Assemblage Types Research Articles

Biological indicators of disturbance at a dredged-material disposal site in Liverpool Bay, UK: an assessment using time-series data

Abstract Whomersley, P., Ware, S., Rees, H. L., Mason, C., Bolam, T., Huxham, M., and Bates, H. 2008. Biological indicators of disturbance at a dredged-material disposal site in Liverpool Bay, UK: an assessment using time-series data. – ICES Journal of Marine Science, 65: 1414–1420. The development of reliable indicators of disturbance in the marine environment is essential because of increasing anthropogenic pressures and the need for more effective regulation. Our objective was to evaluate 13 nationally and internationally recommended metrics, using a large dataset derived from annual (1996–2003) macro-invertebrate infaunal surveys of a Liverpool Bay dredged-material disposal site. The primary and derived univariate metrics, along with multivariate derivations, were assessed and scored against six selection criteria. Metrics that did not correlate with the pressure indicator (the annual quantity of material disposed of) were discounted from further analysis. Of the 13 metrics evaluated, only measures of species number and Margalef’s species richness index were significantly correlated. Although assemblage types were significantly different between stations, common time patterns were observed, indicating that underlying larger scale, low-frequency events may have influenced assemblage development at all locations.

Lithic Technology and the Cultural Identity of Early Mesolithic Groups

Until now the assignment of Mesolithic sites to specific assemblage types has been largely based on their microliths, although these tools form less than 3% of the total number of artifacts. A redefinition of Mesolithic assemblage types based on the typological and technological characteristics of the entire industry has been tested on a number of assemblages from Sandy Flanders (Belgium) that are representative of the four typological groups currently identified in the Early Mesolithic of northwestern Europe. The results of these analyses provide new insights into the lithic technology and allow a reassessment of these typological groups. The use of an extensive dating strategy in combination with technological analysis makes it possible to interpret the assemblages both chronologically and functionally and to identify cultural differences among them.

Concordance of stream macroinvertebrate assemblage classifications: How general are patterns from single-year surveys?

We examined how the assemblage structure and assemblage–environment relationships of stream macroinvertebrates varied over three consecutive years in a boreal drainage system. We specifically examined whether classifications produced assemblage types that were stable through time, and how these assemblages could be predicted based on local environmental variables. We also used a combination of Procrustes rotation analysis and NMDS ordinations to examine the degree of year-to-year concordance of assemblage patterns. The composition of site clusters varied among years, resulting in only moderate among-year concordance of assemblage classifications. Stream width and in-stream habitat conditions, especially macrophyte cover, were the most important variables discriminating among the cluster groups. Despite temporally variable assemblage classifications, the overall macroinvertebrate assemblage structure was concordant among years. Among-year concordance was higher in-streams with low temporal variation in the physical environment, as well as high abundance and low variability of macrophytes. Due to among-year variability in cluster composition and weakly predictable assemblage–environment relationships, a posteriori assemblage classifications may be of limited value in the conservation planning of headwater streams.

Early Magdalenian Variability: New Evidence from El Mirón Cave, Cantabria, Spain

One of the most important and longstanding debates in Paleolithic prehistory is over the significance of interassemblage variability. The problem of variability among artifact assemblages pertaining to the Lower Cantabrian Magdalenian phenomenon (ca. 16,000–14,000 uncalibrated years B.P.) is much like the Mousterian facies question, but with far less international attention. Are the different assemblage types temporal, stylistic, or functional in nature, or are they merely products of the vagaries of archaeological sampling? Ongoing excavations in separate areas of the large El Mirón Cave in the Cantabrian Cordillera are yielding the same range of assemblage variability demonstrated for classic lowland coastal zone sites such as Altamira and El Juyo. Here we present a preliminary comparative analysis of the extraordinarily rich and diverse Lower Magdalenian (and Initial Magdalenian, ca. 17,000–16,000 uncalibrated years B.P.) contents of a sondage excavated in the center of the El Mirón vestibule and contribute to the empirical basis for the debate regarding the existence and significance of cultural facies versus temporal phases. We also briefly summarize post-Magdalenian data from the larger area of the mid-vestibule trench in El Mirón, highlighting evidence for the abrupt appearance of a fully-formed Neolithic lifeway at ca. 4500 CAL B.P., the earliest yet found in northern Atlantic Spain.

Waterbird assemblages in the Aspen Parkland of western Canada: the influence of fishes, invertebrates, and the environment on species composition

We conducted a survey of biotic and abiotic factors correlated with water-bird assemblage composition in the Aspen Parkland, an endangered transitional zone between prairies and boreal forest, rich in waterbirds but poor in information relating avian distributions to features of aquatic habitats. We surveyed breeding aquatic bird species, plus invertebrates, fishes and limnological factors on 25 naturally eutrophic to hypertrophic lakes in Alberta, Canada. We observed 43 non-passerine species. Canonical Correspondence Analysis revealed two assemblage types: (a) a “grebe-gull” assemblage of gulls, grebes and waterfowl on hypertrophic lakes with small-bodied fishes and invertebrate assemblages of Diptera, Cladocera, Amphipoda and Glossiphoniidae, or (b) a “teal-shorebird” assemblage of ducks and shorebirds on eutrophic fishless lakes with invertebrate assemblages of Gastropoda, Erpobdellidae, Dytiscidae and Trichoptera. Lakes with “grebe-gull” assemblages were deeper and the presence of fish added to the resource base of these systems, perhaps contributing to greater species richness in “grebe-gull” lakes (x̄=12.5 species in presence of fishes, x̄=8.1 species in absence of fishes). Phytoplankton (chlorophyll-a) and nitrogen (TDN) concentrations were the most important limnological factors correlated with bird-assemblage composition, and may influence composition of invertebrate resources for birds on the two types of lakes. Our multivariate approach could be useful to managers for identifying key environmental factors associated with the successful management of multiple waterbird species in the Aspen Parkland.

Fish assemblages in European Western Highlands and Western Plains: a type‐specific approach to assess ecological quality of running waters

Abstract After typological pre‐classification of 398 calibration sites, fish‐based metric models were used to predict the impact of human activities on river quality in European Western Highlands and Western Plains ecoregions. Calibration sites were grouped into six assemblage types and according to their geomorphology; test sites were assigned to their corresponding assemblage type. Five anthropogenic variables were used to describe the impact level of each site and stepwise discriminant analysis was performed to: (i) avoid redundancy between metrics; (ii) examine how selected metrics discriminated impact classes and (iii) predict ecological status for each site of the given fish type. Globally, this approach predicted the impact class correctly for 64% of sites. The difference between observed and predicted impact was more than one class for only 2.5% of the sites. When validating this approach with an independent data set, differences between observed and predicted impact values never exceeded 2 impact classes, but these differences varied in size among countries.

Spatially based methods to assess the ecological status of riverine fish assemblages in European ecoregions

Abstract The objective was to develop spatially based (type‐specific) methods to assess the ecological status of European rivers according to the EU Water Framework Directive. Some 15 000 samples from about 8000 sites were pre‐classified within a five‐tiered classification system based on hydromorphological and physico‐chemical pressures. The pre‐classification was used to identify reference conditions and to calibrate the assessment methods. Clustering reference sites based on relative species composition resulted in 60 fish assemblage types within 11 of the ecoregions under study. Discriminant function analyses (DFAs) were employed to identify environmental parameters characterising fish assemblage types; altitude, river slope, wetted width, mean air temperature and distance from source were the principal predictors. These environmental parameters were used to assign impacted sites with altered fish assemblage composition to the reference fish assemblage type. Metrics (fish assemblage descriptors) responding to human pressures were selected based on correlation and DFAs. Assessment methods were developed for 43 fish assemblage types. Metrics based on individual sentinel species were more often used in type‐specific methods than metrics related to reproduction, habitat and feeding. Metrics based on long‐distance migrants and potamodromous species were more sensitive to human pressures than overall composition metrics, e.g. total number of species. Only some of the tested metrics showed pressure‐specific responses, i.e. reacted to one type of pressure but not to others. Insectivorous, intolerant and lithophilic species exclusively responded (decreased) to chemical and hydromorphological pressures in 14–19%. Omnivorous species was the only metric type that showed a consistent reaction (increase) to continuum disruptions in 25% of the cases. Accuracy of methods based on cross‐validation with pre‐classification varied between 47% and 98% (mean 81%) when contrasting calibration data set (class 1 and 2) with degraded sites (class 3, 4 and 5).

Spatially based methods to assess the ecological status of European fish assemblage types

Abstract A spatially based, river type‐specific approach was used to develop an ecological assessment method for European rivers based on existing sampling data. The methodology comprised two main steps: (1) description of a river and fish assemblage typology based on minimally or slightly impacted sites and (2) analyses of impacted conditions for each type. Hierarchical cluster analysis of fish species assemblages identified 15 homogeneous groups in 11 European ecoregions. Discriminant analyses, based on abiotic characteristics, were used to predict fish types at impacted sites. The latter encompassed both regional (geographic position in Europe) and local factors (longitudinal zonation) influencing the distribution of riverine fishes. To assess ecological status, the responses of more than 400 metrics (species composition, abundance and age–length structure) to human pressures were tested for each river type separately. A maximum of 10 metrics per river type was selected using discriminant analysis. The density of intolerant species and feeding guilds had the highest capacity to predict the intensity of perturbation.

Lake depth and geographical position modify lake fish assemblages of the European ‘Central Plains’ ecoregion

Summary1. Classification of European lake fish assemblages can be based on fish‐assemblage structure or morphological, geographical, physical and chemical lake attributes. However, substantial gaps in knowledge exist with respect to the correspondence between both classification approaches.2. Here, we compiled fish assemblage data from 165 lakes situated in the European ‘Central Plains’ ecoregion. Cluster analysis of fish abundances was performed to compare fish assemblage types of the entire ecoregion with those from previous country‐specific studies. Nonparametric group comparisons, classification trees and partial canonical ordinations were used to infer the correspondence between fish assemblage types and morphology, geographical position and nutrient concentration of the lakes.3. Three distinct fish assemblages were revealed: vendace (Coregonus albula), ruffe (Gymnocephalus cernuus) and roach (Rutilus rutilus) lake types. Both latitude and lake depth were the best determinants of lake type, but total phosphorus (TP) concentrations were also important. Vendace lakes were deep and had low TP concentrations, whereas the shallower ruffe and roach lakes had higher TP values. Roach lakes were more frequent in the north‐west area of the ecoregion, whereas ruffe lakes were more often found south of the Baltic Sea.4. Controlling for the influence of nutrient concentration showed that lake morphology and geographical position were important determinants of fish assemblages. However, the variance explained was low (<20%), implying that biological interactions may also be important in forming the lake‐specific fish assemblages.5. The results suggest that fish assemblages differ between deep and shallow lakes, and between the north‐west and south‐east locations within the Central Plains ecoregion. Accordingly, establishment of depth‐related lake morphotypes is needed, and the European ecoregions recommended to be used in evaluation systems according to the Water Framework Directive seem to be too coarse to reflect the subtle differences of fish species richness along geographical gradients.

Distribution and richness of diadromous fish assemblages in Western Europe: large‐scale explanatory factors

Abstract – The aim of this study was to analyse the distribution of 14 diadromous fish at the beginning of the 20th century in western Europe. This study was conducted on a set of 41 water basins. Five environmental variables were selected and we used generalised additive models for explaining the presence–absence of species. The richest basins were located in the centre of the study area. Six main assemblage types were identified along a latitudinal gradient; they were constituted of a common species basis but differed by the absence or presence of other species. The 10 single species models produced have moderate to very good discrimination level and they can correctly predict both absence and presence. Temperature is included in all but one model, response curves vary according to the species; surface area is included in six models.

Diversity and structural patterns for tropical montane and premontane forests of central Peru, with an assessment of the use of higher-taxon surrogacy

The Chanchamayo valley in the Peruvian Andes formerly contained large areas of montane and premontane tropical forests, although logging and agricultural expansion has resulted in extensive deforestation and habitat fragmentation. This study evaluates the regional context of the valley by a comparison of data from a series of one hectare plots giving data on the diversity and structure of trees ≥10 dbh, and then examines in more detail data from a 1 ha plot located in a newly declared conservation area (Pampa Hermosa Reserved Zone) embodying one of the most intact forest remains. An explicit goal was also to test the efficacy of sampling using taxonomic surrogacy, which could provide an effective means of making more efficient such work among diverse tropical forests. The Cedros de Pampa Hermosa plot contained 444 individuals belonging to 135 species, 66 genera and 35 families. The families Lauraceae, Meliaceae, Moraceae and Urticaceae provided over half of the individuals counted. The high representation of Urticaceae species suggests a disturbance regime driven by the large sizes of the Meliaceae species and their dynamics on steep slopes. Indicator species analyses supported other evidence that this site at 1,600 m is located in a broad ecotonal area transitioning to premontane and lowland rain forests. Ordinations (nMDS) based on Bray–Curtis similarities and total abundance, basal areas and presence-absence data of the 598 species (3,469 individuals) found on all seven one hectare plots sampled in the valley showed a clear separation into three tree assemblage types, namely the lower montane site, and two others on the eastern and western sides of the valley. Ordination patterns were quite similar at species and family level, but did not show any site groupings at the generic level, suggesting important turnover of species and families along environmental gradients. A number of species could not be allocated to known taxonomic groups, and were evaluated as morphotaxa. The inclusion or exclusion of such taxa did not dramatically alter the main ordination patterns within taxonomic levels of botanical family or of species, which implies that rapid inventory methods and incomplete identifications can still provide data useful for conservation planning in this and similar forests.

REDISCOVERING THE SPECIES IN COMMUNITY-WIDE PREDICTIVE MODELING

Broadening the scope of conservation efforts to protect entire communities provides several advantages over the current species-specific focus, yet ecologists have been hampered by the fact that predictive modeling of multiple species is not directly amenable to traditional statistical approaches. Perhaps the greatest hurdle in community-wide modeling is that communities are composed of both co-occurring groups of species and species arranged independently along environmental gradients. Therefore, commonly used "short-cut" methods such as the modeling of so-called "assemblage types" are problematic. Our study demonstrates the utility of a multiresponse artificial neural network (MANN) to model entire community membership in an integrative yet species-specific manner. We compare MANN to two traditional approaches used to predict community composition: (1) a species-by-species approach using logistic regression analysis (LOG) and (2) a "classification-then-modeling" approach in which sites are classified into assemblage "types" (here we used two-way indicator species analysis and multiple discriminant analysis [MDA]). For freshwater fish assemblages of the North Island, New Zealand, we found that the MANN outperformed all other methods for predicting community composition based on multiscaled descriptors of the environment. The simple-matching coefficient comparing predicted and actual species composition was, on average, greatest for the MANN (91%), followed by MDA (85%), and LOG (83%). Mean Jaccard's similarity (emphasizing model performance for predicting species' presence) for the MANN (66%) exceeded both LOG (47%) and MDA (46%). The MANN also correctly predicted community composition (i.e., a significant proportion of the species membership based on a randomization procedure) for 82% of the study sites compared to 54% (MDA) and 49% (LOG), resulting in the MANN correctly predicting community composition in a total of 311 sites and an additional 117 sites (n = 379), on average, compared to LOG and MDA. The MANN also provided valuable explanatory power by simultaneously quantifying the nature of the relationships between the environment and both individual species and the entire community (composition and richness), which is not readily available from traditional approaches. We discuss how the MANN approach provides a powerful quantitative tool for conservation planning and highlight its potential for biomonitoring programs that currently depend on modeling discrete assemblage types to assess aquatic ecosystem health.

Relationship of species composition of tropical seagrass meadows to multiple physical environmental factors

AbstractThe purpose of this study was to examine the relationship between species composition of tropical seagrasses and various physical environmental factors: depth, sediment thickness and silt–clay content in the sediments. We investigated species composition and abundance of seagrasses as well as the physical environmental factors for six transects around Ishigaki Island, southwest Japan. Eight species occurred in the quadrat census. The occurrence frequencies ranged from 66.8% (Thalassia hemprichii) to 4.5% (Enhalus acoroides). Both canonical correspondence analysis (CCA) and cluster analysis elucidated that depth was mainly responsible for the distributions of species and assemblage type. Monte Carlo permutation for partial CCA revealed that 37.5% of the variance was explained by depth, 10.3% by sediment thickness and 4.6% by silt–clay content in the sediment. Twenty‐six sites were categorized into four assemblage types by a cluster analysis using the leaf area index (LAI; the ratio of total leaf area to bottom area) as a measure of species abundance. Type I was dominated by T. hemprichii and Cymodocea rotundata, Type II by C. serrulata, Type III by E. acoroides, and Type IV by Halodule pinifolia and Halophila ovalis. Type I occurred mostly in the intertidal zone (91.3±30.5 cm below MSL, mean sea level), Type II in the subtidal zone (179.1±75.0 cm below MSL) and Type IV in both shallow sites (between 47.8 and 75.6 cm below MSL) and in those with low silt–clay contents (between 2.0 and 3.8%).

The Development of ISIS: A Habitat-based Invertebrate Assemblage Classification System for Assessing Conservation Interest in England

A database summarising the relationships between invertebrate species and habitat type could help inform the development of site management plans, the assessment of trends within the wider countryside and the evaluation of site quality. The requirements for such a habitat-based invertebrate assemblage classification system are discussed. For the purposes of nature conservation, it is clear that a system that details both type and quality of any given invertebrate assemblage would be very beneficial. Such a system would clarify biodiversity interest for both entomologists and conservation staff alike. English Nature’s approach to this system is detailed, the basic approach employing a series of broad assemblage types that are sensitive to changes in hydrology and disturbance regimes, and a series of specific assemblage types that can be used to assess changes in site quality. Examples of the current wetland assemblage types are given. This approach is tested using pairwise Bray–Curtis similarity indices. The results are promising, although it is clear that the system requires further work. Finally, the future of the project is outlined, with the expectancy that a fully operational prototype will be ready by 2006.

Stream fish assemblages and basin land cover in a river network

This study focused on characterizing fish assemblages in the Adour–Garonne basin and identifying the relative influences of landscape-scale features on observed patterns in stream fish assemblages. Two different artificial neural network algorithms were used: a self-organizing map (SOM) and a multilayer perceptron (MLP). A SOM was applied to determine fish assemblage types, and a MLP was used to predict the fish assemblage types defined by the SOM. Thirty four species were collected at 191 sampling sites in a major river-system, the Adour–Garonne basin, and topographical factors, namely altitude, distance from source and surface area of drainage basin were measured. Using GIS, land cover types (agricultural land, forests and urbanized artificial surface) were calculated for each site and expressed as percentage of the surface area of basin. These variables were introduced to the MLP and factorial discriminant analysis for the prediction of assemblage types. As a result, the SOM distinguished three fish assemblage types according to the differences of species composition, and the assemblage types were better predicted with landscape-scale features by MLP than discriminant analysis. The percentages of agricultural land and the surface area of a basin showed the greatest influence on assemblage types 1 and 2, and distance from source was the most important factor to determine assemblage type 3.

Unionid Habitat and Assemblage Composition in Coastal Plain Tributaries of Flint River (Georgia)

Effective conservation of mussels in streams of the lower Flint River basin, southwest Georgia, requires more rigorous understanding of mussel-habitat associations and factors shaping assemblage composition in stream reaches. We surveyed mussels and habitat conditions at 46 locations, and used regression, correlation and multivariate direct gradient analysis (Canonical Correspondence Analyses) to identify species-habitat relationships and characteristic species-assemblage types in Flint basin streams. Riparian wetland and catchment forest cover, average mid-channel depth, and drainage network position accounted for 49% of the variability in mussel species richness, 36% of the variability in unionid abundance, and 32% of the variability observed in Shannon-Wiener diversity across survey sites. Species were grouped into four assemblage types based on their habitat associations: large-river-riffle associates, slackwater associates, habitat generalists, and stream-run associates. Results are broadly concordant with anecdotal reports of mussel-habitat relationships and provide insight into the habitat conservation needs of mussels.

Requirements for marine protected areas to conserve the biodiversity of rocky reef fishes

Abstract This study describes spatial patterns in the biodiversity (species, assemblages) of rocky reef fishes at a spatial scale relevant to management, and compared the outcomes for this biodiversity from alternative procedures for selecting marine protected areas (MPAs) and from the selection of MPAs for fisheries‐related objectives. The study area included 104 species in two assemblage types; 36 species and 14 species occurred only in one or two locations respectively. MPAs selected by hotspot richness, greedy richness complementarity, and summed irreplaceability included similar percentages of species and significantly more species than randomly selected MPAs. A combined species‐assemblage selection ensured representation of assemblage diversity. Representation of all species and assemblage types required 92% of locations. MPAs chosen using density of all fishes or density of exploitable fishes as selection criteria included fewer species (than MPAs selected using species identity) and the percentage of species accumulated did not differ from a random selection. Use of an established MPA as the seed for an expanded network was inefficient, leading to additional locations being required and an accumulation of species that did not differ from a random selection. The smallest MPA network that fulfilled multiple management objectives (representation of assemblage diversity and majority of species, population viability, support for fisheries, connectivity) required 30% of the surveyed locations. This study concluded that: MPAs selected without the benefit of data on intra‐habitat variation in species assemblages will be unrepresentative; the upper range of currently promoted targets for MPA establishment (i.e. 30%) should be regarded as a minimum for biodiversity conservation; MPAs selected for fisheries‐related reasons may not provide expected benefits for the remainder of the fish assemblage. Copyright © 2006 John Wiley & Sons, Ltd.

Metacommunity patterns of highly diverse stream midges: gradients, chequerboards, and nestedness, or is there only randomness?

Abstract. 1. Several non‐random patterns in the distribution of species have been observed, including Clementsian gradients, Gleasonian gradients, nestedness, chequerboards, and evenly spaced gradients. Few studies have examined these patterns simultaneously, although they have often been studied in isolation and contrasted with random distribution of species across sites.2. This study examined whether assemblages of chironomid midges exhibit any of the idealised distribution patterns as opposed to random distribution of species across sites within the metacommunity context in a boreal drainage system. Analyses were based on stream surveys conducted during three consecutive years. Analytical approaches included ordinations, cluster analysis, null models, and associated randomisation methods.3. Midge assemblages did not conform to Clementsian gradients, which was evidenced by the absence of clearly definable assemblage types with numerous species exclusive to each assemblage type. Rather, there were signs of continuous Gleasonian variability of assemblage composition, as well as significant nested subset patterns of species distribution.4. Midge assemblages showed only weak relationships with any of the measured environmental variables, and even these weak environmental relationships varied among years.5. Midge assemblages did not appear to be structured by competition. This finding was somewhat problematic, however, because the two indices measuring co‐occurrence provided rather different signs of distribution patterns. This was probably a consequence of how they actually measure co‐occurrence.6. Although midge assemblages did not show a perfect match with any of the idealised distribution patterns, they nevertheless showed a resemblance to the empirical patterns found previously for several plant and animal groups.

Inventory of Intertidal Marine Habitats, Boston Harbor Islands National Park Area

The intertidal zone of the 34 islands that are the Boston Harbor Islands national park area encompasses over half of the total park area, thereby representing a significant natural resource. The purpose of this study was to inventory the intertidal zone by classifying and mapping all habitats and compiling species lists for major taxonomic groups. The Boston Harbor Intertidal Classification System was developed for mapping substrate and biotic assemblage types—a system specific to the local area, but capable of application throughout the Gulf of Maine. Intertidal habitats were mapped from GPS-based field delineations. Mixed coarse, consisting of rocks, boulders, cobbles, gravel, shell, and sand, was by far the most common substrate type; however, the islands were variable with a total of 13 discrete substrate types mapped, ranging from bedrock and boulders to mud. The outer islands (e.g., Outer and Little Brewster) were dominated by rocky substrate, while islands close to the mainland (e.g., Thompson, Slate) had high percentages of fine sediments. Of the 31 biotic assemblages mapped, Mytilus edulis (blue mussel) reef was the dominant assemblage on many of the middle and Hingham Bay islands, while the outer islands had assemblages common to the more exposed rocky substrates. The species inventory recorded 95 species of invertebrates, 70 marine algae, and 15 vascular plants. The information generated from this inventory will provide a foundation for natural resource management decisions, design of a long-term intertidal monitoring program, and identification of research needs.

Chalcolithic Settlements in the Western Samaria Foothills

This paper presents new data on the history of the Chalcolithic settlement system in western Samaria and offers a picture of the Chalcolithic occupation of the country's highlands. Pottery assemblages found in the area suggest that clay vessels were locally produced. Given the particular assemblage types it can now be assumed that they served sedentary agrarian populations.