Metacommunity analyses show increase in ecological specialisation throughout the Ediacaran

The first animals appear during the late Ediacaran (572 – 541 Ma); an initial diversity increase was followed by a drop, interpreted as catastrophic mass extinction. We investigate the processes underlying these changes using the “Elements of Metacommunity Structure” framework. The oldest metacommunity was characterized by taxa with wide environmental tolerances, and limited specialisation and inter-taxa interactions. Structuring increased in the middle metacommunity, with groups of taxa sharing synchronous responses to environmental gradients, aggregating into distinct communities. This pattern strengthened in the youngest metacommunity, with communities showing strong environmental segregation and depth structure. Thus, metacommunity structure increased in complexity, with increased specialisation and resulting competitive exclusion, not a catastrophic environmental disaster, leading to diversity loss in the terminal Ediacaran, revealing that the complex eco-evolutionary dynamics associated with Cambrian diversification were established in the Ediacaran.

Variable elements of metacommunity structure across an aquatic-terrestrial ecotone

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.

Variable elements of metacommunity structure across an aquatic-terrestrial ecotone

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.