The Importance of Vertical and Horizontal Dimensions of the Sediment Matrix in Structuring Nematodes Across Spatial Scales

Intensive surveys have been conducted to unravel spatial patterns of benthic infauna communities. Although it has been recognized that benthic organisms are spatially structured along the horizontal and vertical dimensions of the sediment, little is known on how these two dimensions interact with each other. In this study we investigated the interdependence between the vertical and horizontal dimensions in structuring marine nematodes assemblages. We tested whether the similarity in nematode species composition along the horizontal dimension was dependent on the vertical layer of the sediment. To test this hypothesis, three-cm interval sediment samples (15 cm depth) were taken independently from two bedforms in three estuaries. Results indicated that assemblages living in the top layers are more abundant, species rich and less variable, in terms of species presence/absence and relative abundances, than assemblages living in the deeper layers. Results showed that redox potential explained the greatest amount (12%) of variability in species composition, more than depth or particle size. The fauna inhabiting the more oxygenated layers were more homogeneous across the horizontal scales than those from the reduced layers. In contrast to previous studies, which suggested that reduced layers are characterized by a specific set of tolerant species, the present study showed that species assemblages in the deeper layers are more causal (characterized mainly by vagrant species). The proposed mechanism is that at the superficial oxygenated layers, species have higher chances of being resuspended and displaced over longer distances by passive transport, while at the deeper anoxic layers they are restricted to active dispersal from the above and nearby sediments. Such restriction in the dispersal potential together with the unfavorable environmental conditions leads to randomness in the presence of species resulting in the high variability between assemblages along the horizontal dimension.     

Sphagnum-dwelling testate amoebae in subarctic bogs are more sensitive to soil warming in the growing season than in winter: the results of eight-year field climate manipulations

Sphagnum-dwelling testate amoebae are widely used in paleoclimate reconstructions as a proxy for climate-induced changes in bogs. However, the sensitivity of proxies to seasonal climate components is an important issue when interpreting proxy records. Here, we studied the effects of summer warming, winter snow addition solely and winter snow addition together with spring warming on testate amoeba assemblages after eight years of experimental field climate manipulations. All manipulations were accomplished using open top chambers in a dry blanket bog located in the sub-Arctic (Abisko, Sweden). We estimated sensitivity of abundance, diversity and assemblage structure of living and empty shell assemblages of testate amoebae in the living and decaying layers of Sphagnum. Our results show that, in a sub-arctic climate, testate amoebae are more sensitive to climate changes in the growing season than in winter. Summer warming reduced species richness and shifted assemblage composition towards predominance of xerophilous species for the living and empty shell assemblages in both layers. The higher soil temperatures during the growing season also decreased abundance of empty shells in both layers hinting at a possible increase in their decomposition rates. Thus, although possible effects of climate changes on preservation of empty shells should always be taken into account, species diversity and structure of testate amoeba assemblages in dry subarctic bogs are sensitive proxies for climatic changes during the growing season.     

Some distributional characteristics of small zooplankton at two stations in the Otranto Strait (Eastern Mediterranean)

The qualitative composition, numerical abundance and vertical distribution of protozoan and microcopepod communities were studied in the Otranto Strait at two stations during five cruises from August 1986 to May 1990. The samples were collected with a plankton net of 53-m mesh size equipped with a closing system in six or seven vertical layers. The principal component analysis (PCA) was used to analyse the spatial and temporal variability of small zooplanktonic assemblages. Data are presented for 36 species of radiolarians, 46 tintinnines and for 22 oncaeid copepods. Differences between the eastern shore and the western shore were not significant, according to the PC analysis of the total density values for all assemblages. However, on the basis of the distribution of PC loadings, it was possible to distinguish three vertical layers whose variability contributes in different amounts to the total variability in the small zooplankton community at both stations. The water masses have crucial significance for the spatial and seasonal distribution of all assemblages. Each type of water mass is connected by the presence of characteristic species.     

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.     

Recruitment response of methane-seep macrofauna to sulfide-rich sediments: An in situ experiment

Hydrodynamically unbiased colonization trays were deployed for 6 months (Oct. 2000 to April 2001) on the northern California margin (Eel R. region; 525 m) to examine macrofaunal colonization rates at methane seeps. The influence of sulfide on recruitment and survival was examined by deploying sediments with and without sulfide added; effect of seep proximity was evaluated by placing trays inside and outside seeps. The trays contained a two-layer system mimicking vesicomyid clam bed habitat geochemistry, with 8-9 mM sulfide in a lower agar layer at the start of the experiment. After 6 month on the seabed, the lower agar layer contained 2-4 mM H₂S. We observed rapid macrofaunal colonization equivalent to 50% of initial non-seep ambient densities. There was no difference in total colonizer densities, number of species, or rarefaction diversity among 3 treatments: (1) controls (no sulfide added) placed outside seeps, (2) trays with sulfide added placed outside seeps and (3) trays with sulfide added placed inside seep patches. Colonization trays with sulfide placed at seeps had different species composition from trays without sulfide place outside seeps; there were more amphipods (non-ampeliscid) and cumaceans in the seep/sulfide treatment and more nemerteans, Nephtys cornuta and tanaids in the non-seep/no-sulfide treatment. Outside seeps, annelids comprised < 15% of tray colonists; within seep patches, annelids comprised 5 of the top 10 dominant colonizing taxa (24% of the total). The polychaetes Mediomastus sp., Aphelochaeta sp., Paraonidae sp., and Nerillidae sp. exhibited significantly higher densities in sulfide additions. Tanaids, echinoderms, and N. cornuta exhibited sulfide avoidance. At least 6 dorvilleid polychaete species colonized the experiments. Of these, 4 species occurred exclusively in trays with sulfide added and 80% of all dorvilleid individuals were found in trays with sulfide placed inside seep sediments. Counts of large sulfur bacterial filaments were positively correlated with maximum sulfide concentration in each tray, and with proximity of sulfide to the sediment surface. However, total macrofaunal densities were not correlated with tray sulfide concentrations. As a group, tray assemblages achieved some but not all characteristics of ambient seep assemblages after 6-month exposure on the sea floor. Distinctive colonization patterns at methane seeps contribute to the dynamic mosaic of habitat patches that characterize the eastern Pacific continental margin.Overall, proximity of seep habitats had at least as great an influence on macrofaunal colonization as tray sulfide concentrations. Taxa characteristic of seep sediments were more likely to settle into trays placed inside rather than outside seep patches. Whether this is due to limited dispersal ability or local geochemical cues remains to be determined.     

Flourish or Flush: Effects of Simulated Extreme Rainfall Events on Sphagnum-dwelling Testate Amoebae in a Subarctic Bog (Abisko, Sweden)

Extreme precipitation events are recognised as important drivers of ecosystem responses to climate change and can considerably affect high-latitude ombrotrophic bogs. Therefore, understanding the relationships between increased rainfall and the biotic components of these ecosystems is necessary for an estimation of climate change impacts. We studied overall effects of increased magnitude, intensity and frequency of rainfall on assemblages of Sphagnum-dwelling testate amoebae in a field climate manipulation experiment located in a relatively dry subarctic bog (Abisko, Sweden). The effects of the treatment were estimated using abundance, species diversity and structure of living and empty shell assemblages of testate amoebae in living and decaying layers of Sphagnum. Our results show that increased rainfall reduced the mean abundance and species richness of living testate amoebae. Besides, the treatment affected species structure of both living and empty shell assemblages, reducing proportions of hydrophilous species. The effects are counterintuitive as increased precipitation-related substrate moisture was expected to have opposite effects on testate amoeba assemblages in relatively dry biotopes. Therefore, we conclude that other rainfall-related factors such as increased infiltration rates and frequency of environmental disturbances can also affect testate amoeba assemblages in Sphagnum and that hydrophilous species are particularly sensitive to variation in these environmental variables.     

Miospore assemblages from the Silurian–Devonian boundary,in borehole A1-61, Ghadamis Basin,Libya

Well preserved and diversified miospore assemblages have been recorded from a relatively continuous sequence in borehole A1-61 which spans the Silurian–Devonian boundary in the northwestern part of the Ghadamis Basin, Libya. The sequence is represented by early Devonian Lochkovian beds of the Tadrart Formation that transgress onto the Silurian Ludlow-Pridoli beds of the upper part of the ‘Alternances Argilo-gréseuses’ Formation. The present work demonstrates a succession of miospore assemblages from closely sampled layers that have been stratigraphically dated as Ludlow–middle Pridoli and early Lochkovian by chitinozoans and acritarchs. Over 80 species of cryptospores and trilete spores have been identified. Modified detailed morphological interpretations are given. The miospore assemblages are correlated with miospore zonation schemes established for the type sequences of the Welsh Borderland, and those previously described from Libya. Early occurrences of some species as Streelispora newportensis on the western Gondwana plate, are put forward by comparison with the Old Red Sandstone continent. Phytogeographic and palaeobotanic implications based on these observations are discussed.     

Variations in the sulfide regime and the distribution of macrofauna in an intertidal flat in the North Sea

Sulfide concentrations were measured in the inner and outer Königshafen (Sylt, Wadden Sea) from November 1990 to December 1991 to assess the fluctuations of sulfide levels in natural tidal habitats. Three different areas were compared: (1) muddy sediment (2) fine-medium sand, and (3) a mussel bed. Other abiotic factors such as Eh, pH, temperature, grain size and organic content were measured. After assessment of the macrofaunal distribution, an attempt was made to relate the distribution to the sulfide concentrations in the benthic habitat. Sulfide concentrations varied between sites throughout the year with considerable differences ranging from below 5 μM (limit of detection) to about 1 mM (Oct. 1991). The faunal composition (Table 2) at the different sites hardly varied; it was always dominated by annelids: The cirratulidTharyx marioni was the most abundant species in the upper layers of all sites, where it occurred at low sulfide concentrations (<50 μM).Heteromastus filiformis was commonly found in the deeper sediment layers of the muddy site where it was regularly exposed to sulfide levels around 75 μM and peak concentrations in autumn up to 1 mM.Capitella capitata, Tubificoides pseudogaster andTubificoides benedii were very common in the upper sediment layers where sulfide levels were about 150 μM in autumn. These species also occurred, however, in the deeper layers with higher sulfide concentrations. These results document not only the wide annual range of sulfide concentrations at different depths in a tidal flat, they also emphasize that under natural conditions tidal flat annelids are exposed to considerable concentrations of hydrogen sulfide.     

Spider assemblages in the overstory, understory, and ground layers of managed stands in the western boreal mixedwood forest of Canada

Logging is the main human disturbance in the boreal forest; thus, understanding the effects of harvesting practices on biodiversity is essential for a more sustainable forestry. To assess changes in spider composition because of harvesting, samples were collected from three forest layers (overstory, understory, and ground) of deciduous and conifer dominated stands in the northwestern Canadian boreal mixedwood forest. Spider assemblages and feeding guild composition were compared between uncut controls and stands harvested to 20% retention. In total, 143 spider species were collected, 74 from the ground, 60 from the understory, and 71 from the overstory, and species composition of these three pools differed considerably among layers. Distinctive spider assemblages were collected from the canopy of each forest cover type but these were only slightly affected by harvesting. However, logging had a greater impact on the species composition in the understory and ground layers when compared with unharvested controls. Guild structure differed among layers, with wandering and sheet-weaving spiders dominant on the ground while orb-weaving and ambush spiders were better represented in the understory and overstory, respectively. Given the ecological importance of spiders and the expectation of faunal changes with increased harvesting, further efforts toward the understanding of species composition in higher strata of the boreal forest are needed.     

Nestedness, anti-nestedness, and the relationship between prevalence and intensity in ectoparasite assemblages of marine fish: a spatial model of species coexistence

Nested species subset patterns consist in a hierarchical structure of species composition in related assemblages, with the species found in depauperate assemblages representing non-random subsets of progressively richer ones. This pattern has been found at the infracommunity level in about a third of the fish ectoparasite assemblages studied to date. Here we present evidence for another non-random structural pattern in assemblages of fish ectoparasites, anti-nestedness, which corresponds to situations in which parasite species are always absent from infracommunities richer than the most depauperate one in which they occur. We show that this pattern is exactly as common as nestedness, and that anti-nested assemblages are characterised by significantly lower prevalence and mean intensities of parasites than nested assemblages. In addition, we found a positive relationship between the prevalence and the mean intensity of parasites across the different assemblages. We propose a link between the nestedness/anti-nestedness continuum and the prevalence-intensity relationship that may involve colonisation-extinction processes. The results presented here suggest that, although nestedness may not be common in parasite communities, other departures from random species assembly are possible, and that some form of structure may be present in many communities. The continuum between nestedness and anti-nestedness also has implications for recent models of species coexistence in communities.     

A functional classification for analysis of the structure of dung beetle assemblages

Abstract. 1. Regional scarabaeid dung beetle assemblages in southern Africa may contain over 100 species, ranging in live weight from 10 mg to 10 g. These show a wide variety of dung-use and reproductive strategies.
2. To facilitate analysis of these diverse assemblages, a system of classification analogous to guilds is proposed. Scarabaeid dung beetle species are allocated to one of seven functional groups (FGs) according to the way they use and disrupt dung. Each group therefore contains a set of species which are functional analogues of each other. This classification provides a conceptual framework within which to analyse the structure of dung beetle assemblages and the interactions between dung beetles and other dung-breeding species such as coprophagous flies.
3. There is a clear hierarchy of functional groups in their ability to compete for dung. Competitively dominant groups such as the large ball rollers (FG I) and fast-burying tunnellers (FG III) are mostly large, aggressive beetles which rapidly remove dung from the pad. The smaller ball rollers (FG II) are also effective competitors for dung. Subordinate groups are those which bury dung slowly over many days (FG IV and V) and those which breed inside the pad (FG VII, endocoprids). Kleptocoprids (FG VI) breed in dung buried by other beetles and so are not part of the hierarchy.
4. The use of this classification is illustrated by reference to three contrasting assemblages of dung beetles in a summer rainfall region of southern Africa. The potential of these beetles for biological control of dung-breeding flies is discussed.     

Early Cretaceous rhynchonellids of Dagestan: System, morphology, stratigraphic and paleobiogeographic significance

A comprehensive report on Early Cretaceous Dagestan rhynchonellids is provided for the first time. It includes the rhynchonellid system based on detail morphofunctional studies, recognition of the boundary in the evolutionary development of Late Mesozoic rhynchonelloids at the Barremian-Aptian boundary, analysis of changes in shell matter structure during successive time periods of the Early Cretaceous, elucidation of stratigraphic importance of species assemblages allocated stratigraphically by layers to six sections of the Lower Cretaceous deposits described by the author, and revelation of possibilities of using this group in paleobiogeographic reconstructions. The study describes 37 species, 7 genera, and 2 families; 16 species and 2 genera are new. This paper is useful for a wide range of paleontologists, experts on the Mesozoic fauna, biostratigraphers, and geologists dealing with Mesozoic deposits. The study provides 8 plates, 58 figures, 71 references.     

Spread of introduced Caulerpa species in macroalgal habitats

A short-term field experiment was designed to identify layers of Mediterranean macroalgal assemblage conducive to successful spread of two introduced Caulerpa species (Bryopsidales, Chlorophyta). By manipulation of species presence, three experimental assemblages were obtained: (1) encrusting algae, having removed the turf and erect species; (2) encrusting and turfing algae, having removed erect species; (3) encrusting, turfing and erect algae, that is, unmanipulated assemblages, which served as a control. Fragments of the two introduced species Caulerpa taxifolia (Vahl) C. Agardh and Caulerpa racemosa (Forsskål) J. Agardh were transplanted in each of the three assemblages. Width of the colony, blade density and percentage of the substratum covered by the two species were measured.

The susceptibility of the indigenous community to the spread of Caulerpa species was related to type of assemblage. Blade density and amount of substratum covered by the two Caulerpa species were different between species and generally greater for C. taxifolia than for C. racemosa. Overall, the spread of these species was strongly dependent on the type but not directly on the complexity of the assemblage. Turf was more favourable than encrusting species alone, while the least advantageous habitat was where the macroalgal assemblage is composed of encrusting, turf and erect species. In other words, increased number of species in the assemblage reduces invasion of the Caulerpa species but the type of algae in the assemblage is likely to be more important than number of species. The presence of turf promotes the spread of Caulerpa species.     

Microfungi associated with Abies needles and Betula leaf litter in a subalpine coniferous forest

We investigated microfungal assemblages on leaf litter within a subalpine forest in central Japan and their variation with season, litter depth, and litter species. Microfungal assemblages were compared for Abies needles and Betula leaf litter collected from litter and fermentation layers of the forest floor during the growing season in spring, summer, and autumn. A total of 35 and 42 species were isolated from Abies needles and Betula leaf litter, respectively. The observed variation in microfungal assemblages was primarily attributable to seasonal differences. The frequencies of Trichoderma viride, Volutella ciliata, Mucor sp., and Umbelopsis ramanniana increased in summer, leading to a high degree of similarity of microfungal assemblages in different litter depths and litter species. Microfungal assemblages on Abies needles in spring and autumn and those on Betula leaves in spring were characterized by Trichoderma viride, V. ciliata, Thysanophora penicillioides, Trichoderma polysporum, and (or) Mortierella alpina. Microfungal assemblages on Betula leaves in autumn were characterized by the absence of these species and the occurrence of Cladosporium cladosporioides. The results were discussed with an emphasis on the role of microfungi in decomposition processes and the impact on fungi of predicted future increases in global temperature.     

Alvinellids and Sulfides at Hydrothermal Vents of the Eastern Pacific: A Review

SYNOPSIS. At Eastern Pacific hydrothermal vents, alvinellidpolychaetes are among the first metazoans to colonize newlyformed surfaces of sulfide chimneys. In this environment ofrapid mineral precipitation, alvinellids are confronted by steepphysico-chemical gradients and high temporalvariability. Thispaper examines the interaction of alvinellids with chimney mineralizationprocesses and then reviews what is known of mechanisms thatcould enable these worms to deal with potentially toxic levelsof sulfide in their environment. Studies of sulfide chimneysconsistently show mineralogy to be locally modified around alvinellidtubes. This may be linked to sulfide oxidation products thataccumulate in tube material or to the circulation of seawaterthrough the tube. At high worm densities, these local effectsmay have a significant influence on larger scale sulfide accretionprocesses that determine chimney morphology. Alvinellid polychaetesmay have several lines of defense against sulfide. Tubes andmucous layers could act as passive barriers to reduce inwarddiffusion of sulfide across posterior surfaces. Colonizationof epidermal and tube surfaces by bacteria that might be sulfideoxidizing, could create an active external barrier in some species.Sulfide oxidation by tissue homogenates has been demonstratedin two Paralvinella species, where it may serve to protect oxidativerespiration from sulfide entering worm tissues. Sulfide bindingin blood has not been studied in any of the alvinellids.     

Hypogaeic pitfall traps: methodological advances and remarks to improve the sampling of a hidden ant fauna

Ant assemblages present a great vertical stratification, with microhabitats showing strong differences in relation to species composition. Among the microhabitats, the hypogaeic has been poorly studied. Hypogaeic or subterranean ants live in the deeper soil layers, which make the sampling logistics and operability a difficult work. The fact that the hypogaeic ant fauna is diversified and abundant, with low similarity to ant assemblages in other microhabitats, has promoted the development of several collecting techniques to sample this hidden ant fauna. Here, we verify the ability of hypogaeic pitfall traps to sample subterranean ants. In addition, we propose methodological advances and remarks about the use of this ant sampling technique.     

Vertical distribution of protozoan and microcopepod communities in the South Adriatic Pit

The qualitative composition, numerical abundance and verticaldistribution of radiolarians, tintinnines, nauplii and smallcopepod assemblages were studied in the central area of theSouthern Adriatic Pit at three stations during 10 cruises fromOctober 1985 to May 1990. The samples were collected with aplankton net of 53 µm mesh size equipped with a closingsystem in eight vertical layers. Data are presented for 53 radiolarians,61tintinnines and for the first time for 22 poecilostomatoidspecies in the Adriatic Sea. According to the numerical abundanceof assemblages and the frequency of occurrence of the bulk ofthe individual species population in the water column, fourcommunities could be defined: the surface (0–50 m), thesubsurface (50–100m), the midwater (100–600 m) andthe deep-sea community (below 600 m). The euphotic layer wascharacterized by tintinnines, copepod nauplii, cyclopoids andjuvenile calanoid copepods, while radiolarians and poecilostomatoidcopepods dominated in the deeper layers. The highest numericaldifferences between stations and seasons were noted only onthe surface. Towards the deeper layers, the differences wereconstantly smaller, and below400 m there was a uniform distributionof all assemblages. This research, on the basis of the numericalabundance of protozoans and micrometazoans, shows that the centralpart of the South Adriatic Pit is considerably richer than mentionedby earlier authors.     

Grassland invertebrate assemblages in managed landscapes: Effect of host plant and microhabitat architecture

Abstract Grasslands are often considered as two‐dimensional habitats rather than complex, multilayered habitats. However, native grasslands are complex habitats, with multiple layers of annual and perennial grasses, sedges, shrubs and mosses. Vegetation complexity, including plant type, quality and three‐dimensional structure is important for providing a variety of food and habitat resources for insects. Grazing by domestic livestock can affect these processes through the loss or fragmentation of habitats, as well as altering the vertical and horizontal vegetation structure. This study aimed to investigate the role of host plants and microhabitat architecture for determining foliage invertebrate assemblages. Different plant species supported distinct invertebrate assemblages and less complex host plants supported fewer invertebrate individuals and species. Manipulations of plant architecture changed the species composition of invertebrates, with most species found in more complex vegetation. This study illustrates the importance of host diversity and pasture complexity for invertebrate communities. Management practices that encourage a heterogeneous environment with diverse and structurally complex pastures should also sustain a more diverse and functional invertebrate assemblage.     

Taxonomic homogenization and differentiation across Southern Ocean Islands differ among insects and vascular plants

Aim To investigate taxonomic homogenization and/or differentiation of insect and vascular plant assemblages across the Southern Ocean Islands (SOI), and how they differ with changing spatial extent and taxonomic resolution. Location Twenty‐two islands located across the Southern Ocean, further subdivided into five island biogeographical provinces. These islands are used because comprehensive data on both indigenous and non‐indigenous insect and plant species are available. Methods An existing database was updated, using newly published species records, identifying the indigenous and non‐indigenous insect and vascular plant species recorded for each island. Homogenization and differentiation were measured using Jaccard’s index (JI) of similarity for assemblages across all islands on a pairwise basis, and for island pairs within each of the biogeographical provinces. The effects of taxonomic resolution (species, genus, family) and distance on levels of homogenization or differentiation were examined. To explore further the patterns of similarity among islands for each of the taxa and groupings (indigenous and non‐indigenous), islands were clustered based on JI similarity matrices and using group averaging. Results Across the SOI, insect assemblages have become homogenized (0.7% increase in similarity at species level) while plant assemblages have become differentiated at genus and species levels. Homogenization was recorded only when pairwise distances among islands exceeded 3000 km for insect assemblages, but distances had to exceed 10,000 km for plant assemblages. Widely distributed non‐indigenous plant species tend to have wider distributions across the SOI than do their insect counterparts, and this is also true of the indigenous species. Main conclusions Insect assemblages across the SOI have become homogenized as a consequence of the establishment of non‐indigenous species, while plant assemblages have become more differentiated. The likely reason is that indigenous plant assemblages are more similar across the SOI than are insect assemblages, which show greater regionalization. Thus, although a suite of widespread, typically European, weedy, non‐indigenous plant species has established on many islands, the outcome has largely been differentiation. Because further introductions of insects and vascular plants are probable as climates warm across the region, the patterns documented here are likely to change through time.     

Benthic foraminiferal fauna during the time of the Indian-Asian contact, in southern Balochistan, Pakistan

Cretaceous and early Paleocene benthic foraminifera were studied from one section along the western Gaj River, southern Balochistan, Pakistan, to reconstruct the paleoenvironment of the Tethys Sea during the Indian-Asian contact. We recognize three lithostratigraphic units in ascending order: the Mughal Kot Formation, the Pab Sandstone, and the Jamburo Group. Both the Maastrichtian Mughal Kot Formation, which consists of shale with grey marly limestone, and the Maastrichtian Pab Sandstone, which consists of quartzose sandstone, indicate an open ocean environment as they have diversified planktic and benthic foraminiferal assemblages. The Maastrichtian-Paleocene Jamburo Group, consisting of dark grey, calcareous shale and marlstone with some sulfide grains, is characterized by low diversities of benthic assemblages. The change to the lower diversities may be associated with the development of poor circulation of deeper water that was caused by narrowing of the Tethys Sea.The Trochammina spp. Assemblage from the Jamburo Group, which can be correlated with flysch-type agglutinated foraminiferal assemblages, has a low benthic species diversity, indicating an unfavorable condition for calcareous foraminifera because of the development of oxygen-depleted water. The absolute abundance of agglutinated specimens shows a remarkable change from low numbers in the Maastrichtian to high ones in the Paleocene. The benthic foraminiferal evidence supports the hypothesis that the collision of the Asian and Indian plates occurred near the end of the Cretaceous.