1,721,304 research outputs found
Carbon budget consequences of deciduous shrub expansion in alpine tundra ecosystems
Full text linkArctic and alpine tundra ecosystems are important for global carbon sequestration, as they store more than half of the global soil carbon (C), and these systems are predicted to have the greatest soil C loss following climate warming. Deciduous shrub cover has increased in tundra ecosystems during recent decades, but herbivory can counteract this. An open question is how shrub expansion will affect the carbon balance of these ecosystems? Where some studies predict increased ecosystem C storage with shrub expansion because of more vegetation biomass, a growing body of literature indicate that shrubs release soil C through below-ground processes. The overall aim of this thesis was to investigate how deciduous shrub expansion affects the growing season ecosystem CO2 fluxes and C pools in an Empetrum-dominated heath, an herb-and cryptogam-dominated meadow, and a Salix shrub-dominated community in Dovrefjell, Central Norway. Additionally, experimental treatment effects of exclusion of small and large herbivores together with planting of small Salix plants was measured, and abiotic and biotic drivers of C dynamics identified.
The results from this thesis indicate how shrub expansion into low statured alpine tundra communities may influence the summer C cycling differently depending on plant community. Also, soil C pools might decrease due to below-ground differences and processes happening outside of the growing season. In this way, shrub expansion into alpine ecosystems might contribute to increased atmospheric CO2 through a net CO2 release from below-ground pools.Sammendrag:
Hvordan påvirker gjengroing av kratt og buskvekster karbonsyklusen på fjellet?
Mer enn halvparten av det globale karbonlagret finnes lagret i jorden i alpine og arktiske tundraer. Økte temperaturer i tundraens økosystemer som en konsekvens av klimaendringer kan derfor føre til frigjøring av karbon fra disse store lagrene.
Tundraens økosystemer har de siste tiårene endret seg ved at det har blitt mer og større kratt og buskvekster, men økt beiting kan bidra til å minske denne gjengroingen.
Hittil har forskning vist motstridende resultater om hvordan denne gjengroingen påvirker karbonbalansen i disse økosystemene. Noen studier mener at gjengroing bidrar til økt karbonlagring som følge av mer biomasse, mens andre tyder på at buskene via underjordiske prosesser heller frigir karbon bundet i jorden. Formålet med denne avhandlingen var å undersøke hvordan gjengroingen av fjellet påvirker syklusen og lagrene av karbondioksid i tre ulike plantesamfunn på Dovrefjell. Dette ble gjort ved å undersøke hvordan eksklusjon av beiting og planting av vierplanter påvirker disse prosessene i ei kreklinghei, en eng og et vierkratt. Vi undersøkte også hvilke abiotiske og biotiske faktorer som har størst påvirkning på karbonsyklusen i disse tre områdene.
Resultatene tyder på at avhengig av plantesamfunnet kan gjengroing føre til ulike endringer i karbonsyklusen midt i vekstsesongen, men karbonlagringen i jorda kan avta på grunn av abiotiske og biotiske faktorer i jorden utenfor vekstsesongen. Økt gjengroing ved større og flere kratt og buskvekster kan dermed føre til frigjøring av karbon og bidra til økte nivåer av karbondioksid i atmosfæren
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
Temperature-size responses match latitudinal-size clines in Arthropods, revealing critical differences between aquatic and terrestrial species
Full text linkTwo major intraspecific patterns of adult size variation are plastic temperature-size (T-S) responses and latitude-size (L-S) clines. Yet, the degree to which these co-vary and share explanatory mechanisms has not been systematically evaluated. We present the largest quantitative comparison of these gradients to date, and find that their direction and magnitude co-vary among 12 arthropod orders (r2 = 0.72). Body size in aquatic species generally reduces with both warming and decreasing latitude, whereas terrestrial species have much reduced and even opposite gradients. These patterns support the prediction that oxygen limitation is a major controlling factor in water, but not in air. Furthermore, voltinism explains much of the variation in T-S and L-S patterns in terrestrial but not aquatic species. While body size decreases with warming and with decreasing latitude in multivoltine terrestrial arthropods, size increases on average in univoltine species, consistent with predictions from size vs. season-length trade-off
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
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Conquering the terrestrial environment: the evolution of xylem anatomy in early tracheophytes
No full textSince the first land plants appeared 480-360 million years ago, natural selection has resulted in continued colonization into increasingly drier and harsher environments. The evolution of traits associated with water transport and avoidance of embolisms allowed plants to conquer increasingly more seasonal and drier terrestrial environments. However, it is unclear just how the xylem anatomy of the first Embryophytes differed from extant (living) taxa and if these differences translated to differences in plant functioning. I measured and compared hydraulic traits from stem cross-sections from extant plants and extinct fossil specimens. For 231 stems comprising 115 extant and 116 extinct taxa, measures of xylem conduit diameter/frequency and segment diameter were measured. Comparing these measures of xylem conductive traits indicates that extant plants, for their size, have more and wider conduits leading to a larger total conductive area and higher rates of water conductance. Further, the combination of xylem traits found in extinct paleo plants suggests that they were less efficient at water transport and likely more restricted to less seasonal and more wet environments. Together, these results reveal a unique insight into the functioning of extinct paleo plants and the evolution of xylem form and function
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
Latitudinally structured variation in the temperature dependence of damselfly growth rates
No full textThe Metabolic Theory of Ecology predicts that the slope of the rate–temperature relationship, E, remains
consistent across traits and organisms, acting as a major determinant of large-scale ecological patterns.
Although E has recently been shown to vary systematically, we have a poor understanding of its ecological
significance. To address this question, we conducted a common-garden experiment involving six damselfly
species differing in distribution, estimating E at the level of full-sib families. Each species was sampled
throughout its latitudinal range, allowing us to characterise variation in E along a latitudinal gradient spanning
3600 km. We show that E differs among populations and increases with latitude. E was right-skewness
across species, but this was largely an artefact of the latitudinal trend. Increased seasonality towards
higher latitude may contribute to the latitudinal trend in E. We conclude that E should be seen as a trait
involved in local adaptation.status: Publishe
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