gaston 2010). Moreover, common species determine the spatial patterns of species distribution and biodiversity gradients even above that expected for their abundance (Lennon et al 2003, Vázquez and Gaston 2004, Sizling et al 2009, Pérez-Quesada and Brazeiro 2013. The two-dimensional approach to commonness is of great practical importance because it could shed light on the mapping of vast unvisited areas and large-scale planning of ecosystems management (Pitman et al 2001, Gaston and Fuller 2008.…”