Geo‐climatic factors drive diatom community distribution in tropical South American freshwaters

Abstract

Patterns that maintain and generate biodiversity of macro‐organisms in the Neotropics are widely discussed in the scientific literature, yet the spatial ecology of micro‐organisms is largely unknown. The unique character of the tropical Andes and adjacent Amazon lowlands generates a wide gradient of environmental conditions to advance our understanding of what drives community assembly and diversity processes. We analysed the distribution patterns of benthic diatoms (unicellular siliceous algae) as a model group of microbial passive dispersers, including predictors that describe limnological and geo‐climatic gradients for a total of 113 waterbodies (0–28°S and 58–80°W), including lakes and streams. Complementary multivariate statistical analyses were performed to correlate (1) community composition and (2) diatom species richness with environmental and spatial factors to infer niche‐based and dispersal‐based assembly processes, respectively. Results showed that two gradients structured both diatom assemblages and waterbodies, namely climate and landscape configuration. Variance partitioning revealed that broadscale spatial variables (distance‐based Moran's Eigenvectors) outperformed the two environmental components (limnological and geo‐climatic), suggesting dispersal‐assembled communities. However, diatom assemblages were structured by geo‐climatic (regional) factors in certain lakes in the northern and central Andes, although their effects were partially manifested via local variables after the geographical distances were factored out. In a similar way, climatic and topographic structuring homogenized lake and stream communities within ecoregions, as indicated by the strong overlap between the two community types and the weak correlation between biota and limnological variables. Notably, a significant increase in diatom species richness was related to increased water connectivity, interpreted to indicate that a decrease in the remoteness of the system increase species number. Synthesis. We emphasize the strength of macroecological gradients (landscape configuration and climatic factors) in affecting both diatom diversity and community composition in the South American tropics. In this context, our results and the commonalities of ecoregion patterning with groups of macro‐organisms (vegetation) suggest the need to integrate microbial ecology into a macroecology framework to unravel mechanisms behind diversity gradients.

Lake regionalization and diatom metacommunity structuring in tropical South America

“…A previous study of the region, Benito et al. () showed that water temperature and climatic variables (MAP, MAT) are correlated at the spatial scale of the data used for this study. Also, other limnological variables (conductivity, pH, and nutrients) were outperformed by macroecological gradients associated with distinct climatic and topographic conditions, because local environmental conditions are temporally unstable compared with geo‐climatic variables, such as elevation, catchment geology, and ecoregion in lakes of tropical Andes and adjacent lowlands (Benito et al., ).…”

“…() show that geo‐climatic variables might be partially manifested via local limnological variables in Andean lakes of Peru and Ecuador. Here, we used PCA site scores to capture latent environmental variables and likely those local variables (e.g., nutrients) that are spatially patterned and outperformed by macroecological variables in most groups of our study lakes (Benito et al., ), and hence use environmental drivers of lakes’ clustering to infer niche‐based assembly processes (e.g., Steinitz‐Kannan et al., ). Nonetheless, the relative influence of space over environmental factors, as indicated by variance partitioning (Figure ), provided limited evidence for niche assembled diatom communities at a regional metacommunity scale.…”

Identifying temporal and spatial patterns of diatom community change in the tropical Andes over the last c. 150 years

“…We also detected covariance between large‐scale spatial effects and water chemistry, suggesting that diatom species respond to limnological gradients imposed by spatial structure (Figure d and Table S2). Previous studies comparing the limnological characteristics of inter Andean and páramo lakes of Ecuador found covariation of nutrient concentrations with topography (Benito, Fritz, Steinitz‐Kannan, Tapia, et al., ; Steinitz‐Kannan et al., ). Lakes located in the inter Andean plateau have larger ranges of nutrients and conductivity (Table ), primarily driven by higher human population densities and land use.…”

Fifteen important questions in the spatial ecology of diatoms

“…Recently, a study on South American lakes and streams (210–5,070 m a.s.l.) revealed more evidence for the negative effect of elevation on diatom richness (Benito et al., ). In contrast, in a survey of Himalayan streams stretching from 350 to 4,700 m a.s.l., no apparent relationship between diatom richness and elevation was observed, possibly due to disturbance frequency in such systems (Jüttner, Chimonides, Ormerod, & Cox, ).…”