The roles of elevation and local environmental factors as drivers of diatom diversity in subarctic streams

Abstract

Summary High latitude and altitude freshwater systems are highly sensitive to the effects of global warming and associated environmental changes. Diatoms are widely used as sentinels of environmental change, yet knowledge of diatom community patterns in high latitude and altitude streams remains limited. The aim of this study was to examine alpha and beta diversity of diatoms in subarctic streams in Finland and Norway, and to determine the importance of local environmental factors and elevation in shaping their community patterns. We also aimed at testing, for the first time, whether microbes conform to Rapoport's elevational rule, which states that species occurring at higher elevations have generally larger elevational ranges than species at lower elevations. Three streams (44 sites in total) with an altitudinal gradient of 21–877 m a.s.l. were sampled. Generalized linear models, hierarchical partitioning, and a boosted regression tree method were used to identify drivers of diatom species richness. We ran Mantel tests, and calculated initial similarities and elevational halving distances to examine beta diversity. There were no apparent richness–elevation relationships within streams. Across all study streams, the water depth was the most important factor for richness, with additional influences by stone size, conductivity, pH and elevation. Diatoms in subarctic streams did not conform to Rapoport's elevational rule. Community similarity decreased significantly with elevational distance while distance decay was weaker with environmental distance. Our results suggest that diatom alpha and beta diversity along stream elevational gradients are shaped by interacting local environmental factors such as water depth and substrate size, indicating vulnerability of diatoms to physical disturbances, and regional factors such as dispersal and geographical variables. Diatom diversity patterns do not seem to concur with patterns often observed for larger organisms as no consistent elevational patterns in richness or range sizes were found.

Biodiversity change is uncoupled from species richness trends: Consequences for conservation and monitoring

“…Empirically, we showed that the relative magnitude of richness change was orders of magnitude smaller than the actual occurrences of extinctions and immigrations (see Figure ), leading to substantial turnover not only of rare species, but also in identity and relative abundance of dominant species (SER a , see Figure d–f). Thus, major aspects of biodiversity change are not (and cannot be) reflected by changes in species richness—consistent with previous studies showing larger changes in composition than richness across temporal and spatial environmental gradients (Hillebrand, Soininen, & Snoeijs, ; Teittinen, Kallajoki, Meier, Stigzelius, & Soininen, ). In addition, our analyses showed that richness trends in and of themselves do not allow conclusions on the effect of a management practice, be it a negative impact or a positive conservation effort, on biodiversity.…”

Association between temporal and spatial beta diversity in phytoplankton

“…The significant pattern in summer agreed with the studies reviewed by Soininen et al (2007b) and recent studies in diatoms (Teittinen et al 2016). This finding may be due to the relatively small ranges in the measured environmental variables or the fact that we missed some spatially structured abiotic or biotic factors that may have been influential to the distance decay patterns (Teittinen et al 2016). The lack of consistency in distance decay pattern between spring and summer could be explained by comparing the effects of the environmental and spatial variables on beta diversity (based on abundance and presence-absence data).…”

“…However, there is no consensus on the distance decay relationship across organism groups, geographic gradients and environments (Soininen et al 2007b). The significant pattern in summer agreed with the studies reviewed by Soininen et al (2007b) and recent studies in diatoms (Teittinen et al 2016). The non-significant pattern in spring was consistent with the findings of 18 lakes in Canada (Beisner et al 2006) and in the floodplain lakes of Brazil (Nabout et al 2009).…”

“…The importance of pH for diatom composition was also found in some streams (Teittinen et al 2016, Wang et al 2017). The two-season temporal turnover was also remarkably affected by the difference in temperature and pH between spring and summer, lake areas and nitrogen levels, and increased with these variables.…”

Geo‐climatic factors drive diatom community distribution in tropical South American freshwaters

“…For diatoms (unicellular siliceous algae), all the above‐mentioned ecological drivers have been recognized as key factors in driving community structure (diversity and community composition) across mid‐ and high‐latitude regions of Eurasia and North America (Bennett, Cumming, Ginn, & Smol, ; Bouchard, Gajewski, & Hamilton, ; Passy, ; Potapova & Charles, ; Teittinen, Kallajoki, Meier, Stigzelius, & Soininen, ; Vyverman et al., ). Yet, studies in tropical South America are often restricted to a single geographical region (e.g.…”