Characterization,Ecological Status and Type-specific Reference Conditions of Surface Water Bodies in Wallonia (Belgium) using Biocenotic Metrics based on Benthic Invertebrate Communities

The river types in Wallonia (Belgium) were defined according to the system B of the European Water Framework Directive (WFD) taking into account obligatory and optional factors synthesized in three criteria: ‘size’, ‘slope’ and ‘natural region’. Under the hypothesis that benthic invertebrate assemblages would be specialized according to river type, a set of 627 faunal samples originating from an 11-year sampling period was tested to characterize river types with faunal assemblages. A multivariate approach led to gather 23 river types into seven groups exhibiting similar faunal assemblages. Using biocenotic metrics based on benthic invertebrate assemblages (e.g., the French standard IBGN), type-specific reference conditions and ecological status class limits were defined for each ‘natural’ river type group. Ecological potential was defined for heavily modified and for artificial (i.e., man-made canals) types. An ‘ecological status’ evaluation strategy was therefore developed and applied in the southern – and more natural – part of Wallonia, where many reference sites were available. In the northern part of Wallonia (i.e., the ‘Loess region’) where no high quality site was available, the expert judgement took a larger part in the definition of the reference conditions and of the ecological status class limits, in addition to the calculations. Two independent distribution gradients of taxa assemblages resulted from multivariate ordination: a first ‘saprobity axis’, as the taxa-sensitivity to organic contamination was increasing from ‘very resistant’ taxa (mainly located in the ‘Loess region’) to ‘sensitive’ and ‘very sensitive’ taxa (from the river types belonging to the Condroz, the Famenne, the Arden and the Jurassic regions) and a second axis characterizing the Meuse-specific faunal assemblage, gathering exotic species and typical limnophilous taxa of large heavily modified rivers. The ecological status monitoring management system developed in this study – i.e., the definition of faunal river type groups, related reference conditions and ecological status class limits – represents a proposal to be integrated in the ecological status assessment of biological elements for the implementation of the WFD and was tested in Wallonia. For the period 2000–2002 involving 349 different sites, the element ‘benthic invertebrate fauna’ was in that way classified ‘high status’ for 31.5% of sites, ‘good status’ for 31.5% and below ‘good status’ for 37% of sites. The best ecological status (i.e., 100% ‘high’ and ‘good’ status) was found in river type ‘Arden’s xenotrophic brooks with strong slope’ and in river types 8large rivers with medium slope’. The worst status was found in river types ‘Loess brooks and rivers with medium slope’.     

Comparison of wood-inhabiting myxomycetes in subalpine and montane coniferous forests in the Yatsugatake Mountains of Central Japan

To demonstrate altitudinal gradients (and resulting temperatures) that affect myxomycete biodiversity and species composition, we statistically compared myxomycete assemblages between a subalpine coniferous forest and a montane pine forest within the region of the Yatsugatake Mountains, Nagano Prefecture, Central Japan. In summer and autumn field surveys during 2003–2010, 53 myxomycete taxa (with varieties treated as species) were observed from 639 records of fruiting bodies in the subalpine forest and 32 taxa were detected from 613 records in the montane forest. There were 20 species in common between the assemblages and the percentage similarity index was 0.400. Myxomycete biodiversity was higher in the subalpine than in the montane forest. Nine myxomycete species were statistically frequent occurrences in the subalpine forest and appeared in autumn: Lamproderma columbinum, Cribraria macrocarpa, Trichia botrytis, Physarum newtonii, Diderma ochraceum, Enteridium splendens, Elaeomyxa cerifera, Trichia verrucosa, and Colloderma oculatum. Five species were restricted to appear in the subalpine forest: Cribraria purpurea, Cribraria rufa, Cribraria ferruginea, Cribraria piriformis, and Lepidoderma tigrinum. Dead wood in the subalpine forest provided a breeding habitat for specific myxomycetes that inhabit cold areas; that is those areas having geographical features of decreasing temperature and increasing elevation, such as the temperate area of Central Japan.     

Recommendations for the use of species diversity indices with reference to a recently published article as an example

There are some recommendations for the use of species diversity indices in a paper recently published in this journal by M. Ohsawa on the species richness and composition of weevils in five forest types in the middle region of Japan. Because several factors, such as small sample size, calculation of Simpson’s diversity index by the use of the original equation of Simpson’s measure of concentration D, and a weak point in the Shannon–Wiener diversity index H′, may have led to biased estimates, I recalculated these indices using combined species diversity values of the five forest types. As the general tendencies of 1−D and H′ values calculated here were similar to those in Ohsawa’s paper, there is no need to propose any change to his view. However, these recalculated diversity indices indicated that they are values which are more suitable for use. It should be noted that the characteristics and weak point associated with the diversity indices need to be taken into account in future studies.     

Spring airborne pollen data in two sites in Trentino (Northern Italy): a comparison with meteorological data

In this paper airborne pollen concentration is compared to meteorological data of Trento and S. Michele all’Adige, two sites in the Adige Valley, in Trentino (North Italy). Pollen ofCorylus, Alnus, Betula andOstrya, four winter-spring flowering plants are considered. Pollen sampling was carried out in 1996 by volumetric Hirst-type samplers. For all pollen types considered, maximum pollen concentration coincided in both stations and there was a good overlap of the main pollen season length; the pollen curves of S. Michele a/A and Trento showed a highly positive correlation. The daily airborne pollen concentrations, defined as the number of pollen grains per cubic meter of air (P/m³), were compared to daily meteorological data: minimum and maximum air temperature (°C), average relative humidity (%), precipitation (mm), global incident radiation (cal/cm²), average wind direction (°) and wind speed (m/s). A highly positive correlation was found forCorylus and maximum temperature in both monitoring stations.Betula was positively, whereasOstrya was negatively correlated to relative humidity. With this first analytical approach sharp differences in the atmospheric pollen presence between the stations located at Trento and S. Michele all’Adige were not found.     

An alien in an archipelago: Spathodea campanulata and the geographic variability of its moth (Lepidoptera) communities in the New Guinea and Bismarck Islands

Aim This analysis of moth (Lepidoptera) communities colonizing an alien tree invading secondary rain forest vegetation in Melanesia examines the predictability of insect herbivorous communities across distances of tens to thousands of km and the effect of dispersal barriers on community composition in the tropics. Location Six secondary rain forest sites were studied within four equidistant yet distinct geographic areas of the New Guinea mainland and the Bismarck Archipelago, including two watershed areas (Madang and Sepik) on mainland New Guinea and the adjacent large island of New Britain and small island of Unea. Methods The analysis is based on feeding records obtained by quantitative sampling and rearing of caterpillars from the alien host Spathodea campanulata (Bignoniaceae). It examines the variation in Lepidoptera community composition at six study sites distributed on three adjacent islands ranging in size from 30 to 865,000 km². Results Spathodea campanulata was colonized by 54 folivorous species of Lepidoptera. Most of them were generalists, feeding on > 1 native plant family. However, the three most abundant species representing 83% of all individuals (Acherontia lachesis, Hyblaea puera complex and Psilogramma menephron) were relatively host specific, feeding predominantly on a single native family that is not the Bignoniaceae. Most of the 23 species analysed in detail had a wide geographic distribution, including 13 species spanning the entire 1000‐km study transect. While the Lepidoptera in two New Guinea areas 280 km apart were similar to each other, there was a discontinuity in species composition between New Guinea and the smaller islands. However, no negative effect of small islands on species richness was detected. Main conclusions Spathodea campanulata was rapidly colonized by folivorous Lepidoptera communities with species richness and dominance structure indistinguishable from the assemblages feeding on native hosts, despite its phylogenetic isolation from the native vegetation. Although most species were generalists, the highest population densities were reached by relatively specialized species, similar to the communities on native hosts. The species turnover across distances from 10 to 1000 km was relatively low as most of the species had wide geographic ranges.     

Quantitative classification and carbon density of the forest vegetation in Lüliang Mountains of China

Forests play a major role in global carbon (C) cycle, and the carbon density (CD) could reflect its ecological function of C sequestration. Study on the CD of different forest types on a community scale is crucial to characterize in depth the capacity of forest C sequestration. In this study, based on the forest inventory data of 168 field plots in the study area (E 111°30′–113°50′, N 37°30′–39°40′), the forest vegetation was classified by using quantitative method (TWINSPAN); the living biomass of trees was estimated using the volume-derived method; the CD of different forest types was estimated from the biomass of their tree species; and the effects of biotic and abiotic factors on CD were studied using a multiple linear regression analysis. The results show that the forest vegetation in this region could be classified into 9 forest formations. The average CD of the 9 forest formations was 32.09 Mg ha⁻¹ in 2000 and 33.86 Mg ha⁻¹ in 2005. Form. Picea meyeri had the highest CD (56.48 Mg ha⁻¹), and Form. Quercus liaotungensis + Acer mono had the lowest CD (16.14 Mg ha⁻¹). Pre-mature forests and mature forests were very important stages in C sequestration among four age classes in these formations. Forest densities, average age of forest stand, and elevation had positive relationships with forest CD, while slope location had negative correlation with forest CD.     

Variation in diet and ranging of black and white colobus monkeys in Kibale National Park,Uganda

Recently, considerable intraspecific variation in the diets and ranging behavior of colobine monkeys has been described, although in most cases this has involved documenting variation between, not within, sites. Some African colobines, such as guerezas (Colobus guereza), are relatively abundant in disturbed habitats that are very heterogeneous, raising the intriguing possibility that even groups with overlapping home ranges may exhibit large behavioral differences. If such differences occur, it will be important to understand what temporal and spatial scales adequately portray a species’ or population’s diet and ranging behavior. This study documents within-site variation in the diet and ranging behavior of guerezas in the habitat types in which they are described to be most successful—forest edge and regenerating forest. We collected data on eight groups of guerezas with overlapping home ranges for 3–5 months each in Kibale National Park, Uganda. The guerezas were highly folivorous, with leaves constituting 78.5–94.0% of the groups’ diets. The percentage of mature leaves and fruit in the diet varied widely among and within groups. We show that differences among groups in the intensity with which they fed on specific tree species were not just related to phenology, but also to differences in the forest compositions of groups’ core areas. Range size estimates varied more than fivefold among groups and the minimum distance from groups’ core areas to eucalyptus forest (which all groups regularly fed in) was a better predictor of range size than was group size. These results reveal considerable variation in the diet and ranging behavior among groups with overlapping ranges and have implications for comparative studies, investigations of within- and between-group feeding competition, and the potential for populations to adapt to anthropogenic or natural environmental change.     

Assessing habitat and resource availability for an endangered desert bird species in eastern Morocco: the Houbara Bustard

In Morocco we tested the consistency between an a priori habitat classification based on topography, hydrology, vegetation structure and composition, and an a posteriori classification based on arthropod assemblages, in a plain supporting wild endangered Houbara Bustards. According to vegetation structure, we defined seven a priori habitats that differed significantly in perennial cover and height. A multivariate multiple regression analysis showed a significant relationship between arthropod assemblages and vegetation structure. Canonical Analyses of Principal Coordinates, conducted simultaneously on direct searches of arthropods and trapping data, showed significant differences between assemblages in both cases, and produced two similar constrained ordinations of six a posteriori habitats: esparto grass (Stipa tenacissima), temporarily flooded areas, fields, “reg” with short perennials, “reg” with tall perennials and wadis. The two sampling methods reflected a dominance of ants and beetles. Arthropod biomasses increased significantly in spring and then decreased significantly in summer for beetles, and in autumn for ants. No strong differences appeared between habitats within seasons, especially in spring, indicating a uniform distribution of food resources during the Houbara breeding season. The “reg” with short perennials had the highest ant biomass in summer. This “reg” and fields also supported the highest arthropod biomass in autumn. Variation in arthropod biomass was a pertinent factor that should be integrated into Houbara habitat selection studies. The definition of habitat availability based on easily identifiable landscape units, combined with empirical tests on arthropod communities provided an accurate classification for habitat selection studies and conservation planning.     

The ecology of Araucaria species in New Guinea. I. Ordination studies of forest types and environments

Previous studies of the ecology and regeneration strategies of Araucaria cunninghamii and A. hunsteinii in New Guinea rainforests have treated these species as ecologically identical and disagree concerning their ability to maintain a stable population size in forest communities dominated by angiosperms. Vegetation data from a number of 0.5 ha forest sites in New Guinea are analysed in order to characterize forest types and their environmental regimes in the altitudinal zone from 700 to 1500 m a.s.l. Particular attention is paid to forests containing Araucaria species. Nodal component analysis identifies a number of distinct forest types or ‘series’, each dominated by a different species. Continuity analysis displays the location of sites and species in non-linear ordination space. Subsequent regression of environmental data on the position of sites in ordination space shows that forest types are separated along gradients related to altitude and rainfall on the one hand, and soil nutrient concentrations on the other. A. cunninghamii is generally found in wetter and less nutrient-rich sites than A. hunsteinii. The analysis of species presence data, as opposed to quantitative data, shows that whilst forest types are easily differentiated according to their dominant species, changes in floristic composition are subtle along the altitudinal and other gradients recognized.     

Canopy herbivore community structure: large-scale geographical variation and relation to forest composition

Abstract. 1. Geographical distributions of individual foliage‐feeding forest herbivore species have been found to be aligned closely with the distribution of their host trees, however little is known about the extent to which broad herbivore communities are geographically associated with distinct host communities. 2. Large‐scale geographic variation in canopy herbivore communities in a 80 000 km² area (the state of Maine, U.S.A.) was characterised using historical insect survey data. Variation in insect communities was compared with corresponding variation in forest over‐storey composition, which was quantified using data from a regional forest inventory survey. 3. Principal components analysis was used to characterise associations among herbivore and tree species. Analysis of the herbivore data identified three main insect groups: group A corresponded to a single species (Choristoneura fumiferana), group B corresponded to pine‐feeding species including Semiothisa sp., and group C corresponded to the spruce‐feeding species Gilpinia hercyniae and Pikonema alaskensis. Analysis of the forest inventory data characterised three important forest types: northern hardwoods, eastern white pine, and northern spruce‐fir forest types. 4. Spatial analyses were carried out on the first two components of each of the principal components analyses. Factor 1 of the insect data showed a trend of decreasing values from south to north, while factor 2 of the forest inventory data showed an opposite trend. These inverse trends reflected the distribution of the main contributing species to the principal components analysis, C. fumiferana and Pinus strobus respectively. These distributions were highlighted further by the significant negative cross‐correlations that were found between the two factors up to distances of 120 km. 5. Analyses indicated a parallel between the geographic variation in the insect guilds associated with conifers and the geographic pattern of their conifer hosts. Hardwood‐feeding caterpillars, on the other hand, did not form well‐defined guilds and showed varying geographical distributions. The survey data showed varying quality in defining large‐scale associations in the structures of herbivore and host communities. 6. Implications for biodiversity management are discussed.     

Spatial and temporal variations in moss-inhabiting summer diatom communities from Potter Peninsula (King George Island, Antarctica)

This work represents the first analysis of the spatial and temporal variations in the diversity and community structure of diatoms associated with mosses, either dry or wet, sampled during the summer season from the littoral zone of three ponds in Potter Peninsula (King George Island, South Shetland Islands). It also seeks to explore the effect moisture content in the mosses can have on the structure of the diatom assemblages. The ponds approximately had the same number of species, and differences were found between the dry and wet sampling points. The same 4 species were predominant in the three ponds (Nitzschia alpina, N. perminuta, Staurosira oldenburgiana, and Pinnularia subantarctica var. elongata), but not in the same proportions. The first three species differed from those which were found to be dominant in other basins covered by mosses in southern South America and in the sub-Antarctic region. The latter, P. subantarctica var. elongata, had only been found to be abundant in a moss sample from another South Shetland Island. The diatom assemblages were found to be more strongly related to habitat traits (e.g. distance to the sea, ponds’ areas, and the vegetation’s moisture levels) than to the physical–chemical variables measured in the water.     

The Balkan wet grassland vegetation: a prerequisite to better understanding of European habitat diversity

The knowledge of broad-scale floristic variation in wet grasslands, which are endangered throughout Europe, is still limited and some regions have remained unexplored so far. In addition, hitherto published phytosociological studies were concentrated at the national level and therefore national vegetation classifications are not consistent with each other. In order to overcome these shortcomings of traditional phytosociology, we gathered original data from Bulgaria and analysed them together with the data from Central Europe. We further analysed major compositional gradients within Bulgarian wet grasslands and changes in species richness along them. We sampled 164 wet grassland vegetation plots throughout Bulgaria. We further prepared a restricted data set of wet grasslands from Central-European phytosociological databases. Both data sets were merged and classified by modified TWINSPAN. Four distinct vegetation types were differentiated. Even if they correspond with traditional alliances, which are primarily drawn as geographically defined units in Western and Central Europe (sub-Mediterranean Trifolion resupinati, sub-continental Deschampsion cespitosae and Molinion caeruleae and sub-oceanic Calthion palustris), they all occur in Bulgaria. When more precise classification was applied, two types of sub-Mediterranean wet grasslands and one high-altitude type of Calthion grasslands were detected solely in Bulgaria. DCA analysis showed that altitude is a dominant gradient controlling variation in Balkan wet grasslands. The second DCA axis was interpreted as the gradient of nutrient availability. Species richness shows skewed-unimodal trends along both major gradients, with the highest species richness in intermittently wet nutrient-limited grasslands. Tukey post-hoc test of altitudinal differences amongst vegetation types is significant for all pairs of clusters, suggesting that altitudinal differentiation is responsible for co-occurrence of nearly all European types of wet grasslands in Bulgaria. Our results suggest that (1) climate is an important factor for the diversity of wet grasslands; (2) Balkan vegetation of middle altitudes matches with that of Central Europe, whereas that of the lowest altitudes corresponds rather to the sub-Mediterranean region and high mountains are specific; (3) upward shift of Central-European vegetation types in southern Europe, so often described in forest vegetation is also evident for grassland vegetation and (4) the high diversity of Balkan vegetation is determined by a diverse relief enabling confluence of habitats possessing different climatic conditions.     

A review of gamasid mites (Parasitiformes,Mesostigmata) dwelling in the taiga of the Pechoro-Ilychskii Nature Reserve (northern Cis-Ural Region) with analysis of their assemblages in spruce forests

In the plain taiga of the Pechoro-Ilychskii Nature Reserve, 91 species of gamasid mites have been revealed. Cheiroseius (7 species), Veigaia (6), Arctoseius (5), Dendrolaelaps (5), and Dinychus (4) are the most diverse genera. European (29%), Palaearctic (27%), and Holarctic species (30%) are represented in the fauna by somewhat equal fractions, whereas cosmopolitan and semicosmopolitan species constitute about 14%. Comparison of gamasid assemblages populating certain habitats allowed revealing two distinct groupings, namely, forest and floodplain ones. Forest assemblages are characterized by high population density (220–760 ind./dm²) and by predominance of Parazercon radiatus, Zercon forsslundi, Veigaia nemorensis, Gamasellus montanus, and Trachytes spp. Floodplain assemblages are less abundant (80–130 ind./dm²) and comprise mainly meadow and hydrophilic species (A. cetratus, Cheiroseius spp. Gaeolaelaps spp., and Gamasellodes bicolor). Low diversity of the family Parasitidae (4 species) and structural peculiarities of assemblages dwelling in coniferous forests (namely, the absence of Pergamasinae and significant fractions of Veigaia, Gamesellus, Trachytes, and also of representatives of the family Zerconidae) demonstrate similarities between the mesostigmatan population of this northern European region and that of the Siberian taiga. Solitary records of such Arctic species as Arctoseius ornatus and Zerconopsis labradorensis, and of the hypoarcto-montane species Iphidinychus gaieri within the taiga belt, seem to reflect the instability of range margin. Taking into account the literary data, we recognize a complex of boreal and borealmountain species (Trachytes edleri, Dinychus septentrionalis. D. crassus, Caurozercon duplex, Neozercon smirnovi, Zercon forsslundi, and Z. zelawaiensis) in the Palaearctic fauna. Their habitats, however, are not restricted only to dark coniferous forest along. The structure of gamasid mite assemblages in mesophytic spruce forests of the Palaearctic varies strongly. By contrast to vascular plants, where many species accompany the dark coniferous taiga everywhere, there is not a single mesostigmatic mite species common to all the spruce forests analyzed, ranging from Romania in the west to Sakhalin Island in the east. On the whole, changes in gamasid mite assemblages across the spruce forest belt seem to follow a succession of meridional changes in gamasid faunas regardless of an edificatory spruce species.     

Biomass carbon stocks in China’s forests between 2000 and 2050: A prediction based on forest biomass-age relationships

China’s forests are characterized by young forest age, low carbon density and a large area of planted forests, and thus have high potential to act as carbon sinks in the future. Using China’s national forest inventory data during 1994–1998 and 1999–2003, and direct field measurements, we investigated the relationships between forest biomass density and forest age for 36 major forest types. Statistical approaches and the predicted future forest area from the national forestry development plan were applied to estimate the potential of forest biomass carbon storage in China during 2000–2050. Under an assumption of continuous natural forest growth, China’s existing forest biomass carbon (C) stock would increase from 5.86 Pg C (1 Pg=10¹⁵ g) in 1999–2003 to 10.23 Pg C in 2050, resulting in a total increase of 4.37 Pg C. Newly planted forests through afforestation and reforestation will sequestrate an additional 2.86 Pg C in biomass. Overall, China’s forests will potentially act as a carbon sink for 7.23 Pg C during the period 2000–2050, with an average carbon sink of 0.14 Pg C yr⁻¹. This suggests that China’s forests will be a significant carbon sink in the next 50 years.     

Structure of the diatom community of the River Adige (North-Eastern Italy) along a hydrological gradient

Physical constrains such as water discharge, suspended solids and turbidity act as dominant factors in driving the planktonic diatom assemblages of the River Adige (North-Eastern Italy). Two sampling stations, characterised by different hydromorphological features (Cortina all’Adige and Boara Pisani, with torrential and more potamal characteristics, respectively) were sampled fortnightly following an integrated approach encompassing physical, chemical and biological measurements and aiming at identifying the dominant factors controlling the temporal development of the community. A morpho-functional approach was used to classify the diatom assemblages where Morpho-Functional Diatom Groups (MFDG) were defined for diatom genera, according to their morphology, habitat selection and modality of adhesion to river substrate. In the two sampling points, algal growth was never limited by nutrients or zooplankton. The irregular development of MFDG was determined by the stochastic hydrological events and changes in variables related to water discharge (suspended solids and light attenuation). Tychoplanktonic, benthic and drifted taxa (such as Diatoma spp., Encyonema spp., Navicula spp. and Nitzschia spp.) were dominant in the torrential station (Cortina all’Adige), while the contribution of euplanktonic unicellular centric taxa (such as Cyclotella spp., and Stephanodiscus spp.) was higher in the potamal station (Boara Pisani).     

Structure of multi-species ant assemblages (Hymenoptera,Formicidae) in the Mountain Crimea

The multi-species ant assemblages were studied in the Crimea Mountains, in 9 types of plant associations in the plateau pastures as well as on the southern and northern slopes of the Main Range. A list of 18 ant species with data on their distribution in biotopes and also layers and the structure of their foraging territories is given. The hierarchical organization of multi-species ant assemblages and different strategies of nest location of the influents depending on the dominant species and its territoriality were investigated. Territoriality of each dominant species was determined by the frequency of foraging areas without nests of other species. Depending on dominant territoriality and the number of dominant species, the following classification of multi-species assemblages is proposed. (1) Monodominant assemblages with weakly expressed territoriality of the dominant species. Low density of the workers of Camponotus aethiops in the foraging territory determines weak interactions with influent species. The settling pattern of the influents shows no evident dependence on the dominant. Weakly expressed territoriality of the dominant allows non-territorial species to exist on the dominant’s territory. Such species were not found in other types of ant assemblages. (2) Monodominant assemblages with strongly expressed territoriality of the dominant species. The settling pattern of the influents shows the subordinate species to avoid those of higher ranks in the hierarchy, thus decreasing the probability of conflicts. The influents settle in the neutral zones as well as in the foraging territory of the dominant, so as to reduce competition with the subdominant species Formica cunicularia. Such a strategy reduces the probability of interspecific conflicts in biotopes with fewer vegetation layers than in the forests. (3) Bidominant assemblages with a variable dendrobiont dominant are typical among forest assemblages. Coexistence of two dominant species is possible when foraging of one of them is completely or partly restricted to one vegetation layer. The subdominant species avoid settling in the foraging territory of the dominant that occupies the same layer. When the dendrobiont dominant Crematogaster schmidti drops out of the assemblage, it (and its role in the assemblage) is replaced by other dendrobiont species Lasius emarginatus which otherwise acts as the 1st order subdominant in C. schmidti assemblages. (4) Polydominant assemblages are characterized by the presence of as many as 3 dominant species, namely Crematogaster schmidti, Camponotus aethiops, and Plagiolepis tauricus. The coexistence of the dominants is possible due to use of different layers (one species is a dendrobiont, the other two are herpeto-hortobionts), different activity periods (round-the-clock in Crematogaster schmidti, night in Camponotus aethiops, and daytime in P. tauricus), and different size classes of the workers (3rd, 5th, and 1st, respectively). The different size classes of workers reduce competition for food. Thus, when the number of dominant species in the assemblage increases, so does the number of mechanisms facilitating their coexistence.     

Evaluating diatom community composition in the absence of marked limnological gradients in the high Arctic: a surface sediment calibration set from Cornwallis Island (Nunavut,Canada)

Fossil diatom assemblages preserved within the sedimentary record in Arctic lakes provide the potential to reconstruct past changes in important limnological variables. During the summers of 1992 and 1993, we examined previously unstudied freshwater ecosystems on Cornwallis Island, Arctic Canada, with the specific objectives of (1) documenting the limnology and modern diatom assemblages from this region, and (2) determining which environmental variables most influence diatom species distributions. The Cornwallis Island study sites displayed the least amount of variance in measured water chemistry variables in comparison to nearly all of our labs’ previous freshwater surveys in the Arctic. The small limnological gradients precluded the development of a statistically robust diatom inference model, but perhaps more importantly, allowed us to explore variations in diatom composition in the absence of marked variations in water chemistry. Diatom species turnover was minimal, with the most common diatom taxa being Achnanthidium minutissima, Nitzschia perminuta, N. frustulum, with lesser percent abundances of Chaemaepinnularia soehrensis, Navicula chiarae, Psammothidium marginulata, and A. kryophila. A small number of study sites differed from the majority with respect to water chemistry (e.g., coastal sites with high specific conductivities) and habitat availability (e.g., ephemeral ponds with extensive moss habitats), and these sites had markedly different diatom assemblages. These data reinforce previous observations that water chemistry and other climate-related factors are the primary environmental controls influencing diatom distributions at high latitudes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Thecamoebians from the small streams of the Boubín area (Šumava Mts,Czech Republic)

From 1999–2005, seventy-eight samples were collected from the small streams in the area of the Boubín Mountain including also the natural preserve “Boubínsky prales” (Boubín primeval forest) (Šumava Mts, Czech Republic). Nineteen species of thecamoebians were identified in the samples; the most abundant species were Centropyxis orbicularis, Pontigulasia compressa, Centropyxis aculeata, Difflugia oblonga and Centropyxis arcula. Species composition of assemblages as well as ecological affinities of the most common taxa are comparable with data from the previously analysed streams in the Šumava Mts. This correlation improves the quality of data for environmental preferences of thecamoebian assemblages contained in the streams and these can be used for interpretation of ancient environments. Though species composition of assemblages changes gradually, two end-member assemblages can be defined. For both assemblages, environmental conditions were defined: Lower-diversity assemblages dominated by centropyxids originated mainly from standing water with low content of organic debris. Relative abundances of C. orbicularis showed negative correlations with abundances of other Centropyxis spp. which may indicate different ecological affinities of this species. Centropyxis orbicularis may tolerate higher levels of fine organic debris in stream sediments. Assemblages with common to abundant occurrences of P. compressa and/or D. oblonga prefer running water. Difflugia oblonga dominated in samples with higher content of fine organic debris. Relation between test size of D. oblonga and flow rate was recorded: large D. oblonga prevailed in standing water while small specimens dominated in fast streams.