1,720,971 research outputs found
Niche properties constrain occupancy but not abundance patterns of native and alien woody species across Hawaiian forests
No full textQuestions Islands harbour a disproportionate amount of global plant diversity, yet their unique native assemblages are particularly vulnerable to biological invasions. It is therefore critical to identify the macroecological constraints that mediate spatial distributions of alien species on islands. Here, we examined abundance-occupancy relationships of native and alien woody plant species, and the role of niche properties and functional traits related to dispersal and competition in shaping occupancy and abundance patterns. Location Hawaiian Islands. Methods We calculated relative abundance and occupancy for 64 woody species (42 natives, 22 naturalized aliens), and estimated each species' niche breadth and position. We fitted phylogenetic hierarchical Bayesian models to evaluate abundance-occupancy relationships and the impacts of niche properties and functional traits on occupancy and abundance of native and alien species. Results Our analyses revealed that locally more abundant native species were also more widespread, but that the abundance of alien species was unrelated to their occupancy. Yet, we found evidence that alien species with longer residence times on the Hawaiian Islands were more widespread. While widespread native and alien woody species both had broad niches, widespread alien woody species exhibited a tendency to occur in more marginal niche positions than widespread native woody species. Niche properties did not affect abundances of either native or alien woody species. Traits associated with dispersal capacity and competitive ability had minimal impacts on either occupancy or abundance of native and alien woody species. Conclusions We found that niche properties shape the occupancy but not the abundance of native and alien woody species across Hawaiian forests. Our results suggest that, because of substantial invasion debts, the impacts of alien woody invasions in native forests have yet to fully manifest.</p
Seed conservation biology in the Hawaiian flora
No full textThe estimated rate of ongoing plant extinctions per year is up to 500 times the background extinction rate, and this is of even greater concern when the species at risk are endangered and endemic. Endemism-scaled richness of vascular plants is 9.5 times higher on oceanic islands than on continents, with land cover change being a primary threat. Hawaiʻi, the most isolated archipelago on Earth, has less than 1% of the land mass of the rest of the United States, it contains over half of all the federally listed endangered species, and has over 250 plant taxa with fewer than 50 individuals remaining in the wild. Therefore, the need for understanding plant conservation practices in Hawaiʻi and beyond are more urgent than ever. Fortunately, seed banking provides the most efficient and cost-effective means of ex situ plant conservation. However, not all species can be conserved by conventional seed banking methods and even in those that can, current genebank standards may not be maximizing seed longevity. Seed traits that lend to a species being able to be conserved long-term by conventional methods include desiccation (i.e. drying) and long-term freeze tolerance (i.e. orthodox seed storage behavior). Although many species of the Hawaiian flora produce desiccation tolerant seeds, some sensitivity to long-term freezing stress (reduced longevity) has been detected in Hawaiian Lobelioideae (Campanulaceae), Cyperaceae, Rubiaceae, and Urticaceae. To date, the Hawaiian flora is the largest reported with this curious intermediate “freeze-sensitive” storage behavior.Recently each of the 256 Kauaʻi endemic taxa were reviewed for the IUCN Red List of Threatened Species and in Chapter I our synthesis of these Red List Assessments showed that 95% were threatened by extinction and 5% were already extinct at least in the wild. This emphasized the need for urgent and effective seed banking intervention in support of global and local plant conservation strategies.Both seed banking efforts and restoration efforts can be challenged by lack of information on seed germination and dormancy, thus germination studies are especially relevant for seed accessions of rare plants where seed lot size is usually small. In order to answer the many questions pertaining to longevity and storage behavior, it is necessary to have a reliable estimate of viability, and this is usually quantified through germination testing. However, when seed dormancy is present, germination and viability are not necessarily of equal value. Thus, we need to first investigate seed dormancy and germination ecology to interpret seed survival data and improve seed banking and restoration outcomes. In Chapter II we found physiological dormancy (PD) in the majority of the 29 Hawaiian montane species studied. In Chapter III we found that Coprosma kauensis exhibited physiological dormancy (PD), and was desiccation tolerant, and initially freeze tolerant after six months of storage at the conventional (-20°C) temperature. In Chapter IV we studied six species of Hawaiian Lobelioids and found morphophysiological dormancy (MPD), but did not study the endemic genus Brighamia. We therefore examined Brighamia rockii in Chapter V and found the species to exhibit morphological (MD) or morphophysiological dormancy (MPD). B. rockii germinated in the dark, which is very rare for Campanulaceae, but also means that the species is unlikely to form a persistent soil seed bank. In Chapter VI we investigated the effect of environmental variables and seed zone on initial viability and found that there was no correlation with environmental variables, but there was with seed zone. With climate change comes increasing storm frequency and intensity, drought, and sea level rise, all of which increase salinity especially in coastal habitats. In Chapter VII we investigated the effects of increased salinity on 21 species of Hawaiian coastal plants and found varying levels of salinity tolerance among species.Germination modelling of rare species can be hindered by limited seed availability, which can severely restrict experimental design. Previously, a novel approach to model germination was developed for complex germination experiments that use fully parametric statistical models that are readily interpretable, produces biologically meaningful and important parameters, and accounts for random effects between replicates (Petri dishes). In Chapter VIII we propose an improved two-step analysis of germination data from complex experimental designs.Understanding the relative longevity between accessions, genotypes, species, or experimental treatments is relevant to anyone concerned retention of viability. In Chapter IX we explain why we consider p50, defined as the time during storage when seed lot viability, as measured through a germination test, has declined to 50%, is a suitable longevity trait parameter. Moisture content determination is one of the most important and common assessments made on seeds, and controlling the amount of moisture in seeds is one of the biggest factors that determine seed longevity. In Chapter X we review various methods for assessing the moisture status of seeds, and also discuss various ways to adjust the moisture content of seeds in preparation for longevity assessments or seed banking.In Chapter XI we targeted Kauaʻi species with fewer than 50 individuals remaining in the wild and harvested seeds from herbarium specimens and tested for viability and actual longevity. Only one of >2000 seeds sown germinated, thus we recommend that these types of “resurrection” projects be carried out sooner rather than later before seed viability further decreases under the suboptimal environmental conditions of herbaria. In Chapter XII, we used differential scanning calorimetry to generate lipid thermal fingerprints for Hawaiian and related Lobelioideae, and test several hypotheses relating to temperature sensitive seed storage traits. We found, among other things, large lipid melting events around the conventional seed banking temperature (-20°C) which could explain why desiccation tolerant “freeze sensitive” seed storage behavior is reported for this group in Hawaiʻi
R code and output for "Improved two-step analysis of germination data from complex experimental designs"
No full textThis document contains all R code and output used for the manuscript entitled "Improved two-step analysis of germination data from complex experimental designs" , which describes an improved two-step analysis of germination data for complex experiments. The analysis involves simultaneous modelling of all estimated model parameters for separate fits of event-time data obtained from each container (Petri dish or pot). This approach allows visualization of observed cumulated data together with fitted curves
Seed longevity: analysing post-storage germination data in R to fit the viability equation
No full textFor many decades, seed germination data have been modelled by probit analysis. In particular, it is the basis of the seed viability equation used, in the first instance, to describe the decline in germination of seeds in storage, but then also the rate of the decline, depending on seed moisture content and the temperature of storage. The underlying assumption of a probit model is that the response follows a normal distribution, in this case, loss of the ability to germinate over time. Probit analysis also takes into account the binomial error associated with germination data. Many statistical packages have probit analysis as an option within the generalized linear modelling framework; here, we present code for applying probit analysis in the free software, R. Codes are provided for fitting a single survival curve, for a single seed lot stored in a constant storage environment; for fitting multiple survival curves and evaluating the effect of constraining parameters for the different seed lots; and lastly, to model the moisture relations of seed longevity. The code bases provided could also be used in pollen and fern/bryophyte spore longevity modelling
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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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