Diatom β‐diversity in streams increases with spatial scale and decreases with nutrient enrichment across regional to sub‐continental scales

Abstract

Aim To quantify the relative contributions of local community assembly processes versus γ‐diversity to β‐diversity, and to assess how spatial scale and anthropogenic disturbance (i.e. nutrient enrichment) interact to dictate which driver dominates. Location France and the United States. Time period 1993–2011. Major taxa studied Freshwater stream diatoms. Methods β‐diversity along a nutrient enrichment gradient was examined across multiple spatial scales. β‐diversity was estimated using multi‐site Sørensen dissimilarity. We assessed the relative importance of specialists versus generalists using Friedley coefficient, and the contribution of local community assembly versus γ‐diversity to β‐diversity across spatial scales, with a null model. Finally, we estimated the response of β‐diversity to environmental and spatial factors by testing the correlations between community, environmental and geographical distance matrices with partial Mantel tests. Results β‐diversity generally increased with spatial scale but the rate of increase depended on nutrient enrichment level. β‐diversity decreased significantly with increasing nutrient enrichment level due to the loss of specialist species. Local assembly was an important driver of β‐diversity especially under low nutrient enrichment. Significant partial Mantel correlations were observed between diatom β‐diversity and pure environmental distances under these conditions, highlighting the role of species sorting in local assembly processes. Conversely, in heavily enriched sites, only spatial distances were significantly correlated with β‐diversity, which indicated a substantial role of dispersal processes. Main conclusions Nutrient concentration mediated the expected increase in β‐diversity with spatial scales. Across spatial scales, β‐diversity was more influenced by local assembly processes rather than by γ‐diversity. Nutrient enrichment was associated with an overall decline in diatom β‐diversity and a shift in assembly processes from species sorting to dispersal, notably due to the elimination of some specialists and their subsequent replacement by generalists.

Biodiversity patterns of Arctic diatom assemblages in lakes and streams: Current reference conditions and historical context for biomonitoring

“…pH, alkalinity, nutrients), providing additional important influences on the richness and composition of diatom assemblages (Douglas & Smol, 2010; Michelutti, Douglas, & Smol, 2006; Passy et al, 2018; Smol & Douglas, 2007a; Wolfe, 2002). It is likely that diatom richness in circum‐Arctic streams is influenced by similar factors as in lakes, but stream system studies are less common (but see Leboucher et al, 2019; Pajunen, Luoto, & Soininen, 2016). In a recent study using data from stream localities in the U.S.A. and Finland, Passy et al (2018) showed that a decline in diatom species richness with increasing latitude could be coupled to decreasing temperature and nutrients (total phosphorus concentrations), suggesting that factors other than climate are also important drivers of species richness in high latitude regions.…”

“…It is likely that diatom richness in circum-Arctic streams is influenced by similar factors as in lakes, but stream system studies are less common (but see Leboucher et al, 2019;Pajunen, Luoto, & Soininen, 2016). In a recent study using data from stream localities in the U.S. A.…”

Environment regimes play an important role in structuring trait‐ and taxonomy‐based temporal beta diversity of riverine diatoms

“…the regional species pool) diversities (Whittaker, 1960; Whittaker, 1972). During the past several decades, researchers have paid considerable attention to beta diversity (Anderson et al, 2011; Leboucher et al, 2019). However, a common limitation of those investigations is that community information was often collected from a single date (Heino et al, 2015; Sinclair et al, 2021), either because of the complications involved in sampling across seasons or due to the study objective that did not consider temporal variation.…”

A metacommunity approach for detecting species influenced by mass effect

“…Our results are thus consistent with Goldenberg Vilar et al (2014), who concluded that in high productivity environments the mass effect process seems to play a prominent role in structuring diatom communities. More generally, previous studies suggested that nutrient enrichment weakened the influence of species sorting in favour of mass effect, which became a more important driver of community composition (Leboucher et al., 2019). This may also explain the basin‐specific differences in the group assignments of the species.…”

“…We tested our approach on microscopic passive dispersers, stream diatoms, which are important primary producers in freshwater ecosystems (Likens, 1975; Potapova & Charles, 2002). Diatoms were shown to be structured by environmental filtering (Verleyen et al., 2009), dispersal (Göthe, Angeler, Gottschalk, Löfgren, & Sandin, 2013; Vanormelingen, Verleyen, & Vyverman, 2008; Vyverman et al., 2007) or both (Jamoneau et al., 2018; Leboucher et al., 2019; Soininen, Jamoneau, Rosebery, & Passy, 2016). In this respect, biovolumes and ecological guilds have been, in some studies, related to the strength of the spatial patterns (De Bie et al., 2012; Goldenberg Vilar et al, 2014; Heino & Soininen, 2006; Jamoneau et al., 2018), small organisms being more sensitive to dispersal‐driven processes and motile species being more strongly affected by mass effect.…”