The metacommunity concept has the potential to integrate local and regional dynamics within a general community ecology framework. To this end, the concept must move beyond the discrete archetypes that have largely defined it (e.g. neutral vs. species sorting) and better incorporate local scale species interactions and coexistence mechanisms. Here, we present a fundamental reconception of the framework that explicitly links local coexistence theory to the spatial processes inherent to metacommunity theory, allowing for a continuous range of competitive community dynamics. These dynamics emerge from the three underlying processes that shape ecological communities: (1) density-independent responses to abiotic conditions, (2) density-dependent biotic interactions and (3) dispersal. Stochasticity is incorporated in the demographic realisation of each of these processes. We formalise this framework using a simulation model that explores a wide range of competitive metacommunity dynamics by varying the strength of the underlying processes. Using this model and framework, we show how existing theories, including the traditional metacommunity archetypes, are linked by this common set of processes. We then use the model to generate new hypotheses about how the three processes combine to interactively shape diversity, functioning and stability within metacommunities.

Statement of authorship:This project was conceived at the sTURN working group, of which all authors are members. PLT developed the framework and model with input from all authors. PLT wrote the model code. PLT and LMG performed the simulations. PLT produced the figures and wrote the first draft with input from LMG and JMC. All authors provided feedback and edits on several versions of the manuscript. Data accessibility:All code for running the simulation model and producing the figures will be archived on Zenodo upon acceptance and the doi will be included at the end of the manuscript. AbstractThe metacommunity concept has greatly advanced our understanding of how spatial dynamics shape ecological communities. To date, this framework has emphasized discrete differences between mechanisms structuring metacommunities (e.g. niche vs. neutral), despite the recognition that assembly processes are continuous. Here we present a fundamental reconception of the framework that explicitly links local coexistence theory to metacommunity theory and allows for a continuous range of competitive metacommunity dynamics. These dynamics emerge from the underlying processes that shape the dynamics of ecological communities: 1) density-independent responses to abiotic conditions, 2) density-dependent biotic interactions, and 3) dispersal. We also incorporate stochasticity in the demographic realization of each of these processes. The traditional metacommunity archetypes exist as discrete regions within this space, but our framework highlights a range of dynamics that are missed in classic metacommunity theory. We formalize this framework using a simulation model that explores the full range of competitive metacommunity dynamics by varying the strength of the underlying processes. We illustrate how the different processes interactively shape the diversity, functioning, and stability of metacommunities. This process-based framework extends the rich history of metacommunity ecology and can be used to generate testable hypotheses on the processes structuring metacommunities in nature.

When habitats are lost, species are lost in the region as a result of the sampling process. However, it is less clear what happens to biodiversity in the habitats that remain. Some have argued that the main influence of habitat loss on biodiversity is simply due to the total amount of habitat being reduced, while others have argued that fragmentation leads to fewer species per site because of altered spatial connectance among extant habitats. Here, we use a unique data set on invertebrate species in ponds spanning six decades of habitat loss to show that both regional and local species richness declined, indicating that species loss is compounded by habitat loss via connectivity loss, and not a result of a sampling process or changes in local environmental conditions. Overall, our work provides some of the clearest evidence to date from a longitudinal study that habitat loss translates into species loss, even within the remaining habitats.

-We investigated the chemical characteristics of the astatic soda pans in the Carpathian Basin based on comprehensive new and archive data. Analysed parameters were salinity and ionic composition. The most frequent type of soda waters was the basic alkaline type (Na-HCO 3 ) that represented more than half of the natural soda pans. Besides 11 subtypes occurred. The second and third most frequent types were the chloride (13%) and sulphate subtypes (11%), with the secondary dominance of these anions. The other subtypes meant < 4% of the pans. Magnesium sometimes occurred as a secondary dominant cation beside sodium. Until now, this subtype of soda waters has not been published in any part of the world, because of the general rule of soda lake formation (depending on low levels of magnesium and calcium). We found a regionally constant correction factor [Salinity (mg.L x1 ) = 0.8 r El.Cond. (mS.cm x1 )] for confidentially estimating salinity from electrical conductivity in these habitats. Salinity varied between sub-(0.5-3 g.L x1 ) and hypersaline (> 50 g.L x1 ) ranges, with its mean value (y 4 g.L x1 ) in the hyposaline range (3-20 g.L x1 ). The basic alkaline type had random geographical distribution, while the other subtypes were restricted to certain regions of the Basin. The high number of subtypes reflects the high chemical diversity of alkaline soda pans in the relatively small territory of the Carpathian Basin.

Salinity represents a major structuring factor in aquatic habitats which strongly affects species richness. We studied the relationships among species richness, density and phylogenetic diversity of zooplankton communities along a natural salinity gradient in astatic soda pans in the Carpathian Basin (Hungary, Austria and Serbia). Diversity and density showed opposing trends along the salinity gradient. The most saline habitats had communities of one or two species only, with maximum densities well above 1000 ind l−1. Similarity of communities increased with salinity, with most of the highly saline communities being dominated by one highly tolerant calanoid copepod, Arctodiaptomus spinosus, which was at the same time the only soda‐water specialist. Salinity obviously constrained species composition and resulted in communities of low complexity, where few tolerant species ensure high biomass production in the absence of antagonistic interactions. The pattern suggests that environmental stress may result in highly constrained systems which exhibit high rates of functioning due to these key species, in spite of the very limited species pool.