The challenges of detecting underlying mechanisms for priority effects in complex bacterial lake communities
During community coalescence, immigration history can be decisive for the composition of the developing community. For example, an early arriving pioneer can inhibit the immigration success of a late invader by resource consumption/alteration, also known as priority effects. In simple model communities, the strength of priority effects has been shown to vary with nutrient availability as it promotes growth and, thus, the impact of the first pioneer. However, little is known about the effect of nutrient availability on priority effects in complex bacterial communities. In this study, we conducted an experiment with the aim to test the importance of priority effects in bacterial lake communities at different nutrient levels and over different dispersal rates of two dissimilar communities. One community was incubated first (“pioneer”) and a second community invaded later (“invader”). We hypothesized strongest priority effects in high nutrient levels and in low dispersal rates of the invader.  Our results showed highest importance of environmental selection for community composition in the experiment. While arrival history also had a weak effect, we were not able to link our results to priority effects. Instead, we determined methodological errors in the experiment and gave an outlook to future studies working on priority effects with complex bacterial communities.