1,721,170 research outputs found
Prolonged coexistence of humans and megafauna in Pleistocene Australia
No full textRecent claims for continent wide disappearance of megafauna at 46.5 thousand calendar years ago (ka) in Australia have been used to support a "blitzkrieg" model, which explains extinctions as the result of rapid overkill by human colonizers. A number of key sites with megafauna remains that significantly postdate 46.5 ka have been excluded from consideration because of questions regarding their stratigraphic integrity. Of these sites, Cuddie Springs is the only locality in Australia where megafauna and cultural remains are found together in sequential stratigraphic horizons, dated from 36-30 ka. Verifying the stratigraphic associations found here would effectively refute the rapid-overkill model and necessitate reconsideration of the regional impacts of global climatic change on megafauna and humans in the lead up to the last glacial maximum. Here, we present geochemical evidence that demonstrates the coexistence of humans and now-extinct megafaunal species on the Australian continent for a minimum of 15 ka
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
Impact of transition to a subterranean lifestyle on morphological disparity and integration in talpid moles (Mammalia, Talpidae)
Full text linkBackground: Understanding the mechanisms promoting or constraining morphological diversification within
clades is a central topic in evolutionary biology. Ecological transitions are of particular interest because of their
influence upon the selective forces and factors involved in phenotypic evolution. Here we focused on the humerus
and mandibles of talpid moles to test whether the transition to the subterranean lifestyle impacted morphological
disparity and phenotypic traits covariation between these two structures.
Results: Our results indicate non-subterranean species occupy a significantly larger portion of the talpid moles
morphospace. However, there is no difference between subterranean and non-subterranean moles in terms of the
strength and direction of phenotypic integration.
Conclusions: Our study shows that the transition to a subterranean lifestyle significantly reduced morphological
variability in talpid moles. However, this reduced disparity was not accompanied by changes in the pattern of traits
covariation between the humerus and the mandible, suggesting the presence of strong phylogenetic conservatism
within this pattern
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
Looking for the archaeological signature in Australian Megafaunal extinctions
No full textThe decline and disappearance of a range of giant marsupials, reptiles and birds from the Australian landscape during the last Glacial cycle continues to capture the imagination of both researchers and the general public. The events hinted at in the Australian fossil sequences appear to be mirrored on other continents through similar time periods, though the exact cause or sequence of extinctions remains largely unresolved. In recent years debate over megafaunal extinctions in Australia has been dominated by reports that humans were the primary drivers, leading some to assert that it is no longer a question of whether humans drove these extinctions, only how. Following the review of Wroe and Field, new reports have been published that claim support for a human-driven extinction (HDE). On closer scrutiny however, the key sites and samples lack firm contextual data and/or clear provenance. These studies fail to prove a key tenet of the HDE – that all, or even most now-extinct species were present at the time of human colonization of the continent. As compared with the easy assertion 5 years ago that this had been established, there are now more faunal species (c. 69% of total known to have become extinct) that cannot be placed within 50–100 ka of human arrival. There are still only two sites that demonstrate a coexistence of humans with some species of megafauna – Nombe Rockshelter in the PNG highlands and Cuddie Springs in the semi-arid southeast of Australia. If there is so little empirical evidence for coexistence or association of megafauna with humans, then support for an HDE through overhunting and ecosystem disruption is seriously compromised. Furthermore, the popularly cited “extinction window”, proposed as c. 51–39 ka when the HDE is argued to occur, is still only a theoretical construct. There is no clear evidence indicating that this period was particularly significant in terms of faunal loss. At present, the great majority of ‘Pleistocene’ sites remain poorly dated and the understanding of faunal turnover through this epoch is almost non-existent. Small datasets, poorly constructed hypotheses and assertive rhetoric are the prominent features of current discussions on a human role in megafaunal extinctions. Importantly, it is yet to be established whether the extinctions are an archaeological problem. The sparse fossil record known from Australia hampers a clear resolution as to how and when the megafauna disappeared, a situation likely to continue into the near future
Unexpectedly uneven distribution of functional trade-offs explains cranial morphological diversity in carnivores
Full text linkFunctional trade-offs can affect patterns of morphological and ecological evolution as well as the magnitude of morphological changes through evolutionary time. Using morpho-functional landscape modelling on the cranium of 132 carnivore species, we focused on the macroevolutionary effects of the trade-off between bite force and bite velocity. Here, we show that rates of evolution in form (morphology) are decoupled from rates of evolution in function. Further, we found theoretical morphologies optimising for velocity to be more diverse, while a much smaller phenotypic space was occupied by shapes optimising force. This pattern of differential representation of different functions in theoretical morphological space was highly correlated with patterns of actual morphological disparity. We hypothesise that many-to-one mapping of cranium shape on function may prevent the detection of direct relationships between form and function. As comparatively only few morphologies optimise bite force, species optimising this function may be less abundant because they are less likely to evolve. This, in turn, may explain why certain clades are less variable than others. Given the ubiquity of functional trade-offs in biological systems, these patterns may be general and may help to explain the unevenness of morphological and functional diversity across the tree of life
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
Simple larvae sustain the world's smallest marine vertebrates
No full textCryptobenthic reef fishes (small, camouflaged, benthic-dwelling fishes) face exceptionally high mortality rates, yet they are the most abundant fishes on coral reefs. To maintain local adult populations in the face of these mortality rates, larval cryptobenthics may have adaptations that limit dispersal. However, the basis for this larval retention is unknown. Here, we compared the body shapes of adult and larval cryptobenthics with those of adult and larval large reef fishes to explore how morphological adaptations may enable cryptobenthic larvae to stay near their natal reefs. We found that while adults and larvae of large reef fishes and adult cryptobenthics display different 'average' morphological characteristics (i.e. different locations of the morphospace centroid), they all display a similar range of body shapes (i.e. similar morphospace sizes around their centroids). Larval cryptobenthics, however, exhibit a greatly constrained range of morphologies (occupying less than 20% of the morphospace of any other category). Larval cryptobenthics appear to be limited to a simple body plan, with elongate bodies and small fins. This simple body shape is likely to result in relatively poor swimming abilities, which may limit the ability of cryptobenthic larvae to maintain their position against prevailing currents in the pelagic zone. As such, limited dispersal in cryptobenthic larvae is likely to depend upon behavioural adaptations, such as flow-refuging, to avoid being washed away from their natal reefs
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