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Bottom trawling and eutrophication are well known for their impacts on the marine benthic environment in the last decades. Evaluating the effects of these pressures is often restricted to contemporary benthic data, limiting the potential to observe change from an earlier (preimpact) state. In this study, we compared benthic species records from 1884 to 1886 by CGJ Petersen with recent data to investigate how benthic invertebrate species in the eastern Kattegat have changed since preimpact time. The study shows that species turnover between old and recent times was high, ca. 50%, and the species richness in the investigation area was either unchanged or higher in recent times, suggesting no net loss of species. Elements of metacommunity structure analysis of datasets from the 1880s, 1990s, and 2000s revealed a clear change in the depth distribution structure since the 1880s. The system changed from a Quasi‐nested/Random pattern unrelated to depth in the 1880s with many species depth ranges over a major part of the studied depth interval, to a Clementsian pattern in recent times strongly positively correlated with depth. Around 30% of the 117 species recorded both in old and in recent times, including most trawling‐sensitive species, that is large, semiemergent species, showed a decrease in maximal depth of occurrence from the deeper zone fished today to the shallower unfished zone, with on average 20 m. Concurrently, the species category remaining in the fished zone was dominated by species less sensitive to bottom trawling like infauna polychaetes and small‐sized Peracarida crustaceans, most likely with short longevity. The depth interval and magnitude of the changes in depth distribution and the changes in species composition indicate impacts from bottom trawling rather than eutrophication. Furthermore, the high similarity of results from the recent datasets 10 years apart suggests chronic impact keeping the system in an altered state. Because impacts of several threats to marine benthic habitats in recent times in eastern Kattegat are water depth dependent, we ask the question whether benthic invertebrate species depth distributions have changed since preimpact times in the late 1800s. EMS analyses suggest dramatic change in depth distribution structure in the eastern Kattegat from a quasi‐nested/random structure with great overlaps between species distributions in the 1880s, to Clementsian patterns in the 1990s and 2000s strongly correlated with water depth. These results suggest that some factor(s) has reinforced the influence of water depth on species distributions in the Kattegat since hypothetically pristine times and underpin suggestions that chronic fishing disturbance has changed benthic community structure over wide areas of the shelf seas using a temporal reference.

ABSTRACT Our knowledge of aquatic fungal communities, their assembly, distributions and ecological roles in marine ecosystems is scarce. Hence, we aimed to investigate fungal metacommunities of coastal habitats in a subarctic zone (northern Baltic Sea, Sweden). Using a novel joint species distribution model and network approach, we quantified the importance of biotic associations contributing to the assembly of mycoplankton, further, detected potential biotic interactions between fungi–algae pairs, respectively. Our long-read metabarcoding approach identified 493 fungal taxa, of which a dominant fraction (44.4%) was assigned as early-diverging fungi (i.e. Cryptomycota and Chytridiomycota). Alpha diversity of mycoplankton declined and community compositions changed along inlet–bay–offshore transects. The distributions of most fungi were rather influenced by environmental factors than by spatial drivers, and the influence of biotic associations was pronounced when environmental filtering was weak. We found great number of co-occurrences (120) among the dominant fungal groups, and the 25 associations between fungal and algal OTUs suggested potential host–parasite and/or saprotroph links, supporting a Cryptomycota-based mycoloop pathway. We emphasize that the contribution of biotic associations to mycoplankton assembly are important to consider in future studies as it helps to improve predictions of species distributions in aquatic ecosystems. Using recently developed approaches, this study reveals the ecology of aquatic fungal metacommunities of coastal habitats in a subarctic zone.

Natural river floodplains are among the Earth's most biologically diverse and productive ecosystems but face a range of critical threats due to human disturbance. Understanding the ecological processes that support biodiversity and productivity in floodplain rivers is essential for their future protection and rehabilitation. Fish assemblage structure on tropical river floodplains is widely considered to be driven by dispersal limitation during the wet season and by environmental filtering and interspecific interactions during the dry season. However, the individual‐level movement behaviours (e.g. site attachment, nomadism, homing) that regulate dispersal of fish on floodplains are poorly understood. We combined radiotelemetry and remote sensing to examine the movement behaviour of two large‐bodied fishes (barramundi Lates calcarifer, forktail catfish Neoarius leptaspis) over the flood cycle in a tropical river‐floodplain system in northern Australia to: (a) quantify movement responses in relation to dynamic habitat resources at a landscape scale; and (b) determine the extent of spatial ‘reshuffling’ of individual fish following the wet season. Both species altered their behaviour rapidly in response to changes in the availability and distribution of aquatic habitat, with most individuals undertaking extensive movements (up to ~27 km from the tagging location) on the inundated floodplain during the wet season. Although there was considerable individual variation in movement patterns, overall barramundi distributions closely tracked the extent of floodplain primary productivity, whereas catfish distributions were most closely associated with the extent of flooded area. Most individuals of both species exhibited homing back to previously occupied dry season refugia during the wet‐to‐dry transition, even though other potential refugia were available in closer proximity to wet season activity areas. We postulate that homing behaviour modulates temporal variation in fish assemblage composition and abundance and limits the transfer of aquatic‐derived energy and nutrients into terrestrial food webs by reducing fish mortality on drying floodplains. Our study demonstrates the importance of quantifying individual‐level behaviour across the three stages of dispersal (emigration, inter‐patch movement, immigration) for our understanding of how animal movement influences energetic subsidies and other large‐scale ecosystem processes. This manuscript describes a landscape‐scale study of the movements of two riverine fish species over a wet season in tropical northern Australia. The study combines radiotelemetry and remote sensing to address key gaps in our understanding of factors that drive species assemblage structure and ecosystem processes in floodplain rivers. Photo credit for the image is Michael Lawrence‐Taylor.

AIM Metacommunity theories attribute different relative degrees of importance to dispersal, environmental filtering, biotic interactions and stochastic processes in community assembly, but the role of spatial scale remains uncertain. Here we used two complementary statistical tools to test: (1) whether or not the patterns of community structure and environmental influences are consistent across resolutions; and (2) whether and how the joint use of two fundamentally different statistical approaches provides a complementary interpretation of results. Location Grassland plants in the French Alps. METHODS We used two approaches across five spatial resolutions (ranging from 1 km 9 1 km to 30 km 9 30 km): variance partitioning, and analysis of metacommunity structure on the site-by-species incidence matrices. Both methods allow the testing of expected patterns resulting from environmental filtering, but variance partitioning allows the role of dispersal and environmental gradients to be studied, while analysis of the site-by-species metacommunity structure informs an understanding of how environmental filtering occurs and whether or not patterns differ from chance expectation. We also used spatial regressions on species richness to identify relevant environmental factors at each scale and to link results from the two approaches. RESULTS Major environmental drivers of richness included growing degreedays, temperature, moisture and spatial or temporal heterogeneity. Variance partitioning pointed to an increase in the role of dispersal at coarser resolutions, while metacommunity structure analysis pointed to environmental filtering having an important role at all resolutions through a Clementsian assembly process (i.e. groups of species having similar range boundaries and co-occurring in similar environments). MAIN CONCLUSIONS The combination of methods used here allows a better understanding of the forces structuring ecological communities than either one of them used separately. A key aspect in this complementarity is that variance partitioning can detect effects of dispersal whereas metacommunity structure analysis cannot. Moreover, the latter can distinguish between different forms of environmental filtering (e.g. individualistic versus group species responses to environmental gradients).

Aim: To examine metacommunity structuring in stream communities over large elevational gradients by disentangling physical and environmental structuring and the importance of different dispersal routes and niche characteristics. Location: Headwater streams in three catchments in the Hindu-Kush Himalaya of central and eastern Nepal. Methods: We explored metacommunity structuring of stream invertebrates (including deconstructed assemblages by niche position and breadth) using a combination of approaches, including the elements of metacommunity structure and distance-decay relationships. We compared the importance of dispersal routes, elevation and local environmental conditions through five distance matrices: Euclidean, topographic, river network, elevational and environmental. Results: Communities were structured along the elevational gradient with clear turnover apparent in two catchments, with Clementsian (compartmentalized) and Gleasonian (individualistic) distributions. Local environment played a minor role, and the selected distance matrices (i.e. elevation, three physical distances and environment) varied between catchments and niche groups. Contrary to expectation, specialists were more spatially than environmentally controlled, potentially reflecting dispersal limitation. Main conclusions: In these physically dominated systems, local environment was overridden by dispersal limitation, particularly when considering specialists. Where barriers were not limiting dispersal, niche sorting along the elevational gradients represented the key structuring force. Overall, our findings reveal the importance of elevation and the spatial arrangement of sites in structuring metacommunities. We emphasize the value of considering physical structuring and spatial extent in modulating species sorting in metacommunities.

Revealing community patterns and driving forces is essential in community ecology and a prerequisite for effective management and conservation efforts. However, the mangrove ecosystem and its important fauna group such as the crabs, still lack multi‐processes research under metacommunity framework, resulting in evidence and theorical application gaps. To fill these gaps, we selected China's most representative mangrove bay reserve in tropical zone as a stable experimental system and conducted a seasonal investigation (July 2020, October 2020, January 2021, and April 2021) of mangrove crabs. We performed a multi‐approach analysis using both pattern‐based and mechanistic method to distinguish the processes driving the mangrove crab metacommunity. Our results showed that the crab metacommunity exhibits a Clementsian pattern in the bay‐wide mangrove ecosystem but is influenced by both local environmental heterogeneity and spatial processes, thus representing a combined paradigm of species sorting and mass effect. Moreover, the long‐distance spatial constraints are more pronounced compared to the local environmental factors. This is reflected in the greater importance of the broad‐scale Moran's Eigenvector Maps, the distance‐decay pattern of similarity, and the difference in beta diversity dominated by the turnover component. This pattern changes throughout the year, mainly due to changes in dominant functional groups caused by the stress of changes in water salinity and temperature induced by air temperature and precipitation. This research provides multi‐dimension research data and relevant analysis, offering clear evidence for understanding the patterns and related driving forces of crab metacommunity in tropical bay mangroves, and verifies the applicability of some general laws in the system. Future studies can address more diverse spatiotemporal scales, gaining a clearer understanding to serve the conservation of mangrove ecosystems and economically important fishery species. Evidence from the mangrove crab metacommunity in a tropical bay indicates that large benthic fauna, which rely on the passive larval dispersal, continue to be predominantly influenced by dispersal constraints and spatial processes. Moreover, local environmental factors remain crucial, primarily by shaping seasonal community structures and driving functional diversities under the impact of climatic conditions. This study enriches our current understanding and highlights the significance of employing multi‐process research approaches to better comprehend dynamics of crab taxa.

Checkerboards have emerged as a metaphor to (1) describe mutually exclusive patterns of co-occurrence for ecologically similar species that are geographically interspersed (i.e., checkerboard distributions), and (2) characterize relationships among species distributions along gradients that involve entire metacommunities (i.e., checkerboard metacommunity structure). Critical differences exist in the conceptual foundations that characterize these patterns. Checkerboard distributions are characterized by mutual exclusion of geographically interspersed species, usually pairs of ecologically similar species for which competition prevents syntopy. In contrast, checkerboard metacommunity structures are more restrictive: groups of species must exhibit mutually exclusive distributions, and each of these groups must be spatially independent of all other groups. Consequently, in a checkerboard metacommunity, competition defines one relationship for each species (i.e., that with its mutually exclusive partner), whereas independence characterizes all other interspecific associations. Consequently, a structure designed to be consistent with this concept will conclude that the metacommunity has random rather than checkerboard structure. Indeed, empirical checkerboard metacommunities are quite rare (7 of 766 reported empirical structures), and likely arise because of poor characterization of species ranges due to detection errors (i.e., a preponderance of rare or hard-to-detect species), rather than from underlying ecological mechanisms. Importantly, no ecological mechanism has been identified that is consistent with the concept of negative coherence. Consequently, the evaluation of checkerboards should be restricted to small sets of ecologically similar species for which interspecific interactions may lead to mutual exclusion, and coherence should be used only to evaluate if species distributions are more coherent than expected by chance (i.e., one-tailed tests).

We evaluated the relative importance of environmental and spatial variables in structuring tadpole metacommunities at three hierarchical spatial scales in two ecoregions of the Atlantic Forest. Tadpole communities were generally more spatially structured at larger spatial scales. Environmental filtering processes seemed to be equally important at both large and small scales, however, spatially structured environmental variables were more important at larger scales, whereas non-spatially structured ones were more important at smaller scales. The importance of local environmental filters was also greater in the ecoregion that exhibits harsher environmental conditions, such as higher intensity of land-use patterns and dryer climate. This may indicate a greater role for stochastic assembly processes in more benign environments. Species co-occurrence patterns at the larger spatial scale mostly indicated biogeographical differences between the two ecoregions in a Clementsian structure, exhibiting two clear groups of species composition. Co-occurrence patterns at the smallest spatial scale were coherent only when strong environment gradients such as canopy cover were present. However, at the intermediate spatial scale the metacommunities became consistently non-coherent suggesting that species may be responding to processes acting at different spatial scales.

Ecological communities show extremely complex patterns of variation in space, and quantifying the relative importance of spatial and environmental factors underpinning patterns of species distributions is one of the main goals of community ecology. Although we have accumulated good knowledge about the processes driving species distributions within metacommunities, we have few insights about whether (and how) environmental and spatial features can actually generate consistent species distributional patterns across multiple metacommunities. In this paper we applied the elements of metacommunity structure (EMS) framework to identify and classify metacommunities according to multiple but discrete patterns of species distributions. Given that each pattern has unique underlying structuring mechanisms, exploring and comparing such patterns across multiple metacommunities spanning large geographical areas provides a way to test the existence of general principles underlying species distributions within metacommunities. In this study, we applied the EMS framework into a data set containing about 9000 lakes distributed across 85 fish metacommunities across Ontario, Canada, and estimated the relative importance of local and spatial factors in explaining their distributional patterns. Nested and Clementsian gradients were the patterns that fitted most metacommunities; nested metacommunities were distributed throughout the province, while Clementsian gradient metacommunities were concentrated in the southeastern region. Sixty-five percent of nested metacommunities were located in low-energy watersheds (i.e., colder climate and shorter growing season), whereas metacommunities representing Clementsian gradients were present in high-energy watersheds (i.e., relatively warmer climate and longer growing season). Taken together, our results reveal that the environmental and spatial properties in which metacommunities are embedded are at least partially responsible for their species distributional patterns.

The study of altitudinal gradients has made enduring contributions to the theoretical and empirical bases of modern biology. Unfortunately, the persistence of these systems and the species that compose them is threatened by land-use change at lower altitudes and by climate change throughout the gradients, but especially at higher altitudes. In this review, we focus on two broad themes that are inspired by altitudinal variation in tropical montane regions: (1) dimensions of biodiversity and (2) metacommunity structure. Species richness generally decreased with increasing altitude, although not always in a linear fashion. Mid-altitudinal peaks in richness were less common than monotonic declines, and altitudinal increases in richness were restricted to amphibian faunas. Moreover, gradients of biodiversity differed among dimensions (taxonomic, phylogenetic and functional) as well as among faunas (bats, rodents, birds) in the tropical Andes, suggesting that species richness is not a good surrogate for dimensions that reflect differences in the function or evolutionary history of species. Tropical montane metacommunities evinced a variety of structures, including nested (bats), Clementsian (rodents, bats, gastropods), quasi-Clementsian (reptiles, amphibians, passerines) and quasi-Gleasonian (gastropods) patterns. Nonetheless, compositional changes were always associated with the ecotones between rain forest and cloud forest, regardless of fauna.