1,720,994 research outputs found
A cellular automaton approach to spatial and temporal plant population dynamics
No full textThis thesis examines how prolonged coexistence can be maintained in a grassland plant assemblage with a particular emphasis on spatial arrangement of individuals. Thus a multispecies cellular automation model is used which is explicitly spatial, individual-based and its dynamics are determined by local interactions. We test the various methods of model implementation and find that they can have a significant effect on the population dynamics, but these effects are local in nature and do not alter the final outcome. Having established our model we find that it exhibits the competitive exclusion principle in that a monoculture is always reached. We then impose different disturbance regimes on the system by varying the amount and the sizes of the individual patches and find that the model exhibits behaviour consistent with the 'intermediate disturbance hypothesis'. By introducing another variable of the disturbance regime we find that the behaviour of the system as a whole becomes much more complicated and that the resultant diversity of the system indicates a very strong link between characteristics of the disturbance regime and the inter-relationships of the life-history strategies of the various species. We also produce 3 non-spatial models, comparing results with those of the cellular automata and find that the spatial nature of the latter makes a great difference. Thus we examine how the spatial arrangements of individuals in an undisturbed homogeneous system could prolong coexistence. We find that same-species aggregation is a natural consequence of the modular growth of plants and that it can slow down the extinction of a species by lowering the interface length with a dominant invader.</p
A novel sponge disease caused by a consortium of micro-organisms
No full textIn healthy sponges, microbes have been shown to account for up to 40 % of tissues. The majority of these are thought to originate from survivors evading digestion and immune responses of the sponge and growing and residing in the microenvironments of the mesophyll. Although a large percentage of these microbes are likely commensals, they may also include potentially pathogenic agents, which under specific conditions, such as temperature stress, may cause disease. Here we report a novel disease (sponge necrosis syndrome) that is severely affecting populations of the sponge Callyspongia (Euplacella) aff biru. Both ITS fungal and 16S rDNA bacterial diversities were assessed in healthy and diseased individuals, highlighting six potential primary causal agents for this new disease: two bacteria, a Rhodobacteraceae sp. and a cyanobacterium, Hormoscilla spongeliae (formally identified as Oscillatoria spongeliae), and four fungi, a Ascomycota sp., a Pleosporales sp., a Rhabdocline sp., and a Clasosporium sp. Furthermore, histological analysis showed the dominance of fungal hyphae rather than bacteria throughout the disease lesion, which was absent or rare in healthy tissues. Inoculation trails showed that only a combination of one bacterium and one fungus could replicate the disease, fulfilling Henle–Koch’s postulates and showing that this sponge disease is caused by a poly-microbial consortium
Habitat structure mediates biodiversity effects on ecosystem properties
No full textMuch of what we know about the role of biodiversity in mediating ecosystem processes and function stems from manipulative experiments, which have largely been performed in isolated, homogeneous environments that do not incorporate habitat structure or allow natural community dynamics to develop. Here, we use a range of habitat configurations in a model marine benthic system to investigate the effects of species composition, resource heterogeneity and patch connectivity on ecosystem properties at both the patch (bioturbation intensity) and multi-patch (nutrient concentration) scale. We show that allowing fauna to move and preferentially select patches alters local species composition and density distributions, which has negative effects on ecosystem processes (bioturbation intensity) at the patch scale, but overall positive effects on ecosystem functioning (nutrient concentration) at the multi-patch scale. Our findings provide important evidence that community dynamics alter in response to localized resource heterogeneity and that these small-scale variations in habitat structure influence species contributions to ecosystem properties at larger scales. We conclude that habitat complexity forms an important buffer against disturbance and that contemporary estimates of the level of biodiversity required for maintaining future multi-functional systems may need to be revised
How biodiversity affects ecosystem processes: implications for ecological revolutions and benthic ecosystem function
Get PDFCurrent and projected rates of extinction provide impetus to investigate the consequences of biodiversity loss for ecosystem processes. Yet our understanding of present day biodiversity-ecosystem functioning relations contrasts markedly with our understanding of the responses of species to changes that have occurred in the geological record. Of the experiments that have explicitly tested the relationship between biodiversity and ecosystem functioning, few have attempted to reconcile whether the underlying process that gives rise to the observed response is affected by biodiversity in the same way as the observed response. In the present study, we use benthic macrofaunal invertebrates to examine and distinguish the effects of species richness and species identity on bioturbation intensity, a key mechanism that has been important on evolutionary timescales regulating ecosystem functioning in the marine benthos. Our study identifies significant effects of species richness that reflect species-specific impacts on particle reworking that, in turn, lead to elevated levels of nutrient generation. However, our findings also suggest that the consideration of only bioturbation intensity forms an incomplete evaluation of bioturbation effects because the way in which species interact with the benthic environment does not necessarily reflect organism traits only associated with particle transport. Our study emphasises the need for caution when extrapolating from assumed knowledge of organism traits to how changes in species composition associated with ecological crises may impact ecosystem function. Nonetheless, the empirically derived mechanistic effects of bioturbation on ecosystem functioning documented here are sufficiently general to seek correlations between diversity and function in natural systems, including those from the palaeoecological record
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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