Proposed Metacommunity dynamics

Our study shows kettle holes within a certain area (here, the analyzed Uckermark region) to harbour similar species in the active soil egg banks, irrespective of local environmental parameters (such as hydroperiod or pH) and geographic distance. We cannot rule out the possibility that our hatching conditions acted as an unconscious filter, as we may have overlooked some species that did not hatch under our experimental conditions. However, this was an unavoidable trade-off because we intended to examine ”true” dispersal (vertical/horizontal), which only occurs when viable resting stages are present/transported. An investigation of the whole soil without a previous hatching test would not have allowed for a distinction between dead and living organisms. We found higher species richness in the resting egg bank of ephemeral, relative to permanent kettle holes, in line with findings of Olmo et al. (2020). Yet, there is a similar community of resting stages in the soils of different kettle holes, implying that there is sufficient dispersal at the landscape scale to homogenize occurrence of those zooplankton groups which generate resting stages (ostracods, cladocerans, copepods, and rotifers). This similarity of the species found as viable resting stages in the sediment of different kettle holes, irrespective of distance, points towards no current or previous dispersal limitation within our metacommunity (Kleyheeg et al., 2017; Vanschoenwinkel et al., 2008). It appears – on the geographic scale of our study - that potentially any species could reach any kettle hole. In so far, our studied kettle hole system is indeed a true metacommunity, in which dispersal limitations (paradigm of patch dynamics ) and random loss and gain of species from the regional species pool (neutral model ) most likely can be excluded as major determinants of community assembly (Cottenie & De Meester, 2005). The overall similarity in species composition locally present as resting stages would have gone undetected, if only the open water community composition had been analysed. This further underlines that the underlying dynamics of a zooplankton metacommunity can only be understood, if dormant stages are included (Wisnoski et al., 2019).
Despite of an apparent lack of dispersal limitations among open water bodies and soil egg banks, we found a high species heterogeneity among the different kettle holes. Here, the positive correlation of environmental distance and community dissimilarity renders environmental filtering /species sorting the most likely driver of the observed zooplankton communities. Consequently, distinct local communities reflect the differences of the heterogeneous environments in the studied metacommunity system. Species sorting may be particularly pronounced in permanent systems because those might be more stable through time (Cottenie et al., 2003), exhibiting more competition and potentially competitive exclusion.
The prevalence of species sorting over dispersal limitations for metacommunity assembly may however be related to the geographic scale of our study. It might change across spatial scales, with species sorting as the main process on the smaller spatial scale we had focussed on, while dispersal limitations potentially becoming a structuring force over a larger spatial scale (Declerck et al., 2011; Heino et al., 2015).
The data on which our study is based meet the criteria proposed for the analysis of metacommunity dynamics (Louge et al., 2011) by providing species abundances, spatial data, and environmental data. In addition, by providing a ”temporal” component, we were able to compare different seasonal stages, as well as to gain insight into the active egg bank and thus putative vertical dispersal in these kettle holes. By focusing on only two years, however, we cannot yet draw conclusions about evolutionary (Pillar & Duarte, 2010) or historical community assembly processes (Fukami et al., 2010).