Diverse Assemblage Research Articles

Latitudinal Patterns and Macroclimatic Drivers of Phylogenetic Structure in Regional Liverwort Assemblages in North America

ABSTRACTAimMost plant groups originated under tropical conditions, leading to the hypothesis of tropical niche conservatism, according to which species assemblages of a clade originating and diversifying in tropical climates are expected to have low phylogenetic diversity and dispersion in temperate climates because only few lineages have adapted to these novel conditions. The opposite may be expected for clades originating under temperate conditions, but this temperate niche conservatism hypothesis has not been tested for a broad temperature gradient including both tropical and arctic climates. Liverworts are thought to have originated in temperate climates, and may thus follow the pattern of temperate niche conservatism. Here, we test this hypothesis using regional liverwort floras across a nearly full temperature gradient from tropical through temperate to arctic climates in North America. In addition, we investigate whether temperature‐related variables and climate extreme variables play a more important role in determining phylogenetic structure of liverwort assemblages, compared to precipitation‐related variables and climate seasonality variables, respectively.LocationNorth America.TaxonLiverworts (Marchantiophyta).MethodsPhylogenetic diversity (measured as mean pairwise distance) and phylogenetic dispersion (measured as standardised effect size of mean pairwise distance) in liverworts in regional floras in North America were related to latitude and climatic variables. Variation partitioning analysis was used to assess the relative importance of temperature‐ versus precipitation‐related variables and of climate extremes versus seasonality on phylogenetic diversity and dispersion.ResultsPhylogenetic diversity and dispersion in liverworts is highest in temperate climates, compared to both tropical and arctic climates. Temperature‐related variables and climate extreme variables explained more variation in phylogenetic diversity and dispersion of liverwort assemblages than did precipitation‐related variables and climate seasonality variables, respectively.Main ConclusionsVariations in phylogenetic diversity and dispersion in liverworts along the latitudinal gradient in North America are consistent with the temperate niche conservatism hypothesis.

Recognizing primary paleotopography utilizing Ichnofossils and 3-D models: Mill Canyon Dinosaur track site, Utah

Preservation and recognition of primary paleotopography along a bedding surface is often a neglected component in paleogeographic reconstruction. The Mill Canyon Dinosaur track site (MCDT) is a spectacular bedding plane exposure with a diverse assemblage of vertebrate ichnnofauna. Small-scale 3D-photogrammetric and ichnofossil analyses of two areas on the periphery of the MCDT surface demonstrate the presence of preserved primary paleotopography. The first area consists of a paleotopographic bench that drops off to a minimum of ∼0.5–0.6 meters. On this bench is at least one resting trace analogous to modern traces of crocodiles documented from topographic highs along rivers and lakes. At the second locality, systematic variations in track morphology indicate that the trackmaker gait was influenced by changes in surface elevation with movement across the ridge, thus affirming that paleorelief is preserved. The ichnofossils on this Cretaceous bedding surface likely represent months- to years-worth of biological activity.

Fish–Seascape Associations Within an Offshore Protected Area in the Arabian Gulf

ABSTRACTCoral reef ecosystems support high fish biodiversity through ecological interactions with structural complexity across multiple spatial scales including coral colony architecture and the surrounding seascape structure. In an era where the complexity of coral reef ecosystems is being diminished, understanding the importance of structural characteristics beyond single focal patches has the potential to better inform actions for protecting, restoring or creating habitat for reef‐associated species. A seascape ecology approach was applied to explore the associations between multiple scales of seascape structure and fish assemblage response variables within a small (49.6 km2) offshore no‐take MPA, Sir Bu Nair Island Protected Area, in Sharjah, United Arab Emirates. Fish–seascape associations were modelled with single regression trees. Both in situ and remote sensing–derived variables produced the best models with highest contributions from coral cover, amount of hard‐bottom habitat type and structural complexity of the seafloor terrain. Fish species richness was significantly higher where coral cover exceeded 35%. The hard‐bottom areas with coral supported diverse assemblages dominated by carnivorous and omnivorous fishes. The Sir Bu Nair Island Protected Area provides a critical refuge for threatened and regionally overexploited species including those with low resilience to fishing. The ecological success of this protected area is key to safeguarding regional marine biodiversity and recovering fish populations to enhance food security.

The oldest fossil record in the Iberian Peninsula; lower Ediacaran acritarchs of the Tentudía Formation, Ossa-Morena Zone (OMZ), Southwest Iberian Massif.

AbstractA diverse assemblage of acritarchs, that represents the oldest fossil record of the Iberian Massif, is described from Ediacaran metasedimentary rocks of the Tentudía Formation included in the Ossa Morena Zone stratigraphy (Southwestern Iberia). The microfossils found include Assesserium pyramidalis, Cavaspina sp. A, Ceratosphaeridium sp. A, Dictyotidium sp. A, Multifronsphaeridium sp. A, Schizofusa zangwenlongii, Tanarium megaconicum Tanarium sp. A, and Tanarium ? sp. B, This assemblage is diagnostic of the mainly lower Ediacaran Doushantuo-Pertatataka acritarchs (c. 633—565 Ma.). The lithological diversity of the Tentudía Formation suggests that these Ediacaran sedimentary rocks were deposited in a diversity of environments (platform, slope and submarine fans, including mass transport deposits in a back-arc basin that extended into the southern part of the Central Iberian Zone. The mass transport deposits are represented in the Ossa-Morena Zone by the Salvaleón Olistostrome composed by turbidites including chert clast probably derived from the shelf. The migration of the mass transport deposits into the Central Iberian Zone (Orellana Formation) indicates the migration of the back-arc basin depocenter. Later inversion of the back-arc basin is marked by the deformation of the lower Ediacaran sedimentary rocks Serie Negra Group in the Ossa-Morena Zone and Domo Extremeño Group in the Central Iberian Zone. In the upper Ediacaran-Terreneuvian a carbonate platform (Ibor Group) was established in the southern part of the Central Iberian Zone unconformably overlying the previously deformed Domo Extremeño Group. The most proximal areas in the Ossa-Morena Zone are represented by the Malcocinado Formation which overlies the Serie Negra Group and the distal areas of the southern part of the Central Iberian Zone are represented by distal shelf and slope deposits of the Cijara Formation, which are overlain by mass transport deposits that include carbonate olistolites from the Ibor Group (such as the Fuentes and Membrillar olistostromes).

Temporal and spatial variations of soil nematode assemblages across distinct forest ecosystems

Temporal and spatial variations of soil nematode assemblages across distinct forest ecosystems

Ultrastructural Perspectives on the Biology and Taphonomy of Tonian Microfossils From the Draken Formation, Spitsbergen.

Silicified peritidal carbonates of the Tonian Draken Formation, Spitsbergen, contain highly diverse and well-preserved microfossil assemblages dominated by filamentous microbial mats, but also including diverse benthic and/or allochthonous (possibly planktonic) microorganisms. Here, we characterize eight morphospecies in focused ion beam (FIB) ultrathin sections using transmission electron microscopy (TEM) and X-ray absorption near-edge structure (XANES) spectromicroscopy. Raman and XANES spectroscopies show the highly aromatic molecular structure of preserved organic matter. Despite this apparently poor molecular preservation, nano-quartz crystallization allowed for the preservation of various ultrastructures distinguished in TEM. In some filamentous microfossils (Siphonophycus) as well as in all cyanobacterial coccoids, extracellular polysaccharide sheaths appear as bands of dispersed organic nanoparticles. Synodophycus microfossils, made up of pluricellular colonies of coccoids, contain organic walls similar to the F-layers of pleurocapsalean cyanobacteria. In some fossils, internal content occurs as particulate organic matter, forming dense networks throughout ghosts of the intracellular space (e.g., in Salome svalbardensis filaments), or scarce granules (in some Chroococcales). In some chroococcalean microfossils (Gloeodiniopsis mikros, and also possibly Polybessurus), we find layered internal contents that are more continuous than nanoparticulate bands defining the sheaths, and with a shape that can be contracted, folded, or invaginated. We interpret these internal layers as the remains of cell envelope substructures and/or photosynthetic membranes thickened by additional cellular material. Some Myxococccoides show a thick (up to ~ 0.9 μm) wall ultrastructure displaying organic pillars that is best reconciled with a eukaryotic affinity. Finally, a large spheroid with ruptured wall, of uncertain affinity, displays a bi-layered envelope. Altogether, our nanoscale investigations provide unprecedented insights into the taphonomy and taxonomy of this well-preserved assemblage, which can help to assess the nature of organic microstructures in older rocks.

The repatriation of wolves to Isle Royale alters the foraging of meso-carnivores

Abstract Due to the disproportionate role that large carnivores can have on communities and their global decline over the last century, carnivores are increasingly being repatriated across their historic ranges. The reintroduction of gray wolves (Canis lupus) can precipitate substantive changes to communities and ecosystems. Notably, wolves could have strong effects on smaller and subordinate carnivores, especially in altering their foraging behavior and prey selection. Past studies investigating wolf effects on other carnivores, however, have generally been conducted in relatively complex communities featuring a diverse assemblage of carnivores and prey and have lacked baseline (i.e., pre-repatriation) data. Consequently, researchers have quantified what a community looks like after wolf return, with little information on how the community behaved before. To better understand the effect of large carnivore repatriation on the foraging ecology of a carnivore community, we investigated the impact of reintroduced gray wolves on 2 meso-carnivores: Red Fox (Vulpes vulpes); and American Marten (Martes americana) within an insular and simple vertebrate community at Isle Royale National Park before and after wolf reintroduction. We analyzed >600 scats from 20 individual martens and 63 individual foxes as well as the stable isotopes of 9 and 22 tissue samples from martens and foxes, respectively, at both individual and population levels. We found that the wolf reintroduction had little effect on marten diet but strongly influenced fox diet depending on the analysis conducted. At the population level, our analysis revealed that both foxes and martens were dietary generalists consuming an array of food items including small prey, berries, and human food regardless of wolf presence. However, at the individual level, we found that prior to wolf repatriation foxes primarily consumed berries and small prey but following wolf repatriation the diet of foxes shifted to berries and human foods as well as large carrion. This post-wolf reintroduction shift in diet increased the dietary overlap between foxes and martens. Our work provides new insights into how the return of a large carnivore can alter the foraging ecology of small-bodied carnivores and act both to provision carrion resources as well drive other carnivores to consume more human food and increase dietary overlap.

Small Streams Support Beta Diversity in Neotropical Fish Assemblages in the Upper Paraná River Basin

ABSTRACTVariation in species composition along an environmental gradient (β‐diversity) can inform our understanding of biodiversity patterns and species composition. Beta diversity can be partitioned into species contributions to beta diversity (SCBD) and local contributions to beta diversity (LCBD). While SCBD describes the variations in species composition among samples, LCBD measures the uniqueness of a biological community within a larger ecosystem. Recently developed metrics enabled the estimation of species contribution to total beta diversity (SCBD) and the contribution of individual sites to total beta diversity (LCBD). Utilising these metrics, a one‐time survey of 275 sampling points within four sub‐basins of the Upper Paraná River Hydrographic Basin (low‐flow streams, < 5 m3/s) was conducted to assess fish community composition. Our results show that limnological influences at different scales contribute to higher LCBD. However, land use and species richness were not directly linked to this outcome, suggesting that sites with fewer fish species along sub‐basins contributed to higher beta diversity. It was concluded that beta diversity is more influenced by limnological characteristics and the position of sampling sites along the longitudinal gradient than that based on variations in species composition (SCBD). Moreover, high LCBD values were even found in portions of the gradient with lower species richness. This means that small streams in the sub‐basins of the upper Paraná River are unique and are comprised of varied habitats that contribute to increasing diversity. As such, they should be seen as a target in the development of environmental policies designed to conserve their pristine condition.

The osteohistology of Orthosuchus stormbergi using synchrotron radiation microcomputed tomography.

Orthosuchus stormbergi was a small-bodied crocodyliform, representative of a diverse assemblage of Early Jurassic, early branching crocodylomorph taxa from the upper Elliot Formation of South Africa. The life history of these early branching taxa remains poorly understood, with only sparse investigations into their osteohistology, yet species like Orthosuchus have potential to inform about the macroevolution of growth strategies on the stem leading to crown crocodilians. In order to elucidate the growth patterns of Orthosuchus, we used propagation phase contrast X-ray synchrotron micro-computed tomography to virtually image the osteohistology of the postcrania of two specimens, including multiple elements from the type (SAM-PK-K409), and the femur of a referred specimen (BP/1/4242). In total, we scanned nine mid-diaphyseal sections of the humerus, radius, ulna, radiale, femur, tibia, fibula, and a rib. We then compared our results to osteohistological sections of crocodylomorph taxa from the published literature. Our results show that the most predominant bone tissue type in Orthosuchus is lamellar, with a few patches of woven and parallel-fibred bone. The type specimen contains four to five lines of arrested growth and the hindlimb elements present outer circumferential lamellae, whereas the referred specimen contains six to seven. Both specimens grew at similar rates, reaching adult skeletal body size at year four or five. The sectioned bones, most notably the radius and ulna, are comparatively thick walled and compact. Our virtual osteohistological sections are one of the first for an early branching crocodyliform, and the broad sample of skeletal elements makes Orthosuchus a key anchor point for understanding the plesiomorphic life history traits of the clade.

Lessons from long‐term research: Diptera species turnover and dominance shifts with respect to climate‐driven changes

Abstract The diverse pressures of climate change have influenced many habitats, especially freshwater ones, due to their greater sensitivity to stressors. Aquatic Diptera make up more than 50% off all aquatic insect species described, which makes them an ideal group to monitor changing climate as their diverse assemblages can reflect functions within the entire community. The aim of this research was to identify variations in the aquatic dipteran community during a 15‐year period at a tufa barrier in a karst barrage lake system and to determine the environmental factors that have the highest influence on this community. We analysed monthly data collected between 2007 and 2021, when we collected adult specimens using 6 pyramid‐type emergence traps. In total, 167 taxa from 13 different families were gathered. NMDS based on Bray–Curtis similarity analysis amongst assemblages revealed the segregation of samples based on different current velocities and substrates, indicating the importance of microhabitats in dipteran community structuring. Dipteran taxa indicative of specific 5‐year time periods within the research were identified and were associated with changes in environmental conditions especially discharge. The threshold indicator taxa analysis revealed specific species' responses to changing discharge rates. The study shows that discharge rate, not water temperature, is the critical factor shaping dipteran composition, whether by removing or adding taxa to the community. Species turnover showed an overall decrease in species numbers, that is, species richness, throughout the research period. We conclude that changes in the dipteran community, because of the vast functional traits, niches, adaptations and species diversity of the group, are not visible when analysing just the diversity indices. When determining environmental influence on the community in long‐term research, they should be combined with other data such as the overall abundance, the total number of species, as well as the species turnover.

Evaluating Environmental Programs: Long-Term Monitoring of Crustacean Assemblages in a Polluted Estuary

We assessed the environmental quality of the Odiel-Tinto estuary, one of the most polluted in the world, by analysing the spatial variation of subtidal soft-bottom crustacean assemblages from 2000 to 2016. Our primary goal was to evaluate whether corrective measures implemented since 1986 have resulted in significant ecological improvement. The assemblages were structured according to the natural gradient from the estuary to the marine environment. Throughout the study, the assemblages exhibited low species richness and abundance (e.g., over 3 species and 180 individuals/m2 in the inner areas; 19 species and 510 individuals/m2 in the mouth zone). However, 2016 saw an increase in both species number and total abundance (e.g., over 5 and 24 species in the inner and mouth areas, respectively). Despite these observations, the Odiel-Tinto system harboured fewer species (24 species) compared to nearby estuaries like the Guadiana and Guadalquivir (over 50 species). Although there were signs of changes in the estuary over the sampling periods (e.g., a slight increase in richness and diversity in 2016 compared to 2002 and 2004), these fluctuations are likely characteristic of a highly dynamic environment rather than indications of genuine ecological recovery. These findings highlight the need for a long-term monitoring program, which should also encompass intertidal mudflats due to their higher density and biomass, easy accessibility, and reduced exposure to the impacts of recurrent maintenance dredging of the navigation channel.

The structure of epiphytic and planktonic bacterial assemblages under two contrasting lake regimes

Abstract In contrast to the macrophyte‐dominated regime (MDR), the phytoplankton‐dominated regime (PDR) in shallow lakes is characterized by relatively high nutrient concentrations, excessive phytoplankton growth and turbid water column. Some floating‐leaved plants can grow under both regimes and aid in reducing nutrient concentrations in water bodies. Their epiphytic bacterial assemblages play an essential role in the health and adaptation of these plants; however, there is limited understanding of this plant‐bacteria interaction. Here, we used 16S rRNA gene‐based high‐throughput sequencing to compare the diversity, composition and co‐occurrence patterns of planktonic and epiphytic bacterial assemblages associated with the submerged roots and floating leaves of Trapa natans, growing under the PDR and MDR in Lake Taihu, China. Alpha diversity of PDR epiphytic bacterial assemblages was lower than in MDR. The opposite trend was observed for planktonic bacterial assemblages. We detected a strong compositional difference between epiphytic and planktonic bacterial assemblages. Bacterial assemblages found on root and leaf surfaces showed only minimal compositional overlap with those in the water column. The composition of epiphytic bacterial assemblages differed more between the two regimes than did planktonic bacterial assemblages. The PDR co‐occurrence network of bacterial assemblages was more complex than that of the MDR, with the PDR epiphytic habitats enriched more network keystone taxa. The proportion of positive edges was also greater in the PDR networks of epiphytic bacterial assemblages than in the epiphytic MDR networks, whereas it was lower in the planktonic bacterial network from the PDR than from the MDR. The comprehensive view of the diversity, composition and co‐occurrence patterns of epiphytic and planktonic bacterial assemblages of MDR and PDR in large shallow lakes provided by our results showed that the structure of epiphytic bacterial assemblages was mediated by both host and water properties, and the observed core taxa and network keystone species may play an important role in maintaining plant growth and adaptation to environmental change.

Scent-mediated bee pollination and myrmecochory in an enigmatic geophyte with pyrogenic flowering and subterranean development of fleshy fruits.

Volatile emissions from flowers and fruits play a key role in signalling to animals responsible for pollination and seed dispersal. Here, we investigated the pollination biology and chemical ecology of reproduction in Apodolirion buchananii, an African amaryllid that flowers in a leafless state soon after grassland vegetation is burnt in the dry late-winter season. Pollinators were identified through field collection and pollen loads were quantified. Floral traits including spectral reflectance and scent chemistry were documented. Bioassays using cup traps were used to test the function of floral volatiles. Fruiting biology was investigated using controlled hand-pollination experiments and chemical analysis of fruit scent. Seed germination was scored in greenhouse trials. Seed dispersal was monitored using observations and camera trapping. The sweetly scented white flowers of A. buchananii are pollen-rewarding and pollinated mainly by a diverse assemblage of bees. Cup-trap experiments demonstrated that pollinators are attracted to phenylacetaldehyde, the dominant volatile in the floral scent. Plants are shown to be self-incompatible, and the fleshy fruits were found to emerge from the soil six months after pollination during the peak of the summer rains. Fruits emit a diverse blend of aliphatic and aromatic esters and contain large fleshy recalcitrant seeds which germinate within days of fruits splitting open. Seed dispersal by ants was recorded. This first account of the reproductive biology of a species in the genus Apodolirion highlights an outcrossing mating system involving bees attracted to color and scent as well as the unusual fruiting biology and ant-mediated system of seed dispersal.

Obruchevodid petalodonts (Chondrichthyes, Holocephali) from the Upper Mississippian (Serpukhovian) Bangor Limestone of northern Alabama, U.S.A.

ABSTRACT Undocumented collections and new field studies have revealed a diverse chondrichthyan assemblage within the Upper Mississippian (Serpukhovian/middle-upper Chesterian) Bangor Limestone in northern Alabama, U.S.A. which includes multiple new occurrences of holocephalians. Included in these new records are the first occurrences of Obruchevodidae (Euchondrocephalii, Petalodontiformes) outside of the synchronic Bear Gulch Limestone Member of the Heath Formation in Montana, U.S.A. Isolated teeth from Fissodopsis robustus and Netsepoye hawesi represent the first specimens to provide three-dimensional tooth morphology that is otherwise obscured in the holotypes. Additionally, these specimens represent the first reported occurrences from the southern coast of the subcontinent Laurentia. The significance of these new specimens is discussed in regard to the comparative morphology of Petalodontiformes and the paleobiogeography of Obruchevodidae.

Role of mesoscale eddies in the biogeochemistry of the Mozambique Channel

This study aims to characterize how eddies shape the biogeochemistry of the Mozambique Channel using a physical-biogeochemical model that realistically simulates its interannual dynamics. The 20-year-long numerical simulation provides a comprehensive dataset for robust statistical analysis of thousands of mesoscale features using an eddy detection method. We show that all eddy types significantly shape the biogeochemical landscape over the Mozambique Channel, with varying effects across different areas: (1) Sofala Bank and Delagoa Bay: Cyclonic eddies enhance diatom production. (2) Comoros Basin: Cyclonic eddies favor diatom growth via nutrient-rich waters from the NEMC. (3) Central Mozambique Channel: Anticyclonic eddies and rings promote nanophytoplankton through eddy-topography interactions. (4) Southern Mozambique Channel: A mix of eddies from the MC and South Madagascar influences diverse responses due to coastal upwelling. This diversity of processes results in distinct biological signatures of eddy types, leading to diverse ecosystem assemblages with a clear oligotrophic signature.

Comparative analysis of crop rotation systems: the impact of ginger (Zingiber officinale) and sponge gourd (Luffa aegyptiaca) residues on growth of Chinese cabbage (Brassica rapa var. chinensis).

Continuous cropping in greenhouse cultivation often leads to increased pest and disease problems, reducing crop quality and yield. Crop rotation is a common strategy to address these issues. This study compared the growth of Chinese cabbage (Brassica rapa var. chinensis) following rotations with ginger (Zingiber officinale) and sponge gourd (Luffa aegyptiaca). The Chinese cabbage exhibited normal growth following ginger rotation but showed abnormal growth after sponge gourd rotation. The study investigated the underlying causes by analyzing soil physicochemical properties and rhizosphere microbial communities of Chinese cabbage using 16S rRNA and ITS sequencing. The results revealed that soil from ginger-Chinese cabbage rotation had higher levels of soil organic carbon (SOC) and available phosphorus (AP), but lower total nitrogen (TN) and available potassium (AK). Despite similar alpha-diversity for both bacterial and fungal communities, distinct bacterial and fungal community structures between two rotation cropping systems were observed. This suggests that even if the alpha-diversity does not change, the composition of the microbial community can shift in ways that might influence soil health and plant growth. Furthermore, redundancy analysis revealed a significant correlation between microbial community structures and soil physicochemical properties of two rotation cropping systems. The SOC and TN were revealed to be the most significant of the investigated soil physicochemical parameters with respect to the variation of both bacterial and fungal assemblages, respectively. The identified biomarkers in bacterial community composition further emphasize the potential for specific microbes to influence crop health positively or negatively. We found that the indicator genera of the bacterial community composition of the ginger-Chinese cabbage rotation system were Amycolatopsis (genus), Pseudonocardiales (order), Pseudonocardiaceae (family), and Amycolatopsis mediterranei, which are known as producers of secondary metabolites, such as antibiotics. These findings highlight the importance of crop selection in rotation strategies for optimizing agricultural outcomes.

Spatial variability of sedimentary assemblages reflects variations in bioerosion pressure of adjacent coral reefs.

The composition of coral-reef sediments is highly variable across space and time, and differences in the life histories of the dominant calcifying organisms on reefs contribute to the heterogeneity of reef sediments. Previous studies have suggested that variations in coral-reef bioerosion can influence spatial and temporal variations of sedimentary assemblages: elevated erosion rates of dead coral skeletons can trigger a pulse of coral-derived sediments and cause a shift in the dominance of sedimentary grains from coralline algae, such as Halimeda, to coral. We assessed the variability of the sedimentary composition and bioerosion rates of reefs at different spatial scales to determine the association between these two variables. We surveyed the benthic assemblages on reefs exhibiting different ecological states and collected samples of the associated sediments. We calculated the carbonate budget for each site and compared their variability at different hierarchical levels to the variability of their respective sedimentary assemblages. At the scale of sites (1-10 km), Halimeda cover was a significant predictor of the relative abundance of Halimeda grains. Both the relative abundance of coral grains and reef bioerosion rates varied significantly at the scale of locality (tens to hundreds of km), with high abundances of coral grains in the sediments coinciding with high rates of bioerosion. The main drivers of bioerosion at our localities were parrotfish assemblages dominated by large size classes of excavating species such as Sparisoma viride. Reef sediments may reflect the gross degree of bioerosion pressure that reefs experience, and historical changes in bioerosion rates could potentially be assessed by examining the sediments across temporal scales.

The Diversity of Arachnid Assemblages on the Endemic Tree Zelkova abelicea (Ulmaceae): An Evaluation of Fragmentation and Connectivity in Crete (Greece).

Zelkova abelicea is an endemic tree growing only on eight mountain stands on the Greek island of Crete. The aim of this study was to determine the structure of the assemblages and analyze the diversity of the arachnid assemblages living on Zelkova abelicea, an endemic tree species in Crete. Material for the analyses was collected from tree trunks, oftentimes covered by bryophytes or lichens. In the examined material, 85 taxa were recorded. The most numerous groups represented in the analyzed material were Acari, including representatives of the orders Mesostigmata (78 ind. of 18 spp.) and Oribatida (1056 ind. of 51 spp.). In the order Mesostigmata the species represented by the highest numbers of specimens were Onchodellus karawaiewi (15 individuals) and Hypoaspisella sp. (13), which is probably a species new to science. In turn, representatives of the order Oribatida were much more numerous, with Zygoribatula exilis (284) and Eremaeus tuberosus (210) being identified in the largest numbers. Among the eight sampled localities, Gerakari (646 ind. and 50 spp.) and Omalos (409 ind. and 43 spp., respectively) had by far the richest assemblages. Statistical analyses confirmed the highly diverse character of the arachnid assemblages at the individual sites, which is a consequence not only of the varied numbers of arachnids found, but also of the presence of very rare species, such as Androlaelaps shealsi, Cosmolaelaps lutegiensis or Hoploseius oblongus. These results highlight the high species diversity of the arachnids found on Z. abelicea but also suggest the lack of connectivity between the isolated and fragmented forest stands on Crete.

Factors shaping pelagic-benthic coupling in the process of settlement in an Arctic fjord

Benthic organisms typically possess a planktonic propagule stage in the form of larvae or spores, which enables them to spread over large distances before settlement, and promotes tight pelago-benthic coupling. However, factors driving dispersal and epibenthos recruitment in shallow hard-bottom Arctic communities are poorly known. We therefore conducted a year-round in situ colonization experiment in Isfjorden (Svalbard), and found out that variation in early-stage epibenthic assemblages was explained by the combination of: abiotic (45.9%) and biotic variables (23.9%), and their interactions (30.2%). The upward-facing experimental plates were dominated by coralline algae, and this is the first study showing that at high latitudes coralline algae Lithothamnion sp. settle in high numbers on available substrates during the polar night in winter. The downward-facing plates, which had much less exposure to light, contained more diverse organisms, with a predominance of polychaetas and bryozoans. However, in summer, the barnacle Semibalanus balanoides outcompeted all the other recruits, as a result of massive occurrence of meroplanktonic Cirripedia larvae, triggered by the phytoplankton bloom. In conclusion, the rate and success of epibenthic settlements were dependent mostly on light availability and temperature, suggesting that larval settlement will be impacted by global warming with some taxa benefitting, while others losing.

Stable isotope analysis of western Lake Superior predatory fishes, part one: Trophic niche overlap

Characterizing food web interactions between introduced and native fish predators is important to quantify niche overlap, assess predator–prey balance, and support fisheries management. Lake Superior provides an ideal setting to investigate potential trophic overlap between native top predators, lake trout (Salvelinus namaycush) and walleye (Sander vitreus), and a diverse assemblage of introduced salmonids. Angler-caught fish were used to measure trophic position and niche overlap between predatory fishes in the western arm of Lake Superior based on carbon and nitrogen stable isotope ratios (δ13C, δ15N). Within a species, we did not find consistent differences in either δ13C or δ15N values by sex, collection year, capture location, or length. Among species, the range in δ15N values was >5 ‰, indicating that these species occupy ∼2 trophic positions, with dietary reliance ranging from primarily invertebrates to primarily fish, whereas the range in δ13C values indicated dietary reliance on a mix of pelagic and benthic prey. Combined, the δ13C and δ15N values revealed siscowet lake trout as the apex predator having a distinct trophic niche, while walleye and lean lake trout were intermediate trophic position predators with overlapping isotopic niches, and introduced salmonids were the lowest trophic position predators with overlapping trophic niches. Overlapping trophic niches indicated similar resource reliance and habitat occupancy among native lake trout and walleye, as well as among introduced salmonids, but less so between native and introduced predators.