Latitudinal patterns and environmental drivers of taxonomic, functional, and phylogenetic diversity of woody plants in western Amazonian terra firme forests

Abstract

Elucidating how environmental factors drive plant species distributions and how they affect latitudinal diversity gradients, remain essential questions in ecology and biogeography. In this study we aimed: 1) to investigate the relationships between all three diversity attributes, i.e., taxonomic diversity (TD), functional diversity (FD), and phylogenetic diversity (PD); 2) to quantify the latitudinal variation in these diversity attributes in western Amazonian terra firme forests; and 3) to understand how climatic and edaphic drivers contribute to explaining diversity patterns. We inventoried ca. 15,000 individuals from ca. 1,250 species, and obtained functional trait records for ca. 5,000 woody plant individuals in 50 plots of 0.1 ha located in five terra firme forest sites spread over a latitudinal gradient of 1200 km covering ca. 10°C in latitude in western Amazonia. We calculated all three diversity attributes using Hill numbers: q = 0 (richness), q = 1 (richness weighted by relative abundance), and q = 2 (richness weighted by dominance). Generalized linear mixed models were constructed for each diversity attribute to test the effects of different uncorrelated environmental predictors comprising the temperature seasonality, annual precipitation, soil pH and soil bulk density, as well as accounting for the effect of spatial autocorrelation, i.e., plots aggregated within sites. We confirmed that TD (q = 0, q = 1, and q = 2), FD (q = 0, q = 1, and q = 2), and PD (q = 0) increased monotonically towards the Equator following the latitudinal diversity gradient. The importance of rare species could explain the lack of a pattern for PD (q = 1 and q = 2). Temperature seasonality, which was highly correlated with latitude, and annual precipitation were the main environmental drivers of variations in TD, FD, and PD. All three diversity attributes increased with lower temperature seasonality, higher annual precipitation, and lower soil pH. We confirmed the existence of latitudinal diversity gradients for TD, FD, and PD in hyperdiverse Amazonian terra firme forests. Our results agree well with the predictions of the environmental filtering principle and the favourability hypothesis, even acting in a 10°C latitudinal range within tropical climates.

Floristic diversity, composition and dominance across Amazonian forest types respond differently to latitude

“…Our study showed latitudinal changes in soils properties, with an increase in soil fertility and a decrease in pH towards the Equator (Figure S1;Ben Saadi et al, 2022). These properties affect the species diversity, performance and composition at local scales (Bañares- de-Dios et al, 2022).…”

“…A higher ecosystem productivity results in higher speciation, and ability to maintain species in the ecosystem (Loreau, 2000), resulting in lower extinction rates (Brown, 2014). Our study showed latitudinal changes in soils properties, with an increase in soil fertility and a decrease in pH towards the Equator (Figure S1;Ben Saadi et al, 2022). These properties affect the species diversity, performance and composition at local scales (Bañares- de-Dios et al, 2022).…”

“…This, along with the terrain flatness and low elevation, leads to homogeneous soil conditions between sites. Rare species occurrence is susceptible to changing edaphic conditions (Ben Saadi et al, 2022), then the contribution of rare species to alpha diversity decreases in stable soils. Thereby, homogeny in floodplain soils suggests that diversity might be primarily driven by the most limiting factor: flooding regimes and its effect on soil water content and saturation.…”

“…Since both climatic and edaphic variables can affect floristic patterns (Bañares- de-Dios et al, 2022), we first retrieved regional values of all BIOCLIM V1.1 layers from the global 'CHELSA' model at 1 km 2 resolution (Karger et al, 2017), and soil data (pH, soil organic carbon in fine earth g/kg, clay, sand, silt, volume fraction of coarse fragments (>2 mm)) from the global 'SoilGrids' database at 1 km 2 resolution and 15 cm depth (Hengl et al, 2017). Pearson's correlation coefficients between the variables and latitude were high (r > ± 0.7); therefore, the latitudinal gradient might imply a gradient also in the selected variables.…”

Ecological drivers of taxonomic, functional, and phylogenetic diversity of bryophytes in an oceanic island

“…This result aligns with previous evidence showing that vegetation structure and climate play a key role in explaining patterns of biodiversity facets at both global and regional scales (Feng et al., 2020 ; Prescott et al., 2016 ; Rurangwa et al., 2021 ), including bryophytes (Chen et al., 2017 ; Collart et al., 2024 ; Ilić et al., 2023 ; Mežaka et al., 2012 ; Shen et al., 2023 ). At the local scale, environmental filtering associated with elevation, climate, and habitat structure played a more important role in shaping α‐ and β‐components of TD, FD, and PD in bryophytes (Araújo et al., 2022 ; Chen et al., 2017 ) and spermatophytes (Ben Saadi et al., 2022 ; Culmsee & Leuschner, 2013 ). On Madeira Island, both precipitation and vegetation are strongly determined by elevation and slope at the local scale (Capelo et al., 2005 ; Sim‐Sim et al., 2014 ), a situation that reinforces the role of these ecological drivers on the three facets of α‐ and β‐diversities and community assembly.…”