Patterns Of Assemblage Structure Research Articles

Geographical and climate‐dependent patterns in spatial distributions of snail (Mollusca: Gastropoda) assemblages in freshwater wetlands across Northeast China

Abstract A central goal of community ecology and biogeography involves understanding the spatial patterns of organisms and their underlying mechanisms. Understanding how the structure of wetland biomes vary throughout geographical or climatic gradients has critical implications for the ecological restoration and management of wetlands. However, the geographical patterns of snails in freshwater wetlands and the relative contributions of climatic and local environment variables remain poorly elucidated. We investigated 126 freshwater wetlands across four ecoregions (Da Xing'an Mountains, Songnen Plain, Sanjiang Plain and Changbai Mountains) in Northeast China, and collected 105578 individual snails (Mollusca: Gastropoda) belonging to 17 families, 34 genera and 64 species. Overall, snail richness and functional alpha diversity was higher in the wetlands of the Sanjiang Plain than the other three regions. Multivariate analyses results revealed that the taxonomic, functional and phylogenetic structures of snail assemblages differed significantly across the four regions. Higher taxonomic dissimilarities, as well as functional and phylogenetic dissimilarities existed between the wetlands of the Songnen Plain and the other three regions. The variations in taxonomic, functional and phylogenetic structures of snail assemblages were predominantly explained by climatic variables rather than by local environmental variables. For taxonomic structure, salinity explained the greatest variation among all variables, whereas precipitation seasonality explained the greatest variation for functional and phylogenetic structure. Considering extant patterns in assemblage structure and its predictors, aggravated salinization and seasonality of precipitation are expected to act as powerful factors shaping future assemblages. Also, climate‐related factors cause changes and spatial distribution of invertebrate assemblages of freshwater wetlands should be considered to formulate differentiated strategy for biodiversity conservation.

Assessing Assemblage Composition of Reproductively Mature Resource Fishes at a Community Based Subsistence Fishing Area (CBSFA)

Nearshore fisheries in Hawai‘i have been steadily decreasing for over a century. Marine protected areas (MPAs) have been utilized as a method to both conserve biodiversity and enhance fisheries. The composition of resource fishes within and directly outside of the recently established Hā‘ena Community Based Subsistence Fishing Area (CBSFA) on the island of Kaua‘i were assessed to determine temporal and spatial patterns in assemblage structure. In situ visual surveys of fishes, invertebrates, and benthos were conducted using a stratified random sampling design to evaluate the efficacy of the MPA between 2016 and 2020. L50 values—defined as the size at which half of the individuals in a population have reached reproductive maturity—were used as proxies for identifying reproductively mature resource fishes both inside and outside the CBSFA. Surveys between 2016 and 2020 did not indicate strong temporal or spatial changes in overall resource fish assemblage structure; however, some species-specific changes were evident. Although overall resource species diversity and richness were significantly higher by 2020 inside the MPA boundaries, there is currently no strong evidence for a reserve effect.

Macroecological patterns of mammals across taxonomic, spatial, and temporal scales

The field of macroecology has made many contributions to our understanding of mammalian ecology and evolution through its use of big data and the examination of statistical patterns that emerge. Here, we review the advances in three areas of mammalian macroecology: 1) spatial and temporal patterns of assemblage structure and space use, 2) the processes and constraints underlying the evolution of body size and life history, and 3) advances in understanding and predicting loss of biodiversity. We highlight the important role that studies of mammals have played in the advancement of macroecological theories and patterns, and note that both mammalogy and macroecology are richer because of this linkage.

Coralligenous formations dominated by Eunicella cavolini (Koch, 1887) in the NE Mediterranean: biodiversity and structure

Coralligenous formations are biogenic structures typical of the underwater Mediterranean seascape. Their intricate, multi-layered species assemblages are composed of perennial, long-lived organisms, particularly vulnerable to natural or human-induced disturbances. Despite their high ecological role and conservation value, few studies have addressed the assemblages outside the NW Mediterranean. This is the first quantitative assessment of coralligenous in the N Aegean Sea (NE Mediterranean), specifically focusing at the upper bathymetric limit of assemblages that are dominated by the yellow gorgonian Eunicella cavolini. The number and percent cover of macrobenthic species were studied at depths of 18 to 35 m, using a photoquadrat method. A total of 99 benthic taxa were identified, out of which 89 perennial ones were used to investigate spatial patterns in assemblage structure, composition, and biodiversity. A mean number of 47 perennial taxa were recorded per site, with encrusting coralline algae and sponges being the dominant groups in percent cover and species number, respectively. Across the studied localities, structural complexity and community composition were overall similar, but assemblages presented distinctive differences at the level of sites highlighting the role of local abiotic and anthropogenic factors in the shaping of the coralligenous. Compared to the rest of the Mediterranean, assemblages hosted a similar number of taxa. However, the number and percent cover of erect bryozoans were generally low, while, apart from E. cavolini, other erect anthozoan species were absent. This work provides an important baseline for comparisons and monitoring at a local or Mediterranean scale level.

Higher taxa can be effective surrogates for species‐level data in detecting changes in invertebrate assemblage structure due to disturbance: a case study using a broad range of orders

AbstractCost‐effective assessment tools are needed to manage the impacts of natural and human disturbances on communities. Higher taxa are widely used as surrogates for species‐level identification in invertebrates; however, few studies have compared their effectiveness with species‐level data for terrestrial invertebrates or assessed the mechanistic basis for their performance, and none of these studies have used a broad range of orders. Here, a terrestrial invertebrate dataset comprising 21 orders, 197 families and 751 species was used to investigate whether order‐ and family‐level identifications were effective surrogates for species‐level identification in representing patterns in assemblage structure and detecting the effects of fire. Factors potentially influencing the performance of surrogates among invertebrate orders were also investigated. Family‐level identification of invertebrates in moorland sites with a wide range of fire history was found to be an effective surrogate for species‐level identification. Order‐level identification was also an effective surrogate, but the level of discrimination among sites was typically lower than for species‐ or family‐level identification. Higher taxonomic surrogates performed well for invertebrate orders comprising a few species that were abundant and with a small mean and variance in the number of species per higher taxon. Use of higher taxa as surrogates for species‐level identification can be a cost‐effective approach to monitoring impacts of disturbance, but outcomes are influenced by taxonomic diversity and community structure.

Cross-taxon congruence in benthic communities: Searching for surrogates in marine sediments

Cross-taxon congruence has been suggested as an efficient tool in conservation planning and biodiversity monitoring. It corresponds to the degree to which patterns in assemblage structure in a set of sites are similar among different taxonomic groups. If different groups ordinate the sampling sites similarly, they are concordant and this information is frequently used as an indicative that one group could be used as a surrogate for the other. Using spatiotemporal benthic data from a biodiverse coastal ecosystem (the Araçá Bay in southeast Brazil), we first assessed if macro- and meiofaunal assemblages inhabiting marine soft-sediments show concordant patterns. Then, we used multi- and univariate analysis to examine the relationship of both groups with the environment. Macro- and meiofaunal assemblages exhibited strong congruent patterns in all periods analyzed. Moreover, both groups responded to similar environmental features and their ordination patterns matched those generated by the environmental data. These results show that the patterns of concordance are probably mediated by similar responses to environmental gradients. Overall, our results suggest the potential for use of the surrogacy approach in conservation planning and monitoring purposes of marine benthic biodiversity, and that macro- and meiofauna can be used as a surrogate for each other.

Patterns of Assemblage Structure Indicate a Broader Conservation Potential of Focal Amphibians for Pond Management.

Small freshwater ponds host diverse and vulnerable biotic assemblages but relatively few conspicuous, specially protected taxa. In Europe, the amphibians Triturus cristatus and Pelobates fuscus are among a few species whose populations have been successfully restored using pond restoration and management activities at the landscape scale. In this study, we explored whether the ponds constructed for those two target species have wider conservation significance, particularly for other species of conservation concern. We recorded the occurrence of amphibians and selected aquatic macro-invertebrates (dragonflies; damselflies; diving beetles; water scavenger beetles) in 66 ponds specially constructed for amphibians (up to 8 years post construction) and, for comparison, in 100 man-made ponds (created by local people for cattle or garden watering, peat excavation, etc.) and 65 natural ponds in Estonia. We analysed nestedness of the species assemblages and its dependence on the environment, and described the co-occurrence patterns between the target amphibians and other aquatic species. The assemblages in all ponds were significantly nested, but the environmental determinants of nestedness and co-occurrence of particular species differed among pond types. Constructed ponds were most species-rich irrespective of the presence of the target species; however, T. cristatus was frequent in those ponds and rare elsewhere, and it showed nested patterns in every type of pond. We thus conclude that pond construction for the protected amphibians can serve broader habitat conservation aims in the short term. However, the heterogeneity and inconsistent presence of species of conservation concern observed in other types of ponds implies that long-term perspectives on pond management require more explicit consideration of different habitat and biodiversity values. We also highlight nestedness analysis as a tool that can be used for the practical task of selecting focal species for habitat conservation.

Diel variations in the assemblage structure and foraging ecology of larval and 0+ year juvenile fishes in a man-made floodplain waterbody.

This study investigated diel variations in zooplankton composition and abundance, and the species composition, density, size structure, feeding activity, diet composition and prey selection of larval and 0+ year juvenile fishes in the littoral of a man-made floodplain waterbody over five 24 h periods within a 57 day period. There was a significant difference in the species composition of diurnal and nocturnal catches, with most species consistently peaking in abundance either during daylight or at night, reflecting their main activity period. There were no consistent diel patterns in assemblage structure or the abundance of some species, however, most likely, respectively, due to the phenology of fish hatching and ontogenetic shifts in diel behaviour or habitat use. There were few clear diel patterns in the diet composition or prey selection of larval and 0+ year juvenile roach Rutilus rutilus and perch Perca fluviatilis, with most taxa consistently selected or avoided irrespective of the time of day or night, and no obvious shift between planktonic and benthic food sources, but dietary overlap suggested that interspecific interactions were probably strongest at night. It is essential that sampling programmes account for the diel ecology of the target species, as diurnal surveys alone could produce inaccurate assessments of resource use. The relative lack of consistent diel patterns in this study suggests that multiple 24 h surveys are required in late spring and early summer to provide accurate assessments of 0+ year fish assemblage structure and foraging ecology.

Effects of water level fluctuations on phytoplankton in a Changjiang River floodplain lake (Poyang Lake): Implications for dam operations

Abstract As one of the few remaining lakes that is freely connected with the Changjiang (Yangtze) River, Poyang Lake exhibits highly variable water level fluctuations. In this study, we examined the phytoplankton biomass and community including two hydrological and climatic variables (high water flow velocity, low water temperature in low water season and low water flow velocity, high water temperature in high water season). Diatoms dominated (40–87% of total) the community in periods of low water levels. In periods of high water levels, the community was dominated by cyanobacteria (45–93% of total). Various functional groups were also analyzed to assess the effects of hydrological conditions on phytoplankton community structure. The well-developed populations during the low water periods were representatives of functional groups P ( Aulacoseira granulata , 28.7% of total) and Y ( Cryptomonas spp., 12.4% of total). In the high water periods, A. granulata and Microcystis spp. (M and L M ) increased to 39.8% and 12.7% of the total phytoplankton biomass, respectively. We then used parabolic curves to identify the optimal lake water levels for each phytoplankton group. The total phytoplankton, diatom, cyanobacteria, and green algae responded positively to low water level and negatively to high water level. The water level of 14–15 m is crucial for phytoplankton biomass patterns and succession through the alternations of washing-out and dilution effects and biological competition. These results support the hypothesis that water level control projects (e.g., dams) may affect phytoplankton biomass and assemblage structure patterns in Poyang Lake by altering its seasonal hydrology.

Spatial and temporal organization of macroinvertebrate assemblages in a lowland floodplain ecosystem

An important goal in ecology is to understand controls on community structure in spatially and temporally heterogeneous landscapes, a challenge for which riverine floodplains provide ideal laboratories. We evaluated how spatial position, local habitat features, and seasonal flooding interact to shape aquatic invertebrate community composition in an unregulated riverine floodplain in western Alabama (USA). We quantified sediment invertebrate assemblages and habitat variables at 23 sites over a 15-month period. Dissolved oxygen (DO) varied seasonally and among habitats, with sites less connected to the river channel experiencing frequent hypoxia ( 14 °C during spring and summer as sites became isolated. Overall, local habitat conditions were more important in explaining patterns in assemblage structure than was spatial position in the floodplain (e.g., distance to the main river channel). DO was an important predictor of taxonomic richness among sites, which was highest where hydrologic connections to the main river channel were strongest. Compositional heterogeneity across the floodplain was lowest immediately following inundation and increased as individual sites became hydrologically isolated. Our results illustrate how geomorphic structure and seasonal flooding interact to shape floodplain aquatic assemblages. The flood pulse of lowland rivers influences biodiversity through effects of connectivity on hydrologic flushing in different floodplain habitats, which may prevent the development of harsh environmental conditions that exclude certain taxa. Such interactions highlight the ongoing consequences of river regulation for taxonomically diverse floodplain ecosystems.

Rocky reef fish assemblages at six Mediterranean marine protected areas: broad-scale patterns in assemblage structure, species richness and composition

Fish assemblages inhabiting shallow rocky reefs at six Italian marine protected areas (MPAs) were investigated to assess broad-scale patterns in assemblage structure, species richness and composition, and to evaluate the presence of a latitudinal gradient in the distribution pattern of a thermophilic fish, the ornate wrasse Thalassoma pavo. Fish abundance was estimated by visual censuses carried out within the integral reserve zones, within the 1--7 m depth range and during four sampling periods. Multivariate analyses revealed significant differences in the assemblage structure among MPAs, although patterns of variation changed considerably from time to time and they were not consistent with latitudinal or longitudinal gradient. Fish assemblages of Miramare (northern Adriatic) and those of the other MPAs clearly separated into two groups. Multivariate differences among MPAs mainly relied upon some relatively common species (e.g. Diplodus puntazzo and Muraena helena). Substantial contribution to these differences was also accounted for by T. pavo. Significant differences among MPAs were detected also in species richness and total density of fish, although the effect of MPA on species richness varied significantly from time to time. Both species richness and total density of fish at Miramare were always higher compared to the other MPAs, likely in relation to peculiar habitat characteristics. Density of T. pavo declined significantly from south to north, thus confirming the thermophily of this species. Present data point out the importance of monitoring marine fish diversity through long-term surveys across a wide spatial scale, in order to detect the early effects of water warming and to develop future plans of management and conservation.

Importance of scalar and riparian habitat effects for assessment of ecological status using littoral diatoms

The classification of waterbodies under the Water Framework Directive is dependent on the ability of monitoring programmes to reflect habitat quality using biotic elements including benthic diatom communities. This study investigated the influence of specific riparian habitats, of mixed woodland, grassland and lake artificial structures such as jetties and slipways, on benthic diatom assemblages in nine lakes across gradients of total phosphorus, alkalinity and in the presence or absence of Dreissena polymorpha. The heterogeneity of the benthic diatom assemblages at riparian and lake scale was assessed by taking three replicates per site category per lake, following standard European Union protocols. Canonical correspondence analysis (CCA) and mixed effect modelling was used to investigate the main environmental controls on assemblage structure. Non-metric Multidimensional Scaling (NMDS) was used to examine patterns in assemblage structure. No single environmental gradient was found to control benthic diatom composition, with differences among assemblages influenced both by riparian habitat type within lakes and interaction of multiple environment gradients, including presence of D. polymorpha. Greater control was exerted on community structure at the lake than local riparian scale. The influence of scalar factors on diatom assemblages increased with increasing scale. We recommend that for effective monitoring and assessment of ecological status, standard sampling protocols should include localised littoral habitats with individual samples pooled across riparian habitat types, thereby accounting for both multiple environmental and spatial controls on community structure.

Determinants of ground-dwelling spider assemblages at a regional scale in the Yukon Territory, Canada

Arctic fauna is undergoing significant alteration in response to global climate change, yet we know little regarding the factors that determine species assemblages at northern latitudes. We used a latitudinal transect to assess environmental determinants of ground-dwelling spider assemblages across the boreal forest-tundra transition at a regional scale. Using multivariate techniques, we tested 3 complementary hypotheses regarding the factors that best explain patterns of assemblage structure. We predicted that spider assemblages would respond most strongly to vegetation composition and structure and that climate and spatial variables would explain less of the variation in the data. We sampled ground dwelling spiders using pitfall traps placed at 36 sites along the latitudinal transect. We constructed 3 separate matrices of spatial, climate, and vegetation variables, with each matrix representing a hypothesis. We used redundancy analysis with variation partitioning to determine which matrix of environmental variables best explained patterns in a matrix of spider abundances. We then used a separate redundancy analysis to determine which environmental variables best explained the variation in measures of species richness and activity density. We collected a total of 2890 individual spiders representing 103 species, 58 genera, and 13 families. Our analysis supports the hypothesis that vegetation composition and its related structure best explain patterns in northern spider assemblages at a regional scale.

Assemblage structure, but not diversity or density, change with depth on a northeast Pacific seamount

AbstractAlthough depth‐related patterns in assemblage structure are documented in several deep‐sea systems, variation in diversity, assemblage structure, and abundance with depth on individual seamounts remains unexplored. Knowledge of alpha‐ and beta‐diversity on single seamounts is needed for any robust generalization about large‐scale biodiversity patterns on seamounts. Here, we explore bathymetric variation in benthic megafauna, based on ROV video transects, on Davidson seamount (1246–3656 m) in the Northeast Pacific Ocean. We found that substantial change in assemblage structure can occur over vertical scales on an individual seamount. Changes of 50% in assemblage composition (beta‐diversity, faunal turnover) were observed over as little as a ∼1500 m depth interval down the flanks of the seamount, although bathymetric clines in composition were not uniform across major taxa. Diversity and density exhibit no consistent bathymetric pattern and can vary greatly on a single isobath. Our findings suggest that ecological and evolutionary processes may vary considerably on a single seamount. As such, seamounts should be viewed as patchworks of habitats where high beta‐diversity may ultimately increase total biodiversity.

Temporal dynamics of fish assemblages of natural and artificial tropical estuaries

We sampled the fish fauna of 9 small natural estuaries and 2 constructed estuarine lakes in Australia’s dry tropics over 15 mo to detail the dynamics of fish assembly structures over time. The estuaries chosen were small enough that the cast net sampling method which we used could cover the full extent of the estuary, obviating the problem that within-estuary migration might lead to the false appearance of assemblage change over time. Temporal patterns in assemblage structure were consistent across the natural estuaries, overprinting complex spatial differences. Nursery ground utilisation and assemblage composition were intimately interlinked. In natural estuaries, assemblage change was a function of changes in both probability of encounter of individual species and in species compositions, and the recruitment, growth and subsequent emigration from the estuaries of juveniles was the main contributor to overall assemblage change. In contrast, in artificial lakes where connectivity with offshore sources of recruits was restricted, species compositions were attenuated and temporal change was not driven by the recruitment of offshore species.

Large Nektonic Fishes in Marsh Creek Habitats in the Delaware Bay Estuary

Larger nektonic fishes, many of which are economically important, comprise a large portion of the biomass in estuaries and may influence energy flow through their migrations and feeding, yet we know relatively little of this faunal component. To elucidate the patterns of species composition, distribution, and abundance in Delaware Bay, we sampled (n = 2298 sets) nektonic fishes (n = 3693 individuals, mean length = 261.4 mm, range = 53–600 mm) with multi-mesh gill nets in near-shore bay and marsh creek habitats during the summer and fall (June-November 2001) when fishes are more abundant in temperate estuaries. For the most abundant species, the older and larger individuals (age 1 ) often dominated the catches. Patterns of assemblage structure were influenced by spatial gradients in salinity and dissolved oxygen and temporal changes in temperature. Many of the large nektonic fishes that dominate in Delaware Bay are also found in other temperate estuaries from the Gulf of Maine to Chesapeake Bay, in part, because these species are highly migratory.

Fish assemblage patterns in the littoral zone of a European reservoir

Summary1. Although reservoirs are common aquatic habitats in Europe, there is little quantitative information on the spatial organisation of fish assemblages inhabiting their littoral zones. Consequently, we characterised fish assemblage structure in the littoral zone of a reservoir (Lake Pareloup) in SW France during late spring, summer and early autumn (the growing season).2. We measured the relative abundance of fish weekly, from mid‐May to mid‐October, using point abundance sampling by electrofishing. We identified temporal patterns in assemblage structure using hierarchical cluster analysis, and then characterised the spatial distribution of 17 defined ecospecies using a Kohonen self‐organising map (SOM, an unsupervised Artificial Neural Network).3. Our analyses revealed three distinct faunal structures within the littoral zone. From mid‐May to mid‐July, adults and young‐of‐the‐year (0+) occupied separate habitats, with most 0+ fish in vegetated habitats and adults in open water. From mid‐July to late August, some 0+ co‐occurred with adults, but most 0+ fishes remained in vegetated areas. Finally, from late August to mid‐October, most fish (both 0+ and adults) left the vegetation for unvegetated littoral habitats, the exception being fish species known to be dependent on macrophytes.4. Contrary to patterns for adult fishes, the 0+ fish assemblage was dynamic. These dynamics were driven by ontogenetic species‐specific habitat changes. Consequently, there was little evidence of stable assemblages or strong assemblage–habitat relationships that would be expected of an ‘interactive’ assemblage. It is likely that the patterns observed are a result of species‐specific response to habitat availability in the lake.

Human impacts in soft‐sediment assemblages at Casey Station, East Antarctica: Spatial variation, taxonomic resolution and data transformation

Abstract Differences between marine soft‐sediment assemblages at disturbed (two waste dumps, a sewage outfall and a wharf) and control locations were found at Casey Station, Antarctica. These differences were significant against considerable background spatial variability. Core samples were collected by divers using a hierarchical, spatially nested sampling design incorporating four scales: (i) locations (thousands of metres apart); (ii) sites (hundreds of metres apart); (iii) plots (tens of metres apart); and (iv) among replicates within plots (approximately 1 metre apart). Control locations had greater species richness and diversity than disturbed locations and there were many taxa found at control locations that were not recorded at disturbed locations. Assemblages at disturbed locations were less variable than those at control locations. In contrast, populations of some dominant species were more variable at disturbed locations than at control locations. Significant variation in populations of individual taxa was also found at all scales and although greatest at the level of location, variation was also large at the smallest scale, between replicate cores, indicating significant small‐scale patchiness in populations of taxa. Patterns of assemblage structure were similar at fine (77 taxa) and medium (aggregated to 33 taxa) levels of taxonomic resolution, but changed at coarse levels of resolution (nine phyla). Soft‐sediment assemblages at Casey Station are markedly different from those reported from other areas of Antarctica. Assemblages at Casey are almost completely dominated by crustaceans (up to 99% total abundance) and polychaetes are rare or in very low abundances in most areas investigated in the region. This is also the first demonstration that small Antarctic research stations (population 20–50 people) may cause impacts that are detectable in the adjacent marine environment.

Responses of turtle assemblage to environmental gradients in the St. Croix River in Minnesota and Wisconsin, U.S.A.

We investigated how environmental gradients measured along the St. Croix River in Minnesota and Wisconsin, U.S.A., influenced the turtle assemblage. Among seven species, the five most common species were generalists and had wide distributions throughout the study area. However, patterns in assemblage structure were related to environmental gradients along the river. Sex ratios were male-dominated for the five most common species, and few or no juveniles were captured during the study. The first two canonical axes of a canonical correspondence analysis accounted for 92.7% of the variation in species-environment gradients. Most of the variation in distribution and abundance was attributed to gradients in channel morphology and physical characteristics along the river channel. Abundances of common snapping (Chelydra serpentina), false map (Graptemys pseudogeographica), and painted (Chrysemys picta bellii) turtles were associated with muck substrates and the number of basking sites (i.e., snags, rocks), which increased farther downstream. Abundance of spiny softshell turtles was closely related to increased water velocity and depth, which were related to hydraulic control points in the river. Abundance of common map turtles was associated with the presence of open sandy areas, uniform channel bottom, and gravel substrates. Geomorphic changes along the St. Croix River clearly influence the turtle assemblage and these specific relations should be considered in efforts to preserve and restore components of the assemblage.

Some Methodological Issues in Macroecology

Recent years have seen the emergence of “macroecology” as a distinct research program in biology. It is concerned with geographical scale patterns in assemblage structure and, as such, of necessity relies heavily on approaches that are nonexperimental and that depend on the availability of reliable information for large numbers of species. This gives rise to a particular set of analytical issues that need to be addressed when conducting studies of macroecological patterns. In this article, we draw attention to nine such issues that we consider to be of particular importance. Our aim is to aid the development of what we believe to be an important subject area by identifying some of the more common problems that may confound studies, as well as some of their solutions.