Browsing by Author "Aarnio, Sonja"

Species are distributed to small-scale local communities by an interplay of environmental and spatial factors. As microbial species with efficient passive dispersal capacity and thus mainly under local environmental control, diatom communities nevertheless consistently show a strong spatial structuring as well. Different metacommunity perspectives have been developed to describe the relationship between environmental and spatial factors and their relative role for local communities. This study aims to examine the relative roles of environmental and spatial factors for diatom species composition and community similarity for defining the dominating metacommunity type among coastal rock pool communities. Factors affecting local species richness are also studied. Rock pools are granitic water-filled depressions occurring in high numbers on coastal rocky outcrops. Due to their clearly delineated borders, hierarchical spatial structure and interacting biota, rock pools are well suited for ecological metacommunity studies. In this study, 30 brackish-watered rock pools located on the coast of the northern Baltic Sea were studied over a three-month period from May to July in the summer of 2016. The data consisted of benthic diatom samples, estimated pool spatial coordinates and relative isolation, and water physiochemical characteristics. Environmental and spatial factors most responsible for variation in species richness and community composition were determined with generalized linear models and redundancy analysis, respectively. The relative roles of environmental and spatial factors for community composition were quantified with variation partitioning. Distance decay in community similarity was further determined with Mantel and partial Mantel tests. According to the results of monthly GLMs, diatom species richness was best explained by water conductivity and rock pool spatial location. Specifically, the distance from the sea had a clear role in regulating pool water physiochemistry and species richness. Variation partitioning revealed that diatom community composition was significantly explained by both environmental and spatial variables in each month. The joint effect of these factors was consistently larger than the pure effects of neither variable group. Environmental and spatial variables most in charge of diatom community composition in RDAs were water conductivity and pool distance from the sea, with a lesser impact of water pH, total phosphorus concentration, temperature and pool isolation. According to Mantel tests, community similarity was significantly related to both environmental and spatial distance between the pools. The influence of environmental factors increased during the summer, accounting for the largest share of the variation in community composition and distance decay of community similarity in June and July. In the light of these findings, the significant role of both environmental ans spatial factors and the overall metacommunity organization in the studied rock pools are best explained by mass effect. It seems that while the variable physiochemical conditions maintain strong environmental control over the local diatom communities consisting of mainly highly specialized species, efficient passive dispersal acts as a continuous supply of more generalist species. This pattern, accompanied with significant distance decay of community similarity eventually leads to spatially heterogeneic and diverse communities with weaker yet significant spatial control.