Abstract
Disentangling the relative importance of deterministic and stochastic processes in shaping natural communities is central to ecology. Studies about community assembly over broad temporal and spatial scales in aquatic microorganisms are scarce. Here, we used 16S rDNA sequence data from lake sediments to test for community assembly patterns in cyanobacterial phylogenies across ten European peri-Alpine lakes and over a century of eutrophication and climate warming. We studied phylogenetic similarity in cyanobacterial assemblages over spatial and temporal distance, and over environmental gradients, comparing detected patterns with theoretical expectations from deterministic and stochastic processes. We found limited evidence for deviation of lake communities from a random assembly model and no significant effects of geographic distance on phylogenetic similarity, suggesting no dispersal limitation and high levels of stochastic assembly. We detected a weak influence of phosphorus, but no significant effect of nitrogen levels on deviation of community phylogenies from random. We found however a significant decay of phylogenetic similarity for non-random communities over a gradient of air temperature and water column stability. We show how phylogenetic data from sedimentary archives can improve our understanding of microbial community assembly processes, and support previous evidence that climate warming has been the strongest environmental driver of cyanobacterial community assembly over the past century.
Highlights
Understanding the mechanisms that determine changes in the structure and composition of natural communities over large spatial and temporal scales is critical, given the impacts that human activities have on biodiversity and ecosystem functions[1]
Based on Nearest Taxon Index (NTI), 58% of cyanobacterial communities showed a phylogenetic structure that significantly differed from the null expectation (Fig. 2)
Our previous work has shown that DNA-based reconstructions of cyanobacterial communities are robust[16,29], the observed patterns are unlikely to be driven by biases in sedimentary DNA-based community reconstructions[2]
Summary
Understanding the mechanisms that determine changes in the structure and composition of natural communities over large spatial and temporal scales is critical, given the impacts that human activities have on biodiversity and ecosystem functions[1]. The relative importance of stochastic and deterministic processes driving community assembly might vary over space and time: environmental conditions, dispersal, demographic stochasticity, ecological interactions and evolutionary processes can all influence the structure of natural communities across scales[2,3,4,5,6,7]. We expect that comparison of phylogenetic structures to null-model simulations, combined with the patterns of community phylogenetic similarity across lakes and spatial or ecological distance, will allow us to test for deterministic and stochastic signatures in cyanobacterial community assembly
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