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Community Diversity (community + diversity)

Distribution by Scientific Domains
Life Sciences83%
Earth and Environmental Science13%
Distribution within Life Sciences
Ecology & Organismal Biology38%
Conservation Science19%
Microbial Ecology9%
8 Other Subdomains34%

Kinds of Community Diversity

  • plant community diversity
    		•

    Selected Abstracts

    Detecting the Effects of Fishing on Seabed Community Diversity: Importance of Scale and Sample Size

    CONSERVATION BIOLOGY, Issue 2 2003
    Michel J. Kaiser
    I investigated the importance of the extent of area sampled to the observed outcome of comparisons of the diversity of seabed assemblages in different areas of the seabed that experience either low or high levels of fishing disturbance. Using a finite data set within each disturbance regime, I pooled samples of the benthic communities at random. Thus, although individual sample size increased with each additional level of pooled data, the number of samples decreased accordingly. Detecting the effects of disturbance on species diversity was strongly scale-dependent. Despite increased replication at smaller scales, disturbance effects were more apparent when larger but less numerous samples were collected. The detection of disturbance effects was also affected by the choice of sampling device. Disturbance effects were apparent with pooled anchor-dredge samples but were not apparent with pooled beam-trawl samples. A more detailed examination of the beam-trawl data emphasized that a whole-community approach to the investigation of changes in diversity can miss responses in particular components of the community ( e.g., decapod crustacea ). The latter may be more adversely affected by disturbance than the majority of the taxa found within the benthic assemblage. Further, the diversity of some groups ( e.g., echinoderms ) actually increased with disturbance. Experimental designs and sampling regimes that focus on diversity at only one scale may miss important disturbance effects that occur at larger or smaller scales. Resumen: Las perturbaciones antropogénicas de ambientes terrestres y marinos, tales como la tala y la pesca, se identifican generalmente con impactos negativos sobre la diversidad de especies. Sin embargo, observaciones empíricas a menudo no apoyan este supuesto. Investigué la importancia de la extensión del área muestreada sobre los resultados observados de comparaciones de la diversidad de ensamblajes de fondos marinos en diferentes áreas que experimentaron niveles bajos o altos de perturbación por pesca. Usando un juego finito de datos dentro de cada régimen de perturbación, se combinaron las muestras de comunidades bénticas de manera aleatoria. Por lo tanto, a pesar de que el tamaño de muestra individual incrementó con cada nivel adicional de datos combinados, el número de muestras disminuyó en consecuencia. La detección de los efectos de la perturbación sobre la diversidad de especies dependió en gran medida de la escala. A pesar del incremento en replicación de las escalas pequeñas, los efectos de la perturbación fueron más visibles cuando las muestras recolectadas fueron más grandes pero menos numerosas. La detección de los efectos de la perturbación también fueron afectados por la selección del equipo de muestreo. Los efectos de la perturbación eran evidentes cuando se usaron muestras mezcladas de dragas de ancla, pero no fueron evidentes para muestras mezcladas de redes de arrastre con vigas. Un análisis más detallado de los datos de las redes de arrastre muestran que una aproximación a nivel de toda la comunidad para investigar los cambios de diversidad puede resultar en la pérdida de información a nivel de componentes específicos ( por ejemplo crustáceos decápodos ) de la comunidad. Estos pueden ser adversamente afectados en mayor medida por la perturbación que la mayoría de los taxones que integran el ensamblaje béntico. Además, la diversidad de algunos grupos ( por ejemplo los equinodermos ) de hecho aumentó con la perturbación. Los diseños experimentales y los regímenes de muestreo que se enfocan en la diversidad a una sola escala pueden no detectar los efectos importantes de la perturbación que ocurren a mayores o menores escalas. [source]

    Heterogeneity, speciation/extinction history and climate: explaining regional plant diversity patterns in the Cape Floristic Region

    DIVERSITY AND DISTRIBUTIONS, Issue 3 2002
    R. M. Cowling
    Abstract. This paper investigates the role of heterogeneity and speciation/extinction history in explaining variation in regional scale (c. 0.1,3000 km2) plant diversity in the Cape Floristic Region of south-western Africa, a species- and endemic-rich biogeographical region. We used species-area analysis and analysis of covariance to investigate geographical (east vs. west) and topographic (lowland vs. montane) patterns of diversity. We used community diversity as a surrogate for biological heterogeneity, and the diversity of naturally rare species in quarter degree squares as an indicator of differences in speciation/extinction histories across the study region. We then used standard statistical methods to analyse geographical and topographic patterns of these two measures. There was a clear geographical diversity pattern (richer in the west), while a topographic pattern (richer in mountains) was evident only in the west. The geographical boundary coincided with a transition from the reliable winter-rainfall zone (west) to the less reliable non-seasonal rainfall zone (east). Community diversity, or biological heterogeneity, showed no significant variation in relation to geography and topography. Diversity patterns of rare species mirrored the diversity pattern for all species. We hypothesize that regional diversity patterns are the product of different speciation and extinction histories, leading to different steady-state diversities. Greater Pleistocene climatic stability in the west would have resulted in higher rates of speciation and lower rates of extinction than in the east, where for the most, Pleistocene climates would not have favoured Cape lineages. A more parsimonious hypothesis is that the more predictable seasonal rainfall of the west would have favoured non-sprouting plants and that this, in turn, resulted in higher speciation and lower extinction rates. Both hypotheses are consistent with the higher incidence of rare species in the west, and higher levels of beta and gamma diversity there, associated with the turnover of species along environmental and geographical gradients, respectively. These rare species do not contribute to community patterns; hence, biological heterogeneity is uniform across the region. The weak topography pattern of diversity in the west arises from higher speciation rates and lower extinction rates in the topographically complex mountains, rather than from the influence of environmental heterogeneity on diversity. [source]

    Impacts of Dreissena invasions on benthic macroinvertebrate communities: a meta-analysis

    DIVERSITY AND DISTRIBUTIONS, Issue 2 2007
    Jessica M. Ward
    ABSTRACT Dreissenid mussels (the zebra mussel Dreissena polymorpha and the quagga mussel Dreissena bugensis) have invaded lakes and rivers throughout North America and Europe, where they have been linked to dramatic changes in benthic invertebrate community diversity and abundance. Through a meta-analysis of published data from 47 sites, we developed statistical models of Dreissena impact on benthic macroinvertebrates across a broad range of habitats and environmental conditions. The introduction of Dreissena was generally associated with increased benthic macroinvertebrate density and taxonomic richness, and with decreased community evenness (of taxa excluding Dreissena). However, the strength of these effects varied with sediment particle size across sites. The effects of Dreissena differed among taxonomic and functional groups of macroinvertebrates, with positive effects on the densities of scrapers and predators, particularly leeches (Hirudinea), flatworms (Turbellaria), and mayflies (Ephemeroptera). Gastropod densities increased in the presence of Dreissena, but large-bodied snail taxa tended to decline. Dreissena was associated with declines in the densities sphaeriid clams and other large filter-feeding taxa, as well as burrowing amphipods (Diporeia spp.), but had strong positive effects on gammarid amphipods. These patterns are robust to variation in the methodology of primary studies. The effects of Dreissena are remarkably concordant with those of ecologically similar species, suggesting universality in the interactions between introduced byssally attached mussels and other macroinvertebrates. [source]

    Stream communities across a rural,urban landscape gradient

    DIVERSITY AND DISTRIBUTIONS, Issue 4 2006
    Mark C. Urban
    ABSTRACT Rapid urbanization throughout the world is expected to cause extensive loss of biodiversity in the upcoming decades. Disturbances associated with urbanization frequently operate over multiple spatial scales such that local species extirpations have been attributed both to localized habitat degradation and to regional changes in land use. Urbanization also may shape stream communities by restricting species dispersal within and among stream reaches. In this patch-dynamics view, anthropogenic disturbances and isolation jointly reduce stream biodiversity in urbanizing landscapes. We evaluated predictions of stream invertebrate community composition and abundance based on variation in environmental conditions at five distinct spatial scales: stream habitats, reaches, riparian corridors and watersheds and their spatial location within the larger three-river basin. Despite strong associations between biodiversity loss and human density in this study, local stream habitat and stream reach conditions were poor predictors of community patterns. Instead, local community diversity and abundance were more accurately predicted by riparian vegetation and watershed landscape structure. Spatial coordinates associated with instream distances provided better predictions of stream communities than any of the environmental data sets. Together, results suggest that urbanization in the study region was associated with reduced stream invertebrate diversity through the alteration of landscape vegetation structure and patch connectivity. These findings suggest that maintaining and restoring watershed vegetation corridors in urban landscapes will aid efforts to conserve freshwater biodiversity. [source]

    Negative per capita effects of purple loosestrife and reed canary grass on plant diversity of wetland communities

    DIVERSITY AND DISTRIBUTIONS, Issue 4 2006
    Shon S. Schooler
    ABSTRACT Invasive plants can simplify plant community structure, alter ecosystem processes and undermine the ecosystem services that we derive from biotic diversity. Two invasive plants, purple loosestrife (Lythrum salicaria) and reed canary grass (Phalaris arundinacea), are becoming the dominant species in many wetlands across temperate North America. We used a horizontal, observational study to estimate per capita effects (PCEs) of purple loosestrife and reed canary grass on plant diversity in 24 wetland communities in the Pacific Northwest, USA. Four measures of diversity were used: the number of species (S), evenness of relative abundance (J), the Shannon,Wiener index (H,) and Simpson's index (D). We show that (1) the PCEs on biotic diversity were similar for both invasive species among the four measures of diversity we examined; (2) the relationship between plant diversity and invasive plant abundance ranges from linear (constant slope) to negative exponential (variable slope), the latter signifying that the PCEs are density-dependent; (3) the PCEs were density-dependent for measures of diversity sensitive to the number of species (S, H,, D) but not for the measure that relied solely upon relative abundance (J); and (4) invader abundance was not correlated with other potential influences on biodiversity (hydrology, soils, topography). These results indicate that both species are capable of reducing plant community diversity, and management strategies need to consider the simultaneous control of multiple species if the goal is to maintain diverse plant communities. [source]

    Heterogeneity, speciation/extinction history and climate: explaining regional plant diversity patterns in the Cape Floristic Region

    DIVERSITY AND DISTRIBUTIONS, Issue 3 2002
    R. M. Cowling
    Abstract. This paper investigates the role of heterogeneity and speciation/extinction history in explaining variation in regional scale (c. 0.1,3000 km2) plant diversity in the Cape Floristic Region of south-western Africa, a species- and endemic-rich biogeographical region. We used species-area analysis and analysis of covariance to investigate geographical (east vs. west) and topographic (lowland vs. montane) patterns of diversity. We used community diversity as a surrogate for biological heterogeneity, and the diversity of naturally rare species in quarter degree squares as an indicator of differences in speciation/extinction histories across the study region. We then used standard statistical methods to analyse geographical and topographic patterns of these two measures. There was a clear geographical diversity pattern (richer in the west), while a topographic pattern (richer in mountains) was evident only in the west. The geographical boundary coincided with a transition from the reliable winter-rainfall zone (west) to the less reliable non-seasonal rainfall zone (east). Community diversity, or biological heterogeneity, showed no significant variation in relation to geography and topography. Diversity patterns of rare species mirrored the diversity pattern for all species. We hypothesize that regional diversity patterns are the product of different speciation and extinction histories, leading to different steady-state diversities. Greater Pleistocene climatic stability in the west would have resulted in higher rates of speciation and lower rates of extinction than in the east, where for the most, Pleistocene climates would not have favoured Cape lineages. A more parsimonious hypothesis is that the more predictable seasonal rainfall of the west would have favoured non-sprouting plants and that this, in turn, resulted in higher speciation and lower extinction rates. Both hypotheses are consistent with the higher incidence of rare species in the west, and higher levels of beta and gamma diversity there, associated with the turnover of species along environmental and geographical gradients, respectively. These rare species do not contribute to community patterns; hence, biological heterogeneity is uniform across the region. The weak topography pattern of diversity in the west arises from higher speciation rates and lower extinction rates in the topographically complex mountains, rather than from the influence of environmental heterogeneity on diversity. [source]

    Scale dependence of diversity measures in a leaf-litter ant assemblage

    ECOGRAPHY, Issue 2 2004
    Maurice Leponce
    A reliable characterization of community diversity and composition, necessary to allow inter-site comparisons and to monitor changes, is especially difficult to reach in speciose invertebrate communities. Spatial components of the sampling design (sampling interval, extent and grain) as well as temporal variations of species density affect the measures of diversity (species richness S, Buzas and Gibson's evenness E and Shannon's heterogeneity H). Our aim was to document the small-scale spatial distribution of leaf litter ants in a subtropical dry forest of the Argentinian Chaco and analyze how the community characterization was best achieved with a minimal sampling effort. The work was based on the recent standardized protocol for collecting ants of the leaf litter ("A.L.L.": 20 samples at intervals of 10 m). To evaluate the consistency of the sampling method in time and space, the selected site was first subject to a preliminary transect, then submitted after a 9-month interval to an 8-fold oversampling campaign (160 samples at interval of 1.25 m). Leaf litter ants were extracted from elementary 1 m2 quadrats with Winkler apparatus. An increase in the number of samples collected increased S and decreased E but did not affect much H. The sampling interval and extent did not affect S and H beyond a distance of 10 m between samples. An increase of the sampling grain had a similar effect on S than a corresponding increase of the number of samples collected, but caused a proportionaly greater increase of H. The density of species m,2 varied twofold after a 9-month interval; the effect on S could only be partially corrected by rarefaction. The measure of species numerical dominance was little affected by the season. A single standardized A.L.L. transect with Winkler samples collected <45% of the species present in the assemblage. All frequent species were included but their relative frequency was not always representative. A log series distribution of species occurrences was oberved. Fisher's , and Shannon's H were the most appropriate diversity indexes. The former was useful to rarefy or abundify S and the latter was robust against sample size effects. Both parametric and Soberón and Llorente extrapolation methods outperformed non-parametric methods and yielded a fair estimate of total species richness along the transect, a minimum value of S for the habitat sampled. [source]

    Behavioural interactions between ecosystem engineers control community species richness

    ECOLOGY LETTERS, Issue 11 2009
    Paul E. Gribben
    Abstract Behavioural interactions between ecosystem engineers may strongly influence community structure. We tested whether an invasive ecosystem engineer, the alga Caulerpa taxifolia, indirectly facilitated community diversity by modifying the behaviour of a native ecosystem engineer, the clam Anadara trapezia, in southeastern Australia. In this study, clams in Caulerpa -invaded sediments partially unburied themselves, extending >30% of their shell surface above the sediment, providing rare, hard substrata for colonization. Consequently, clams in Caulerpa had significantly higher diversity and abundance of epibiota compared with clams in unvegetated sediments. To isolate the role of clam burial depth from direct habitat influences or differential predation by habitat, we manipulated clam burial depth, predator exposure and habitat (Caulerpa or unvegetated) in an orthogonal experiment. Burial depth overwhelmingly influenced epibiont species richness and abundance, resulting in a behaviourally mediated facilitation cascade. That Caulerpa controls epibiont communities by altering Anadara burial depths illustrates that even subtle behavioural responses of one ecosystem engineer to another can drive extensive community-wide facilitation. [source]

    Reciprocal relationships and potential feedbacks between biodiversity and disturbance

    ECOLOGY LETTERS, Issue 9 2007
    A. Randall Hughes
    Abstract Two major foci of ecological research involve reciprocal views of the relationship between biodiversity and disturbance: disturbance determines community diversity or diversity determines realized disturbance severity. Here, we present an initial attempt to synthesize these two approaches in order to understand whether feedbacks occur, and what their effects on patterns of diversity might be. Our review of published experiments shows that (i) disturbance severity can be both a cause and a consequence of local diversity in a wide range of ecosystems and (ii) shapes of the unidirectional relationships between diversity and disturbance can be quite variable. To explore how feedbacks between diversity and disturbance might operate to alter expected patterns of diversity in nature, we develop and then evaluate a conceptual model that decomposes the relationships into component parts, considering sequentially the effect of diversity on disturbance severity, and the effect of realized disturbance on diversity loss, subsequent recruitment, and competitive exclusion. Our model suggests that feedbacks can increase mean values of richness, decrease variability, and alter the patterns of correlation between diversity and disturbance in nature. We close by offering ideas for future research to help fill gaps in our understanding of reciprocal relationships among ecological variables like diversity and disturbance. [source]

    Do biotic interactions shape both sides of the humped-back model of species richness in plant communities?

    ECOLOGY LETTERS, Issue 7 2006
    Richard Michalet
    Abstract A humped-back relationship between species richness and community biomass has frequently been observed in plant communities, at both local and regional scales, although often improperly called a productivity,diversity relationship. Explanations for this relationship have emphasized the role of competitive exclusion, probably because at the time when the relationship was first examined, competition was considered to be the significant biotic filter structuring plant communities. However, over the last 15 years there has been a renewed interest in facilitation and this research has shown a clear link between the role of facilitation in structuring communities and both community biomass and the severity of the environment. Although facilitation may enlarge the realized niche of species and increase community richness in stressful environments, there has only been one previous attempt to revisit the humped-back model of species richness and to include facilitative processes. However, to date, no model has explored whether biotic interactions can potentially shape both sides of the humped-back model for species richness commonly detected in plant communities. Here, we propose a revision of Grime's original model that incorporates a new understanding of the role of facilitative interactions in plant communities. In this revised model, facilitation promotes diversity at medium to high environmental severity levels, by expanding the realized niche of stress-intolerant competitive species into harsh physical conditions. However, when environmental conditions become extremely severe the positive effects of the benefactors wane (as supported by recent research on facilitative interactions in extremely severe environments) and diversity is reduced. Conversely, with decreasing stress along the biomass gradient, facilitation decreases because stress-intolerant species become able to exist away from the canopy of the stress-tolerant species (as proposed by facilitation theory). At the same time competition increases for stress-tolerant species, reducing diversity in the most benign conditions (as proposed by models of competition theory). In this way our inclusion of facilitation into the classic model of plant species diversity and community biomass generates a more powerful and richer predictive framework for understanding the role of plant interactions in changing diversity. We then use our revised model to explain both the observed discrepancies between natural patterns of species richness and community biomass and the results of experimental studies of the impact of biodiversity on the productivity of herbaceous communities. It is clear that explicit consideration of concurrent changes in stress-tolerant and competitive species enhances our capacity to explain and interpret patterns in plant community diversity with respect to environmental severity. [source]

    Effect of PCR amplicon size on assessments of clone library microbial diversity and community structure

    ENVIRONMENTAL MICROBIOLOGY, Issue 5 2009
    Julie A. Huber
    Summary PCR-based surveys of microbial communities commonly use regions of the small-subunit ribosomal RNA (SSU rRNA) gene to determine taxonomic membership and estimate total diversity. Here we show that the length of the target amplicon has a significant effect on assessments of microbial richness and community membership. Using operational taxonomic unit (OTU)- and taxonomy-based tools, we compared the V6 hypervariable region of the bacterial SSU rRNA gene of three amplicon libraries of c. 100, 400 and 1000 base pairs (bp) from each of two hydrothermal vent fluid samples. We found that the smallest amplicon libraries contained more unique sequences, higher diversity estimates and a different community structure than the other two libraries from each sample. We hypothesize that a combination of polymerase dissociation, cloning bias and mispriming due to secondary structure accounts for the differences. While this relationship is not linear, it is clear that the smallest amplicon libraries contained more different types of sequences, and accordingly, more diverse members of the community. Because divergent and lower abundant taxa can be more readily detected with smaller amplicons, they may provide better assessments of total community diversity and taxonomic membership than longer amplicons in molecular studies of microbial communities. [source]

    CONFLICTING SELECTION FROM AN ANTAGONIST AND A MUTUALIST ENHANCES PHENOTYPIC VARIATION IN A PLANT

    EVOLUTION, Issue 4 2010
    Adam M. Siepielski
    The raw material for evolution is variation. Consequently, identifying the factors that generate, maintain, and erode phenotypic and genetic variation in ecologically important traits within and among populations is important. Although persistent directional or stabilizing selection can deplete variation, spatial variation in conflicting directional selection can enhance variation. Here, we present evidence that phenotypic variation in limber pine (Pinus flexilis) cone structure is enhanced by conflicting selection pressures exerted by its mutualistic seed disperser (Clark's nutcracker Nucifraga columbiana) and an antagonistic seed predator (pine squirrel Tamiasciurus spp.). Phenotypic variation in cone structure was bimodal and about two times greater where both agents of selection co-occurred than where one (the seed predator) was absent. Within the region where both agents of selection co-occurred, bimodality in cone structure was pronounced where there appears to be a mosaic of habitats with some persistent habitats supporting only the seed disperser. These results indicate that conflicting selection stemming from spatial variation in community diversity can enhance phenotypic variation in ecologically important traits. [source]

    Summer drought decreases soil fungal diversity and associated phenol oxidase activity in upland Calluna heathland soil

    FEMS MICROBIOLOGY ECOLOGY, Issue 2 2008
    Hannah Toberman
    Abstract Natural moisture limitation during summer drought can constitute a stress for microbial communities in soil. Given globally predicted increases in drought frequency, there is an urgent need for a greater understanding of the effects of drought events on soil microbial processes. Using a long-term field-scale drought manipulation experiment at Clocaenog, Wales, UK, we analysed fungal community dynamics, using internal transcribed spacer-denaturing gradient gel electrophoresis (DGGE), over a 1-year period in the 6th year of drought manipulation. Ambient seasonality was found to be the dominant factor driving variation in fungal community dynamics. The summer drought manipulation resulted in a significant decline in the abundance of dominant fungal species, both independently of, and in interaction with, this seasonal variation. Furthermore, soil moisture was significantly correlated with the changes in fungal diversity over the drought manipulation period. While the relationship between species diversity and functional diversity remains equivocal, phenol oxidase activity was decreased by the summer drought conditions and there was a significant correlation with the decline of DGGE band richness among the most dominant fungal species during the drought season. Climatically driven events such as droughts may have significant implications for fungal community diversity and therefore, have the potential to interfere with crucial ecosystem processes, such as organic matter decomposition. [source]

    Highly diverse community structure in a remote central Tibetan geothermal spring does not display monotonic variation to thermal stress

    FEMS MICROBIOLOGY ECOLOGY, Issue 1 2006
    Lau Chui Yim
    Abstract We report an assessment of whole-community diversity for an extremely isolated geothermal location with considerable phylogenetic and phylogeographic novelty. We further demonstrate, using multiple statistical analyses of sequence data, that the response of community diversity is not monotonic to thermal stress along a gradient of 52,83°C. A combination of domain- and division-specific PCR was used to obtain a broad spectrum of community phylotypes, which were resolved by denaturing gradient gel electrophoresis. Among 58 sequences obtained from microbial mats and streamers, some 95% suggest novel archaeal and bacterial diversity at the species level or higher. Moreover, new phylogeographic and thermally defined lineages among the Cyanobacteria, Chloroflexi, Eubacterium and Thermus are identified. Shannon,Wiener diversity estimates suggest that mats at 63°C supported highest diversity, but when alternate models were applied [Average Taxonomic Distinctness (AvTD) and Variation in Taxonomic Distinctness (VarTD)] that also take into account the phylogenetic relationships between phylotypes, it is evident that greatest taxonomic diversity (AvTD) occurred in streamers at 65,70°C, whereas greatest phylogenetic distance between taxa (VarTD) occurred in streamers of 83°C. All models demonstrated that diversity is not related to thermal stress in a linear fashion. [source]

    Influence of stream geomorphic condition on fish communities in Vermont, U.S.A.

    FRESHWATER BIOLOGY, Issue 10 2006
    EIKA P. SULLIVAN, S. MA
    Summary 1. Evaluations of stream geomorphic condition may increase our understanding of the composite effects of human-induced habitat change on fish communities. Using systematic sampling of 44 reaches spread across 26 rivers in Vermont from 2002 through 2004, we tested the hypothesis that stream reaches in reference geomorphic condition would support fish assemblages that differed in diversity and productivity from fish communities found in reaches of poorer geomorphic condition. 2. At each study reach, we sampled the fish community, identified the morphological unit according to common stream classification systems and then evaluated the extent of deviation from reference geomorphic condition using a regionally adapted geomorphic assessment methodology. 3. We used principal component analysis (PCA) and linear regression to build exploratory models linking stream geomorphic condition to fish community characteristics. 4. Our results suggest that geomorphic condition significantly influences fish community diversity, productivity and condition. Geomorphic condition was a significant factor in all of our fish community models. In conjunction with additional reach characteristics, geomorphic condition explained up to 31% of the total variance observed in models for species diversity of fish communities, 44% of the variance in assemblage biomass and 45% of the variance in a regional index of biotic integrity. 5. Our work builds on single-species evidence that geomorphic characteristics represent important local-scale fish-habitat variables, showing that stream geomorphic condition is a dominant factor affecting entire fish communities. Our results enhance our understanding of the hierarchy of factors that influences fish community diversity and organisation and support the use of geomorphic condition assessments in stream management. [source]

    Geomicrobiology of deep-sea deposits: estimating community diversity from low-temperature seafloor rocks and minerals

    GEOBIOLOGY, Issue 2 2003
    Daniel R. Rogers
    ABSTRACT The role of deep-sea microbial communities in the weathering of hydrothermal vent deposits is assessed using mineralogical and molecular biological techniques. The phylogenetic diversity of varied deep-sea bare rock habitats associated with the oceanic spreading centre at the Juan de Fuca Ridge was accessed using restriction fragment length polymorphism (RFLP) and rDNA sequencing. The mineralogical composition of the deposits used for phylogenetic analysis was determined by X-ray diffraction in order to determine the proportion and composition of sulphide minerals, and to determine degree of alteration associated with each sample. RFLP analyses resulted in 15 unique patterns, or Operational Taxonomic Units (OTUs). Most environments examined were dominated by only one or two OTUs, which often comprised approximately 60% of the rDNA clones generated from that environment. Only one environment, the Mound, had a representative rDNA clone from every OTU identified in this study. For one other environment, ODP sediments, rDNA clones were all contained in a single OTU. The diversity of the microbial community is found to decrease with decreasing reactivity of the sulphide component in the samples and with increasing presence of alteration products. Phylogenetic analyses reveal that OTUs contain representatives of the epsilon-, beta- and gamma-subdivisions of the Proteobacteria. OTU1, which dominates clone libraries from every environment and is increasingly dominant with increasing rock alteration, is closely related to a group of chemolithoautotrophic iron-oxidizing bacteria that have been recently isolated from the deep sea. The apparent abundance and widespread distribution within the samples examined of the putative iron-oxidizing bacteria that may be represented by OTU1 suggests that this physiological group could play an important role in rock-weathering and carbon fixation at the seafloor. [source]

    The role of soil community biodiversity in insect biodiversity

    INSECT CONSERVATION AND DIVERSITY, Issue 3 2010
    ALISON BENNETT
    Abstract., 1.,This study demonstrates that feedback loops between plants and insects contribute to both plant and insect diversity. Synthesis of several studies reveals that both bottom-up and top-down forces are important for plant and insect communities. 2.,Feedback loops between plants and soil organisms contribute to plant and soil diversity. An analysis of multiple systems reveals that pathogens, mutualists, and a wide variety of soil fauna directly influence, and are influenced by, plant diversity. 3.,The connection of plant,insect and soil,plant feedback loops leads to the maintenance of all three groups, and the maintenance of these feedback loops crucially affects insect diversity. Examples of the influence of soil community diversity on insect diversity, and the influence of insect diversity on soil community diversity, as well as feedbacks through all three trophic levels are provided. 4.,Finally, means of conserving and restoring soil communities to influence the conservation and restoration of insect communities are discussed. [source]

    Recovery of anuran community diversity following habitat replacement

    JOURNAL OF APPLIED ECOLOGY, Issue 1 2010
    David Lesbarrères
    Summary 1.,Recently habitat degradation, road construction and traffic have all increased with human populations, to the detriment of aquatic habitats and species. While numerous restoration programmes have been carried out, there is an urgent need to follow their success to better understand and compensate for the decline of amphibian populations. To this end, we followed the colonization success of an anuran community across multiple replacement ponds created to mitigate large-scale habitat disturbance. 2.,Following construction of a highway in western France, a restoration project was initiated in 1999 and the success of restoration efforts was monitored. The amphibian communities of eight ponds were surveyed before they were destroyed. Replacement ponds were created according to precise edaphic criteria, consistent with the old pond characteristics and taking into account the amphibian species present in each. The presence of amphibian species was recorded every year during the breeding period for 4 years following pond creation. 3.,Species richness initially declined following construction of the replacement ponds but generally returned to pre-construction levels. Species diversity followed the same pattern but took longer to reach the level of diversity recorded before construction. Pond surface area, depth and sun exposure were the most significant habitat characteristics explaining both amphibian species richness and diversity. Similarly, an increase in the number of vegetation strata was positively related to anuran species richness, indicating the need to maintain a heterogeneous landscape containing relatively large open wetland areas. 4.,Synthesis and applications. We highlight the species-specific dynamics of the colonization process, including an increase in the number of replacement ponds inhabited over time by some species and, in some cases, an increase in population size. Our work suggests that successful replacement ponds can be designed around simple habitat features, providing clear benefits for a range of amphibian species, which will have positive cascading effects on local biodiversity. However, consideration must also be given to the terrestrial buffer zone when management strategies are being planned. Finally, our study offers insight into the successful establishment of anuran communities over a relatively short time in restored or replacement aquatic environments. [source]

    Beyond control: wider implications for the management of biological invasions

    JOURNAL OF APPLIED ECOLOGY, Issue 5 2006
    PHILIP E. HULME
    Summary 1Government departments, environmental managers and conservationists are all facing escalating pressure to address and resolve a diversity of invasive alien species (IAS) problems. Yet much research to date is primarily concerned with quantifying the scale of the problem rather than delivering robust solutions and has not adequately addressed all stages of the invasion process, and only a few studies embrace the ecosystem approach. 2Three successive steps, prevention, eradication and control, form the cornerstones of recommended best practices aimed at managing IAS. The goal of such actions is the restoration of ecosystems to preserve or re-establish native biodiversity and functions. 3Prevention is widely promoted as being a more environmentally desirable strategy than actions undertaken after IAS establishment, yet is hindered by the difficulty in separating invasive from non-invasive alien species. Furthermore, the high number of candidate IAS, the investment required in taxonomic support and inspection capacity, and the expense of individual risk assessments may act against the net benefits of prevention. More rewarding avenues may be found by pursuing neural networks to predict the potential composition of pest assemblages in different regions and/or model introduction pathways to identify likely invasion hubs. 4Rapid response should be consequent on early detection but, when IAS are rare, detection rates are compromised by low occurrence and limited power to discern significant changes in abundance. Power could be increased by developing composite indicators that track trends in a suite of IAS with similar life histories, shared pathways and/or habitat preferences. 5The assessment of management options will benefit from an ecosystem perspective that considers the manipulation of native competitors, consumers and mutualists, and reviews existing management practices as well as mitigates other environmental pressures. The ease with which an IAS can be targeted should not only address the direct management effects on population dynamics but also indirect effects on community diversity and structure. Where the goal is to safeguard native biodiversity, such activities should take into account the need to re-establish native species and/or restore ecosystem function in the previously affected area. 6Synthesis and applications. A comprehensive approach to IAS management should include consideration of the: (i) expected impacts; (ii) technical options available; (iii) ease with which the species can be targeted; (iv) risks associated with management; (v) likelihood of success; and (vi) extent of public concern and stakeholder interest. For each of these issues, in addition to targeting an individual species, the management of biological invasions must also incorporate an appreciation of other environmental pressures, the importance of landscape structure, and the role of existing management activities and restoration efforts. [source]

    Ecosystem engineering across ecosystems: do engineer species sharing common features have generalized or idiosyncratic effects on species diversity?

    JOURNAL OF BIOGEOGRAPHY, Issue 2 2006
    Ernesto I. Badano
    Abstract Aim, To integrate the effects of ecosystem engineers (organisms that create, maintain or destroy habitat for other species) sharing the same archetype on species diversity, and assess whether different engineer species have generalized or idiosyncratic effects across environmentally similar ecosystems. Location, High-Andean habitats of Chile and Argentina, from 23° S to 41° S. Methods, We measured and compared the effects of eight alpine plants with cushion growth-form on species richness, species diversity (measured as the Shannon,Wiener index) and evenness of vascular plant assemblages across four high-Andean ecosystems of Chile and Argentina. Results, The presence of cushion plants always increased the species richness, diversity (measured as the Shannon,Wiener index) and evenness of high-Andean plant assemblages. However, while the presence of different cushion species within the same ecosystem controlled species diversity in the same way, these effects varied between cushion species from different ecosystems. Main conclusions, Results consistently supported the idea that increases in habitat complexity due to the presence of ecosystem engineers, in this case cushion plants, would lead to higher community diversity. Results also indicate that effects of the presence of different cushion species within the same ecosystem could be generalized, while the effects of cushion species from different ecosystems should be considered idiosyncratic. [source]

    Effects of genetic impoverishment on plant community diversity

    JOURNAL OF ECOLOGY, Issue 5 2003
    Rosemary E. Booth
    Summary 1Established individuals removed at random from populations of 11 long-lived herbaceous species coexisting in a local area of ancient limestone pasture at Cressbrookdale in North Derbyshire were subjected to clonal propagation to produce stocks of genetically identical individuals sufficient to create 36 model communities identical in species composition but widely contrasted in genetic diversity. 2Three levels of genetic diversity were imposed. In one treatment, all individuals of each species were genetically unique. The second contained four randomly selected genotypes of each species. In the third, there was no genetic diversity in any of the species but each community contained a unique combination of genotypes. 3Over a period of 5 years the communities were allowed to develop in microcosms containing natural rendzina soil and exposed to a standardized regime of simulated grazing and trampling. The treatments were maintained by the removal of flowers, immature seed-heads and seedlings originating from the seed-bank and seed rain. Point quadrat surveys were used to monitor changes in species composition and diversity in the three experimental treatments. 4During the experiment a distinction rapidly developed between five canopy dominants and five subordinates, a process that caused the vegetation structure to closely resemble that occurring at Cressbrookdale. 5A gradual loss of species diversity occurred in all three treatments but by the end of the fifth growing season species diversity was higher in the most genetically diverse communities. 6Ordination of the 36 communities at intervals over a 5-year period revealed a gradual convergence in the species composition of the 4-genotype and 16-genotype communities and this effect was more strongly developed in the latter. A comparable process was not observed in the 1-genotype communities, suggesting that interaction between particular genotypes of different species in local neighbourhoods may be an essential part of the mechanism that determines the predictable composition of a mature pasture community. 7It is concluded that, under the conditions of this experiment, genetic diversity within component species reduced the rate at which species diversity declined. The relative importance in this effect of factors such as greater disease resistance and moderated competitive interactions remains uncertain. [source]

    Spatial patterns of association at local and regional scales in coastal sand dune communities

    JOURNAL OF VEGETATION SCIENCE, Issue 5 2009
    Estelle Forey
    Abstract Questions: Are positive understorey-dominant associations important in physically severe dune communities and does the strength of positive associations vary with disturbance at the local scale and with stress at the regional scale? Do associational patterns observed at the neighbourhood scale predict diversity at higher scales? Location: Coastal sand dunes, Aquitaine (France). Methods: Associational patterns with five dominant species were recorded along a local gradient of disturbance and a 240-km long regional gradient. Density, richness, cover and variance ratio of understorey species were recorded in quadrats located in dominant and in open areas. Spatial pattern of dominant plant species was recorded using a distance-based method. Results: Positive understorey-dominant associations were most frequent at both regional and local scale, although negative associations with understorey species were observed for one of the five dominants. At the regional scale, there was a shift in the magnitude of spatial associations, with higher positive associations in the most stressful sites, whereas spatial associations where not affected by the local disturbance gradient. Positive associations were not related to the size of the dominants but rather influenced by the identity of the dominant species. Conclusions: Our study highlights the potential crucial role of facilitation together with the importance of turnover of the dominants in explaining large-scale variation in diversity. However, because positive associations may also be attributed to environmental heterogeneity or co-occurrence of microhabitat preferences of species, experiments are needed to fully assess the relative importance of facilitation versus other drivers of community diversity. [source]

    Tree spacing and area of competitive influence do not scale with tree size in an African rain forest

    JOURNAL OF VEGETATION SCIENCE, Issue 5 2008
    Michael J. Lawes
    Abstract Questions: Is the area of influence of individual trees determined by tree size? Does competition, inferred from spatial pattern between neighbouring trees, affect adult tree spacing patterns in an tropical forest? At what size-class or stage is competition between neighbours most likely to affect adult tree spacing patterns? Location: Kibale National Park, western Uganda. Methods: Relationships between focal tree size and nearest neighbour distance, size, density, and species in a 4-ha permanent plot, using point pattern analyses. Results: We found non-random patterns of distribution of nearest tree neighbours (stems > 10 cm DBH). Independent of identity, tree density was highest and neighbours were regularly spaced within 3,5m of an individual. Tree densities were lower and relatively constant at distances >5m and neighbours were typically randomly spaced. In general, conspecific patterns conformed to the latter trends. Thus, individual area of influence was small (within a radius of 3,5 m). Rarer species were more clumped than common species. Weak competitive thinning occurred among more densely packed small trees (<20 cm DBH), and rapidly disappeared with increasing tree size and distance from an individual. The clumping and density of individuals was not significantly affected by tree size. Conclusions: Negative effects of competition among trees are weak, occur within the crown radius of most individuals, and are independent of adult tree size and identity. The density of neighbouring trees (aggregation) did not decline with increasing focal tree size at either the conspecific or the community level and tree diameter (tree size) was not a good estimator of the implied competitive influence of a tree. Mechanisms operating at the recruitment stage may be important determinants of adult tree community diversity and spacing patterns. [source]

    Phylogenetic similarity and structure of Agaricomycotina communities across a forested landscape

    MOLECULAR ECOLOGY, Issue 7 2010
    IVAN P. EDWARDS
    Abstract The Agaricomycotina are a phylogenetically diverse group of fungi that includes both saprotrophic and mycorrhizal species, and that form species , rich communities in forest ecosystems. Most species are infrequently observed, and this hampers assessment of the role that environmental heterogeneity plays in determining local community composition and in driving ,-diversity. We used a combination of phenetic (TRFLP) and phylogenetic approaches [Unifrac and Net Relatedness Index (NRI)] to examine the compositional and phylogenetic similarity of Agaricomycotina communities in forest floor and surface soil of three widely distributed temperate upland forest ecosystems (one, xeric oak , dominated and two, mesic sugar maple dominated). Generally, forest floor and soil communities had similar phylogenetic diversity, but there was little overlap of species or evolutionary lineages between these two horizons. Forest floor communities were dominated by saprotrophic species, and were compositionally and phylogenetically similar in all three ecosystems. Mycorrhizal species represented 30% to 90% of soil community diversity, and these communities differed compositionally and phylogenetically between ecosystems. Estimates of NRI revealed significant phylogenetic clustering in both the forest floor and soil communities of only the xeric oak-dominated forest ecosystem, and may indicate that this ecosystem acts as a habitat filter. Our results suggest that environmental heterogeneity strongly influences the phylogenetic ,-diversity of soil inhabiting Agaricomycotina communities, but has only a small influence on forest floor ,-diversity. Moreover, our results suggest that the strength of community assembly processes, such as habitat filtering, may differ between temperate forest ecosystems. [source]

    Invasibility of grassland and heath communities exposed to extreme weather events , additive effects of diversity resistance and fluctuating physical environment

    OIKOS, Issue 10 2008
    Juergen Kreyling
    Understanding the resistance of plant communities to invasion is urgent in times of changes in the physical environment due to climate change and changes in the resident communities due to biodiversity loss. Here, we test the interaction between repeated drought or heavy rainfall events and functional diversity of grassland and heath communities on invasibility, measured as the number of plant individuals invading from the matrix vegetation. Invasibility of experimental plant communities was influenced by extreme weather events, although no change in above-ground productivity of the resident communities was observed. Drought decreased invasibility while heavy rainfall increased invasibility, a pattern that is consistent with the fluctuating resource hypothesis. Higher community diversity generally decreased invasibility, which can be explained by a combination of the fluctuating resource hypothesis and niche theory. The effects of the physical environment (extreme weather events) and diversity resistance (community composition) were additive, as they were independent from each other. Differences in the composition of invading species sets were found, and Indicator Species Analysis revealed several invading species with significant affinity to one particular extreme weather event or community composition. This finding supports niche theory and contradicts neutral species assembly. Our data supports theories which predict decreased resistance of plant communities due to both increased climate variability and biodiversity loss. The effects of these two factors, however, appear to be independent from each other. [source]

    The relative role of dispersal and local interactions for alpine plant community diversity under simulated climate warming

    OIKOS, Issue 8 2007
    Kari Klanderud
    Most studies on factors determining diversity are conducted in temperate or warm regions, whereas studies in climatically harsh and low productivity areas, such as alpine regions, are rare. We examined the relative roles of seed availability and different biotic and abiotic factors for the diversity of an alpine plant community in southern Norway. Furthermore, because climate warming is predicted to be an important driver of alpine species diversity, we assessed how the relative impacts of dispersal and local interactions on diversity might change under experimental warming (open top chambers, OTCs). Addition of seeds from 27 regional species increased community diversity. The establishment of the species was negatively related both to the diversity of the existing system and the cover of the abundant dwarf shrub Dryas octopetala. These results show that both species dispersal limitation and local biotic interactions are important factors for alpine plant community diversity. Despite relatively harsh environmental conditions and low productivity, competition from the resident vegetation appeared to have a greater role for species establishment and diversity than facilitation and experimental warming. Higher temperature appeared to increase the negative relationship between resident species diversity and species establishment. This may suggest that climate warming can increase the role of interspecific competition for alpine plant community structure, and thus alter the long-term effects of biotic interactions on diversity. [source]

    Above- and belowground insect herbivores differentially affect soil nematode communities in species-rich plant communities

    OIKOS, Issue 6 2007
    Gerlinde B. De Deyn
    Interactions between above- and belowground invertebrate herbivores alter plant diversity, however, little is known on how these effects may influence higher trophic level organisms belowground. Here we explore whether above- and belowground invertebrate herbivores which alter plant community diversity and biomass, in turn affect soil nematode communities. We test the hypotheses that insect herbivores 1) alter soil nematode diversity, 2) stimulate bacterial-feeding and 3) reduce plant-feeding nematode abundances. In a full factorial outdoor mesocosm experiment we introduced grasshoppers (aboveground herbivores), wireworms (belowground herbivores) and a diverse soil nematode community to species-rich model plant communities. After two years, insect herbivore effects on nematode diversity and on abundance of herbivorous, bacterivorous, fungivorous and omni-carnivorous nematodes were evaluated in relation to plant community composition. Wireworms did not affect nematode diversity despite enhanced plant diversity, while grasshoppers, which did not affect plant diversity, reduced nematode diversity. Although grasshoppers and wireworms caused contrasting shifts in plant species dominance, they did not affect abundances of decomposer nematodes at any trophic level. Primary consumer nematodes were, however, strongly promoted by wireworms, while community root biomass was not altered by the insect herbivores. Overall, interaction effects of wireworms and grasshoppers on the soil nematodes were not observed, and we found no support for bottom-up control of the nematodes. However, our results show that above- and belowground insect herbivores may facilitate root-feeding rather than decomposer nematodes and that this facilitation appears to be driven by shifts in plant species composition. Moreover, the addition of nematodes strongly suppressed shoot biomass of several forb species and reduced grasshopper abundance. Thus, our results suggest that nematode feedback effects on plant community composition, due to plant and herbivore parasitism, may strongly depend on the presence of insect herbivores. [source]

    Control of plant species diversity and community invasibility by species immigration: seed richness versus seed density

    OIKOS, Issue 1 2003
    Rebecca L. Brown
    Immigration rates of species into communities are widely understood to influence community diversity, which in turn is widely expected to influence the susceptibility of ecosystems to species invasion. For a given community, however, immigration processes may impact diversity by means of two separable components: the number of species represented in seed inputs and the density of seed per species. The independent effects of these components on plant species diversity and consequent rates of invasion are poorly understood. We constructed experimental plant communities through repeated seed additions to independently measure the effects of seed richness and seed density on the trajectory of species diversity during the development of annual plant communities. Because we sowed species not found in the immediate study area, we were able to assess the invasibility of the resulting communities by recording the rate of establishment of species from adjacent vegetation. Early in community development when species only weakly interacted, seed richness had a strong effect on community diversity whereas seed density had little effect. After the plants became established, the effect of seed richness on measured diversity strongly depended on seed density, and disappeared at the highest level of seed density. The ability of surrounding vegetation to invade the experimental communities was decreased by seed density but not by seed richness, primarily because the individual effects of a few sown species could explain the observed invasion rates. These results suggest that seed density is just as important as seed richness in the control of species diversity, and perhaps a more important determinant of community invasibility than seed richness in dynamic plant assemblages. [source]

    Molecular markers for assessing community diversity of coastal ciliates

    THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2005
    MARY DOHERTY
    Biogeography of microbial eukaryotes is widely debated. While some claim that all microbial organisms have a cosmopolitan distribution, other data suggest evidence of endemism. To assess these hypotheses for the distribution of ciliates in the orders Choreotrichia and Oligotrichia, coastal community samples were taken from Long Island Sound. We are obtaining sequences of SSU rRNA, ITS rRNA, and mitochondrial genes to use as molecular markers for assessing gene flow across time and space. These data will serve as a basis for continued study of phylogeographic distribution of Choreotrichia and Oligotrichia. [source]

    Fungal community diversity and soil health in intensive potato cropping systems of the east Po valley, northern Italy

    ANNALS OF APPLIED BIOLOGY, Issue 2 2009
    L.M. Manici
    Abstract An ecological approach was used to investigate the relationship between diversity of soil fungal communities and soil-borne pathogen inoculum in a potato growing area of northern Italy affected by yield decline. The study was performed in 14 sites with the same tillage management practices: 10 named ,potato sites', that for many years had been intensely cultivated with potatoes, and 4 named ,rotation sites', subject to a 4-year rotation without potatoes or any recurrent crop for many years. Fungal communities were recorded using conventional (soil fungi by plate count and endophytic fungi as infection frequency on pot-grown potato plant roots in soil samples) and molecular approaches [Basidiomycetes and Ascomycetes with specific and denaturing gradient gel electrophoresis (DGGE) analysis]. Diversity of fungal communities in potato sites was significantly lower than that in rotation sites. In addition, fungal communities in rotation sites showed lower Berger,Parker dominance than those in the potato sites, suggesting that rotation sites had a higher diversity as well as a better fungal community balance than potato sites. The ANalysis Of SIMilarity test of soil fungi and root endophytic fungi revealed that the two cropping systems differed significantly for species composition. Root endophytic fungal communities showed a greater ability to colonise potato roots in soil samples from potato sites than those from rotation sites. Moreover, the majority of endophytic root fungal community species in potato sites belonged to the potato root rot complex and storage disease (Colletotrichum coccodes, Fusarium solani and Fusarium oxysporum), while those in rotation sites were mainly ubiquitous or saprobic fungi. Soil rDNA analyses showed that Ascomycetes were much more frequent than Basidiomycetes in all the soils examined. DGGE analysis, with the Ascomycete-specific primer (ITS1F/ITS4A), did not reveal distinctions between the communities found at the potato and rotation sites, although the same analysis showed differences between the communities of Basidiomycetes (specific primer ITS1F/ITS4B). These findings showed that recurrent potato cropping affected diversity and composition of soil fungal communities and induced a shift in specialisation of the endophytic fungi towards potato. [source]