BIO-ENV Procedure Research Articles

Landscape genetics of the blotched tiger salamander (Ambystoma tigrinum melanostictum)

The field of landscape genetics has great potential to identify habitat features that influence population genetic structure. To identify landscape correlates of genetic differentiation in a quantitative fashion, we developed a novel approach using geographical information systems analysis. We present data on blotched tiger salamanders (Ambystoma tigrinum melanostictum) from 10 sites across the northern range of Yellowstone National Park in Montana and Wyoming, USA. We used eight microsatellite loci to analyse population genetic structure. We tested whether landscape variables, including topographical distance, elevation, wetland likelihood, cover type and number of river and stream crossings, were correlated with genetic subdivision (F(ST)). We then compared five hypothetical dispersal routes with a straight-line distance model using two approaches: (i) partial Mantel tests using Akaike's information criterion scores to evaluate model robustness and (ii) the BIOENV procedure, which uses a Spearman rank correlation to determine the combination of environmental variables that best fits the genetic data. Overall, gene flow appears highly restricted among sites, with a global F(ST) of 0.24. While there is a significant isolation-by-distance pattern, incorporating landscape variables substantially improved the fit of the model (from an r2 of 0.3 to 0.8) explaining genetic differentiation. It appears that gene flow follows a straight-line topographic route, with river crossings and open shrub habitat correlated with lower F(ST) and thus, decreased differentiation, while distance and elevation difference appear to increase differentiation. This study demonstrates a general approach that can be used to determine the influence of landscape variables on population genetic structure.

Characterization of bacterial communities in four freshwater lakes differing in nutrient load and food web structure

The phylogenetic composition of bacterioplankton communities in the water column of four shallow eutrophic lakes was analyzed by partially sequencing cloned 16S rRNA genes and by PCR-DGGE analysis. The four lakes differed in nutrient load and food web structure: two were in a clearwater state and had dense stands of submerged macrophytes, while two others were in a turbid state characterized by the occurrence of phytoplankton blooms. One turbid and one clearwater lake had very high nutrient levels (total phosphorus > 100 μg/l), while the other lakes were less nutrient rich (total phosphorus < 100 μg/l). Cluster analysis, multidimensional scaling and ANOSIM (analysis of similarity) were used to investigate differences among the bacterial community composition in the four lakes. Our results show that each lake has its own distinct bacterioplankton community. The samples of lake Blankaart differed substantially from those of the other lakes; this pattern was consistent throughout the year of study. The bacterioplankton community composition in lake Blankaart seems to be less diverse and less stable than in the other three lakes. Clone library results reveal that Actinobacteria strongly dominated the bacterial community in lake Blankaart. The relative abundance of Betaproteobacteria was low, whereas this group was dominant in the other three lakes. Turbid lakes had a higher representation of Cyanobacteria, while clearwater lakes were characterized by more representatives of the Bacteroidetes. Correlating our DGGE data with environmental parameters, using the BIOENV procedure, suggests that differences are partly related to the equilibrium state of the lake.

Climate and habitat barriers to dispersal in the highly mobile grey wolf

We reanalysed published data to evaluate whether climate and habitat are barriers to dispersal in one of the most mobile and widely distributed mammals, the grey wolf (Canis lupus). Distance-based redundancy analysis (dbRDA) was used to examine the amount of variation in genetic distances that could be explained by an array of environmental factors, including geographical distance. Patterns in genetic variation were also examined using MDS plots among populations and relationships between genetic structure and individual environmental variables were further explored using the BIOENV procedure. We found that, contrary to a previous report, a pattern of isolation with distance is evident on a continental scale in the North American wolf population. This pattern is apparently related to climate and habitat. Specifically, vegetation types appear to play a role in the genetic dissimilarities among populations. When we controlled for the effect of spatial variation, climate was still associated with genetic distance. Further, partitioning of geographical distances into latitudinal and longitudinal axes revealed that the east-west gradient had the strongest relationship with genetic distance. We suggest two possible mechanisms by which environmental conditions may influence the dispersal decisions made by wolves.

Soft bottom mollusc assemblages and pollution in a harbour with two opposing entrances

Conventional harbours, provided with only one entrance and devoid of channels, are enclosed areas with low water renewal, high sedimentation rate and high concentrations of pollutants in sediments; the soft bottom communities are characterised by low species richness and low values of the diversity and evenness indexes. The harbour of Ceuta, North Africa, presents an unusual structure since it is provided with two opposing entrances and a channel, which increase the water renewal across the middle of the harbour. These unusual characteristics turn the harbour of Ceuta into an adequate locality to test its environmental implications on macrofaunal assemblages. In the present study, the spatial distribution of mollusc community associated with soft bottoms was studied in relation to the influence of environmental factors on the harbour of Ceuta and nearby areas, North Africa. Twenty-one stations (15 inside and six outside the harbour) were sampled and 26 variables were measured in the sediment of each station: depth, %sand, organic matter, lipids, P, N, Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, S, Sr, Zn. The special configuration of Ceuta harbour created a great variability in sediment characteristics and environmental measures depending on the stations and, due to this heterogeneity, the mollusc species richness in the sediments inside the harbour (45 species) was higher than in conventional harbours. The multivariate approach based on MDS analysis was much more sensitive than univariate techniques to detect differences between internal and external stations of the harbour of Ceuta. The percentage of sand was the main factor to affect the distribution of the mollusc assemblages according to the BIO-ENV procedure and the CCA. SIMPER showed that the bivalves Parvicardium exiguum, Ervilia castanea, Spisula subtruncata and Digitaria digitata were the species that most contributed to the dissimilarity between internal and external stations; P. exiguum, S. subtruncata and D. digitata were more abundant in the internal stations whereas E. castanea was more abundant in the external stations. The bivalves P. exiguum, Abra alba and Corbula gibba and the opistobranch Retusa obtusa dominated in the most enclosed stations inside the harbour where sediments contained very high values of organic matter, lipids, and heavy metals. The data of the present study might assist in the building of new harbours in the future.

Macrobenthic subtidal communities in relation to sediment pollution: the phylum-level meta-analysis approach in a south-eastern coastal region of South America

The relationships between macrobenthic subtidal community structure and the status of sediment pollution were analysed at 24 sampling stations in the Montevideo coastal zone. In order to judge the status of community perturbation a phylum-level meta-analysis was applied to the production data from the Montevideo coastal zone samples alone and combined with the original training data set from 50 samples collected on the NE European shelf. The community was dominated by the gastropod Heleobia cf. australis. The MDS (multi-dimensional scaling) ordination with abundance data (species-level) and the MDS ordination with production data (phylum level), using only our samples, showed the formation of three groups of stations. Results of the BIO-ENV procedure showed that lead, salinity and polycyclic aromatic hydrocarbons (PAHs) were the variables that best explained the biological pattern observed. However, a clear salinity gradient was observed from the inner stations of Montevideo Bay to the outer coastal stations; the high levels of Pb, PAH and Cr concentrations recorded at stations B, C and D in Montevideo Bay were important in discriminating these locations from the others. The MDS ordination combining the production data from the 24 samples from the Montevideo coastal zone with the original data set showed correct assessment of the pollution status for the 24 samples from Montevideo on a common scale of perturbation. The separation of the Montevideo coastal zone samples seems to be mainly due to the high proportion of molluscs. Our results suggest general applicability of the phylum-level meta-analysis approach, even in such cases as this, with high dominance of only one phylum; however, more studies are still necessary.

Changes in benthic communities along a presumed pollution gradient in Vancouver Harbour.

Samples of macrobenthic organisms were obtained at seven stations on a presumed pollution gradient from the head of Vancouver Harbour through to outer Howe Sound. Polychaetes (83 apparent species) and molluscs (43 apparent species) were the most abundant faunal groups numerically (44.8 and 47.9%, respectively). Molluscs accounted for most of the biomass (87.9%). The following univariate and multivariate methods were used to investigate structural changes in the benthic communities: ANOVA, Abundance-Biomass Comparisons and related statistics, cluster analysis, multidimensional scaling, and the BIOENV procedure. Most of the analyses divided the seven stations into three groups: Port Moody Arm (Inner Harbour): two stations; Inner and Outer Harbour: four stations, and Gibsons (Howe Sound): one station. Further cause-effect investigations are needed to determine the sensitivity to organic pollution of indicator species identified in the survey. However our data correlating benthic community changes to sediment chemistry suggest the inner harbour was dominated by pollution-tolerant species. Depth and sediment grain size were confounding factors for the interpretations.

Evaluation of adverse biological effects induced by pollution in the Bilbao Estuary (Spain)

The physical nature of the Bilbao Estuary (Spain) has been highly modified since the end of the last century, mainly by means of dyking, canalization, and dredging to meet the needs of navigation. Together with its industrial use, the estuary is also used for the disposal of domestic sewage. Until the completion of a sewerage plan in the year 2002, the sewage of about 1 million people and the wastes from industries will continue to be discharged into this 15-km-long estuary with a limited freshwater flow of 25 m 3 s −1. An abrupt decrease in faunal abundance followed by defaunation characterized the biotic response to the disturbance in almost three-quarters of its tideway. Relationships between biotic and environmental variables were investigated using the BIO-ENV procedure of the PRIMER computer package. Gross organic enrichment, water oxygen depletion and anaerobic sediment conditions appear to be the dominant anthropogenic influences on the Bilbao Estuary. It is concluded that the level of wastewater discharges into the estuary may substantially drop below that concentration which assures the protection and propagation of native heterotrophic resources within sediments. Biological monitoring is thus essential to assess the efficacy of the sewerage plan promoted by the local Water Authority.

Effects of environmental stress on ascidian populations in Algeciras Bay (southern Spain). Possible marine bioindicators?

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 144:119-131 (1996) - doi:10.3354/meps144119 Effects of environmental stress on ascidian populations in Algeciras Bay (southern Spain). Possible marine bioindicators? Naranjo SA, Carballo JL, García-Gómez JC The distribution and abundance of littoral ascidians were analyzed with respect to their possible relationships with environmental stress. As part of a multidisciplinary research project on the benthic communities in Algeciras Bay, southern Spain, a suite of environmental variables was measured (hydrodynamism, silting, suspended solids and organic matter). After displaying the similarities of fauna through clustering and ordination of sampling sites, the relationships between community differences and changes in the abiotic component were established based on the BIO-ENV procedure and Canonical Correspondence Analysis. Hydrodynamism and the percentage of organic matter in the silt is the variable combination that best explains (Spearman correlation of 0.82) the biotic structure. While all ascidians show a certain tolerance to diverse environmental factors, some species such as Ciona intestinalis, Diplosoma spongiforme, Phallusia mammillata, Microcosmus squamiger, Styela plicata and Synoicum argus could be considered as indicators of areas which have been subject to intense stress (substrate transformation, water stagnation and sedimentation excess) over long periods of time, whereas others such as Aplidium conicum, Aplidium punctum, Clavelina dellavallei, Halocynthia papillosa and Stolonica socialis, which live only in natural and non-perturbed rock areas, could be categorized as species very sensitive to stress, as well as indicators of good conditions. Ascidian communities · Environmental stress · Multivariate community measurements · Bioindicators Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 144. Publication date: December 05, 1996 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1996 Inter-Research.

Comparison of meiobenthic crustacean community structure across freshwater acidification gradients

Analytical procedures that use the structure of natural communities to detect anthropogenic disturbance in marine systems were applied to freshwater data for the first time. Species data for meiobenthic crustaceans from streams in two regions of Britain affected by acidification (southern England and mid-Wales) were ordinated using non-metric Multidimensional Scaling (MDS) to determine if an influence from pH could be detected either: i) at taxonomic levels higher than species (genus and family); or ii) across regions. Relationships between community structure, pH and other environmental variables were investigated using the BIOENV procedure. In English streams, pH had a clear influence on community structure that was most clearly detected at species level but was still evident after data were aggregated to genus and family. In contrast, pH had no influence on communities in the Welsh streams, but there was a significant difference in community structure at all taxonomic levels between streams in conifer plantations and those in moorland. There was also a significant difference in community structure between regions, which tended to override any influence from pH, although, at family level, there was a gradient from acidic sites in southern England and those draining conifer plantations in Wales to less disturbed sites in both regions. This study suggests that meiobenthic communities can be used for the detection of pollution gradients in freshwaters, but that this approach may only be of use where regional differences in stream physicochemistry are minimal.