The effects of macroalgal cover on the spatial distribution of macrobenthic invertebrates: the effect of macroalgal morphology

The growth of green macro-algae in response to nutrient inputs is a common phenomenon in marine estuaries and sheltered bays. While the ecological effects of the growth of the most commonly occurring macroalgal taxa (Enteromorpha, Chaetomorpha, Ulva, Cladophora) have been well studied, the effects of a morphologically very different species, Vaucheria subsimplex, have not been investigated. This study investigated the ecological effects of the establishment of V. subsimplex on a relatively exposed intertidal sandflat, Drum Sands, Firth of Forth, Scotland. Because of the spatially heterogeneous development of the weed, the short term (4 weeks) and long term (20 weeks) effects of the weed could be studied using a survey approach in which the weed-affected and weed-free plots were interspersed. After 4 weeks, V. subsimplex significantly increased the mean number of individuals and diversity of the macrofauna, eight of the ten most abundant species showed significant increases in abundance compared to weed-free areas. After 20 weeks, mean number of species and individuals were significantly higher under weed patches, while species diversity was reduced due to the numerical dominance of Pygospio elegans (Claparède). The weed, therefore, had an enriching effect on the macrofaunal communities on Drum Sands. The increased numbers of P. elegans, the numerical dominant infaunal species on Drum Sands, resulted mainly from enhanced larval recruitment to weed-affected areas. The effects of V. subsimplex on sediment characteristics were similar to those reported for other macroalgal taxa, i.e., increased water, organic and silt/clay contents, medium particle size and sorting coefficients, and reduced redox potentials. The results from this study are compared to those for other, morphologically different macroalgal species, with particular reference to an Enteromorpha-implanted experiment on the same sandflat. Since the general effect of such macroalgal taxa on macrofaunal communities is a detrimental one, the present study supports the contention that macroalgal morphology is an important feature in algal–faunal interactions.     

Biomass, species composition and diversity of epipelic algae in mire pools

The biomass, species composition and diversity of epipelic algae in two small pools of contrasting physicochemical characteristics in Miyatoko Mire were studied in 1992 (pool 3 =site B4 and pool 50 =site D2). A total of 93 species and 67 species of epipelic algae occurred at sites B4 and D2, respectively. Considerable differences were observed between the two sites in the seasonal fluctuations of species number, biomass and dominant species. At site B4, little changed with species number during April–August and markedly increased in October, while biomass was largest in April and gradually decreased during June–October. Diatoms and desmids occupied 33–82% and 15–63% of total algal biomass, respectively. At site D2, species number and biomass were small in April just after the snow-thaw, and increased in June and decreased in August and October. Diatoms occupied 90–98% of total algal biomass. The species diversity was always higher at site D2 than B4. As a result of analyses of water chemistry in the two pools, pool B4 can be recognized as a habitat experiencing high disturbance frequency. It is predicted that pools experiencing frequent disturbance will have less epipelic algal biomass and diversity.     

Effects of macroalgal species identity and richness on primary production in benthic marine communities

Plant biodiversity can enhance primary production in terrestrial ecosystems, but biodiversity effects are largely unstudied in the ocean. We conducted a series of field and mesocosm experiments to measure the relative effects of macroalgal identity and richness on primary productivity (net photosynthetic rate) and biomass accumulation in hard substratum subtidal communities in North Carolina, USA. Algal identity consistently and strongly affected production; species richness effects, although often significent, were subtle. Partitioning of the net biodiversity effect indicated that complementarity effects were always positive and species were usually more productive in mixtures than in monoculture. Surprisingly, slow growing species performed relatively better in the most diverse treatments than the most productive species, thus selection effects were consistently negative. Our results suggest that several basic mechanisms underlying terrestrial plant biodiversity effects also operate in algal-based marine ecosystems, and thus may be general.     

Epilithic and epipelic diatoms in the Sandusky River,with emphasis on species diversity and water pollution

Benthic diatom communities were collected seasonally from silty and rocky substrates to survey the water quality of the Sandusky River. Even though species composition was highly variable along the river, recurrent changes in relative abundance of specific diatom taxa and changes in overall community composition delineated areas where discharge of treated sewage affected water quality of the river. Changes in species diversity (Shannon formula), not decreases in diversity, marked the site where greatest pollution had occurred. Problems with using species diversity indices to indicate pollution tend to be related to predicting decreases in diversity in response to decreases in water quality. Evidence in the Sandusky River and the theories of diatom community dynamics suggest that species diversity can be greater in polluted areas than less polluted areas.     

The influence of arbuscular mycorrhizae on the relationship between plant diversity and productivity

Ecological theory predicts a positive and asymptotic relationship between plant diversity and ecosystem productivity based on the ability of more diverse plant communities to use limiting resources more fully. This is supported by recent empirical evidence. Additionally, in natural ecosystems, plant productivity is often a function of the presence and composition of mycorrhizal associations. Yet, the effect of mycorrhizal fungi on the relationship between plant diversity and productivity has not been investigated. We predict that in the presence of AMF, productivity will saturate at lower levels of species richness because AMF increase the ability of plant species to utilize nutrient resources. In this study we manipulated old-field plant species richness in the presence and absence of two species of AMF. We found that in the absence of AMF, the relationship between plant species richness and productivity is positive and linear. However, in the presence of AMF, the relationship is positive but asymptotic, even though the maximum plant biomass was significantly different between the two AMF treatments. This is consistent with the hypothesis that AMF increase the redundancy of plant species in the productivity of plant communities, and indicates that these symbionts must be considered in future investigations of plant biodiversity and ecosystem function.     

物种多样性与生态系统功能：影响机制及有关假说

本文主要介绍了有关物种多样性对生态系统功能的影响机制及有关假说,包括冗余种假说、铆钉假说、不确定假说、无效假说、补偿／关键种假说、非线性假说、单调／驼峰模型假说等。尽管这些假说的提出都有一定的理论或实验研究基础,但到目前为止,还没有一种假说被普遍认为反映了两者之间关系的实际情形（如果确实存在这样一种普适机制）。通过分析,我们发现在这些假说之间存在一定的内在联系,它们或者互相包含,或者互相补充,并且都可以归结到冗余种假说有关。     

Relative influence of bioturbation and predation on organic matter processing in river sediments: a microcosm experiment

1. Our objective was to measure the effects of bioturbation and predation on the physical characteristics and biogeochemical processes in river sediments. 2. We investigated the impacts of tubificid worms tested separately and together with an omnivore (Gammarus pulex), which does feed on tubificids, on sediment distribution, water flux, sediment organic carbon, biofilm biomass and microbial activities, and the concentrations of dissolved oxygen, dissolved organic carbon, PO, NO, NO and NH in slow filtration sand–gravel columns. We hypothesised that gammarids, which exploit the top 2–3 cm of the sediment, would modify the impact of worms at the sediment surface. 3. In experiments both with and without gammarids, bioturbation by the tubificids modified both the distribution of surface particles in the sediment column and water flux. In addition, microbial aerobic (oxygen consumption) and anaerobic (denitrification and fermentative decomposition of organic matter) processes in the sediment were stimulated in the presence of tubificid worms. However, G. pulex did not affect either the density or bioturbation activity of the tubificid worms. 4. Bioturbation by the benthos can be a major process in river habitats, contributing to the retention of organic matter in sediment dynamics. The presence of at least one predator had no effect on bioturbation in sediments. In such systems, physical heterogeneity may be sufficient for tubificids to escape from generalist predators, though more specialised ones might have more effect.     

The influence of species diversity on ecosystem productivity: how,where, and why?

The effect of species diversity on ecosystem productivity is controversial, in large part because field experiments investigating this relationship have been fraught with difficulties. Unfortunately, there are few guidelines to aid researchers who must overcome these difficulties and determine whether global species losses seriously threaten the ecological and economic bases of terrestrial ecosystems. In response, I offer a set of hypotheses that describe how diversity might influence productivity in plant communities based on three well-known mechanisms: complementarity, facilitation, and the sampling effect. Emphasis on these mechanisms reveals the sensitivity of any diversity-productivity relationship to ecological context (i.e., where this relationship should be found); ecological context includes characteristics of the surrounding environment, temporal and spatial scales of observation, and the intensity of human management. In particular, the legitimacy of the sampling effect as a mechanism of productivity enhancement is dependent upon the degree to which stochastic events influence immigration and extinction processes in a given ecosystem. A mechanistic approach also requires that the three mechanisms be separated and quantified in diversity experiments, and I examine the most appropriate analyses for doing so, focusing on the overyielding technique. Finally, I question why productivity per se is a relevant management concern in non-agricultural systems once relationships among diversity, productivity, and the qualities of the surrounding environment are considered.     

Secondhand homes: The multilayered influence of woodpeckers as ecosystem engineers

Ecosystem engineers alter, and can be influenced in turn by, the ecosystems they live in. Woodpeckers choose foraging and nesting sites based, in part, on food availability. Once abandoned, these cavities, particularly within areas of high forage, may be crucial to secondary cavity‐nesting birds otherwise limited by cavities formed through decay. Our study examined factors that influence the nesting success of primary cavity nesters and the subsequent impact on secondary cavity‐nesting birds. Using 5 years of point count data, we monitored the outcomes of cavity‐nesting birds in South Texas. We used logistic‐exposure models to predict daily survival rates based on cavity metrics and used woodpecker foraging trends and insect surveys to determine if nesting where woodpeckers actively forage benefits secondary cavity‐nesting birds. Both woodpeckers and secondary cavity nesters shared predictors of daily survival; nests were more successful in cavities with small openings in minimally decayed trees. All secondary cavity nesters had higher probabilities of success when nesting in an abandoned woodpecker cavity, opposed to ones formed by decay. Woodpeckers tended to forage in areas with higher‐than‐average levels of the insect orders Coleoptera, Hymenoptera, and Orthoptera, and secondary cavity nesters had higher rates of success when nesting in these areas. Our results suggest abandoned woodpecker cavities may be constructed in a way that directly benefit secondary cavity nesters. Additionally, we suggest an interplay between these ecosystem engineers, food availability, and secondary cavity nesters: Woodpeckers engineer superior nesting cavities in areas where food is more abundant, and the resultant cavities in areas of high forage may benefit local secondary cavity nesters. Our findings indicate that there is still much to be explored in the role of ecosystem engineers, and how they influence local communities on multiple trophic levels.     

The evolutionary species pool hypothesis and patterns of freshwater diatom diversity along a pH gradient

Aim To interpret the unimodal relationship between diatom species richness and lake pH within the context of the evolutionary species pool hypothesis (SPH). We test the following primary prediction arising from the SPH: the size of the potential species pool (PSP) will increase along a gradient representing the historical commonness of different pH environments (pH commonness). To do this we assume that the present‐day spatial dominance of near‐neutral pH conditions compared with acidic and alkaline conditions reliably mimics the relative spatial availabilities of historical pH conditions among freshwater lakes. We also determine whether local richness represents a constant proportion of PSP size along the pH commonness gradient. Location Two hundred and thirty‐four lakes distributed over a 405,000 km² region of the north‐eastern United States of America. Methods Sediment diatom morphospecies lists and pH data were acquired from the US Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) website. Using 248 morphospecies that occurred in at least 10 of the 234 lakes, four different measures of PSPs were calculated along the pH gradient. Local species richness was equated with the number of species occurring within the lake. Alpha diversity was equated with the average species richness of lakes with similar pH values. A combination of statistical methods were employed, including correlations, quadratic regression and piecewise regression. Results PSP size increased significantly with pH commonness for all four measures of PSP size, thus supporting the primary prediction of the evolutionary SPH. Local richness comprised a larger proportion of the PSP within acidic lakes than within circumneutral lakes. Alpha diversity and lake species richness both increased significantly with pH commonness, but the former did so in a two‐step fashion. We test and reject several alternative contemporary time‐scale explanations for our findings. Main Conclusions Our findings are consistent with the hypothesis that diatom taxonomic richness is presently lower within acidic and highly alkaline lakes than in circumneutral lakes owing to the limited opportunity in space and/or time for the evolution of suitably adapted species. Whereas ecological processes can explain why certain species are excluded from particular habitats, e.g. acidic lakes, they cannot account for why so few species are adapted to those habitats in the first place.     

The diversity, distribution and ecology of diatoms from Antarctic inland waters

Diatoms are abundant and diverse in many Antarctic freshwaters, with a general trend of decreasing diversity moving southwards. They form an important component of many benthic algal communities in streams and standing waters but are generally less common in the phytoplankton. Diatoms are excellent ecological indicator species and, because their remains are preserved in many sedimentary environments, there appears to be a great potential for palaeoenvironmental reconstruction and the examination of past diversity. A lack of taxonomic precision and consistency, coupled with the insufficient collection from some geographical areas, makes the estimation of the number of Antarctic diatom species problematic.     

Effects of species diversity on disease risk

The transmission of infectious diseases is an inherently ecological process involving interactions among at least two, and often many, species. Not surprisingly, then, the species diversity of ecological communities can potentially affect the prevalence of infectious diseases. Although a number of studies have now identified effects of diversity on disease prevalence, the mechanisms underlying these effects remain unclear in many cases. Starting with simple epidemiological models, we describe a suite of mechanisms through which diversity could increase or decrease disease risk, and illustrate the potential applicability of these mechanisms for both vector-borne and non-vector-borne diseases, and for both specialist and generalist pathogens. We review examples of how these mechanisms may operate in specific disease systems. Because the effects of diversity on multi-host disease systems have been the subject of much recent research and controversy, we describe several recent efforts to delineate under what general conditions host diversity should increase or decrease disease prevalence, and illustrate these with examples. Both models and literature reviews suggest that high host diversity is more likely to decrease than increase disease risk. Reduced disease risk with increasing host diversity is especially likely when pathogen transmission is frequency-dependent, and when pathogen transmission is greater within species than between species, particularly when the most competent hosts are also relatively abundant and widespread. We conclude by identifying focal areas for future research, including (1) describing patterns of change in disease risk with changing diversity; (2) identifying the mechanisms responsible for observed changes in risk; (3) clarifying additional mechanisms in a wider range of epidemiological models; and (4) experimentally manipulating disease systems to assess the impact of proposed mechanisms.     

刈割、施肥和浇水对高寒草甸物种多样性、功能多样性与初级生产力关系的影响

通过在高寒矮嵩草(Kobresia humilis)草甸为期4年的刈割(留茬1 cm、3 cm及不刈割)、施肥(尿素7.5 g·m^-2·a^-1+磷酸二铵1.8 g·m^-2·a^-1、不施肥)和浇水(20.1 kg·m^-2·a^-1、不浇水)控制实验, 对该生态系统中功能多样性与物种多样性的变化及其与初级生产力关系进行了研究。结果表明: 刈割和施肥显著影响植物性状和生产力, 而浇水作用微弱。刈割对物种多样性无影响, 但对不同功能多样性指数的影响不同; 施肥降低了物种多样性和以所有性状(除植株高度外)量化的功能多样性; 浇水仅对物种丰富度有微弱影响。各功能多样性的平均值能更好地反映群落物种间的功能差异。功能多样性和物种多样性呈正相关或不相关, 且二者与初级生产力的关系可表现为正相关、负相关和不相关, 说明三者间的关系是性状依赖的, 并受生境资源状况和刈割扰动的影响。植物功能性状对群落初级生产力有更加直接的影响。在考虑生物多样性对生态系统功能的影响时, 应更加注重对植物功能属性变化的研究。     

温带次生林的岛屿化对鸟类物种多样性及密度的影响

由于自然事件的影响和人类活动的干扰,越来越多的大片森林破碎成彼此孤立、面积不一的森林岛屿,这种变化无疑会对某些动物的分布模式及行为特征产生影响。于2000和2001年的春夏季,在吉林省左家自然保护区及土门岭地区,采用点样法对18块森林岛屿(面积范围:4.3–76.9hm2)中的鸟类物种多样性及密度进行了调查。主要目的是检测森林岛屿的面积效应是否对鸟类物种多样性及密度产生影响,同时分析经典的岛屿生物地理理论是否可以解释破碎化后的森林岛屿面积与物种的关系。结果表明,鸟类物种多样性在年间没有显著变化,但鸟类的密度在不同年间变化较大。不同面积森林岛屿中的鸟类物种多样性有所差异,所包含的鸟类物种数从12种到43种不等。尽管有些面积较大的斑块所包含的物种数较少,但鸟类物种数的总体趋势是随着斑块面积的增大而增多。不同鸟类对森林岛屿面积的反应并不相同,灰椋鸟(Sturnuscineraceus)、红尾伯劳(Laniuscristatus)、灰头鹀(Embrizaspodocephala)等在面积较小的斑块中密度较大,而山鹡鸰(Dendronanthusindicus)、树鹨(Anthushodg-soni)、灰背鸫(Turdushortulorum)等几乎不分布于小面积斑块之中。森林岛屿中鸟类物种随着面积变化的变异方式符合经典的岛屿生物地理理论的基本模式,但Z值和C值差异较大     

The influence of habitat availability and adult density on non-diadromous galaxiid fry settlement in New Zealand

This study investigated factors controlling settlement and initial density of two species, Galaxias vulgaris and Galaxias paucispondylus (Galaxiidae), in New Zealand streams. Factors affecting maximum fry abundance were assessed at 10 sites (eight streams) differing in habitat characteristics and the presence or absence of introduced brown Salmo trutta and rainbow trout Oncorhynchus mykiss . Regression analysis indicated that conspecific adult numbers, extent of backwater habitat and brown and rainbow trout density were the most important factors determining initial fry density. Experimental additions of backwater habitat increased fry settlement tenfold compared with control reaches, demonstrating that the area available for fry settlement had a substantial effect on fry abundance. Results from this study indicate that fry settlement may be a critical limiting phase for some non-diadromous galaxiid populations. Increasing settlement area to enhance fry retention offers a practical conservation tool for fisheries managers that may aid conservation of threatened fishes like galaxiids.     

The influence of Acacia tortilis (Forssk.) Subsp. raddiana (Savi) and livestock grazing on grass species composition, yield and soil nutrients in arid environments of South Tunisia

The objectives of the study, conducted during the 2003/2004 growing season in the National Park of Bou Hedma (South Tunisia), were to quantify the effects of the single-woody species Acacia tortilis subsp. raddiana on grass species composition, on total plant cover, on density of perennial species, on dry matter (DM) yield and on soil nutrients at lightly and heavily grazed sites. In each study site, two subhabitats were distinguished, i.e. under tree canopies and open grasslands. In the lightly grazed site, the nutrient status of soil (organic matter, total N, extractable P, K⁺, Ca²⁺, Na⁺, Mg²⁺) under Acacia raddiana canopy, was found to be significantly higher (p<0.05) than under the open grassland. In the same way, total plant cover (p<0.05), density of perennial species (p<0.01) and DM yield (p<0.01) were significantly higher under tree canopies in the lightly grazed site. Heavy grazing proved to exert a strong overriding effect over the positive influences of the woody plants. For most studied parameters, a non-significant difference was recorded between canopied and uncanopied subhabitats. Some palatable species were frequently found under trees. In the heavily grazed site, these species are being replaced by less desirable species. This emphasizes the importance of conservation stocking rates and proper pasture management.     

Ecosystem engineering effects on species diversity across ecosystems: a meta‐analysis

Ecosystem engineering is increasingly recognized as a relevant ecological driver of diversity and community composition. Although engineering impacts on the biota can vary from negative to positive, and from trivial to enormous, patterns and causes of variation in the magnitude of engineering effects across ecosystems and engineer types remain largely unknown. To elucidate the above patterns, we conducted a meta‐analysis of 122 studies which explored effects of animal ecosystem engineers on species richness of other organisms in the community. The analysis revealed that the overall effect of ecosystem engineers on diversity is positive and corresponds to a 25% increase in species richness, indicating that ecosystem engineering is a facilitative process globally. Engineering effects were stronger in the tropics than at higher latitudes, likely because new or modified habitats provided by engineers in the tropics may help minimize competition and predation pressures on resident species. Within aquatic environments, engineering impacts were stronger in marine ecosystems (rocky shores) than in streams. In terrestrial ecosystems, engineers displayed stronger positive effects in arid environments (e.g. deserts). Ecosystem engineers that create new habitats or microhabitats had stronger effects than those that modify habitats or cause bioturbation. Invertebrate engineers and those with lower engineering persistence (<1 year) affected species richness more than vertebrate engineers which persisted for >1 year. Invertebrate species richness was particularly responsive to engineering impacts. This study is the first attempt to build an integrative framework of engineering effects on species diversity; it highlights the importance of considering latitude, habitat, engineering functional group, taxon and persistence of their effects in future theoretical and empirical studies.     

Influence of macrofaunal assemblages and environmental heterogeneity on microphytobenthic production in experimental systems

Despite the complexity of natural systems, heterogeneity caused by the fragmentation of habitats has seldom been considered when investigating ecosystem processes. Empirical approaches that have included the influence of heterogeneity tend to be biased towards terrestrial habitats; yet marine systems offer opportunities by virtue of their relative ease of manipulation, rapid response times and the well-understood effects of macrofauna on sediment processes. Here, the influence of heterogeneity on microphytobenthic production in synthetic estuarine assemblages is examined. Heterogeneity was created by enriching patches of sediment with detrital algae (Enteromorpha intestinalis) to provide a source of allochthonous organic matter. A gradient of species density for four numerically dominant intertidal macrofauna (Hediste diversicolor, Hydrobia ulvae, Corophium volutator, Macoma balthica) was constructed, and microphytobenthic biomass at the sediment surface was measured. Statistical analysis using generalized least squares regression indicated that heterogeneity within our system was a significant driving factor that interacted with macrofaunal density and species identity. Microphytobenthic biomass was highest in enriched patches, suggesting that nutrients were obtained locally from the sediment-water interface and not from the water column. Our findings demonstrate that organic enrichment can cause the development of heterogeneity which influences infaunal bioturbation and consequent nutrient generation, a driver of microphytobenthic production.     

The influence of adult density on larval settlement in a coral reef fish Coryphopterus glaucofraenum

 For marine species with open populations, patterns of larval settlement can have important consequences for performance and abundance at later life-stages. In this study, I tested whether larvae of a reef-dwelling goby (Coryphopterus glaucofraenum) settled differentially to reefs occupied by varying numbers of adults. I monitored settlement daily to reefs on which the density of adult gobies varied naturally, or was manipulated experimentally. Rates of settlement were constant across a broad range of adult densities, suggesting that larvae do not choose settlement sites based on the number of adults in their immediate vicinity. Accepted: 30 October 1998     

Ultrastructural and molecular characterization of diversity among small araphid diatoms all lacking rimoportulae. I. Five new genera,eight new species

Pennate diatoms are important contributors to primary production in freshwater and marine habitats. But the extent of their diversity, ecology, and evolution is still largely unknown. This is particularly evident among the clades of pennate diatoms without raphe slits, whose diversity is likely underestimated due to their small size and features that can be difficult to discern under light microscopy. In this study, we described five new araphid genera with eight new species based on morphological observations (light and electron microscopy) and molecular data (nuclear‐encoded small subunit ribosomal RNA and chloroplast‐encoded rbcL and psbC): Serratifera varisterna, Hendeyella rhombica, H. dimeregrammopsis, H. lineata, Psammotaenia lanceolata, Castoridens striata, C. hyalina, and Cratericulifera shandongensis. We also transferred Dimeregramma dubium to Hendeyella dubia. Phylogenetic analysis of the molecular data revealed that all the newly established taxa fell into a monophyletic group, with Fragilariforma virescens located at the base. The group was composed by two subclades: one comprising Castoridens, Cratericulifera, and Plagiostriata, and the larger including also the rest of the new genera plus some of the smallest known diatoms, such as Nanofrustulum, Opephora, Pseudostaurosira, Staurosirella, and Staurosira with a high level of support. This study enhances the general knowledge on the phylogeny and biodiversity of a group of small araphid diatoms that have been generally poorly described both by electron microscopy and DNA sequence data.