Comparing Continental and Local Distribution Patterns of Protists: A Case Study of Silica-Scaled Chrysophytes

Free-living protists play important roles in biogeochemical cycling and food-web chains in both aquatic and terrestrial environments. However, their biogeography and spatial distribution remain poorly resolved. Here, we used silica-scaled chrysophytes to determine the most important climatic, historical, and environmental variables that explain biodiversity patterns across different geographical scales; the continental scale was represented by 473 European sites (gradient of 3,800 km), the local scale comprised 69 Aquitanien (France) sites (gradient of 186 km). Generalized Additive Models were used to evaluate the relationship between species richness and explanatory variables. Partition of community variance into fractions, explained separately by local environment, history, and climate helped us to track the main drives of community composition. While species richness was evenly influenced by all factors at the European scale and predominantly by environment (pH) at the local scale, the main factor shaping community composition was climate at both scales and history (geographical distance) at the European scale. Our results showed that silica-scaled chrysophytes respond strongly to climate-related variables at a broad geographical scale. Our work highlights the effect of climate on protist biogeographic structuring and suggests that climate-related variables may represent one of the main drivers of protist distribution, similarly as in macroorganisms.