Dissimilarity In Species Composition Research Articles

Edge type determines the intensity of forest edge effect on epiphytic communities

Edge effect involves microclimatic variations (light, temperature and humidity) in the forest edge that become unsuitable for organisms adapted to forest interior conditions. We speculate that under similar edge types (shrubland matrix), the pattern in the response to forest edge might be different and more hostile for epiphytes in south-oriented edges. Because different matrix types have different effects on microclimate, we hypothesized that the magnitude of the edge effects will depend on the contrast between the physiognomy of the matrix and the forest fragment. The study was carried out in central Spain and consisted of a beech fragment surrounded by different types of vegetation matrices: pine plantation (south orientation), semi-deciduous oak forest (south orientation) and shrubland (north and south orientations). For each type of edge, we established ten transects perpendicular to the edge, running 100 m into the forest patch. Data were collected from three plots placed at 5, 50 and 100 m from the beginning of each transect. The results revealed that variations in the epiphytic composition mainly showed a replacement of forest interior species with generalist light-demanding species at forest edge. Shrubs-bordered edges showed the strongest influence on epiphytic composition, with high species dissimilarity between edge and forest interior, whereas the edge effects were mitigated when the patch was surrounded by other forests. Besides, in the case of shrub-bordered edge, the dissimilarity of species composition between edge interior was higher in the south than in the north-facing edge. We conclude that the magnitude of the edge effect on epiphytic communities is modulated by the physiognomy of the surrounding matrix and the orientation of the forest edge. In the case of a hard contrast matrix, at least 100 m of an edge buffer are required for the conservation of the species with high humidity requirements. Therefore, one of the main problems affecting the loss and even disappearance of shaded species is the decreasing of the amount of core conditions under the increasing forest fragmentation scenarios. This potentially exacerbates forest fragmentation effects linked to livestock use, due to the physiognomically different surrounding matrix compared to forest patches.

Bryophyte communities in the Amazon forest are regulated by height on the host tree and site elevation

Summary Community composition of epiphytic bryophyte communities, sampled systematically in nine localities across 2800 km from east to west of the Amazon forest, was mostly explained by their height zone along the vertical microenvironmental gradient from the base to the top of the host tree. Despite the lack of correlation between geographical distance and dissimilarity in species composition, communities within the same locality were significantly more similar than communities from different localities in all height zones, with the highest values of similarity found between outer canopy communities. While height zone on the host tree explained most of the variation in species composition at local scale, elevation and temperature were the variables most strongly related to species composition at a geographical scale. Using the concepts of meta/local community of the Neutral Theory of Biodiversity and Biogeography, we showed that establishment limitation was strongest at the extremes of the vertical gradient. We estimated that communities of the tree base and the outer canopy drew individuals from outside the habitat species pool at a rate of 0.28 and 0.22, respectively, in contrast with values between 0.55 and 0.76 of other height zones. Our results offered contrasting evidence for the hypothesis that species inhabiting the canopy have higher chances of engaging in long‐distance dispersal events. If the stronger establishment limitation at the extremes of the gradient is not compensated by facilitated dispersal compared to other zones, as our results suggest, communities on the base and on the outer canopy might be, through time, subjected to stronger selection. Synthesis. This study indicated that the community composition of epiphytic bryophytes in the Amazon is mainly regulated by environmental conditions, both at local and at geographical scales. Dispersal, although predominantly local, did not show geographical structure across the area.

Impacts of Different Tree Species of Different Sizes on Spatial Distribution of Herbaceous Plants in the Nigerian Guinea Savannah Ecological Zone.

This study was aimed at finding the impacts of different tree species and individual trees of different sizes on species richness, diversity, and composition of the herbaceous layer. All the three tree species have greatly increased species richness and diversity both within and outside their crown zones compared with the open grassland. Both species richness and diversity were found to be higher under all the three tree species than outside their crowns, which was in turn higher than the open field. Daniella oliveri has the highest species richness and diversity both within and outside its crown zone followed by Vitellaria paradoxa and then Parkia biglobosa. The result also revealed that the same tree species with different sizes leads to different herbaceous species richness, diversity, and composition under and around the trees' crowns. P. biglobosa and V. paradoxa trees with smaller sizes showed higher species richness and diversity under their crowns than the bigger ones. The dissimilarity of species composition differs between the inside and outside crown zones of the individuals of the same tree species and among the different trees species and the open field.

Spatial variance in soil microarthropod communities: Niche, neutrality, or stochasticity?

We studied geographic patterns in the soil microarthropods associated with moss carpets on exposed rocky outcrops in southwestern British Columbia, Canada. We related microarthropod composition, abundance, and species richness to 15 ecological variables relevant to either spatial or environmental filtering. Our survey identified 352 morphospecies in 32 sites spanning a 130- × 60-km area. We tested whether the relative importance of spatial and environmental factors was concordant between community composition, abundance, species richness, and 3 major taxonomic groups (Oribatida, Mesostigmata, Collembola). The results depended on the variance partitioning methods used and whether composition was defined by species abundance or presence. Distance-based Mantel tests showed that dissimilarity in species composition between sites was better predicted by spatial distance than by environmental dissimilarity. In contrast, variance partitioning of ordinated abundance data concluded that environmental rather than spatial variables explained most variance in the composition of total microarthropod, especially Collembola, assemblages. Total abundance and species richness were only weakly correlated across space, even though both were explained by environmental factors such as temperature and soil moisture. Given the surprising contradictions between methods, we suggest that different analyses should always be compared to fully uncover the spatial and environmental factors structuring communities.

Phyllostomid Bat Assemblage Structure in Amazonian Flooded and Unflooded Forests

AbstractIn Amazonia, the assemblages of several taxa differ significantly between upland terra firme and white‐water flooded várzea forests, but little is known about the diversity and distribution of bats in these two forest types. We compare the spatio‐temporal patterns of bat assemblage composition and structure in adjacent terra firme and várzea forests in the lower Purus River region of central Brazilian Amazonia. Bats were sampled using mist nets at five sites in each forest type during 40 nights (2400 net‐hours). We captured 1069 bats representing 42 species and Phyllostomidae bats comprised 99.3 percent of all captures. The bat assemblages in várzea and terra firme forests were significantly different, mainly due to a marked dissimilarity in species composition and in the number of captures during high‐water season. In addition, bat assemblages within forest types differed significantly between seasons for both terra firme and várzea. Frugivores dominated the bat assemblages in both forest types. Overall guild structure did not change between várzea and terra firme or between seasons, but frugivore and animalivore abundance increased significantly in várzea forest during the inundation. The difference in assemblage structure observed in the high‐water season is probably caused by the annual várzea flooding, which provides an effective barrier to the persistence of many understory bats. We also hypothesize that some bat species may undertake seasonal movements between forest types in response to fruit abundance, and our results further underline the importance of floodplain habitats for the conservation of species in the Amazon.

Spatio temporal and environmental factors influencing macroalgal β diversity in the Red Sea, Egypt

Abstract β Diversity is an ecological concept used to describe the turnover of species across a wide range of spatial and temporal scales, but such knowledge is lacking for macroalgal assemblages of the Red Sea. β Diversity patterns for Red Sea macroalgae were evaluated from different sites (Hurghada, Safaga, and Al-Quseir) and seasons across different environmental disturbances. β Diversity was studied by partitioning the total number of species (γ diversity) into additive components. Geographical heterogeneity was more important than seasonal heterogeneity in structuring macroalgae both at species and functional group levels. Species replacement as a component of β diversity produced dissimilarity in species composition and taxonomic structure. Replacement of species between sites was responsible for the presence of new functional groups of macroalgae. High β diversity and taxonomic similarity values were characteristic of the macroalgae of the Red Sea. The occurrence of small macroalgal thalli that have short life cycles induced high species replacement and subsequently high β diversity, with spatial heterogeneity and environmental gradient as drivers of β diversity. Anthropogenic disturbance at the Safaga site was suggested to induce variation of macroalgal assemblages and functional groups. Excluding rare species from the data set did not change the high values of b diversity.

Foraging Strategy of Plateau Zokors (Eospalax baileyiThomas) When Collecting Food for Winter Caches

ABSTRACT: Subterranean life style is characterized by limited food resource and energy consuming burrow behavior. Subterranean rodents are usually recognized as dietary generalists. In the current study, we investigated the species composition of winter caches of plateau zokors (Eospalax baileyi), and the dissimilarity of species composition in caches and in the vicinity of the burrows. We have made our research in Kobresia dominated vegetation at the altitude 3200 m a.s.l. We used the non-parametric method to test the similarities between the relative dry mass of the plant species within caches and their closed vicinity. This method was based on measures of distance between pairs of individual multivariate observations. Our results revealed that although plateau zokors cached most (60) of the plant species found in the vicinity of their burrow systems (66), the cached dry mass was dominated by a few species. Nine plant species accounted for 80% dry mass of plants present in zokors' caches, Polygonum vivi...

Avian species composition across the Amazon River: the roles of dispersal limitation and environmental heterogeneity

AbstractAimThe roles of dispersal limitation and environmental heterogeneity in structuring tropical species composition can be better understood by accounting for dispersal barriers and possible niche differentiation effects. We make ecological and historical interpretations of dissimilarity in avian species composition across a riverine dispersal boundary in the light of environmental characteristics, species and subspecies range limits, and geographical distances.LocationLowland rain forest, western Amazon River Basin, Peru.MethodsWe surveyed all birds and one plant family, collected soil samples and measured forest structural characteristics and fragmentation in surrounding landscapes, at sites to the north and south of the Amazon River flood plain. We used Mantel tests, multiple regression on distance matrices, indicator species analysis and ordination methods to assess the relationships among dissimilarities in species composition, geographical distance, position relative to the river and environmental characteristics. We examined compositional variation for all bird species, for only species without range limits between sites, and for species with and without subspecies limits at the Amazon River.ResultsDissimilarity in avian species composition across the river was large, despite a lack of environmental differences. Most of this dissimilarity was accounted for by species and subspecies range limits at the river. Plant species composition did not show any dissimilarity across the river. Plant species composition and forest fragmentation explained additional components of avian compositional dissimilarity not associated with the riverine boundary and involving different bird species.Main conclusionsThe riverine dispersal boundary, floristic heterogeneity and forest fragmentation were associated with distinctive components of avian species compositional dissimilarity, collectively explaining three‐quarters of the total dissimilarity among sites. Compositional dissimilarity was consistent with historical and continuing isolation of avian populations on opposite sides of the river, and may be partly driven by niche differentiation between subspecies. Geographical distance as a measure of dispersal limitation would not have accounted for these relationships. The use of rivers in biogeographical region delineation should address their variable importance for different taxa.

Dissimilarity in plant species diversity between salt marsh and neighboring environments decreases as environmental harshness increases

How species similarity changes between habitats along environmental gradients is still a central challenge in ecological studies. We assessed whether marsh plant characteristics are associated with geographic changes in environmental conditions and whether there are environ- mental factors associated with marshinland dissimilarity in species composition. Field samples of vegetation were collected at 6 sites along the SW Atlantic to determine plant characteristics (cover, tallness, richness and α-diversity), and marsh-inland dissimilarity (β-diversity) in species composi- tion was calculated. PERMANOVA analysis showed that plant assemblage changes among sites. Forward stepwise multiple regression analysis showed that in lower marsh, plant cover increased in association with tidal range and decreased in association with salinity. In the high marsh, plant cover decreased in association with tidal range, salinity and with minimum temperatures. Plant richness increased in association with tidal range and with marsh area, while α-diversity decreased in association with precipitation and increased with salinity. Beta-diversity, estimated by SIMPER analysis, increased in association with precipitation and decreased with salinity and daily thermal amplitude. We present evidence that there is an increase in α-diversity but a decrease in β-diversity with environmental severity among co-specific marshes distributed along the SW Atlantic coast. Thus, communities developing in more benign conditions, regardless of their low local diversity, may increase biodiversity at a landscape scale by decreasing their similarities.

Environment and dispersal paths override life strategies and residence time in determining regional patterns of invasion by alien plants

Abstract We describe a novel dissimilarity framework to analyze spatial patterns of species diversity and illustrate it with alien plant invasions in Northern Portugal. We used this framework to test the hypothesis that patterns of alien invasive plant species richness and composition are differently affected by differences in climate, land use and landscape connectivity ( i.e. Geographic distance as a proxy and vectorial objects that facilitate dispersal such as roads and rivers) between pairs of localities at the regional scale. We further evaluated possible effects of plant life strategies (Grime's C-S-R) and residence time. Each locality consisted of a 1 km 2 landscape mosaic in which all alien invasive species were recorded by visiting all habitat types. Multi-model inference revealed that dissimilarity in species richness is more influenced by environmental distance (particularly climate), whereas geographic distance (proxies for dispersal limitations) is more important to explain dissimilarity in species composition, with a prevailing role for ecotones and roads. However, only minor differences were found in the responses of the three C-S-R strategies. Some effect of residence time was found, but only for dissimilarity in species richness. Our results also indicated that environmental conditions ( e.g. climate conditions) limit the number of alien species invading a given site, but that the presence of dispersal corridors determines the paths of invasion and therefore the pool of species reaching each site. As geographic distances ( e.g. ecotones and roads) tend to explain invasion at our regional scale highlights the need to consider the management of alien invasions in the context of integrated landscape planning. Alien species management should include (but not be limited to) the mitigation of dispersal pathways along linear infrastructures. Our results therefore highlight potentially useful applications of the novel multimodel framework to the anticipation and management of plant invasions.

Assessing resilience and state‐transition models with historical records of cheatgrass Bromus tectorum invasion in North American sagebrush‐steppe

Summary Resilience‐based approaches are increasingly being called upon to inform ecosystem management, particularly in arid and semi‐arid regions. This requires management frameworks that can assess ecosystem dynamics, both within and between alternative states, at relevant time scales. We analysed long‐term vegetation records from two representative sites in the North American sagebrush‐steppe ecosystem, spanning nine decades, to determine if empirical patterns were consistent with resilience theory, and to determine if cheatgrass Bromus tectorum invasion led to thresholds as currently envisioned by expert‐based state‐and‐transition models (STM). These data span the entire history of cheatgrass invasion at these sites and provide a unique opportunity to assess the impacts of biotic invasion on ecosystem resilience. We used univariate and multivariate statistical tools to identify unique plant communities and document the magnitude, frequency and directionality of community transitions through time. Community transitions were characterized by 37–47% dissimilarity in species composition, they were not evenly distributed through time, their frequency was not correlated with precipitation, and they could not be readily attributed to fire or grazing. Instead, at both sites, the majority of community transitions occurred within an 8–10 year period of increasing cheatgrass density, became infrequent after cheatgrass density peaked, and thereafter transition frequency declined. Greater cheatgrass density, replacement of native species and indication of asymmetry in community transitions suggest that thresholds may have been exceeded in response to cheatgrass invasion at one site (more arid), but not at the other site (less arid). Asymmetry in the direction of community transitions also identified communities that were ‘at‐risk’ of cheatgrass invasion, as well as potential restoration pathways for recovery of pre‐invasion states. Synthesis and applications. These results illustrate the complexities associated with threshold identification, and indicate that criteria describing the frequency, magnitude, directionality and temporal scale of community transitions may provide greater insight into resilience theory and its application for ecosystem management. These criteria are likely to vary across biogeographic regions that are susceptible to cheatgrass invasion, and necessitate more in‐depth assessments of thresholds and alternative states, than currently available.

Diversity of Eastern North American Ant Communities along Environmental Gradients

Studies of species diversity patterns across regional environmental gradients seldom consider the impact of habitat type on within-site (alpha) and between-site (beta) diversity. This study is designed to identify the influence of habitat type across geographic and environmental space, on local patterns of species richness and regional turnover patterns of ant diversity in the northeastern United States. Specifically, I aim to 1) compare local species richness in paired open and forested transects and identify the environmental variables that best correlate with richness; and 2) document patterns of beta diversity throughout the region in both open and forested habitat. I systematically sampled ants at 67 sites from May to August 2010, spanning 10 degrees of latitude, and 1000 meters of elevation. Patterns of alpha and beta diversity across the region and along environmental gradients differed between forested and open habitats. Local species richness was higher in the low elevation and warmest sites and was always higher in open habitat than in forest habitat transects. Richness decreased as temperature decreased or elevation increased. Forested transects show strong patterns of decreasing dissimilarity in species composition between sites along the temperature gradient but open habitat transects did not. Maximum temperature of the warmest month better predicted species richness than either latitude or elevation. I find that using environmental variables as key predictors of richness yields more biologically relevant results, and produces simpler macroecological models than commonly used models which use only latitude and elevation as predictors of richness and diversity patterns. This study contributes to the understanding of mechanisms that structure the communities of important terrestrial arthropods which are likely to be influenced by climatic change.

Patterns of plant beta‐diversity along elevational and latitudinal gradients in mountain forests of China

Biodiversity patterns and their underlying mechanisms have long been focal topics of study for ecologists and biogeographers. However, compared with spatial variation in species richness (α‐ and γ‐diversity), β‐diversity, or the dissimilarity of species composition between two or more sites has until recently received limited attention. In this study, we explored the large‐scale patterns of altitudinal turnover (β‐diversity) of plants in montane forests of China, based on systematic inventories of 1153 plots from 46 mountains distributed over ˜30 degrees of latitude (21.9–51.7°N) and ˜4100 m of altitude (160–4250 m). The β‐diversity of trees and shrubs declined significantly with increasing latitude. Along the altitudinal gradient, β‐diversity of both trees and shrubs showed non‐significant trends in most mountains. Differences in climate explained ˜30.0% of the variation in tree β‐diversity (27.7, 36.5, and 26.2% for the Jaccard's, βj, Sorenson's, βs, and Simpson's dissimilarity, βsim, respectively), with mean annual temperature being most important, and ≤ 10.0% of that in shrub β‐diversity (10.0, 8.2, and 7.0% for βj, βs, and βsim, respectively), with annual actual evapotranspiration and annual precipitation as the main predictors. However, climatic controls of β‐diversity varied dramatically in different biogeograpical regions. The β‐diversity of trees exhibited stronger, whereas that of shrubs showed weaker, climatic patterns in temperate and arid than subtropical regions. These results suggest that mechanisms causing patterns of β‐diversity may differ between latitudinal and altitudinal gradients, and among biogeographical regions; as a result, caution should be exercised in drawing close parallels between patterns and causes of β‐diversity along latitudinal and altitudinal gradients and among regions.

Low Functional β-Diversity Despite High Taxonomic β-Diversity among Tropical Estuarine Fish Communities

The concept of β-diversity, defined as dissimilarity among communities, has been widely used to investigate biodiversity patterns and community assembly rules. However, in ecosystems with high taxonomic β-diversity, due to marked environmental gradients, the level of functional β-diversity among communities is largely overlooked while it may reveal processes shaping community structure. Here, decomposing biodiversity indices into α (local) and γ (regional) components, we estimated taxonomic and functional β-diversity among tropical estuarine fish communities, through space and time. We found extremely low functional β-diversity values among fish communities (<1.5%) despite high dissimilarity in species composition and species dominance. Additionally, in contrast to the high α and γ taxonomic diversities, α and γ functional diversities were very close to the minimal value. These patterns were caused by two dominant functional groups which maintained a similar functional structure over space and time, despite the strong dissimilarity in taxonomic structure along environmental gradients. Our findings suggest that taxonomic and functional β-diversity deserve to be quantified simultaneously since these two facets can show contrasting patterns and the differences can in turn shed light on community assembly rules.

Trait but not species convergence during plant community assembly in restored semi‐natural grasslands

Community assembly or succession was traditionally thought of as being deterministic and directional, leading to a clearly defined climax state. The alternative view, however, keeps gaining attention. This view states that community assembly is influenced by historical processes, where differences in the sequence and timing of species arrival result in distinct communities. Here we tested the hypothesis that both views are valid, but at a different level, with increasing dissimilarity in species composition among sites with increasing age (divergence), caused by historical processes (priority effects), and with increasing similarity in mean trait composition (convergence) among sites, indicating a directional development at the niche level. We surveyed a chronosequence of restored semi‐natural grassland patches on former pine plantations over seven restoration age classes, covering 22 grasslands. Pairwise multivariate distances were calculated between the different grassland patches based on species abundance on the one hand, and on mean community trait values for 28 plant life history traits on the other. Trait composition showed a clear decrease in multivariate distance with increasing restoration age, indicating trait convergence through time. At the species level, we found no evidence of convergence through time, with even a trend towards divergence. Furthermore, spatial variation and environmental heterogeneity were found to remain constant through time. These results confirm our hypothesis. At the trait level, limited niches occur, only filled by species having the appropriate traits, resulting in a clear deterministic model of assembly. Species identity, on the contrary, has no role in this niche filling. The first appropriate species to reach a restoration site will be most likely the ones that get established, resulting in divergence of the species composition among restored grasslands.

Hydrologic connection between ponds positively affects macrophyte α and γ diversity but negatively affects β diversity

Connections between habitat patches can positively influence the number of species in respective patches, providing a basis for preferentially conserving interconnected patches. However, from a regional perspective, it is not known whether conserving multiple sets of interconnected habitat patches would include more species (i.e., show higher gamma diversity) than conserving multiple, unconnected, solitary patches. We studied aquatic macrophytes in 15 sets of unidirectionally interconnected ponds and 19 unconnected ponds and also tested whether alpha and beta diversity, expressed as the number of species and dissimilarity in species composition, respectively, differed between connected and unconnected ponds. We found that gamma diversity was higher in connected ponds than in unconnected ponds, even after controlling for surface area. This resulted from a higher alpha diversity in connected ponds, despite lower beta diversity. These results suggest that connections between habitat patches positively influence diversity at both local and regional scales. When the total surface area available for conservation is limited, interconnected habitat patches should be preferentially conserved.

Rethinking the relationship between nestedness and beta diversity: a comment on Baselga (2010)

ABSTRACTBaselga [Partitioning the turnover and nestedness components of beta diversity. Global Ecology and Biogeography, 19, 134–143, 2010] proposed pairwise (βnes) and multiple‐site (βNES) beta‐diversity measures to account for the nestedness component of beta diversity. We used empirical, randomly created and idealized matrices to show that both measures are only partially related to nestedness and do not fit certain fundamental requirements for consideration as true nestedness‐resultant dissimilarity measures. Both βnes and βNES are influenced by matrix size and fill, and increase or decrease even when nestedness remains constant. Additionally, we demonstrate that βNES can yield high values even for matrices with no nestedness. We conclude that βnes and βNES are not true measures of the nestedness‐resultant dissimilarity between sites. Actually, they quantify how differences in species richness that are not due to species replacement contribute to patterns of beta diversity. Finally, because nestedness is a special case of dissimilarity in species composition due to ordered species loss (or gain), the extent to which differences in species composition is due to nestedness can be measured through an index of nestedness.

Beta‐diversity gradients of butterflies along productivity axes

ABSTRACTAim Several lines of evidence suggest that beta diversity, or dissimilarity in species composition, should increase with productivity: (1) the latitudinal species richness gradient is most closely related to productivity and associated latitudinal beta‐diversity relationships have been described, and (2) the scale dependence of the productivity–diversity relationship implies that there should be a positive productivity–beta‐diversity relationship. However, such a pattern has not yet been demonstrated at broad scales. We test if there is a gradient of increasing beta diversity with productivity.Location Canada.Methods Canada was clustered into regions of similar productivity regimes along three remotely sensed productivity axes (minimum and integrated annual productivity, seasonality of productivity) and elevation. The overall (βj), turnover (βsim) and nestedness (βnes) components of beta diversity within each productivity regime were estimated with pairwise dissimilarity metrics and related to cluster productivity with partial linear regression and with spatial autoregression. Tests were performed for all species, productivity breadth‐based subsets (e.g. species occurring in many and a moderate number of productivity regimes), and pre‐ and post‐1970 butterfly records. Beta diversity between adjacent clusters along the productivity gradients was also evaluated.Results Within‐cluster βj and βsim increased with productivity and decreased with seasonality. The converse was true for βnes. All species subsets responded similarly; however, productivity–beta‐diversity relationships were weaker for the post‐1970 temporal subset and strongest for species of moderate breadth. Between‐cluster beta diversity (βj) and nestedness (βnes) declined with productivity.Main conclusions As predicted, beta diversity of communities within productivity regimes was observed to increase with productivity. This pattern was driven largely by a gradient of species turnover. Therefore, beta diversity may make an important contribution to the broad‐scale gradient of species richness with productivity. However, this species richness gradient dominates regional beta diversity between productivity regimes, resulting in decreasing between‐productivity dissimilarity with productivity driven by a concurrent decline in nestedness.

清水港に流人する巴川惑潮域に設置した実験板に付着した海洋付着生物の分布について

The distributions of the species of sessile organisms settling on test plates immersed in the lower reaches of the Tomoe River in Shizuoka, Japan, was investigated during late summer in 2002. Sessile organisms settled actively from the mouth of the river to sites about 2 km upstream, while the settlement of fewer species was confirmed farther upstream at about 5 km from the mouth. The main species found settling on the test plates were the barnacles Fistulobalanus albicostatus and Amphibalanus amphitrite, and the polychaetes Hydroides elegans and Dexiospira foraminosa. Fistulobalanus albicostatus and H. elegans settled from the mouth all the way to 5 km upstream while D. foraminosa settled at only two sites about 2 km from the mouth. Cluster analysis conducted according to the dissimilarity of species composition among the 60 test plates classified the sessile organisms into six sub-communities. Near the mouth of the river, the communities were distributed mainly in the middle layer of the water column, while they were distributed among all layers at the sites 2 km upstream. Farther upstream, the communities were distributed in the bottom layers within the salt wedge and became sparse at the uppermost sites. The distributions of sessile organism species were strongly correlated with salinity in the lower reaches of this river.

Improving the assessment of species compositional dissimilarity in a priori ecological classifications: evaluating map scale, sampling intensity and improvement in a hierarchical classification

Question: Can species compositional dissimilarity analyses be used to assess and improve the representation of biodiversity patterns in a priori ecological classifications? Location: The case study examined the northern-half of the South-east Queensland Bioregion, eastern Australia. Methods: Site-based floristic presence–absence data were used to construct species dissimilarity matrices (Kulczynski metric) for three levels of Queensland's bioregional hierarchy – subregions (1:500 000 scale), land zones (1:250 000 scale) and regional ecosystems (1:100 000 scale). Within- and between-class dissimilarities were compiled for each level to elucidate species compositional patterns. Randomized subsampling was used to determine the minimum site sampling intensity for each hierarchy level, and the effects of lumping and splitting illustrated for several classes. Results: Consistent dissimilarity estimates were obtained with five or more sites per regional ecosystem, 10 or more sites per land zone, and more than 15 sites per subregion. On average, subregions represented 4% dissimilarity in floristic composition, land zones approximately 10%, and regional ecosystems over 19%. Splitting classes with a low dissimilarity increased dissimilarity levels closer to average, while merging ecologically similar classes with high dissimilarities reduced dissimilarity levels closer to average levels. Conclusions: This approach demonstrates a robust and repeatable means of analysing species compositional dissimilarity, determining site sampling requirements for classifications and guiding decisions about ‘lumping’ or ‘splitting’ of classes. This will allow more informed decisions on selecting and improving classifications and map scales in an ecologically and statistically robust manner.