Geographical patterns of micro-organismal community structure: are diatoms ubiquitously distributed across boreal streams?

Abstract

A topic under intensive study in community ecology and biogeography is the degree to which microscopic, as well as macroscopic organisms, show spatially‐structured variation in community characteristics. In general, unicellular microscopic organisms are regarded as ubiquitously distributed and, therefore, without a clear biogeographic signal. This view was summarized 75 years ago by Baas‐Becking, who stated “everything is everywhere, but, the environment selects”. Within the context of metacommunity theory, this hypothesis is congruent with the species sorting model. By using a broad‐scale dataset on stream diatom communities and environmental predictor variables across most of Finland, our main aim was to test this hypothesis. Patterns of spatial autocorrelation were evaluated by Moran's I based correlograms, whereas partial regression analysis and partial redundancy analysis were used to quantify the relative importance of environmental and spatial factors on total species richness and on community composition, respectively. Significant patterns of spatial autocorrelation were found for all environmental variables, which also varied widely. Our main results were clear‐cut. In general, pure spatial effects clearly overcame those of environmental effects, with the former explaining much more variation in species richness and community composition. Most likely, missing environmental variables cannot explain the higher predictive power of spatial variables, because we measured key factors that have previously been found to be the most important variables (e.g. pH, conductivity, colour, phosphorus, nitrogen) shaping the structure of diatom communities. Therefore, our results provided only limited support for the Baas‐Becking hypothesis and the species sorting perspective of metacommunity theory.

Disentangling the roles of spatial and environmental variables in shaping benthic algal assemblages in rivers of central and northern China

“…Envir) contributed 41, 27, and 32 % to the total explained variation, respectively. This result was similar to another study that not only conducted on the same spatial scale but also used eigenvectorbased method to detect geographic patterns of diatom communities in Finnish streams (Heino et al 2010). Actually, the roles of environment and space in shaping stream algal communities are scale-dependent (Cottenie 2005;Soininen 2007).…”

“…Some environmental variables that we did not measure such as geomorphological characteristics, substrate and soil type, and soil erosion rate display certain degree of spatial changes within this region (Zhao 1995). These spatially structured unmeasured environmental variables could also contribute to regional patterns of algal assemblages (Soininen 2007;Heino et al 2010).…”

Environmental and spatial processes determining Ephemeroptera (Insecta) structures in tropical streams

“…Only recently, ecologists have started to realize that local diversity also reflects pressure from global processes, such as dispersal and particular historical conditions (Ricklefs, 1987). The traditional view of community structure, based on local interspecific interactions and spatial niche, was replaced by more recent ideas emphasizing community structure as a result of multiple processes acting on different spatial scales (Heino et al, 2010).…”

Effects of patch connectivity and heterogeneity on metacommunity structure of planktonic bacteria and viruses

“…These predictions are consistent with the wide distribution patterns of many microbial taxa (Short and Suttle, 2002;Fenchel and Finlay, 2004;Short and Suttle, 2005) and strong associations between community composition and environmental gradients (Beisner et al, 2006;De Bie et al, 2012). However, studies covering a broad range of spatial scales, varying from widely separated extreme habitats (Papke et al, 2003;Whitaker et al, 2003), stream networks (Heino et al, 2010), rock pool clusters (Langenheder and Ragnarsson, 2007), and individual salt marshes (Martiny et al, 2011), suggest that microbial dispersal can be too slow to counteract community differentiation resulting from ecological drift. In light of such mixed evidence from field studies, there is a strong need for experimental tests of dispersal limitation in microbial metacommunities.…”