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).