Processes structuring desmid communities - phylogenetic approach

Background/Question/Methods

Our study was aimed at processes forming ecological communities. Are the processes niche-related or neutral? This question is one of the most debated in ecology. As a model we used desmid communities in peat bogs. Desmids are streptophyte algae (Desmidiales, Zygnematophyceae) closely related to vascular plants. In peat bogs they are one of the dominant microphytobethic groups. We took advantage of the method which includes evolutionary history of species into ecological research – phylogenetic structure of communities – as it is useful as a tool for revealing processes structuring those communities. The main idea of this method is that communities facing environmental stress contain closely related species that probably share traits that favour them in harsh environment.

In total, we analysed more than a hundred desmid communities from peat bogs in Europe. As a measure for evolutionary history of species we used phylogenetic relationships inferred from nearly four hundred unique rbcL sequences. We calculated several most used measures of phylogenetic structure and compared those with environmental data available.

Results/Conclusions

Most of examined communities were phylogenetically structured. This is in agreement with the hypothesis that they are structured by classical niche-related processes, such as competition and environmental filtering; however, no predominant pattern of phylogenetic structure was discovered. The usage of environmental information showed the influence of pH on a community structure. There was a significant linear correlation between indices of phylogenetic structure and pH. Low pH acted as a strong environmental filter. Under the influence of this filter communities were composed of closely relates species. Localities with higher pH hosted communities of distantly related species, i.e. significantly phylogenetically overdispersed; in the absence of environmental stress, the communities were possibly structured by competition. No significant influence of conductivity and geographical distance on phylogenetic structure of desmids communities in peat bogs was found. We identify low pH as a single most important stress factor influencing the community assembly of desmids in peat bogs.