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Assemblage Structure (assemblage + structure)
Kinds of Assemblage Structure Selected AbstractsRegional Fragmentation of Rain Forest in West Africa and Its Effect on Local Dung Beetle Assemblage StructureBIOTROPICA, Issue 2 2009Adrian L. V. Davis ABSTRACT Data from Ghana and Côte d'Ivoire, for local dung beetle assemblages of rain forest, plantations, and savanna, suggest that a subset of the savanna fauna has expanded its range across the Eastern Guinean Forest ecoregion, presumably in response to its conversion from continuous rain forest into an archipelago of forest fragments within a disturbance matrix of less shady plantation and farmland vegetation that more resembles moist savanna. [source] Assemblage structure, but not diversity or density, change with depth on a northeast Pacific seamountMARINE ECOLOGY, Issue 2010Craig R. McClain Abstract Although 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. [source] Species richness and structure of three Neotropical bat assemblagesBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2008KATJA REX We compared the assemblages of phyllostomid bats in three Neotropical rainforests with respect to species richness and assemblage structure and suggested a method to validate estimates of species richness for Neotropical bat assemblages based on mist-netting data. The fully inventoried bat assemblage at La Selva Biological Station (LS, 100 m elevation) in Costa Rica was used as a reference site to evaluate seven estimators of species richness. The Jackknife 2 method agreed best with the known bat species richness and thus was used to extrapolate species richness for an Amazonian bat assemblage (Tiputini Biodiversity Station; TBS, 200 m elevation) and an Andean premontane bat assemblage (Podocarpus National Park; BOM, 1000 m elevation) in Ecuador. Our results suggest that more than 100 bat species occur sympatrically at TBS and about 50 bat species coexist at BOM. TBS harbours one of the most species-rich bat assemblages known, including a highly diverse phyllostomid assemblage. Furthermore, we related assemblage structure to large-scale geographical patterns in floral diversity obtained from botanical literature. Assemblage structure of these three phyllostomid assemblages was influenced by differences in floral diversity at the three sites. At the Andean site, where understorey shrubs and epiphytes exhibit the highest diversity, the phyllostomid assemblage is mainly composed of understorey frugivores and nectarivorous species. By contrast, canopy frugivores are most abundant at the Amazonian site, coinciding with the high abundance of canopy fruiting trees. Assemblage patterns of other taxonomic groups also may reflect the geographical distribution patterns of floral elements in the Andean and Amazonian regions. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 617,629. [source] Regional differences in kelp-associated algal assemblages on temperate limestone reefs in south-western AustraliaDIVERSITY AND DISTRIBUTIONS, Issue 6 2003Thomas Wernberg Abstract.,Ecklonia radiata (C. Agardh) J. Agardh kelp beds , a characteristic feature of the nearshore environment along the south-west Australian coastline , contribute significantly to the coastal biodiversity in temperate Australia, yet, little is known about the organization of these macroalgal assemblages. By compiling existing and new data sets from habitat surveys, we have characterized and compared the structure of kelp-associated macroalgal assemblages in three regions (Marmion Lagoon, Hamelin Bay and the marine environment neighbouring the Fitzgerald River National Park) across more than 1000 kilometres of the south-west Australian coastline. 152 macroalgal taxa had been recognized within the three regions and this is in the range of species richness reported from other Australian and African kelp beds. The kelp-associated algal assemblages were regionally distinct, 66% of all taxa were only found in one region and only 17 taxa were found in all three regions. Adjacent regions shared an additional 13,15 taxa. The regional shifts in assemblage structure were evident in species composition of both canopy and understorey. The organization of assemblages followed a spatial hierarchy where differences in assemblage structure were larger among regions (hundreds of kilometres apart) than among sites within regions (kilometres apart) and differences among sites within region were larger than differences among quadrats within sites (metres apart). Despite this hierarchy each level of nesting contributed approximately the same to total variation in assemblage structure and these spatial patterns were stronger than temporal differences from seasons to 2,3 years. Our results suggest that local and small-scale processes contribute considerably to heterogeneity in macroalgal assemblages throughout south-western Australia, and, in particular, our results are consistent with E. radiata exerting a strong influence on macroalgal assemblage structure. Further, our study contradicts the existence of a general south-west Australian kelp assemblage, although a few species may form the core of E. radiata associations across regions. [source] Long-term change to fish assemblages and the flow regime in a southeastern U.S. river system after extensive aquatic ecosystem fragmentationECOGRAPHY, Issue 6 2008Christopher M. Taylor The upper Tombigbee River in northeastern Mississippi now exists as a fragment, confluencing with and fed by an extensively modified aquatic landscape now called the Tennessee-Tombigbee Waterway (TTW). We examined the changes to fish assemblages and flow regime after waterway construction based on contemporary comparisons to historical fish collections and discharge data. The river's flow regime has changed markedly since TTW construction. Analysis of discharge data from two stations for 15 years, pre- and post-waterway, indicated significant differences in flow regime including increased minimum and base flows, lower spring and higher late summer-autumn flows, and lower high flow durations, post-TTW. These changes corresponded to significantly reduced regional and local species richness, and strong shifts in fish assemblage structure across a 20 yr time span. Post-waterway fish assemblages were related strongly to measured environmental variables characterizing local habitats. Several lentic-adapted species increased their abundances in lower reaches of the river, including a recent invader to the TTW system, the Mississippi silverside Menidia audens. Fragmentation of river ecosystems via disruption to hydrologic regimes is a major threat to aquatic biodiversity worldwide. Because the flow regime of this fragmented river is in part controlled by waterway operations via five minimum flow control structures, adaptive conservation and management efforts could be implemented in order to maintain and potentially restore the natural flow regime and the ecological integrity of the system. [source] Consistent spatial patterns across biogeographic gradients in temperate reef fishesECOGRAPHY, Issue 1 2008Maren Wellenreuther Biogeographic gradients may facilitate divergent evolution between populations of the same species, leading to geographic variation and possibly reproductive isolation. Previous work has shown that New Zealand triplefin species (family Tripterygiidae) have diversified in habitat use, however, knowledge about the consistency of this pattern throughout their geographic range is lacking. Here we examine the spatial habitat associations of 15 New Zealand triplefin species at nine locations on a latitudinal gradient from 35°50,S to 46°70,S to establish whether distant populations differ in habitat use. Triplefin diversity and density varied between locations, as did habitat variables such as percentage cover of the substratum, onshore-offshore location, microposition, depth and exposure. Canonical discriminant analysis identified specific species-habitat combinations, and when habitat was statistically partialled from location, most species exhibited consistent habitat associations throughout their range. However, the density of a few species at some locations was lower or higher than expected given the habitat availability. This indicates that the habitat variables recorded were not the sole predictors of assemblage structure, and it is likely that factors influencing larval dispersal (e.g. the low salinity layer in Fiordland and geographic isolation of the Three Kings Islands) play an additional role in structuring assemblage composition. Together these results suggest that New Zealand triplefin species show strong and consistent habitat use across potential biogeographical barriers, but this pattern appears to be modified by variation in larval supply and survival. This indicates that species with broad geographic distributions do not necessarily show phenotypic variation between populations. [source] Differences in litter mass change mite assemblage structure on a deciduous forest floorECOGRAPHY, Issue 6 2006Graham H. R. Osler Few mechanisms that determine the assemblage structure of mites have been identified. Whilst the relative abundance of soil fauna is known to change with humus form, the degree to which the quantity of litter inputs play a part in these changes has not been investigated. We tested the response of oribatid and mesostigmatid mites in litter and soil layers to increasing levels of birch Betula pubescens litter to test whether litter mass could affect the mite assemblage. Six litter treatments (1, 2, 4, 8 and 12×natural litter mass and complete litter removal) were established in November 2004 and the soil and litter communities sampled in October 2005. Species composition of oribatids was distinct for the soil and litter. There was no apparent effect of increasing litter mass on the soil mite assemblage. In the litter layer, the number of oribatids g,1 of litter showed a strong negative relationship with increasing litter mass whilst the number of mesostigmatids g,1 of litter was unresponsive to litter mass. Hence, the relative abundance of these two groups altered with increasing litter mass. The response of the oribatid groups Oppiidae and Poronota followed this negative relationship with litter mass but Phthiracaridae appeared less affected. Consequently, there was a subtle shift in the relative abundance of these groups with increasing litter mass. Our results demonstrate that oribatids as a whole and within groups respond in a predictable manner to increases in litter mass whilst mesostigmatids are unresponsive. Whilst there are undoubtedly biological and physical aspects that vary with litter mass, litter mass itself, is able to explain some patterns in the assemblage of oribatid mites. [source] Benthic macroinvertebrates in Swedish streams: community structure, taxon richness, and environmental relationsECOGRAPHY, Issue 3 2003Leonard Sandin Spatial scale, e.g. from the stream channel, riparian zone, and catchment to the regional and global scale is currently an important topic in running water management and bioassessment. An increased knowledge of how the biota is affected by human alterations and management measures taken at different spatial scales is critical for improving the ecological quality of running waters. However, more knowledge is needed to better understand the relationship between environmental factors at different spatial scales, assemblage structure and taxon richness of running water organisms. In this study, benthic macroinvertebrate data from 628 randomly selected streams were analysed for geographical and environmental relationships. The dataset also included 100 environmental variables, from local measures such as in-stream substratum and vegetation type, catchment vegetation and land-use, and regional variables such as latitude and longitude. Cluster analysis of the macroinvertebrate data showed a continuous gradient in taxonomic composition among the cluster groups from north to south. Both locally measured variables (e.g. water chemistry, substratum composition) and regional factors (e.g. latitude, longitude, and an ecoregional delineation) were important for explaining the variation in assemblage structure and taxon richness for stream benthic macroinvertebrates. This result is of importance when planning conservation and management measurements, implementing large-scale biomonitoring programs, and predicting how human alterations (e.g. global warming) will affect running water ecosystems. [source] Implications of species loss in freshwater fish assemblagesECOGRAPHY, Issue 6 2001Anne E. Magurran Freshwater systems are vulnerable to pollution and species loss often ensues. Are there additional implications for assemblage structure? Here we use Berger-Parker d. Simpson's I/D and Simpson's F to measure the ecological diversity of pristine and perturbed freshwater fish assemblages in Trinidad. West Indies, and Oklahoma. USA. Although the impacted sites typically had fewer species than expected, they could not be distinguished from unperturbed ones of equivalent richness. Changes in the evenness of these assemblages are thus driven by changes in richness. One practical outcome is that diversity indices may not provide independent verification of the detrimental consequences of pollution. The similarity in structure of naturally and anthropogenically impoverished assemblages provides no grounds for complacency, however, since it ignores the evolutionary history of the species concerned. On the basis of our results we suggest that species provenance may be important in tests of ecological function. Moreover, these investigations should replicate natural patterns of evenness as well as richness. [source] Macroecology of a host-parasite relationshipECOGRAPHY, Issue 1 2000Caryn C. Vaughn The larvae of freshwater mussels are obligate ectoparasites on fishes while adults are sedentary and benthic. Dispersal of mussels is dependent on the movement of fish hosts, a regional process, but growth and reproduction should be governed by local processes. Thus, mussel assemblage attributes should be predictable from the regional distribution and abundance of fishes. At a broad spatial scale in the Red River drainage, USA, mussel species richness and fish species richness were positively associated; maximum mussel richness was limited by fish richness, but was variable beneath that constraint. Measured environmental variables and the associated local fish assemblages each significantly accounted for the regional variation in mussel assemblages. Furthermore, mussel assemblages showed strong spatial autocorrelation. Variation partitioning revealed that pure fish effects accounted for 15.4% of the variation in mussel assemblages; pure spatial and environmental effects accounted for 16.1% and 7.8%, respectively. Shared variation among fish, space and environmental variables totaled 40%. Of this shared variation, 36.8% was associated with the fish matrix. Thus, the variation in mussel assemblages that was associated with the distribution and abundance of fishes was substantial (> 50%), indicating that fish community structure is an important determinant of mussel community structure. Although animals commonly disperse plants and, thus, influence the structure of plant communities, our results show a strong macroecological association between two disparate animal groups with one strongly affecting the assemblage structure of the other. [source] Seasonal and spatial variation in a prairie stream-fish assemblageECOLOGY OF FRESHWATER FISH, Issue 3 2002K. G. Ostrand Abstract,,,Stream-fish assemblage and environmental data for 13 sites in the upper Brazos River, Texas, USA during 1997 and 1998 were used to assess the relationship between environmental conditions, and seasonal and spatial variation in fish species abundance and distribution patterns. There was considerable spatial variation in environmental conditions among sites. Spatial variation in species diversity and species composition was related to variation in conductance (salinity), depth and current velocity among sites and streams. Species diversity increased downstream and species composition shifted from primarily cyprinodontids upstream to cyprinids downstream. Among all dominant species, spatial components of variation in fish abundance were greater than seasonal components, suggesting that assemblage structure is determined more by average or persistent differences in environmental conditions among sites than by seasonal variation in environmental conditions. [source] Is scuba sampling a relevant method to study fish microhabitat in lakes?ECOLOGY OF FRESHWATER FISH, Issue 3 2001Examples, comparisons for three European species Abstract , We compared fish microhabitat use patterns in the littoral zone of a lake using a new direct method (point abundance sampling by scuba, PASS) and the widely used point abundance sampling by electrofishing technique (PASE). We collected microhabitat data for age 0+ roach (Rutilus rutilus L.), perch (Perca fluviatilis L.), and pike (Esox lucius L.). The two methods yielded different results for fish assemblage structure and microhabitat patterns. Using PASE, fish were mainly found in "shelter habitats" such as shallow waters and dense vegetation. It is likely that this behavior is caused by the disturbance of the observer stamping around. Using PASS, fish escapement behavior was rarely observed. Therefore, we concluded that this direct and nondestructive sampling technique can be used to provide an accurate microhabitat estimation of a fish community and is assumed to be more suitable than PASE for fish habitat studies., [source] Fish assemblages of perennial floodplain ponds of the Sacramento River, California (USA), with implications for the conservation of native fishesFISHERIES MANAGEMENT & ECOLOGY, Issue 5 2004F. Feyrer Abstract To assess the likelihood of enhancing native fish populations by means of floodplain restoration projects, habitat characteristics and fish assemblages of seven perennial floodplain ponds in Yolo Bypass, the primary floodplain of the Sacramento River, California (USA), were examined during summer 2001. Although all ponds were eutrophic, based upon high chlorophyll a or dissolved nutrient concentrations, relatively large shallow ponds generally exhibited higher specific conductivity and dissolved phosphorus concentrations than small deep ponds, which exhibited greater water transparency and total dissolved nitrogen concentrations. Using multiple gear types, 13 688 fishes comprising 23 species were collected. All ponds were dominated by alien fishes; only three native species contributing <1% of the total number of individuals and <3% of overall biomass were captured. Fish assemblage structure varied among ponds, notably between engineered vs. natural ponds, and was related to specific conductance, total dissolved solids and water transparency. [source] Groundfish species diversity and assemblage structure in Icelandic waters during recent years of warmingFISHERIES OCEANOGRAPHY, Issue 1 2010LILJA STEFANSDOTTIR Abstract Elevated ocean temperatures have been predicted to lead to a poleward shift in the latitudinal distribution ranges of fish species. Different responses of fish species to increased temperatures might lead to changes in assemblage structure and local species richness. In this study, the assemblage structure and diversity of groundfish in Icelandic waters were examined using data from a standardized groundfish survey conducted annually in 1996,2007. We used hierarchical cluster analysis to define assemblages in two time periods and canonical correspondence analysis to explore the relationships between the assemblages and temperature, depth, latitude, longitude and year. We further used two estimates of diversity, species richness and the Shannon index. Four major species assemblages were identified. Assemblages in the hydrographically stable deep waters north of the country were consistent during the study, while assemblage structure in the more variable shallow waters underwent some changes. For this period of generally increasing sea temperature, the canonical correspondence analysis also revealed a shift towards species representative of warmer temperatures. Diversity was shown to be highly variable both temporally and spatially, and also to vary with depth and temperature. Species richness increased with temperature and time southwest of the country, but decreased northeast of the country. The different trends detected between the northern and southern areas illustrate the importance of performing analyses at the most appropriate scale. [source] Interannual and seasonal variability of the diversity and structure of ichthyoplankton assemblages in the central Mexican PacificFISHERIES OCEANOGRAPHY, Issue 3 2008C. FRANCO-GORDO Abstract We examined larval fish diversity and assemblage structure off the central coast of the Mexican Pacific from December 1995 through December 1998, including the 1997,98 El Niño event. A total of 132 taxa were recorded, the dominant species being Bregmaceros bathymaster, Dormitator latifrons, and Harengula thrissina (90, 1.9, and 0.8% of the total abundance, respectively). Only B. bathymaster, D. latifrons, and Gobionellus sp. occurred in all samples. The effects of the 1997,98 El Niño on ichthyoplankton diversity were significant, but typical seasonal patterns were also detected. Diversity null models were used to determine the structural changes in the assemblage related to El Niño; both richness and evenness of the species were highest during this event. The most parsimonious models of assemblage organization include El Niño and seasonality as the most significant environmental variability sources. The small-scale spatial variability expressed as the cross-shore gradient was not significant. The dominant species group formed by B. bathymaster, D. latifrons, and Vinciguerria lucetia typifies, in terms of similarity, both the pre-El Niño and El Niño periods; abundance differed between periods. The El Niño period was characterized locally by the dominant Bentosema panamense and H. thrissina, by the rare Euthynnus lineatus, and species of Lutjanus. Seasonality produced changes also in the relative frequencies of the dominant species plus the occurrence of rare forms. The average taxonomical distinctness, considered herein as an indicator of functional diversity, reflected the seasonal variability of the assemblages, aside from El Niño; this index showed lowest values during tropical and transitional periods, both characterized by warm, oligotrophic waters. The high dominance of B. bathymaster in the area and its effect on diversity stabilized the local ichthyoplankton assemblage. An upgraded analysis of diversity allowed a more detailed description of the variability in this assemblage, thus stressing the differential effects of El Niño at distinct latitudes. [source] Local and ecoregion effects on fish assemblage structure in tributaries of the Rio Paraíba do Sul, BrazilFRESHWATER BIOLOGY, Issue 12 2009BENJAMIN CARVALHO TEIXEIRA PINTO Summary 1.,We examined the effects of physical and chemical habitat variables and ecoregions on species occurrence and fish assemblage structure in streams of the Paraíba do Sul basin, in southeast Brazil. 2.,Fish and environmental data were collected from 42 sites on 26 first to fourth order streams (1 : 50 000 map scale) in three ecoregions. The sites occurred in one valley and two plateau ecoregions at altitudes of 40,1080 m and distances of 0.1,188 km from the main channel of the Rio Paraíba do Sul. Physical habitat (substratum, riparian cover, habitat types) and water quality (dissolved oxygen, pH, temperature and conductivity) variables were measured at each sampling site. 3.,A total of 2684 individuals in 16 families and 59 species were recorded. 4.,Ecoregion was a better predictor of the fish assemblage than the other environmental variables, according to the differences between the mean within-class and mean between-class similarities in assemblage data. 5.,Differing landscape characteristics were associated with differing local variables and thereby with differing fish assemblage structures. Riffles, shrub, grass, dissolved oxygen, conductivity and temperature were closely related to fish assemblage structure. 6.,Fish assemblages in sites far from the main river and at higher altitudes also differed from those near the Paraíba do Sul main channel, presumably as a result of differences in connectivity, covarying environmental factors and anthropogenic influence. 7.,These results reinforce the importance of understanding how stream communities are influenced by processes and patterns operating at local and regional scales, which will aid water resource managers to target those factors in their management and rehabilitation efforts. [source] Spatial and temporal patterns of microcrustacean assemblage structure and secondary production in a wetland ecosystemFRESHWATER BIOLOGY, Issue 7 2009A. MARIA LEMKE Summary 1. In contrast to extensive studies of zooplankton in lakes, the role of microcrustaceans in wetlands is not well studied. In this study, spatial and temporal patterns of microcrustacean assemblage structure and secondary production were quantified over a 2-year period in a southeastern U.S.A. wetland. 2. Thirty-two species, including 19 cladocerans, 10 copepods and three ostracods, generated different temporal patterns of density and production between vegetated (Nymphaea) and non-vegetated (open-water) zones reflecting species-specific differences in life histories. 3. Summer assemblages were dominated by small, planktonic filter-feeders, typified by high annual production/biomass (P/B) and daily production. In contrast, winter assemblages were dominated by larger, epibenthic detritivores with low P/B and high biomass. Seasonal shifts in the relative importance of planktonic species in the warmer months to benthic and epiphytic species in the cooler months suggest that energy flow pathways through microcrustaceans may vary seasonally. 4. Total annual production was higher during both years in the Nymphaea zone (13.0 g and 13.6 g DM m,2 year,1) than the open-water (8.2 and 6.3 g DM m,2 year,1), and was similar between years for the entire wetland pond (12.3 and 12.2 g DM m,2 year,1). 5. Although wetland ecosystems have been the subject of considerable ecological research in the past 20 years, our study is one of the few to demonstrate a highly diverse and relatively productive microcrustacean assemblage. Such comprehensive production studies can be used to quantify the ecological importance of microcrustaceans in freshwater wetland ecosystems. [source] Existing in plenty: abundance, biomass and diversity of ciliates and meiofauna in small streamsFRESHWATER BIOLOGY, Issue 4 2008JULIA REISS Summary 1. The ciliate and metazoan meiofaunal assemblages of two contrasting lowland streams in south-east England were examined over the period of a year, using a high taxonomic resolution. Monthly samples were taken from an oligotrophic, acid stream (Lone Oak) and a circumneutral, nutrient-rich stream (Pant) between March 2003 and February 2004. 2. We assessed the relative importance of ciliates and rotifers within the small-sized benthic assemblage with respect to their abundance, biomass and species richness. In addition, we examined the influence of abiotic and biotic parameters and season on the assemblage composition at two levels of taxonomic resolution (species and groups). 3. Ciliates dominated the assemblages numerically, with maximum densities of over 900 000 and 6 000 000 ind. m,2 in Lone Oak and Pant respectively. Rotifers and nematodes dominated meiofaunal densities, although their contribution to total meiofaunal biomass (maxima of 71.9 mgC m,2 in Lone Oak and of 646.8 mgC m,2 in the Pant) was low and rotifer biomass equalled that of ciliates. 4. Although the two streams differed in terms of total abundance of ciliates and meiofauna and shared only 7% of species, the relative proportion of groups was similar. Sediment grain size distribution (the percentile representing the 0.5,1 mm fraction) was correlated with assemblage structure at the species level, revealing the tight coupling between these small organisms and their physical environment. Seasonal changes in the relative abundance of groups followed similar patterns in both streams, and were correlated with the abundance of cyclopoid copepods and temperature. 5. Information on these highly abundant but often overlooked faunal groups is essential for estimates of overall abundance, biomass, species richness and productivity in the benthos, and as such has important implications for several areas of aquatic research, e.g. for those dealing with trophic dynamics. [source] Temporal changes in replicated experimental stream fish assemblages: predictable or not?FRESHWATER BIOLOGY, Issue 9 2006WILLIAMJ. Summary 1.,Natural aquatic communities or habitats cannot be fully replicated in the wild, so little is known about how initially identical communities might change over time, or the extent to which observed changes in community structure are caused by internal factors (such as interspecific interactions or traits of individual species) versus factors external to the local community (such as abiotic disturbances or invasions of new species). 2.,We quantified changes in seven initially identical fish assemblages, in habitats that were as similar as possible, in seminatural artificial streams in a 388-day trial (May 1998 to May 1999), and compared the change to that in fish assemblages in small pools of a natural stream during a year. The experimental design excluded floods, droughts, immigration or emigration. The experimental fish communities diverged significantly in composition and exhibited dissimilar trajectories in multivariate species space. Divergence among the assemblages increased from May through August, but not thereafter. 3.,Differences among the experimental assemblages were influenced by differences that developed during the year in algae cover and in potential predation (due to differential survival of sunfish among units). 4.,In the natural stream, fish assemblages in small pools changed more than those in the experimental units, suggesting that in natural assemblages external factors exacerbated temporal variation. 5.,Our finding that initially identical assemblages, isolated from most external factors, would diverge in the structure of fish assemblages over time suggests a lack of strong internal, deterministic controls in the assemblages, and that idiosyncratic or stochastic components (chance encounters among species; vagaries in changes in the local habitat) even within habitat patches can play an important role in assemblage structure in natural systems. [source] Hierarchical patterns of invertebrate assemblage structure in stony upland streams change with time and flow permanenceFRESHWATER BIOLOGY, Issue 6 2005B. J. ROBSON Summary 1. Studies in several parts of the world have examined variation in univariate descriptors of macroinvertebrate assemblage structure in perennially flowing stony streams across hierarchies of spatial scale using nested analyses of variance. However, few have investigated whether this spatial variation changes with time or whether these results are representative of habitats other than riffles or of other stream types, such as intermittently flowing streams. 2. We describe patterns in taxon richness and abundance from two sets of samples from stony streams in the Otway Range and the Grampians Range, Victoria, Australia, collected using hierarchical designs. Sampling of riffles was repeated in the Otways, to determine whether spatial patterns were consistent among times. In the Grampians, spatial patterns were compared between intermittent and perennially flowing streams (stream type) by sampling pools. 3. In the Otways streams, most variation in the dependent variables occurred between sample units. Patterns of variation among the other scales (streams, segments, riffles, groups of stones) were not consistent between sampling times, suggesting that they may have little ecological significance. 4. In the Grampians streams, variation in macroinvertebrate taxon richness and abundance differed significantly between replicate streams within each stream type but not between stream types or pools. The largest source of variation in taxon richness was stream type. Little variation occurred among sample units. 5. The pattern of most variation occurring among sample units is robust both to differences in the method of sampling and different dependent variables among studies and increasingly appears to be a property of riffles in stony, perennial upland streams. High variation among sample units (residual variation) limits the explanatory power of linear models and therefore, where samples are from a single sampling time, small but significant components of variation are unlikely to represent features of assemblage structure that will be stable over time. [source] Geomorphology and fish assemblages in a Piedmont river basin, U.S.A.FRESHWATER BIOLOGY, Issue 11 2003D. M. Walters Summary 1.,We investigated linkages between fishes and fluvial geomorphology in 31 wadeable streams in the Etowah River basin in northern Georgia, U.S.A. Streams were stratified into three catchment sizes of approximately 15, 50 and 100 km2, and fishes and geomorphology were sampled at the reach scale (i.e. 20,40 times stream width). 2.,Non-metric multidimensional scaling (NMDS) identified 85% of the among-site variation in fish assemblage structure and identified strong patterns in species composition across sites. Assemblages shifted from domination by centrarchids, and other pool species that spawn in fine sediments and have generalised food preferences, to darter-cyprinid-redhorse sucker complexes that inhabit riffles and runs, feed primarily on invertebrates, and spawn on coarser stream beds. 3.,Richness and density were correlated with basin area, a measure of stream size, but species composition was best predicted (i.e. |r| between 0.60,0.82) by reach-level geomorphic variables (stream slope, bed texture, bed mobility and tractive force) that were unrelated to stream size. Stream slope was the dominant factor controlling stream habitat. Low slope streams had smaller bed particles, more fines in riffles, lower tractive force and greater bed mobility compared with high slope streams. 4.,Our results contrast with the ,River Continuum Concept' which argues that stream assemblages vary predictably along stream size gradients. Our findings support the ,Process Domains Concept', which argues that local-scale geomorphic processes determine the stream habitat and disturbance regimes that influence stream communities. [source] Distribution of benthic diatoms in U.S. rivers in relation to conductivity and ionic compositionFRESHWATER BIOLOGY, Issue 8 2003Marina Potapova Summary 1We quantified the relationships between diatom relative abundance and water conductivity and ionic composition, using a dataset of 3239 benthic diatom samples collected from 1109 river sites throughout the U.S.A. [U.S. Geological Survey National Water-Quality Assessment (NAWQA) Program dataset]. This dataset provided a unique opportunity to explore the autecology of freshwater diatoms over a broad range of environmental conditions. 2Conductivity ranged from 10 to 14 500 ,S cm,1, but most of the rivers had moderate conductivity (interquartile range 180,618 ,S cm,1). Calcium and bicarbonate were the dominant ions. Ionic composition, however, varied greatly because of the influence of natural and anthropogenic factors. 3Canonical correspondence analysis (CCA) and Monte Carlo permutation tests showed that conductivity and abundances of major ions (HCO + CO, Cl,, SO, Ca2+, Mg2+, Na+, K+) all explained a statistically significant amount of the variation in assemblage composition of benthic diatoms. Concentrations of HCO + CO and Ca2+ were the most significant sources of environmental variance. 4The CCA showed that the gradient of ionic composition explaining most variation in diatom assemblage structure ranged from waters dominated by Ca2+ and HCO + CO to waters with higher proportions of Na+, K+, and Cl,. The CCA also revealed that the distributions of some diatoms correlated strongly with proportions of individual cations and anions, and with the ratio of monovalent to divalent cations. 5We present species indicator values (optima) for conductivity, major ions and proportions of those ions. We also identify diatom taxa characteristic of specific major-ion chemistries. These species optima may be useful in future interpretations of diatom ecology and as indicator values in water-quality assessment. [source] Assembly rules and functional groups at global biogeographical scalesFUNCTIONAL ECOLOGY, Issue 5 2002D. R. Bellwood Summary 1The taxonomic and functional composition of reef fish assemblages are quantified in three biogeographical regions: Great Barrier Reef, French Polynesia and Caribbean. Assemblages are described in three habitats of differing wave exposure. Functional abilities are estimated based on published analyses linking fin morphology and swimming performance. 2Two questions were addressed: (1) To what extent are labrid assemblages similar among habitats and regions? (2) To what extent are functional characteristics of fish assemblages shaped by differences in biodiversity, evolutionary history and species composition? 3All three regions display highly congruent patterns of habitat use, in terms of assemblage structure and functional characteristics, despite a five-fold difference in species richness, limited or no species overlap, and a 3·2-Myear history of isolation. Exposed reef crest assemblages were dominated by fishes with fins reflecting lift-based high-speed locomotion. In contrast to abundance-based patterns, species presence/absence data were uninformative. 4The relationship between swimming ability and habitat use reveals underlying assembly rules at a functional level, emphasizing the utility of functional attributes as a metric for comparing system-level properties in taxonomically distinct faunas. [source] Looks are important: parasitic assemblages of agromyzid leafminers (Diptera) in relation to mine shape and contrastJOURNAL OF ANIMAL ECOLOGY, Issue 3 2004Adriana Salvo Summary 1We test the hypothesis that leaf mine appearance can affect the risk of leafminers being discovered by parasitoids, and therefore influence parasitic assemblages, using a comparative study of parasitic complexes associated with 28 agromyzid species in Central Argentina. Analyses were based on size, structure (defined as the number of species in host-range categories) and impact (percentage parasitism) of parasitic complexes on leafminers. Mine appearance was defined in terms of shape (linear, linear-blotch, blotch) and colour (high or low contrast with the leaf lamina). 2Irrespective of the agromyzid species involved, significant differences were found in the structure of the parasitoid complexes: specialists were more abundant and generalists rarer than expected in blotch and cryptically coloured mines. 3There were no differences in average parasitoid species richness and parasitism rates among differently coloured or shaped galleries. However, mine appearance significantly affected parasitic assemblage structure, with shape driving generalist species richness and contrast influencing that of specialists. Mine shape also affected parasitism rates, which were highest for generalists in linear mines, and for specialists in blotch mines. The existence of a gradient of discovery from the cryptically coloured blotch mines to the most apparent highly contrasting linear ones was supported by significant correlations of this gradient with richness and parasitism rates of generalist and specialist parasitoids. 4Taxonomic composition of parasitic complexes (analysed through parasitoid species abundance) was separated significantly according to host mine shape. An even more significant classification of assemblages was achieved when the combination of mine shape and colour was considered in the discoverability gradient. 5Our results suggest that despite leaf mines being an ecologically homogeneous resource, their morphology might offer varying degrees of refuge against different parasitoids. [source] Assessing river biotic condition at a continental scale: a European approach using functional metrics and fish assemblagesJOURNAL OF APPLIED ECOLOGY, Issue 1 2006D. PONT Summary 1The need for sensitive biological measures of aquatic ecosystem integrity applicable at large spatial scales has been highlighted by the implementation of the European Water Framework Directive. Using fish communities as indicators of habitat quality in rivers, we developed a multi-metric index to test our capacity to (i) correctly model a variety of metrics based on assemblage structure and functions, and (ii) discriminate between the effects of natural vs. human-induced environmental variability at a continental scale. 2Information was collected for 5252 sites distributed among 1843 European rivers. Data included variables on fish assemblage structure, local environmental variables, sampling strategy and a river basin classification based on native fish fauna similarities accounting for regional effects on local assemblage structure. Fifty-eight metrics reflecting different aspects of fish assemblage structure and function were selected from the available literature and tested for their potential to indicate habitat degradation. 3To quantify possible deviation from a ,reference condition' for any given site, we first established and validated statistical models describing metric responses to natural environmental variability in the absence of any significant human disturbance. We considered that the residual distributions of these models described the response range of each metric, whatever the natural environmental variability. After testing the sensitivity of these residuals to a gradient of human disturbance, we finally selected 10 metrics that were combined to obtain a European fish assemblage index. We demonstrated that (i) when considering only minimally disturbed sites the index remains invariant, regardless of environmental variability, and (ii) the index shows a significant negative linear response to a gradient of human disturbance. 4Synthesis and applications. In this reference condition modelling approach, by including a more complete description of environmental variability at both local and regional scales it was possible to develop a novel fish biotic index transferable between catchments at the European scale. The use of functional metrics based on biological attributes of species instead of metrics based on species themselves reduced the index sensitivity to the variability of fish fauna across different biogeographical areas. [source] Patternizing of impoundment impact (1985,2002) on fish assemblages in a lowland river using the Kohonen algorithmJOURNAL OF APPLIED ICHTHYOLOGY, Issue 3 2005T. Penczak Summary Impoundment impact on fish assemblage structure was investigated in the dammed middle course of the Warta River. A backwater site (AB) was located 2 km upstream of the Jeziorsko Reservoir, and a tailwater site (CD) 1.5 km downstream of the dam. Both sites were studied for 3 years in the pre-impoundment period (1985,1987) and 15 years after damming (1988,2002). Quantitative electrofishing in spring and autumn assured obtaining yearly average biomass for each population. Most of the data analysis aimed to assess the dam impact on the fish assemblage structure but other accompanying impacts such as discharge manipulations, revetment, different forms of engineering, and water quality improvement in the tailwater and backwater reaches were also discussed. The Kohonen algorithm (self-organizing map, SOM) was used for the analysis, and perfectly separated AB and CD samples into two clusters. Samples from the backwater (AB) proved that this reach of the Warta River had maintained its almost natural character and that fish assemblages had changed moderately, now occupying only five neighbouring hexagons out of a total of 16. In the tailwater (CD), however, because of considerable fluctuations in fish assemblages the SOM produced three subclusters, which engaged nine hexagons: (i) the pre-impoundment period (1985,1987, two hexagons); (ii) 7 years after the definite closure of dam sluices (1988,1994, five hexagons); and (iii) the past 8 years of sampling (1995,2002, two hexagons), when stabilization in the assemblage was observed. The SOM also definitely proved profound changes in fish assemblage composition: most lithophilous species declined and many phytolithophilous and phytophilous species became dominants, particularly in the tailwater site where downstream migration of 0+ of successfully spawned species from the reservoir took place. [source] Sub-population structure of common fish species in the Elbe River estimated from DNA analysisJOURNAL OF APPLIED ICHTHYOLOGY, Issue 5 2003C. Wolter Summary The aim of this study was to analyse the genetic structure of populations for seven common cyprinid fish species within a 120-km-long stretch of the lowland Elbe River, northern Germany. The results are needed for habitat modelling to estimate the proportion that environmentally based variance has of the total variances of home range, species distribution, habitat use and fish assemblage structure. Polymerase chain reaction (PCR)-fingerprinting offers a rapid, efficient method for generating genetic markers and was therefore used to obtain an overview on population-genetic structures of the following seven fish species: asp (Aspius aspius), bleak (Alburnus alburnus), blue bream (Abramis ballerus), common bream (Abramis brama), gudgeon (Gobio gobio), ide (Leuciscus idus) and roach (Rutilus rutilus). Of the 20 random primers, between eight (ide) and 18 (roach) produced polymorphic bands. The mean levels of genetic similarity between samples, estimated as bandsharing frequencies, varied between 76% in bleak and 98% in asp. The corresponding genetic distances among samples varied between 0.02 ± 0.01 in asp and 0.24 ± 0.09 in bleak. The genetic distances among samples were not significant in all of the pairwise comparisons, and correlated only weakly with the geographic distances among sampling sites. It was therefore concluded that the stretch of the Elbe surveyed was inhabited by single, panmictic populations of the species studied and thus that the observed habitat preferences, fish distribution, home range and ecological performance of species within this area will depend on stochastic environmental factors or result from biotic interactions. [source] Fragmentation and pre-existing species turnover determine land-snail assemblages of tropical rain forestJOURNAL OF BIOGEOGRAPHY, Issue 10 2009Dinarzarde C. Raheem Abstract Aim, The main aims of the study were: (1) to investigate the effect of fragment age in relation to other patch- and landscape-scale measures of forest fragmentation, and (2) to assess the relative importance of fragmentation, habitat degradation (i.e. degradation caused by selective logging and past shifting cultivation) and putative pre-existing species turnover in structuring current land-snail assemblages. Location, South-western Sri Lanka. Methods, The land-snail fauna was sampled using standardized belt transects. Fifty-seven transects were sampled in 21 lowland rain forest fragments (c. 1,33,000 ha). The spatial arrangement of fragments in the study area was explicitly considered in an effort to take into account the non-random nature of fragmentation and degradation and the possibility that current species composition may reflect patterns of species turnover that existed prior to fragmentation. The data set of 57 land-snail species and 28 environmental and spatial variables was analysed using canonical correspondence analysis and partial canonical correspondence analysis. Results, Fragment age, mean shape complexity (i.e. a landscape-scale measure of shape complexity), altitude, and the spatial variables x (longitude), y (latitude) and y2 explained significant variation in land-snail species composition. None of the three nominal variables quantifying habitat degradation was significantly correlated with variation in species composition. The independent effects of fragment age and mean shape complexity were similar. The combined effect of the spatial variables alone was larger than the independent effects of fragment age, mean shape complexity or altitude, but was of the same order of magnitude. The total variation explained by the spatial variables was comparable to the total non-spatial variation accounted for by fragment age, mean shape complexity and altitude. Main conclusions, Fragment age was found to be one of only two key determinants (the other was shape complexity at the landscape scale) driving fragmentation-related changes in community composition. The influence of pre-fragmentation patterns of species turnover on assemblage structure can be stronger than the effects of fragmentation measures, such as age, and may override the effects of forest degradation. Thus, strong patterns of pre-existing turnover may potentially confound interpretation of the effects of forest fragmentation and degradation. [source] Multivariate analysis of a fine-scale breeding bird atlas using a geographical information system and partial canonical correspondence analysis: environmental and spatial effectsJOURNAL OF BIOGEOGRAPHY, Issue 11 2004Nicolas Titeux Abstract Aim, To assess the relative roles of environment and space in driving bird species distribution and to identify relevant drivers of bird assemblage composition, in the case of a fine-scale bird atlas data set. Location, The study was carried out in southern Belgium using grid cells of 1 × 1 km, based on the distribution maps of the Oiseaux nicheurs de Famenne: Atlas de Lesse et Lomme which contains abundance for 103 bird species. Methods, Species found in < 10% or > 90% of the atlas cells were omitted from the bird data set for the analysis. Each cell was characterized by 59 landscape metrics, quantifying its composition and spatial patterns, using a Geographical Information System. Partial canonical correspondence analysis was used to partition the variance of bird species matrix into independent components: (a) ,pure' environmental variation, (b) spatially-structured environmental variation, (c) ,pure' spatial variation and (d) unexplained, non-spatial variation. Results, The variance partitioning method shows that the selected landscape metrics explain 27.5% of the variation, whilst ,pure' spatial and spatially-structured environmental variables explain only a weak percentage of the variation in the bird species matrix (2.5% and 4%, respectively). Avian community composition is primarily related to the degree of urbanization and the amount and composition of forested and open areas. These variables explain more than half of the variation for three species and over one-third of the variation for 12 species. Main conclusions, The results seem to indicate that the majority of explained variation in species assemblages is attributable to local environmental factors. At such a fine spatial resolution, however, the method does not seem to be appropriated for detecting and extracting the spatial variation of assemblages. Consequently, the large amount of unexplained variation is probably because of missing spatial structures and ,noise' in species abundance data. Furthermore, it is possible that other relevant environmental factors, that were not taken into account in this study and which may operate at different spatial scales, can drive bird assemblage structure. As a large proportion of ecological variation can be shared by environment and space, the applied partitioning method was found to be useful when analysing multispecific atlas data, but it needs improvement to factor out all-scale spatial components of this variation (the source of ,false correlation') and to bring out the ,pure' environmental variation for ecological interpretation. [source] Size matters sometimes: wall height and the structure of subtidal benthic invertebrate assemblages in south-eastern Australia and Mediterranean SpainJOURNAL OF BIOGEOGRAPHY, Issue 12 2003A. R. Davis Abstract Aim, Variation in the structure of shallow subtidal invertebrate assemblages was examined over three spatial scales; within reef, between reef and between continents. We sought to provide a context from which to examine and interpret ecological processes between continents. In addition, we predicted that variation in pattern would increase as the scale of examination increased. Location, Reefs near Wollongong and within Jervis Bay in south-eastern Australia and Mediterranean reefs on the Costa Brava (Catalonia), north-eastern Spain. Methods, We compared assemblages on vertical rock walls of two heights , short (< 2 m) and tall (> 3 m) in two temperate regions over the same depth range. Specifically we examined the diversity and cover of invertebrates, the cover and biomass of foliose and crustose algae, the size of invertebrate colonies and the biomass of urchins on short and tall walls (n = 3) at each of two locations in each country. Results, Foliose algae dominated rock walls in Spain and although invertebrate cover was high, colonies were generally very small. Two urchin species were commonly encountered on rock walls in Spain, Arbacia lixula and Paracentrotus lividus; their biomass was relatively low and did not differ significantly between short and tall walls. These findings contrasted strongly with south-eastern Australia, where foliose algae were almost completely absent. A single urchin species, Centrostephanus rodgersii occurred with extremely high biomass on short walls, which were dominated by grazer-resistant crustose calcareous algae. In contrast, the biomass of this urchin was low on tall walls, which were dominated by invertebrates, usually exceeding 95% in cover. Invertebrate colonies were significantly larger on both short and tall walls in south-eastern Australia relative to the Mediterranean. Findings within a country were consistent between the replicate rock walls and between locations. In contrast to our prediction, however, there was significant variation among walls within a location, but not among locations within a continent. Temporal variation in the structure of these assemblages was not examined, but appears limited. Main conclusions, We conclude that submarine topography, i.e. the presence of short or tall rock walls, as a function of rock type and structure, has a marked impact on community structure in south-eastern Australia, but made little difference to the structure of the assemblage in Mediterranean Spain. The differences in structure we observed between walls of different heights in Australia were correlated with differences in the biomass of urchins and they appear to be major determinants of assemblage structure. Interactions among species are often reported from disparate parts of the globe with little or no reference to the structure of the assemblage of which they are a part; we contend that this will hinder interpretation. Our data are consistent with the organisms in these two regions experiencing distinct selection pressures; for example high levels of urchin grazing activity in south-eastern Australia, and shading and whiplash associated with an algal canopy in the Mediterranean. It may not be appropriate to contrast processes operating at very large (intercontinental) scales unless context can be established with a clear understanding of ecological pattern. Objectivos, En el presente trabajo hemos examinado la variación en estructura de comunidades de invertebrados de aguas someras a tres escalas espaciales: dentro de arrecifes rocosos, entre arrecifes y entre continentes. Nuestro objetivo era proveer un contexto para examinar y interpretar procesos ecológicos entre continentes. Además, realizamos la predicción de que el modelo de variación aumentaría conforme aumentaba la escala de observación. Localidad, Arrecifes rocosos cerca de Wollongong y en Jarvis Bay en la zona sudeste de Australia y arrecifes rocosos mediterráneos en la Costa Brava (Cataluña), en el nordeste de España. Metodos, Comparamos comunidades en paredes rocosas verticales de dos alturas , bajas (< 2 m) y altas (> 3 m) en dos regiones templadas y dentro del mismo rango de profundidades. Específicamente, examinamos la diversidad y el recubrimiento de invertebrados, el recubrimiento y la biomasa de algas foliosas e incrustantes, la medida de las colonias de invertebrados y la biomasa de erizos en paredes bajas y altas (n = 3) en dos localidades de cada país. Resultados, Las algas foliosas dominaban las paredes rocosas en España y, aunque el recubrimiento de invertebrados era alto, las colonias eran generalmente muy pequeñas. Dos especies de erizos eran comunes en las paredes rocosas en España: Arbacia lixula y Paracentrotus lividus. Su biomasa total era relativamente pequeña y no mostraba diferencias significativas entre paredes bajas y altas. Estos resultados contrastan con los hallados en el sudeste de Australia, donde las algas foliosas eran prácticamente ausentes. Una única especie de erizo, Centrostephanus rodgersii, se encontraba en las paredes bajas, donde presentaba elevadas biomasas. Estas paredes estaban dominadas por algas incrustantes y carbonatadas resistentes al ramoneo por erizos. En cambio, la biomasa de este erizo era baja en paredes altas, que estaban dominadas por invertebrados, con recubrimientos normalmente por encima del 95%. Las colonias de invertebrados eran significativamente más grandes tanto en las paredes altas como bajas en el sudeste de Australia en comparación con el Mediterráneo. Los resultados dentro de cada país eran consistentes entre las réplicas de paredes estudiadas y entre localidades. Contrariamente a nuestra predicción, sin embargo, había una variación significativa entre paredes dentro de una localidad pero no entre localidades dentro de un continente. La variación temporal en estructura en estas comunidades no fue estudiada, pero parece ser limitada. Conclusiones Principales, Concluimos que la topografía submarina, esto es, la presencia de paredes bajas o altas en función del tipo de roca y estructura, tiene un efecto importante en la estructura de las comunidades en el sudeste de Australia. Este factor, sin embargo, tiene un efecto muy limitado en el Mediterráneo español. Las diferencias en estructura observadas entre paredes de diferentes alturas en Australia se correlacionan con diferencias en la biomasa de erizos, los cuales parecen ser determinantes en la estructura de las comunidades. Frecuentemente se estudian interacciones entre especies en zonas alejadas del globo con escasa o nula referencia a la estructura de la comunidad de la que forman parte. En nuestra opinión este hecho impide una correcta interpretación. Nuestros datos son consistentes con la idea de que los organismos en las dos regiones estudiadas experimentan diversas presiones selectivas, por ejemplo, niveles altos de ramoneo por erizos en el sudeste de Australia, y oscurecimiento y disturbancia mecánica asociadas a la cobertura de algas en el Mediterráneo. No parece apropiado comparar procesos que operan a escalas muy amplias (intercontinentales) sin establecer antes un contexto con una comprensión clara de los parámetros ecológicos. [source] | |||||||||||||||||||||||||||||||