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The Elements of Metacommunity Structure (EMS) framework gives rise to important ecological insights through the distinction of metacommunities into several different idealised structures. We examined the EMS in assemblages occupying a low-mountain river system in central Germany, sampled over three consecutive years. We compared the idealised distributions of assemblages in both the riparian floodplain zone (carabid beetles and spiders) and the benthic instream environment (benthic invertebrates). We further grouped instream organisms into taxonomic and trait groups to examine whether greater competition signal emerges in more similar species groups. We found little evidence of strong competition, even for trait-modality groups, and nestedness was almost non-existent. In addition to random distributions, Gleasonian distributions (indicating clear, but individualistic turnover between sites) were the most commonly identified structure. Clear differences were apparent between different trait groups, particularly between within-trait modalities. These were most evident for different dispersal modes and life cycle durations, with strong dispersers showing possible signs of mass effects. While random distributions may have partly reflected small sample sizes, clearly coherent patterns were evident for many groups, indicating a sufficient gradient in environmental conditions. The prevalence of random distributions suggests many species are responding to a variety of environmental filters in these river-floodplain metacommunities in an anthropogenically-dominated landscape, whereas Gleasonian distributions indicate species are responding idiosyncratically to a primary environmental gradient. Our findings further emphasise the prevalence of context dependency (spatio-temporal variability) in metacommunity studies and emphasise the need to further disentangle the causes of such variation.
This will be submitted to Oecologia.
Results of Elements of Metacommunity Structure analysis examining the best-fit idealised metacommunity structure for each group in each year. Results are given for the first two axes of reciprocal averaging ordination on the species by site matrices testing for coherence, species range turnover and boundary clumping in 15 sites along the Kinzig River, central Germany, sampled over three years. Abs = number of embedded absences, Re = number of replacements, MI = Morista’s Index, SD = standard deviation. Mean and SD values are those calculated from the 1000 generated null matrices.