Figure 4: Co-occurence plot of the most common merolimnic
species that occur at least in 10 % of the samples. Diptera are
excluded because species richness was too high to visualize clearly. A
separate plot for Diptera is presented in supplementary figure S19.
The indicator species analysis identified most species indicative for a
certain season or seasons when either winter or spring samples were
included in the combinations: autumn + spring + winter: 35 indicator
species; spring + winter: 30; winter: 24; spring: 20. Groups including
the summer samples showed the lowest number of indicator species: autumn
+ summer: 2 indicator species; summer: 1; autumn + summer + winter: 1;
spring + summer + winter: 1, indicating the presence of few species
characteristic only for summer. Some species were exclusively found in
one season, like the Plecoptera Protonemura nitida in autumn and
the Trichoptera Chaetopteryx major in winter (see also Figure 4
& S18). Species not found in summer, but quite frequently in all other
seasons, were Trichoptera Silo piceus, Potamophylax latipennis,Plecoptera Nemoura flexuosa, Diptera Tipula paludosa,
Rheocricotopus atripes, Coleoptera Platambus maculatus and
Annelida Tubifex tubifex . Species that were almost exclusively
(high A value) and often (high B value) found in spring and winter
included Trichoptera Glyphotaelius pellucidus, Limnephilus
flavicornis, Halesus radiatus and Plecoptera Nemurella pictetii,
Isoperla grammatica . Here, results were congruent with the NMDS and
co-occurrence plots showing a clear distinction between summer and
winter samples. In some cases, more than one OTU was assigned to the
same species. Here, most OTUs showed similar association values.
However, for Baetis vernus the different OTUs showed different
associations even though it had no significant association to any
season(s) when all OTUs were combined. One OTU was significantly
associated with autumn, one with autumn + spring and two with autumn +
spring + summer.