The Influence of Environmental, Biotic and Spatial Factors on Diatom Metacommunity Structure in Swedish Headwater Streams

Abstract

Stream assemblages are structured by a combination of local (environmental filtering and biotic interactions) and regional factors (e.g., dispersal related processes). The relative importance of environmental and spatial (i.e., regional) factors structuring stream assemblages has been frequently assessed in previous large-scale studies, but biotic predictors (potentially reflecting local biotic interactions) have rarely been included. Diatoms may be useful for studying the effect of trophic interactions on community structure since: (1) a majority of experimental studies shows significant grazing effects on diatom species composition, and (2) assemblages can be divided into guilds that have different susceptibility to grazing. We used a dataset from boreal headwater streams in south-central Sweden (covering a spatial extent of ∼14000 km2), which included information about diatom taxonomic composition, abundance of invertebrate grazers (biotic factor), environmental (physicochemical) and spatial factors (obtained through spatial eigenfunction analyses). We assessed the relative importance of environmental, biotic, and spatial factors structuring diatom assemblages, and performed separate analyses on different diatom guilds. Our results showed that the diatom assemblages were mainly structured by environmental factors. However, unique spatial and biological gradients, specific to different guilds and unrelated to each other, were also evident. We conclude that biological predictors, in combination with environmental and spatial variables, can reveal a more complete picture of the local vs. regional control of species assemblages in lotic environments. Biotic factors should therefore not be overlooked in applied research since they can capture additional local control and therefore increase accuracy and performance of predictive models. The inclusion of biotic predictors did, however, not significantly influence the unique fraction explained by spatial factors, which suggests low bias in previous assessments of unique regional control of stream assemblages.

Contribution of microspatial factors to benthic diatom communities

“…4). This was in accordance with Abbreviations of environmental variables as in Table 2 Hydrobiologia (2014) 732:49-60 55 Passy (2007) and Tang et al (2013), but not consistent with Potapova & Charles (2002), Urrea & Sabater (2009), Smucker & Vis (2011 and Göthe et al (2013). For example, Passy (2007) found that the unique contribution of spatial dataset (16%) to the explained diatom variance was higher than that of environmental variables (9%).…”

“…However, Urrea & Sabater (2009) got a less influence of spatial factors (6.1%) than physicalchemistry variables (11.3%) on diatom community. Similarly, local environmental variables were considered to have much higher contribution (than spatial variables) to the total explained variation of diatom data (Potapova & Charles, 2002;Smucker & Vis, 2011;Göthe et al, 2013). The large sampling scale in the present study is likely a reason for the above finding.…”

“…The relative importance of environmental and spatial factors on stream diatom assemblage has been recently assessed in Europe and North America (e.g., Potapova & Charles, 2002;Rimet et al, 2007;Smucker & Vis, 2011;Göthe et al, 2013). However, except for Tang et al (2013), no study to our knowledge has been reported in Asian countries such as China.…”

Similar small-scale variation of diatom assemblages on different substrates in a mesotrophic stream

“…We suggest that in a medium-order stream that it is mainly velocity that is shaping the diatom community at the decimeter scale, as shown by PASSY (2001). At smaller scales, grazing could have an important impact on algal communities (GOTHE et al 2013, O'DRISCOLL et al 2014, probably together with historical events following dispersal (MÜLLER-HAECKEL 1976) and also the named »complex interaction of abiotic conditions« (e.g. KEMP and DODDS 2001).…”

Strong spatial turnover in cichlid fish assemblages in the upper río Madera (Amazon basin) despite the absence of hydrological barriers

“…Unfortunately, our landscape data were limited to a subset of variables, lacking information on habitat structure or occurrences of other species than cichlids. It is likely that cichlid species composition is structured not only by underlying landscape gradients but also by biotic interactions (Rae et al, 2006;Meier et al, 2010;Göthe et al, 2013). Whether this is competition, food resources, or some other aspect of interspecific interactions remains to be seen in future studies.…”