Differences In Assemblage Composition Research Articles

Context‐dependent effects of geographic, climate and land cover factors on hemipteran assemblages in different ecoregions of China

Abstract Understanding variation in assemblage composition (i.e., beta diversity) along geographic and environmental gradients is a central topic in biogeography and ecology. We compared relationships between hemipteran beta diversity (overall dissimilarity: βtotal, Sorensen dissimilarity; turnover component: βsim, the replacement of species between assemblages; nestedness‐resultant component: βsne, the nested difference in richness between assemblages) and geographic, climatic and land cover distances among four ecoregions (Northeast Ecoregion; Northern Ecoregion; Tibet Ecoregion; Southern Ecoregion) across China. The hemipteran assemblage composition differed markedly among ecoregions. In general, βtotal and βsim both significantly increased with increasing geographic, climatic and land cover distances. Intercepts and slopes of dissimilarity‐distance relationships all varied significantly among different ecoregions, suggesting different levels of within‐ecoregion assemblage heterogeneity and change rate in assemblage composition. Moreover, the slopes of βtotal and βsim were highest in Northeast Ecoregion but lowest in Northern Ecoregion, exhibiting latitudinal and longitudinal dissimilarity pattern. According to variation partitioning analysis, although the overall explained variance was relatively low, spatial variables explained a much greater proportion of variance compared to climate and land cover variables. To conclude, our results showed significant regional differences in assemblage composition and biodiversity among ecoregions. Both dispersal‐related and niche‐related processes affect hemipteran assemblage structure, while the low overall explained variance indicates that high dissimilarity in hemipteran composition is affected by multiple factors and processes that remained undetected in this study. Our results may be relevant for wider insect groups because hemipterans constitute a highly diverse group in terms of phylogenetic origins and functional significance.

Using low volume eDNA methods to sample pelagic marine animal assemblages.

Environmental DNA (eDNA) is an increasingly useful method for detecting pelagic animals in the ocean but typically requires large water volumes to sample diverse assemblages. Ship-based pelagic sampling programs that could implement eDNA methods generally have restrictive water budgets. Studies that quantify how eDNA methods perform on low water volumes in the ocean are limited, especially in deep-sea habitats with low animal biomass and poorly described species assemblages. Using 12S rRNA and COI gene primers, we quantified assemblages comprised of micronekton, coastal forage fishes, and zooplankton from low volume eDNA seawater samples (n = 436, 380-1800 mL) collected at depths of 0-2200 m in the southern California Current. We compared diversity in eDNA samples to concurrently collected pelagic trawl samples (n = 27), detecting a higher diversity of vertebrate and invertebrate groups in the eDNA samples. Differences in assemblage composition could be explained by variability in size-selectivity among methods and DNA primer suitability across taxonomic groups. The number of reads and amplicon sequences variants (ASVs) did not vary substantially among shallow (<200 m) and deep samples (>600 m), but the proportion of invertebrate ASVs that could be assigned a species-level identification decreased with sampling depth. Using hierarchical clustering, we resolved horizontal and vertical variability in marine animal assemblages from samples characterized by a relatively low diversity of ecologically important species. Low volume eDNA samples will quantify greater taxonomic diversity as reference libraries, especially for deep-dwelling invertebrate species, continue to expand.

Sites and species contribution to the β-diversity of Odonata assemblages in Haiti: Implications for conservation

Understanding the ecological determinants of assemblage diversity in freshwater insects is of crucial importance for conservation biology and environmental management. This is particularly true in Haiti, where severe and ongoing environmental degradation of aquatic ecosystems is a major threat to the local invertebrate fauna. Here, using Odonates assemblages sampled from 67 waterbodies belonging to 14 different Haitian watersheds, we assessed species uniqueness (U) from both rarity based on spatial occupancy and taxonomic species distinctness (TSD), and species contribution to total β diversity (SCBD). We assessed between-site variation in species richness (SR), relative taxonomic distinctness (RTD), mean species uniqueness per site (Mean U), and the contribution of individual sites to total β diversity (LCBD), based on presence-absence data. We then examined the relationships between these variables and the physico-chemical characteristics of the sites. In total, we recorded 49 different odonate species (including two endemic species of conservation interest), belonging to 40 genera and 7 families, with a relatively high percentage (69.4%) of rare species (i.e. occurring in 10% or less of sampled water bodies). TSD was negatively correlated with spatial occupancy, while U was significantly higher in Zygopeteran species compared to Anisopteran species. SR varied among the 67 sites, ranging from 2 to 17 species, while SCBD was positively correlated with site occupancy. Differences in assemblage composition between sites were mainly due to species replacement, while only a few sites had assemblages consisting of a subset of larger assemblages found at other sites. The observed positive correlation between dissimilarity and geographic distance between sites further suggests that the turnover of species may take place over some ecological gradient and/or might be explained by species ecological requirements and limited ability to disperse. LCBD and Mean U increased with increasing altitude and decreasing temperature and conductivity, whereas SR and RTD did not. All variables were independent of pH. Overall, SR and RTD were higher in lotic than in lentic sites, and in sites with natural riparian vegetation compared to sites with anthropogenic or mixed riparian vegetation. Mean U provided a relevant index for site selection for odonates conservation in Haiti, whereas β diversity appeared to be of limited interest for this purpose. Globally, our results advocate the importance of conserving a wide diversity of waterbodies to protect Odonate diversity in Haïti, and particularly in forested areas at > 1000 m altitude.

Poor performance of acoustic indices as proxies for bird diversity in a fragmented Amazonian landscape

Biodiversity loss is rampant worldwide, particularly in tropical regions like the Amazon. In the last decade, acoustic indices have been proposed as a rapid method for biodiversity assessment. However, their overall effectiveness as proxies for biodiversity is under debate. Here, we tested advanced statistical methods based on acoustic indices recently proposed to estimate species richness more accurately. Using an annotated audio dataset (2356 one-minute files) and song characterization of tropical bird assemblages from land-bridge islands in an Amazonian hydroelectric reservoir, we fitted both regression models and random forest algorithms to address the following questions: (1) do acoustic indices provide accurate estimates of bird species richness? (2) are univariate (a single index) or multivariate models (a combination of indices) better at predicting species richness? (3) at what temporal scale (minutes or hours) and with which measures (raw values or mean and standard deviation values)? (4) do these indices reflect spatial (island size) and temporal patterns (diel cycle) of singing activity? Although we found that multivariate models using a set of acoustic indices computed at a broader scale (hours) performed better than simpler models, their overall predictive power of species richness was poor for these tropical bird assemblages. The high heterogeneity and variation in the acoustic activity and signals of the Amazonian bird species present a considerable challenge for acoustic indices to capture changes in species diversity adequately. In agreement with recent studies, our findings point out the limits of acoustic indices, especially in tropical, highly diverse regions, emphasizing that caution should be used when applying this type of acoustic indices in biodiversity assessment. In contrast, all tested indices reflected distinct spatial and temporal patterns that were often related to habitat features (i.e. island size) and animal activity (i.e. choruses), supporting alternative (large-scale) applications of acoustic indices. Random forest algorithms confirmed the potential to classify island size based on soundscape characteristics. These findings suggest acoustic indices can capture differences in assemblage composition and bird activity along a habitat fragmentation gradient. Hence, they can more efficiently assess habitat and community structure than species diversity, occurrence, or abundance.

Fine-scale variability in coral bleaching and mortality during a marine heatwave

Coral bleaching and mortality can show significant spatial and taxonomic heterogeneity at local scales, highlighting the need to understand the fine-scale drivers and impacts of thermal stress. In this study, we used structure-from-motion photogrammetry to track coral bleaching, mortality, and changes in community composition during the 2019 marine heatwave in Kāneʻohe Bay, Hawaiʻi. We surveyed 30 shallow reef patches every 3 weeks for the duration of the bleaching event (August-December) and one year after, resulting in a total of 210 large-area, high-resolution photomosaics that enabled us to follow the fate of thousands of coral colonies through time. We also measured environmental variables such as temperature, sedimentation, depth, and wave velocity at each of these sites, and extracted estimates of habitat complexity (rugosity R and fractal dimension D) from digital elevation models to better understand their effects on patterns of bleaching and mortality. We found that up to 80% of corals experienced moderate to severe bleaching in this period, with peak bleaching occurring in October when heat stress (Degree Heating Weeks) reached its maximum. Mortality continued to accumulate as bleaching levels dropped, driving large declines in more heat-susceptible species (77% loss of Pocillopora cover) and moderate declines in heat-tolerant species (19% and 23% for Porites compressa and Montipora capitata, respectively). Declines in live coral were accompanied by a rapid increase in algal cover across the survey sites. Spatial differences in bleaching were significantly linked to habitat complexity and coral species composition, with reefs that were dominated by Pocillopora experiencing the most severe bleaching. Mortality was also influenced by species composition, fractal dimension, and site-level differences in thermal stress. Our results show that spatial heterogeneity in the impacts of bleaching are driven by a mix of environmental variation, habitat complexity, and differences in assemblage composition.

Are ancient seep environments distinguishable by benthic foraminiferal assemblages? A case study of the Cretaceous Western Interior Seaway

Methane cold seeps are food-rich seafloor habitats that served as oases for macrofaunal communities in the Cretaceous Western Interior Seaway (WIS). Although seep-obligate taxa occur at modern seeps, macrofaunal inhabitants were not endemic to seep environments in the WIS. Here we investigate benthic foraminiferal assemblages across the WIS and test whether benthic foraminifera from seeps are distinct from non-seep environments. We compile abundance data from Campanian to Maastrichtian seep, nearshore, and offshore environments and use constrained multivariate ordination to center our analysis on differences in assemblage composition as it relates to environment setting. Genus-level analysis reveals that offshore settings have more calcareous taxa than nearshore settings, which, in contrast, have representation from various agglutinated genera. Analyses of guilds and morphotypes disregard test-wall type and still find compositional differences among environments that indicate a nearshore–offshore gradient in organic carbon supply. We also find that seep assemblages are generally more similar to offshore assemblages than nearshore ones, reflecting their position near the central axis of the WIS. However, there are no genera, guilds, or morphotypes unique to seeps. We further compare between assemblages from immature, predominantly soft-ground seeps and mature, predominantly hard-ground seeps. We find compositional differences consistent with abated chemical stressors and a well-developed physical substrate associated with seep maturity. Thus, although seep environments draw their benthic foraminiferal faunas from the surrounding metacommunity, assemblages reflect the environmental differences present at seeps and could be used as an additional proxy for seep settings and seep maturity in the WIS.

Biodiversity monitoring informs forest management in south-west Western Australia: Ten-year findings of Forestcheck

Long-term monitoring is an important element of ecologically sustainable forest management and provides the foundation for adaptive management under conditions of uncertainty and change. Management of the jarrah (Eucalyptus marginata) forest in south-west Western Australia is supported by an integrated monitoring program (Forestcheck) established to inform forest managers about trends in key elements of biodiversity associated with management activities. Forty-eight monitoring grids were established across four jarrah forest ecosystems following timber harvesting and silvicultural treatment, as well as in nearby forest that was unharvested or harvested >40 years previously. Biota monitored includes terrestrial vertebrates (mammals, birds, reptiles, and amphibians), vascular plants, epigeous macrofungi, cryptogams (lichens, mosses, and liverworts) and macro-invertebrates. Initial findings from a first round of monitoring between 2001 and 2006 were published previously. Here we report on a second round of monitoring undertaken between 2007 and 2012 and compare findings with the previous round for taxonomic richness, community structure, and response to silvicultural treatment and time since fire. We tested two hypotheses for each of the groups studied: (1) that silvicultural treatment or (2) time since fire had no effect on (a) richness or (b) assemblage composition.A total of 3787 taxa were recorded. Dominant factors influencing total species richness and composition were forest ecosystem type, time of monitoring, time since harvesting and time since fire. Silvicultural treatment had no significant effect on mean richness of invertebrates, macrofungi, vascular plants and birds for either monitoring period but cryptogam richness was higher in unharvested forest and species richness of terrestrial vertebrate fauna was higher in harvested forest. Time since harvest had a significant influence on all species assemblages except terrestrial vertebrates but over time effects were ameliorated other than for cryptogams and birds. Time since fire had no effect on taxonomic richness for any of the groups examined, but significant differences in assemblage composition were detected between three categories of time since fire for all the groups except terrestrial vertebrates.Knowledge of the distribution of individual organisms and the composition of taxon assemblages in jarrah forest has been significantly improved as a result of monitoring, particularly for invertebrates, macrofungi and cryptogams. Some taxa across all groups were only recorded in forest subject to specific management including unharvested reference forest and forest subject to different intensities of timber harvesting, demonstrating that disturbance associated with timber harvesting and post-harvest burning can create conditions favourable for some organisms that are otherwise encountered rarely in mature forest.These results demonstrate the critical role of well-designed, systematic and multi-taxon ecological monitoring programs for evaluating biological responses to often contentious forest management practices.

Archaeological site types, and assemblage size and diversity in Aotearoa New Zealand

AbstractArchaeological settlement models involve the identification of functional site types like base camps and extraction sites based, in part, on differences in the range and frequency of artefact types and fauna. Using reports describing such assemblages from Aotearoa (New Zealand) archaeological sites dating to the first 300 years after initial colonisation, differences in assemblage composition are assessed against total assemblage size. Aotearoa provides a particularly useful test case for the archaeological identification of site types since human colonisation was relatively late in world human history meaning that assemblage accumulation should show functional site types like those identified in the ethnographic record. To test this, SHE (Richness, Heterogeneity, Evenness) diversity analysis is used to examine 18 artefact and ten faunal assemblages dated pre‐1500 CE from a variety of Aotearoa locations. Results suggest artefact and faunal diversity measures perform poorly when employed to differentiate functional site types, suggesting that the null hypothesis of assemblage size dependency cannot be rejected. This result allows for comment on the appropriateness of ethnographically derived functional site types for the study of the archaeological record even when this record accumulated over short time periods.

Variação espacial e sazonal de assembleias de peixes bentônicos em rios de água branca da Amazônia Central

Abstract Despite the high number of fish species described for the Amazon region, the ichthyofauna that inhabits the depths of the main channels of large tropical rivers is one of the least known. In order to know the diversity patterns of these fish in whitewater rivers of the Central Amazon, we used data from the main channel benthic fish assemblage of the Japurá, Purus and Madeira rivers and tested the hypothesis that there are marked spatial and seasonal differences in the composition of the fish community among them. For this, we used a multivariate dispersion test, total β diversity and its decomposition into local (LCBD) and species contribution to β diversity (SCBD). Additionally, we tested for relationships between LCBD values and richness, total abundance, and environmental variables. We categorized species with higher SCBD values into resident or migratory to investigate the potential importance of floodplains to benthic fish assemblage of the main channel of whitewater rivers. Our results corroborate the proposed hypothesis, showing that there are seasonal and inter-river differences in benthic ichthyofauna, being more evident for the Purus River. LCBD showed strong negative relationships with species richness and total abundance, particularly in the Japurá and Madeira rivers in rising season, indicating that rivers and season with high uniqueness in their composition also had low richness and abundance. LCBD was negatively correlated with conductivity and pH, which increased with declining these environmental variables, as observed mainly in Japurá River in both seasons. Approximately one third of the species had higher than average SCBD values and were considered major contributors to β diversity, as well as classified as migratory. This demonstrates the importance of conducting studies that use spatial and seasonal variables, in addition to including the background fish fauna in conservation studies, expanding the protected area and taking into account the different patterns of diversity between rivers. Furthermore, these differences in assemblage composition might be explained by the asymmetrical spatial use of habitats during different seasons, strongly suggesting the importance of the flood-pulse cycle for maintaining diversity in this environment.

Temporal and spatial variation in adult and juvenile mobile fauna associated with natural and artificial coastal habitats

Coastal habitats are important for commercially exploited and protected species of fish and larger mobile invertebrates. The addition of artificial structures within the marine environment has the potential to alter the connectivity between habitats and to affect metapopulations of a region. Baited remote underwater videos (BRUV) were used to investigate the spatial and seasonal variation in abundance of adult and juvenile mobile species associated with subtidal natural and artificial habitats within Poole Bay on the south coast of England in 2019. Metrics included the relative maximum abundance (MaxN), number of species seen (S), assemblage structure and size range of fish. Higher values of MaxN and S were recorded on artificial structures in the spring and early summer; however, this pattern was reversed by mid-summer and early autumn when more fish were recorded on the natural reefs. Yet overall differences in MaxN and S between habitats were not significant. Differences in assemblage composition between habitats varied monthly, but this was mostly driven by particular sites. Although most fish observed were juveniles, there were some seasonal differences in the size of fish using natural and artificial sites, especially bib (Trisopterus luscus), black bream (Spondyliosoma cantharus), bass (Dicentrarchus labrax) and pollack (Pollachius pollachius). The artificial habitats in this region appeared to be important in certain months, so temporal studies of this type need to be incorporated within surveys, particularly those in proximity to protected areas.

Explanations of variability in Middle Stone Age stone tool assemblage composition and raw material use in Eastern Africa

The Middle Stone Age (MSA) corresponds to a critical phase in human evolution, overlapping with the earliest emergence of Homo sapiens as well as the expansions of these populations across and beyond Africa. Within the context of growing recognition for a complex and structured population history across the continent, Eastern Africa remains a critical region to explore patterns of behavioural variability due to the large number of well-dated archaeological assemblages compared to other regions. Quantitative studies of the Eastern African MSA record have indicated patterns of behavioural variation across space, time and from different environmental contexts. Here, we examine the nature of these patterns through the use of matrix correlation statistics, exploring whether differences in assemblage composition and raw material use correlate to differences between one another, assemblage age, distance in space, and the geographic and environmental characteristics of the landscapes surrounding MSA sites. Assemblage composition and raw material use correlate most strongly with one another, with site type as well as geographic and environmental variables also identified as having significant correlations to the former, and distance in time and space correlating more strongly with the latter. By combining time and space into a single variable, we are able to show the strong relationship this has with differences in stone tool assemblage composition and raw material use, with significance for exploring the impacts of processes of cultural inheritance on variability in the MSA. A significant, independent role for terrain roughness for explaining variability in stone tool assemblages highlights the importance of considering the impacts of mobility on structuring the archaeological record of the MSA of Eastern Africa.

Comprehensive assessment of shallow surf zone fish biodiversity requires a combination of sampling methods

Surf zones of sandy beaches are crucial environments for numerous fishes but one of the most challenging habitats when it comes to sampling, due to high-energy currents and waves. In this study, we compared the efficiency of 2 methods currently used to sample the biodiversity of shallow surf zone fish communities: the traditional method of beach seine nets and the more recently introduced surf zone Baited Remote Underwater Video Stations (surf-BRUVS). We applied both sampling strategies at 67 sites along 27 sandy beaches with different environmental characteristics in southeastern Brazil. We compared overall abundance, species richness, and beta (turnover) and functional trait diversity recorded from both methods. Our results showed that seine nets captured a higher species richness, greater abundance, greater functional richness and more functionally singular species than surf-BRUVS, particularly in areas with low wave energy. Beta diversity analyses, however, showed a clear difference in assemblage composition detected by each method regardless of environmental conditions, mainly driven by species turnover and variations in abundance. Only seine nets captured small species (&lt;10 cm total length), while surf-BRUVS were more effective in recording larger species. Our results suggest that shallow surf zone assemblages sampled with surf-BRUVS and beach seine nets are almost totally taxonomically and highly functionally divergent, and the application of both methods provides complementary results. Additionally, the non-extractive nature of surf-BRUVS presents an opportunity for sampling vulnerable areas or species. However, when using a single method, researchers should take into consideration each method’s biases and be aware that biodiversity may be underestimated for certain groups.

The gateway to the oriental zone: Environmental change and palaeolithic behaviour in the Thar Desert

The global distribution of modern humans is unparalleled amongst other terrestrial fauna and explaining how we have become so uniquely successful is a topic of major debate in palaeoanthropology. Examining how past populations engaged and adapted to new ecologies, rather than just when and where they first appear in the fossil record, can best be rooted in broader studies of biogeography that explicitly recognize key thresholds between major ecozones. In this paper, focus is placed on the Thar Desert, marking the boundary between the Saharo-Arabian desert belt to the west and the monsoonal Oriental zone to the east as an example of such a boundary. The goal of this study is to provide a broad synthesis of available evidence from the region, aiming to clearly communicate the nature of the existing Palaeolithic record and to identify tension and contradiction within it as foci for future research. Following review of modern ecology and palaeoenvironmental archives from the region, a quantitative analysis of the Palaeolithic record of the Thar Desert is presented. Hierarchical clustering is used to evaluate the extent to which typological constellations within stone tool assemblages reflect the top level terminology used to group Palaeolithic behaviour, revealing six broad clusters of assemblages and three clusters of artefact types. A more detailed appraisal of dated and stratified assemblages highlights rare patterns of exclusion between Acheulean, Middle Palaeolithic and Late Palaeolithic assemblages alongside more prominent proportional differences in assemblage composition. These results are discussed in the broader context of key behavioural changes in Palaeolithic South Asia and the expansion of modern humans.

Choice of field and laboratory methods affects the detection of anthropogenic disturbances using stream macroinvertebrate assemblages.

Accurate and precise detection of anthropogenic impacts on stream ecosystems using macroinvertebrates as biological indicators depends on the use of appropriate field and laboratory methods. We assessed the responsiveness to anthropogenic disturbances of assemblage metrics and composition by comparing commonly employed alternative combinations of field sampling and individuals counting methods. Four datasets were derived by, in the field 1) conducting multihabitat sampling (MH) or 2) targeting samples in leaf packs (single-habitat sampling - SH) and, in the laboratory A) counting all individuals of the samples, or B) simulating subsampling of 300 individuals per sample. We collected our data from 39 headwater stream sites in a drainage basin located in the Brazilian Cerrado. We used a previously published quantitative integrated disturbance index (IDI), based on both local and catchment disturbance measurements, to characterize the intensity of anthropogenic alterations at each site. Family richness and % Ephemeroptera, Plecoptera and Trichoptera (% EPT) individuals obtained from each dataset were tested against the IDI through simple linear regressions, and the differences in assemblage composition between least- and most-disturbed sites was tested using Permutational Multivariate Analysis of Variance (PERMANOVA). When counting all individuals, differences in taxonomic richness and assemblage composition of macroinvertebrate assemblages between least- and most-disturbed sites were more pronounced in the MH than in the SH sampling method. Leaf packs seemed to concentrate high abundance and diversity of macroinvertebrates in highly disturbed sites, acting as 'biodiversity hotbeds' in these situations, which likely reduced the response of the assemblages to the disturbance gradient when this substrate was targeted. However, MH sampling produced weaker results than SH when subsampling was performed. The % EPT individuals responded better to the disturbance gradient when SH was employed, and its efficiency was not affected by the subsampling procedure. We conclude that no single method was the best in all situations, and the efficiency of a sampling protocol depends on the combination of field and laboratory methods being used. Although the total count of individuals with multihabitat sampling obtained the best results for most of the evaluated variables, the decision of which procedures to use depends on the amount of time and resources available, on the variables of interest, on the availability of habitat types in the sites sampled, and on the other methods being employed in the sampling protocol.

Community Dynamics of Fish Assemblages on Mid-Shelf and Outer-Shelf Coral Reefs in the Northwestern Gulf of Mexico

Offshore natural banks in the Gulf of Mexico (GOM) are unique model systems for examining the mechanisms structuring reef fish communities due to their substantial geographic isolation, and the presence of replicate experimental units of both low (mid-shelf) and high coral diversity (shelf-edge) reef habitats. Here, we examined the species assemblage structure of juvenile and adult fishes at two mid-shelf reefs (Sonnier and Stetson Bank) and two shelf-edge reefs (East and West Flower Garden Banks) in the northwestern GOM to evaluate the relative importance of habitat (i.e. coral diversity) vs. recruitment in structuring resident fish assemblages. Visual reef fish surveys (n = 400) were conducted at the four coral reefs during two seasons, spring-early summer and late summer-fall in 2009 and 2010. Two depth zones were surveyed at each reef, representing the reef crest (15-23 m depth) and upper slope (23-30 m depth) habitats. Seasonal variability in recruitment to both mid-shelf and shelf-edge reefs was observed, with higher mean juvenile density and diversity (Hʹ) observed during the late season at all reefs in 2009 and all but Stetson in 2010, supporting an early fall recruitment peak. Likewise, considerable inter-annual variability in juvenile recruitment was observed, with significantly lower juvenile density and Hʹ observed at mid-shelf reefs in 2010 relative to 2009. Species diversity was strongly linked to coral diversity, with greater reef fish diversity consistently observed at shelf-edge relative to mid-shelf reefs. Observed differences in the composition of juvenile and adult assemblages at mid-shelf reefs suggest that reef fish communities at these reefs were more strongly influenced by post-settlement processes (e.g. juvenile mortality) than shelf-edge reefs, which may be a function of several limiting factors (e.g., predation, coral diversity, water quality). Results indicate that reef fish assemblages associated with mid-shelf and shelf-edge reefs in the northwestern GOM have sufficient stabilizing mechanisms in place to facilitate recovery from anomalous recruitment events and maintain consistent resident assemblages. The strong, reef type-specific differences in assemblage composition observed throughout the study indicate that mid-shelf and shelf-edge coral reef habitats may fill different functional roles for demersal fishes in the northwestern GOM.

Understanding Fish Assemblage Structure in Lentic Ecosystems: Relative Effects of Abiotic Factors and Management Legacies

AbstractWe investigated associations of fish assemblages and habitat characteristics (e.g., morphology and water chemistry) from 45 natural lakes and reservoirs in Iowa to determine whether species or trophic guild composition and environmental correlations were concordant between waterbodies of different origins. Overall, fish assemblage composition between natural lakes and reservoirs was consistently dissimilar based on a permutational multivariate ANOVA. Species composition from nonmetric multidimensional scaling ordinations for reservoirs was correlated with a variety of limnological and physical characteristics, whereas species composition and trophic composition of natural lakes were weakly associated with habitat characteristics. Species richness was positively related to waterbody and watershed size for reservoirs but not for natural lakes. Conversely, species richness was negatively correlated with increasing eutrophic conditions in natural lakes but not in reservoirs. Overall, distinct differences in assemblage composition were observed between natural and artificial lentic ecosystems and may have resulted from underlying differences in limnological, physical, and anthropogenic influences between systems. Dissimilar management legacies between waterbody types, such as limited or no stocking of nonrecreationally important species and the use of piscicides, may have additionally had overriding effects on the observed assemblage–environmental relationships. For instance, lower trophic richness and species richness in reservoirs appeared to have resulted from replacement of a diversity of small‐bodied native species by relatively few commonly stocked sport fishes. Our results emphasize the need to consider waterbody origin and the potential influence of historical or current management strategies on fish assemblage characterization and subsequent inferences made from environmental correlations.

Dung beetle responses to successional stages in the Amazon rainforest

Amazon rainforest is facing several threats due to anthropogenic activities causing loss of habitat, species, and ecosystem functions. However, several areas are being abandoned after anthropic use allowing secondary succession to occur, which can lead to the passive restoration of community parameters that have been lost. We aimed to investigate the effects of vegetation structure on dung beetle assemblages along a successional gradient in the western Amazon rainforest. Dung beetles were sampled and forest structure variables were measured using standardized protocols along primary, late secondary, and early secondary forests. We used a combination of generalized linear models and multivariate analyses to test for differences in assemblage composition and structure among successional stages and their relationships with vegetation variables. We found that primary forests have different species compositions from both late and early successional forests, with several species strongly associated with primary forests. Dung beetle abundance was higher in primary forests and influenced by variables describing the successional stages (i.e., tree density). Species turnover was the most important β-diversity component among and within each successional stage, with lower values in early secondary forests. Different pathways followed by secondary forests during forest succession may lead to increased species turnover similar to that found in primary forests. Biodiversity conservation will only work if secondary forests are allowed to recover to a late successional stage close to a primary forest stage. The loss of primary forests can cause an irreversible loss of species in need of conservation and with great functional importance in the Amazon rainforest.

Richness and composition of anuran assemblages from an Amazonian savanna.

The Amazonian savannas occupy approximately 150,000 km2 of the Brazilian Amazon, occurring in scattered isolated patches over large areas of forest in the states of Amapá, Amazonas, Pará, Roraima and Rondônia. Despite having considerable variation in the Anuran composition between locations and between the savanna’s physiognomies, a systematic and geographically wide sampling has not been performed for the savanna from Amapá yet, located in the north of Brazil, eastern Amazonia. In this perspective, a study was conducted on the richness, composition, diversity, and abundance of Anuran species in a ​​savanna area in Amapá State. For Anuran sampling, we performed 24 samples in four physiognomies (grassland savanna, scrub grassland savanna, parkland savanna, open woodland savanna) through an active and auditory search more than 20 sampling plots of 100 × 50 meters in each physiognomy. Twenty-one (21) species of frogs belonging to five families were registered: Bufonidae, Hylidae, Leptodactylidae, Microhylidae and Phyllomedusidae. Scrub grassland savanna registered a greater number of individuals regarding the species richness by physiognomy. The species rarefaction curve for the total area reached an asymptote, suggesting that the data collection effort was enough to adequately sample the species richness of the area. The Kruskal-Wallis variance analysis revealed significant differences in the species richness and diversity among the physiognomies. The Bray-Curtis similarity analysis grouped the physiognomies into three main groups: open woodland savanna, grassland savanna and scrub grassland savanna and parkland savanna. Through ordering by non-metric multidimensional scaling, the species composition from the savanna anuran assemblage resulted in a separation among three sampled physiognomies with significant differences, indicating differences in assemblage composition of the three sampled physiognomies. The local richness (21 species) corresponds to 14% of the 15 typical species that have strongly associated distribution with the Cerrado from Central Brazil, and 35.6% of 59 typical species of neighboring domains which only marginally occur in the Cerrado, representing a considerable part of frog species richness recorded in the savanna in the eastern portion of the Brazilian Amazon.

Beta diversity of aquatic invertebrates increases along an altitudinal gradient in a Neotropical mountain

AbstractMountains harbor rich biodiversity and high levels of endemism, particularly due to changes in environmental conditions over short spatial distances, which affects species distribution and composition. Studies on mountain ecosystems are increasingly needed, as mountains are highly threatened despite providing ecosystem services, such as water supply for half of the human population. We aimed to understand the patterns and drivers of alpha and beta diversities of aquatic invertebrates in headwater streams along an altitudinal gradient in the second largest South American mountain range, the Espinhaço mountains. Headwater streams were selected at each 100 m of elevation along an altitudinal gradient ranging from 800 to 1400 m asl, where three substrate types per stream were sampled: leaf litter, gravel, and cobbles. Environmental variables were sampled to represent local riparian canopy cover, instream physical habitat, water quality, climatic data, and land use. Generalized linear models and mixed models were used to test relationships between altitude and the richness and abundance of invertebrates and to assess the influence of environmental variables on the same metrics. Patterns of spatial variation in aquatic invertebrate assemblages along the altitudinal gradient were assessed using multiplicative beta diversity partitioning. The richness and abundance of aquatic invertebrates decreased with increasing altitude, whereas beta diversity increased with increasing altitude. Significant differences in assemblage composition and in relative abundance of invertebrates were observed for both substrates and altitude. We thus show that the high regional beta diversity in aquatic ecosystems in the studied site is due to the high turnover among areas.Abstract in Portuguese is available with online material.

Distribution and habitat preference of Ephemeroptera and Trichoptera in subtropical mountain streams: implications for monitoring and conservation.

The assessment of biotic-habitat relationships provides key information to predict biotic responses to perturbations and important tools for river management and monitoring. This study aimed to assess the spatial distribution of Ephemeroptera and Trichoptera in mountain streams of central Argentina. We evaluated the effect of seasonality and identified the variables conditioning the abundance of the assemblages and the habitat with the highest taxonomic richness. Sampling was carried out in four streams (Carcarañá River basin) during high and low water periods. Three lotic habitats were sampled: riffles, coarse substrate runs, and fine substrate runs; and physicochemical and habitat variables were measured. We found differences in assemblage composition, among the 25 genera of Ephemeroptera and Trichoptera, at the habitat level. The most important variables affecting distribution patterns were substrate and flow type, but macroalgae and organic matter (twigs, leaves, and detritus) were also important predictors. Riffles maintained the highest richness but when considering only the Ephemeroptera taxa, fine substrate runs emerged also as an important habitat for these taxa. Our study provided valuable ecological information related to habitat preference of taxa with a key role in stream functioning and of great usefulness for the monitoring of lotic systems.