Global diversity patterns of larger benthic foraminifera under future climate change

Global warming threatens the viability of tropical coral reefs and associated marine calcifiers, including symbiont-bearing larger benthic foraminifera (LBF). The impacts of current climate change on LBF are debated because they were particularly diverse and abundant during past warm periods. Studies on the responses of selected LBF species to changing environmental conditions reveal varying results. Based on a comprehensive review of the scientific literature on LBF species occurrences, we applied species distribution modeling using Maxent to estimate present-day and future species richness patterns on a global scale for the time periods 2040–2050 and 2090–2100. For our future projections, we focus on Representative Concentration Pathway 6.0 from the Intergovernmental Panel on Climate Change, which projects mean surface temperature changes of +2.2°C by the year 2100. Our results suggest that species richness in the Central Indo-Pacific is two to three times higher than in the Bahamian ecoregion, which we have identified as the present-day center of LBF diversity in the Atlantic. Our future predictions project a dramatic temperature-driven decline in low-latitude species richness and an increasing widening bimodal latitudinal pattern of species diversity. While the central Indo-Pacific, now the stronghold of LBF diversity, is expected to be most pushed outside of the currently realized niches of most species, refugia may be largely preserved in the Atlantic. LBF species will face large-scale non-analogous climatic conditions compared to currently realized climate space in the near future, as reflected in the extensive areas of extrapolation, particularly in the Indo-Pacific. Our study supports hypotheses that species richness and biogeographic patterns of LBF will fundamentally change under future climate conditions, possibly initiating a faunal turnover by the late 21st century.     

Vascular plant species count in a wet forest in the Chocó area on the Pacific coast of Colombia

The total number of vascular plant species was counted and growth form distribution was studied in the Chocó area on the Pacific coast of Colombia, in two transects 400×10m and ten transects 2×50m, for a total sampled area of 0.9ha. The species count of the ten transects (442 species in 0.1ha) appears to be the highest number of species recorded with this methodology. There were 970 species for the total area (0.9ha). Ninety to ninety-five percent of the species were under 10cm dbh and 70–86% under 2.5cm dbh, epiphytes and small trees and treelets 10cm dbh being the most diverse growth forms. The most species-rich families and genera were those represented by herbaceous plants and treelets. Individuals were counted only in the ten 2 × 50 m transects (0.1 ha), where 4459 individuals were found. Palms and ferns were the most abundant growth forms. Arguments are presented against the way diversity is usually measured. Recommendations are made to include other growth forms besides trees when assessing alpha diversity for conservation purposes.     

Assessing the Sulfide Footprint of Mussel Farms with Sediment Profile Imagery: A New Zealand Trial

Growing numbers and increased stocking of marine mussel farms make reliable techniques for environmental effect assessment a priority. Previously, we showed how the color intensity of soft sediment could be used to estimate its acid volatile sulfide (AVS) content, a product of the anaerobic microbial degradation of organic matter deposits. We then proposed to include assessments of the AVS farm footprint in marine farm monitoring, in particular, to investigate temporal changes in the extent of the seafloor area of elevated sediment AVS content. Such assessment requires accurate detection of the AVS footprint boundary. Here, we demonstrate how to detect this boundary with analyses of sediment color intensity. We analyzed 182 sediment profile images taken along three transects leading from approximately 50 m inside to 200 m outside a long-line mussel farm in New Zealand and found that the mean sediment color intensity inside the farm boundary was almost one third lower than that of the sediment distant from the farm. Segmented regression analysis of the combined color intensity data revealed a breakpoint in the trend of increasing grey values with increasing distance from the farm at 56 ± 13 m (± 95% confidence interval of the breakpoint) outside the mussel farm. Statistical analyses indicated that the extent of the color intensity footprint was a function of water column depth, as was shown visually using mapping methods; organic particles disperse further in a deeper seawater column. We conclude that for soft coastal sediments, our sampling and data analysis techniques may provide a rapid and reliable supplement to existing benthic surveys that assess environmental effects of mussel farms.     

Habitat variables determining the occurrence of large benthic foraminifera in the Berau area (East Kalimantan, Indonesia)

Knowledge of the assemblage composition of large benthic foraminifera (LBF) in relation to environmental conditions is needed to interpret fossil records. In this study the assemblage composition of LBF is described for a carbonate shelf with a barrier reef system and some reefs outside the barrier. In a total of 140 samples, 34–35 species of LBF were found. Four clusters, roughly corresponding to substrate type were identified. Several small groups of samples were recognized that were collected locally inside, on, or outside the barrier. Microscale environmental gradients within the substrate or in the benthic boundary layer resulted in spatial differentiation of the microhabitat of each species.     

A particular case and a general pattern: hyperaggressive behaviour by one species may mediate avifaunal decreases in fragmented Australian forests

We quantitatively assessed edge effects associated with elevated abundance of a hyper aggressive bird species, the noisy miner Manorina melanocephala, in fragmented eucalypt forest adjoining developed land. Long‐term data from Toohey Forest, subtropical Australia, show that noisy miner colonies intensively occupy a zone of 20 m from the forest edge, with frequent use occurring up to 100 m from the edge, but little beyond 200 m. Within noisy miner colonies, the abundance and species richness of other birds were both about half those recorded at nearby transects which were outside the colonies' main activity area. Bird species smaller than noisy miners, which are also those with similar diets, were collectively 20–25 times more abundant, and their species richness tenfold greater, outside miner colonies than within them, whereas larger species, which have less dietary overlap, did not differ. Exclusion of small insectivorous birds has been hypothesised to cause elevated insect herbivore density, but we found no difference between tree crown defoliation or dieback rates within versus outside miner colonies. Aggression by noisy miners can be viewed as a mechanism of interspecific competition, since miners have a relatively large body size for their diet and are hence able to exclude virtually all potential competitors at relatively little cost. We examine evidence indicating that reduced bird diversity in eucalypt forest fragments of eastern Australia is often simply the effect of noisy miner occupancy of edges, acting directly on the densities of other species through their aggressive behaviour. With an edge effect 200 m deep, a remnant 10 ha in size is likely to become entirely occupied by noisy miners, and this is a size threshold that has been commonly reported in association with area‐standardised avian diversity reductions. Convergent patterns of species loss from small forest fragments in different continents are the result of different underlying ecological processes.     

The effect of salmon farming on the benthos of a Scottish sea loch

The effects of waste from a salmon farm on the benthos of a fjordic sea loch on the western coast of Scotland have been studied. Within 3 m of the floating cages the sediment was highly reducing, and dissolved oxygen content of the water overlying the sediment ranged from 35 to 75% saturation. At ⩾ 15 m from the cages the sediment was oxygenated, and the dissolved oxygen content of the water overlying the sediment was 50–85% saturation. Sedimentary redox potential and dissolved oxygen content of bottom water showed a seasonal variation. The benthic fauna showed marked changes in species number, species diversity, faunal abundance, and biomass in the region of the fish farm, with four zones of effect identified. Directly beneath, and up to the edge of the cages, there was an azoic zone. A highly enriched zone, dominated byCapitella capitata (Fabricius) andScolelepis fuliginosa (Claparède), occurred from the edge of the cages out to as 8 m. A slightly enriched ″transitional ″ zone occurred at ⩽ 25 m, and a “clean” zone at distances > 25 m. This study showed that salmon farming had similar effects on the benthos as other forms of organic enrichment, but the effects were limited to a small area in the immediate vicinity of the cages     

The Early Pliocene re-colonisation of the deep Mediterranean Sea by benthic foraminifera and their pulsed Late Pliocene–Middle Pleistocene decline

Ninety-five species and 19 genera of cosmopolitan, deep-sea benthic foraminifera belonging to the families Pleurostomellidae, Stilostomellidae and Nodosariidae, became extinct during the Late Pliocene–Middle Pleistocene. Only 50% of these (44 species) were present in the Pliocene or Pleistocene of the deep Mediterranean Sea (ODP Sites 654, 966, 967, 975, 976), being those which had successfully migrated in via the Strait of Gibraltar from the deep Atlantic following the annihilation of the Mediterranean deep-sea fauna during the Late Miocene Messinian Crisis. Most colonisation occurred within the first 0.8 myrs (5.3–4.5 Ma) after re-establishment of the Mediterranean–Atlantic link, with possibly a second lesser period of immigration in the Late Pliocene (3.4–3.0 Ma). We infer that colonisations may have been fortuitous and few in number, as some common members of the group in the Atlantic never succeeded in establishing in the Mediterranean Sea. There is no evidence of any new immigration events during the Pleistocene, implying that the present anti-estuarine circulation may have been in place throughout this period. Our studies suggest that these deep-water, low-oxygen-tolerant foraminifera survived the many periods of deep-water sapropel formation in the Pliocene–Early Pleistocene, possibly in somewhat shallower (~ 500 m) refuges with dysoxic, rather than anoxic conditions.The Pliocene–Pleistocene stratigraphic record of this group of elongate, cylindrical benthic foraminifera with constricted and specialised apertures is similar in the west and east Mediterranean basins. The group declined in abundance (flux) and diversity in two pulses, during the Late Pliocene (3.1–2.7 Ma) and the late Early Pleistocene (1.3–1.0 Ma) in concert with global, southern-sourced, deep-water sites (AABW, CPDW) and earlier than the single decline (1.0–0.6 Ma) in global, intermediate water sites (uNADW, AAIW). All species, with one possible exception, disappeared earlier in the Mediterranean than globally. The highest occurrence of any species of this group in Mediterranean sites was 0.8–0.43 Ma, comparable with 0.7–0.2 Ma outside with the youngest survivors being in abyssal, deep-water.Thus, despite the unusual oceanographic conditions and isolation, the deep Mediterranean Sea was in this case neither the centre for the evolution of new species nor a refuge where species survived after they had disappeared elsewhere.     

Aspects of the population ecology of Lucinomaborealis (L.) (Bivalvia) in Raunefjorden,Western Norway

2194 Lucinoma borealis (L.) were obtained from 99 quantitative (0.2 m²) samples of substratum (stratified random sampling) collected between November 1975 and October 1976 in the archipelago of Eggholmane ≈20 km south of Bergen. The depth range of the 20900 m² area was 0.3–13.3 m, and the bottom sediment (fine to very coarse sand) was rich in calcium carbonate. The highest density was found in the deep (≈ 8–13 m) sub-areas, with fine sediment (median grain-size diameter ≈ 0.3–0.5 mm). L. borealis was the most abundant bivalve species in the area studied (59.6%, by number). The average density was 22.2 (C.I. ± 5.4) ind. · 0.2 m ^?2, and the biomass was 690 (C.I. ± 116) mg AFDW · 0.2 m ^?2. The average size of animals found in shallow water (coarse sediment), with low abundance, was markedly larger than that of those from deeper water. Adults from shallow water consisted of 49.5% females, but in deep water the corresponding figure was only 38.6%.According to the data, spawning in deep water occurred in June, August–September, and possibly also in January–February. The spawning period in shallow water was more diffuse and uncertain. The egg diameter of 123.75 (C.I. ± 1.59) μm, indicates a lecithotrophic development. Maturation occurred at a shell length of 10–13 mm, and the largest animal found was 34.3mm long. The shell of L. borealis grows allometrically.     

Effects of a marine protected area on fish assemblage associated with Posidonia oceanica seagrass beds: temporal and depth variations

This study describes the changes in the structure of the fish assemblage associated with Posidonia oceanica meadows after the establishment of a marine protected area. The survey of the ichthyofauna in the Marine Reserve of Tabarca Island was carried out by visual censuses with SCUBA. Inside and outside the reserve was sampled six times at random from summer 1997 to summer 1999 and in three different depths (1, 5 and 15 m) by applying transects of 150 × 5 m over the P. oceanica meadows. The data were analyzed with multivariant methodologies and with analysis of variance. The most represented families in number of species were the sparids and labrids. Mean abundance, biomass and number of species were higher inside the reserve in all studied periods. Inside the marine protected area, these variables decreased as depth increased; outside the protected area the pattern was the opposite, reaching the maximum at 15 m.     

Coral habitat in the Aleutian Islands of Alaska: depth distribution, fine-scale species associations, and fisheries interactions

The first in situ exploration of Aleutian Island coral habitat was completed in 2002 to determine the distribution of corals, to examine fine-scale associations between targeted fish species and corals, and to investigate the interaction between the areas’ diverse fisheries and coral habitat. Corals, mostly gorgonians and hydrocorals, were present on all 25 seafloor transects and at depths between 27 and 363 m, but were most abundant between 100 and 200 m depth. Mean coral abundance (1.23 colonies m⁻²) far exceeded that reported for other high-latitude ecosystems and high-density coral gardens (3.85 colonies m⁻²) were observed at seven locations. Slope and offshore pinnacle habitats characterized by exposed bedrock, boulders, and cobbles generally supported the highest abundances of coral and fish. Overall, 85% of the economically important fish species observed on transects were associated with corals and other emergent epifauna. Disturbance to the seafloor from bottom-contact fishing gear was evident on 88% of the transects, and approximately 39% of the total area of the seafloor observed had been disturbed. Since cold-water corals appear to be a ubiquitous feature of seafloor habitats in the Aleutian Islands, fisheries managers face clear challenges integrating coral conservation into an ecosystem approach to fisheries management.     

Comparison of survey methods for wintering grassland birds

ABSTRACT Although investigators have evaluated the efficacy of survey methods for assessing densities of breeding birds, few comparisons have been made of survey methods for wintering birds, especially in grasslands. In winter, social behavior and spatial distributions often differ from those in the breeding season. We evaluated the degree of correspondence between density estimates based on different survey methods. Surveys were conducted during two winters (2001–2002 and 2002–2003) on 16 grassland sites in southwestern Oklahoma. Line‐transect (using a detection function to account for birds present but not detected) and area‐search (where density was based on the total count within a given area) methods were employed. Observations on line transects were also analyzed as strip transects, where density was based on total count within a given strip width and no detection function was used. Savannah Sparrows (Passerculus sandwichensis), LeConte's Sparrows (Ammodramus leconteii), Song Sparrows (Melospiza melodia), Smith's Longspurs (Calcarius pictus), Chestnut‐collared Longspurs (C. ornatus), and Eastern Meadowlarks (Sturnella magna) were sufficiently abundant to allow comparison. Area‐search density estimates tended to be higher than line‐transect estimates for Savannah Sparrows, Song Sparrows, and Eastern Meadowlarks, suggesting that some individuals initially located close to the transect line were not detected on line transects. The area‐search and line‐transect methods gave similar density estimates for Chestnut‐collared and Smith's longspurs. Area‐search estimates of Eastern Meadowlarks were significantly higher in the second year of the study only. For this species, area‐search estimates did not differ from those of strip transects covering an equal area, so the reason for the differing meadowlark estimates is not clear. Higher density estimates using the area‐search method likely resulted from: (1) birds that might escape detection by hiding were more likely detected (flushed) during area searches because of the repeated passes through the area, and (2) birds close to the line in line transects escape detection by hiding, biasing those estimates low. We also evaluated the correspondence of density rankings for the six species as determined by the different survey methods and for the same species across survey sites. Correlations among the six species of the area‐search results with those of line transects and strip transects generally were high, increasing in 2002–2003 when densities of birds were greater. All three methods provided similar density rankings among species. Density rankings within species across sites for the four non‐longspur species generally were concordant for the three methods, suggesting that any of them will adequately reflect among‐site differences, especially when densities vary greatly across sites. Further research is needed to determine the extent to which grassland birds are missed on line transects. We suggest that workers using line transects to study these species give careful consideration and make additional efforts to satisfy the distance‐sampling assumption that all birds on or near the line are detected. If density is measured as a total count in a fixed area, we recommend that observers pass within <10 m of all points in the area.     

Determining Methods of Underwater Visual Census for Estimating the Abundance of Coral Reef Fishes

We aimed to determine optimal methods of underwater visual census (UVC) for estimating the abundance of coral reef fishes exploited by fisheries in the tropical Pacific. Two main methods were tested using SCUBA: strip transect and stationary point counts. We assessed their relative accuracy, precision, power and efficiency (cost), and compared different census area dimensions, observer swimming speeds, and number of replicates. Twenty-five comparisons of the two UVC methods were conducted for 73 species from five families of coral reef fishes, on reefs in Australia and Fiji. Species were grouped within families based on their mobility. Few significant differences were found, either among or between strip transects and stationary point counts. The data were characterised by high variability, low precision and low power. A trend for greater accuracy in density estimates of small sedentary species with smaller census area was apparent, which probably reflects searching efficiency. Only one species group, the sedentary Acanthuridae showed differences between transects and point counts. Higher, hence presumably more accurate, density estimates were obtained with 50m×5m transects. Notably, point counts could be deployed in 70% of the time of transects. A bootstrapping procedure demonstrated a consistent improvement in precision of density estimates with increasing number of replicates, but no appreciable change in precision was found beyond 10 to 15 replicates, in all species groups and for both transects and point counts. Consequently, and because of the high variability inherent in fish density estimates, we recommend that at least 10 replicates be used to quantify the species considered here. The power calculations showed that only large differences in density will be detected with the replication levels typical of UVC surveys. Power was greatest for the roving serranids, with a decrease in density of about 50% detectable for this species group. We discuss the importance of carefully defining the behavioural attributes of species prior to selecting a UVC method. A method of temporal stratification in a count is described for censusing a range of species of varying mobilities. We suggest that fish mobility and search efficiency are key factors in optimising UVC methods.     

Recovery of Benthic Megafauna from Anthropogenic Disturbance at a Hydrocarbon Drilling Well (380 m Depth in the Norwegian Sea)

Recovery from disturbance in deep water is poorly understood, but as anthropogenic impacts increase in deeper water it is important to quantify the process. Exploratory hydrocarbon drilling causes physical disturbance, smothering the seabed near the well. Video transects obtained by remotely operated vehicles were used to assess the change in invertebrate megafaunal density and diversity caused by drilling a well at 380 m depth in the Norwegian Sea in 2006. Transects were carried out one day before drilling commenced and 27 days, 76 days, and three years later. A background survey, further from the well, was also carried out in 2009. Porifera (45% of observations) and Cnidaria (40%) dominated the megafauna. Porifera accounted for 94% of hard-substratum organisms and cnidarians (Pennatulacea) dominated on the soft sediment (78%). Twenty seven and 76 days after drilling commenced, drill cuttings were visible, extending over 100 m from the well. In this area there were low invertebrate megafaunal densities (0.08 and 0.10 individuals m⁻²) in comparison to pre-drill conditions (0.21 individuals m⁻²). Three years later the visible extent of the cuttings had reduced, reaching 60 m from the well. Within this area the megafaunal density (0.05 individuals m⁻²) was lower than pre-drill and reference transects (0.23 individuals m⁻²). There was a significant increase in total megafaunal invertebrate densities with both distance from drilling and time since drilling although no significant interaction. Beyond the visible disturbance there were similar megafaunal densities (0.14 individuals m⁻²) to pre-drilling and background surveys. Species richness, Shannon-Weiner diversity and multivariate techniques showed similar patterns to density. At this site the effects of exploratory drilling on megafaunal invertebrate density and diversity seem confined to the extent of the visible cuttings pile. However, elevated Barium concentration and reduced sediment grain size suggest persistence of disturbance for three years, with unclear consequences for other components of the benthic fauna.     

Fern richness,tree species surrogacy,and fragment complementarity in a Mexican tropical montane cloud forest

We related pteridophytes versus tree species composition to identify surrogate measures of diversity, and complementarity of seven cloud forest fragments. Forest structure, and fern and tree composition were determined in 70 (2 × 50 m) transects. Fern density (10,150–25,080 individuals/ha) differed among sites. We recorded 83 fern species in the transects. Nonparametric richness estimators indicated that more sampling effort was needed to complete fern inventories (14 more species). However, ferns recorded outside of the transects increased richness to 103 species (six more species than predicted). Twenty-eight species were unique and rare due to special habitat requirements (Diplazium expansum, Hymenophyllum hirsutum, Melpomene leptostoma, Terpsichore asplenifolia), or were at a geographical distribution edge (Diplazium plantaginifolium, Lycopodium thyoides, Pecluma consimilis, Polypodium puberulum). Correlations between fern richness and tree richness and density were not significant, but were significant between fern richness and fern density, between epiphytic fern density and tree richness and density. Tree richness is not a good surrogate for fern diversity. Only three species were recorded in all fragments (Polypodium lepidotrichum, P. longepinnulatum, P. plebeium); thus fragments pteridophytes compositions are highly complementary, but more similar for ferns than for trees. A regional conservation approach which includes many small reserves needs to focus supplementarity on patterns of tree and fern species richness.     

Distribution and Diversity of Pteridophytes and Melastomataceae along Edaphic Gradients in Yasuní National Park, Ecuadorian Amazonia1

We documented the floristic composition of pteridophytes (ferns and fern allies) and Melastomataceae in Yasuní National Park, Amazonian Ecuador. Our main questions were: (1) Are the density of individuals, species richness, and/or species diversity (measured with Shannon's H′) of the two plant groups related to edaphic differences? and (2) How many of the pteridophyte and Melastomataceae species are non–randomly distributed in relation to a soil base content gradient within terra firme (non–inundated forest). To answer these questions, we sampled 27 line transects of 500 × 5 m distributed in an area of ca 20 × 25 km. The study area included a permanent 50 ha plot established to monitor forest dynamics; thus, our results also provide information on landscape–scale floristic variability to which results from within the plot can be compared. A total of 45,608 individuals and 140 species of pteridophytes, and 4893 individuals and 89 species of the Melastomataceae, were counted in the transects. Both with pteridophytes and with Melastomataceae, a clear negative correlation was found between the amount of extractable bases in the soil and the number of plant individuals encountered in a transect. With Melastomataceae, species richness and species diversity also were negatively correlated with soil base content, but with pteridophytes they were not. More than 50 percent of the common species of both pteridophytes and Melastomataceae were nonrandomly distributed along the soil cation content gradient within terra firme. We conclude that while the species richness patterns observed in one plant group are not indicative of similar patterns in other plant groups, it seems likely that a substantial (but unknown) proportion of species belonging to other plant groups will be found to show distribution patterns that reflect edaphic preferences within terra firme forests.     

Macrobenthic species composition and diversity in the Godthaabsfjord system, SW Greenland

The southwest Greenland coast is made up of large and deep sill fjords. On the shelf, a number of shallow banks separated by deep troughs are located 20–50 km from the coast. We collected three 0.1-m² van Veen grabs at nine stations along a transect spanning from the inner Godthaabsfjord influenced by glaciers, across the shallow Fyllas Bank and out to the slope of the continental shelf at approximately 1,000 m depth. Along this transect, we explored patterns of macrobenthic diversity, species composition, abundance and biomass. The sampled stations were very different in terms of environmental variables, resulting in large differences in species composition primarily related to differences in depth, silt–clay fraction and chl a content of the sediment (BIO-ENV analysis). Habitat differences also reduced species spatial ranges and the majority of species were found at only one (49%) or two (20%) stations and, consequently, species turnover or beta diversity was high and correlated to differences in depth, silt–clay fraction and median sediment grain size. Species richness and diversity were lowest in sites exposed to sediment disturbance: near the glaciers in the inner fjord (physical disturbance by mineral sedimentation) and at selected stations on the shelf (bioturbation by burrowing sand eel). Alpha diversity and richness were only weakly correlated to environmental parameters, indicating that alpha richness and diversity are influenced by several factors or that relationships are non-linear as was found for species richness and silt–clay fraction.     

The ecology of very small-seeded shade-tolerant trees and shrubs in lowland rain forest in Singapore

A study was made in Bukit Timah Nature Reserve of niche differentiation among 11 woody species that have very small seeds (22–460 µg) and establish in deep shade, i.e., where the indirect site factor (isf) under cloudy conditions is 2%, and one taxonomically related light-demander (seed mass 33 µg). Comparative observations were made on changing light requirement with age. The species varied from shrubs and treelets (Urophyllum) via small to medium-height trees (Ficus, Pternandra) to tall trees (Gynotroches and Pellacalyx). In general, the shorter species fruited in deep shade while the taller needed direct irradiance. All produced ripe fruit at least once a year.In 1–3% isf seedling mortality over 11 months was 24% for Urophyllum hirsutum and 57% for Pternandra echinata (two strongly shade-tolerant species); survivors produced appreciable new stem and leaf tissue. For two more light-demanding species (Ficus grossularioides and F. fistulosa) mean lamina area was much larger in small gaps (10% isf) than in the understorey (<3% isf), while for Urophyllum hirsutum it was much smaller. These three species showed the greatest difference in SLA. There were few significant intraspecific differences between gaps and understorey in concentrations of N, P or K. In a valley where there was no significant difference in isf between a path and adjacent understorey, seedlings of species with seeds <1 mg mean dry mass were five times as dense on transects along steep pathside banks as in the understorey 5 m upslope. The mean mid-bank slope was 66° (cf. 20° upslope). On mid-bank transects litter had a cover of 36% (cf. 95% upslope), and was thinner (0.8 vs 3.2 cm). The soil at 0–7 cm depth into the mid-bank had much lower concentrations of organic matter, total N and P (but not total K) and fine roots than that of upslope transects. All species were found to have vesicular-arbuscular mycorrhiza when 1–2 m tall in deep shade, several having very dense infections. Seedling form and responses are discussed in relation to potential adaptive value and possible evolutionary origin.     

互花米草入侵对大型底栖动物群落垂直结构的影响

2012年8月,在浙江省玉环县漩门湾国家湿地公园,利用自制分层采样器,以5 cm为单位对0—25 cm泥层进行分层取样,研究潮间带互花米草滩涂和自然滩涂两种生境中大型底栖动物的垂直分布情况,以及互花米草入侵对大型底栖动物垂直结构的影响。两种生境中共获得大型底栖动物40种,其中软体动物18种,甲壳动物13种,环节动物4种,其他类群5种。在自然滩涂生境中获得的物种数为30种,互花米草生境为31种,两种生境的共有种有21种。互花米草和自然滩涂生境平均栖息密度分别为222.6株/m2和1052.8株/m2。研究结果表明:(1)大型底栖动物主要栖息在0—10 cm泥层深度;(2)大型底栖动物群落沿泥层深度存在分层分布现象;(3)互花米草入侵缩短了底栖动物的垂直分布距离,但对其主要栖息深度影响不大;(4)互花米草入侵改变了原来生境特征,导致大型底栖动物的群落结构发生变化。     

Species-environment relationship in the herb-subshrub layer of a moist Savanna site, Federal District, Brazil.

The soils are seasonally or permanently saturated in the moist grassland savanna, locally known as Campo Limpo Umido. Soil moisture variation seems to determine spatial distribution of communities. The objective of this study is to analyse the relationship between environmental variables and the patterns of spatial distribution of species in the herbaceous-subshrub layer of an area of moist grassland at the Agua Limpa Farm, Brasília, DF (15 degrees 56' to 15 degrees 59' S and 47 degrees 55' to 47 degrees 58' W Gr.). An area of 400 x 400 m was divided into four sections of 200 x 200 m where four transects were randomly sampled. A line intercept method was adopted for the phytossociological study. Superficial soils samples (0-20 cm) were collected for chemical and textural analyses. Gravimetric soil moisture was measured quarterly during the study-year. A total of 85 species in 67 genera and 24 families were found. The diversity was high, Shannon's index, H', was 2.60 nats.cover(-1). Floristic composition of the transects in soils with a high gravimetric soil moisture and high content of organic matter and sand differed from those transects in soils with a lower gravimetric soil moisture indicating seasonal variation. A Canonical Correspondence Analysis (CCA) showed significant correlations between soil texture and soil moisture features and species distribution. Gravimetric soil moisture, organic matter, clay, silt and sand were significantly correlated to species distribution in the moist grassland determining mosaics in the vegetation.