The Role of Edaphic Environment and Climate in Structuring Phylogenetic Pattern in Seasonally Dry Tropical Plant Communities

Abstract

Seasonally dry tropical plant formations (SDTF) are likely to exhibit phylogenetic clustering owing to niche conservatism driven by a strong environmental filter (water stress), but heterogeneous edaphic environments and life histories may result in heterogeneity in degree of phylogenetic clustering. We investigated phylogenetic patterns across ecological gradients related to water availability (edaphic environment and climate) in the Caatinga, a SDTF in Brazil. Caatinga is characterized by semiarid climate and three distinct edaphic environments – sedimentary, crystalline, and inselberg –representing a decreasing gradient in soil water availability. We used two measures of phylogenetic diversity: Net Relatedness Index based on the entire phylogeny among species present in a site, reflecting long-term diversification; and Nearest Taxon Index based on the tips of the phylogeny, reflecting more recent diversification. We also evaluated woody species in contrast to herbaceous species. The main climatic variable influencing phylogenetic pattern was precipitation in the driest quarter, particularly for herbaceous species, suggesting that environmental filtering related to minimal periods of precipitation is an important driver of Caatinga biodiversity, as one might expect for a SDTF. Woody species tended to show phylogenetic clustering whereas herbaceous species tended towards phylogenetic overdispersion. We also found phylogenetic clustering in two edaphic environments (sedimentary and crystalline) in contrast to phylogenetic overdispersion in the third (inselberg). We conclude that while niche conservatism is evident in phylogenetic clustering in the Caatinga, this is not a universal pattern likely due to heterogeneity in the degree of realized environmental filtering across edaphic environments. Thus, SDTF, in spite of a strong shared environmental filter, are potentially heterogeneous in phylogenetic structuring. Our results support the need for scientifically informed conservation strategies in the Caatinga and other SDTF regions that have not previously been prioritized for conservation in order to take into account this heterogeneity.

Phylogenetic community structure reveals differences in plant community assembly of an oligotrophic white-sand ecosystem from the Brazilian Atlantic Forest

“…Positive LifeFormNRI values show that there is a tendency of related species to resemble each other more than species drawn at random from the phylogeny, indicating that close relatives share more functional traits and show higher niche overlap than expected by chance. Similar patterns from other savannalike formations have been detected by previous studies (i.e., Qian & Zhang 2014;Moro et al 2015;Kuhlmann & Ribeiro 2016). …”

Effects of soil and space on the woody species composition and vegetation structure of three Cerrado phytophysiognomies in the Cerrado-Amazon transition

“…By contrast, Abreu et al (2012), who investigated typical and stony cerrado in Goiás State, Brazil, found a clear relationship between the soil and plant species composition, and a much less pronounced link with geographic distance. We believe that, in situations where edaphic properties are more homogeneous, such as the present study, space is the determining factor, whereas in environments with highly distinct substrates (Abreu et al, 2012;Mews et al, 2016;Moro et al, 2015) the properties of the soil determine the distinct structure and species composition of the different Cerrado phytophysiognomies.…”

“…Legendre et al, 2002;Peres-Neto and Legendre, 2010;Moro et al, 2015;Neves et al, 2015;Mews et al, 2016), although Mews et al (2016) used an approach of this type. This new approach may help improve the understanding of the factors and mechanisms that mold the distribution of the flora and the structure of the vegetation of the Cerrado.…”

Patterns of species richness and abundance among cactus communities receiving different rainfall levels in the semiarid region of Brazil

“…Furthermore, this precipitation is heterogeneously distributed as a result of two large moisture gradients, one in the north-south direction determined by decreasing precipitation, and the other in the east-west direction due to the eff ect of increasing continentality (Rodal et al 2008). Th e most common soil of the region is of crystalline origin, but areas of sedimentary soil are also present (Moro et al 2015;Moro et al 2016).…”

“…Th e Caatinga domain (seasonally dry tropical forest), with features that distinguish it from the other main biomes of the world, exhibits marked variation in its response to environmental heterogeneity, which is related to the interaction among edaphic, climatic and historical factors (Moro et al 2015). Th e hyperxerophytic vegetation of the Caatinga grows in crystalline soil and is predominant in this phytogeographical region (Moro et al 2016).…”