Regional species pools control community saturation in lake phytoplankton

Abstract

Recent research has highlighted that positive biodiversity -ecosystem functioning relationships hold for all groups of organisms, including microbes. Yet, we still lack understanding regarding the drivers of microbial diversity, in particular, whether diversity of microbial communities is a matter of local factors, or whether metacommunities are of similar importance to what is known from higher organisms. Here, we explore the driving forces behind spatial variability in lake phytoplankton diversity in Fennoscandia. While phytoplankton biovolume is best predicted by local phosphorus concentrations, phytoplankton diversity (measured as genus richness, G) only showed weak correlations with local concentrations of total phosphorus. By estimating spatial averages of total phosphorus concentrations on various scales from an independent, spatially representative lake survey, we found that close to 70 per cent of the variability in local phytoplankton diversity can be explained by regionally averaged phosphorus concentrations on a scale between 100 and 400 km. Thus, the data strongly indicate the existence of metacommunities on this scale. Furthermore, we show a strong dependency between lake productivity and spatial community turnover. Thus, regional productivity affects beta-diversity by controlling spatial community turnover, resulting in scale-dependent productivity-diversity relationships. As an illustration of the interaction between local and regional processes in shaping microbial diversity, our results offer both empirical support and a plausible mechanism for the existence of common scaling rules in both the macrobial and the microbial worlds. We argue that awareness of regional species pools in phytoplankton and other unicellular organisms may critically improve our understanding of ecosystems and their susceptibility to anthropogenic stressors.

Temporal variation of β-diversity and assembly mechanisms in a bacterial metacommunity

“…Further to this, a significant positive correlation was also found between b-diversity and chlorophyll a concentration, that is, an estimator of the biomass of primary producers, further supporting that the positive b-diversity-productivity relationship was the most prevailing pattern in our study. An increase in b-diversity with increasing productivity is frequently observed in nature as well as in experiments (Chase and Leibold, 2002;Chalcraft et al, 2008;Ptacnik et al, 2010), and previous studies have also shown that regions or metacommunities with higher environmental variability have higher b-diversity (Verleyen et al, 2009) and lower degrees of regional invariance (Ö stman et al, 2010). Here, we show that similar patterns are found within a single bacterial metacommunity over time.…”

Species traits and species diversity affect community stability in a multiple stressor framework

“…This fact emphasises that the concept of super-species depends on species traits and stressor identity. 'Super-species' occur in several phytoplankton bio diversityecosystem functioning experiments, especially under highly con trolled culture conditions (Ptacnik et al 2010). Natural fluctuations in real ecosystems will potentially reduce the role of such species, as the increased potential niche space allows for a variety of successful trait combinations rather than only one.…”

“…However, the importance of species identity effects in biodiversity−production relationships is frequently found and often related to trait combinations (for a discussion see Hillebrand & Matthiessen 2009). The presence of such 'super-species' that show high performance for multiple situations is a frequent phenomenon in experiments with a small species pool and low complexity of physical or biological structure (Weis et al 2008, Ptacnik et al 2010.…”

Importance of space and the local environment for linking local and regional abundances of microbes

“…In the phytoplankton data sets from Mälardalen and Götaland, LRsite decreased in an eastward direction. This finding coincides with an increase in genus richness of phytoplankton in an eastward direction from the Atlantic coast toward Sweden and Finland, which could be related to changes in average phosphorus concentrations over larger spatial scales (>100 km) (Ptacnik et al 2008(Ptacnik et al , 2010. Whether these 2 patterns are linked and caused by the same mechanisms should be addressed in future studies.…”

“…Yet, regional processes may be important as well, as some studies show that microbial communities display patterns related to spatial differences (Crump et al 2007, Soininen et al 2007, 2011, Vyverman et al 2007 or landscape scale environmental properties (e.g. average phosphorus levels in a region; Ptacnik et al 2008Ptacnik et al , 2010 and that variation in dispersal rates may affect community composition (Lindström & Östman 2011). …”