262 research outputs found
The galactic population of white dwarfs
Original paper can be found at: http://www.iop.org/EJ/conf DOI: 10.1088/1742-6596/172/1/012004 [16th European White Dwarfs Workshop]The contribution of white dwarfs of the different Galactic populations to the stellar content of our Galaxy is only poorly known. Some authors claim a vast population of halo white dwarfs, which would be in accordance with some investigations of the early phases of Galaxy formation claiming a top-heavy initialâ massâ function. Here, I present a model of the population of white dwarfs in the Milky Way based on observations of the local white dwarf sample and a standard model of Galactic structure. This model will be used to estimate the space densities of thin disc, thick disc and halo white dwarfs and their contribution to the baryonic mass budget of the Milky Way. One result of this investigation is that white dwarfs of the halo population contribute a large fraction of the Galactic white dwarf number count, but they are not responsible for the lion's share of stellar mass in the Milky Way. Another important result is the substantial contribution of the â often neglected â population of thick disc white dwarfs. Misclassification of thick disc white dwarfs is responsible for overestimates of the halo population in previous investigations.Peer reviewe
Biological invasion hotspots: a trait-based perspective reveals new sub-continental patterns
Invader traits (including plant growth form) may play an important, and perhaps overlooked, role in determining macroscale patterns of biological invasions and therefore warrant greater consideration in future investigations aimed at understanding these patterns. To assess this need, we used empirical data from a national-level survey of forest in the contiguous 48 states of the USA to identify geographic hotspots of forest plant invasion for three distinct invasion characteristics: invasive species richness, trait richness (defined as the number of the five following plant growth forms represented by the invasive plants present at a given location: forbs, grasses, shrubs, trees, and vines), and species richness within each growth form. Three key findings emerged. 1) Th e hotspots identified encompassed from 9 to 23% of the total area of our study region, thereby revealing many forests to be not only invaded, but highly invaded. 2) Substantial spatial disagreement among hotspots of invasive species richness, invasive trait richness, and species richness of invasive plants within each growth form revealed many locations to be hotspots for invader traits, or for particular growth forms of invasive plants, rather than for invasive plants in general. 3) Despite eastern forests exhibiting higher levels of plant invasion than western forests, species richness for invasive forbs and grasses in the west were respectively greater than and equivalent to levels found in the east. Contrasting patterns between eastern and western forests in the number of invasive species detected for each growth form combined with the spatial disagreement found among hotspot types suggests trait-based variability in invasion drivers. Our findings reveal invader traits to be an important contributor to macroscale invasion patterns
Plant height and seed yield of castor (Ricinus communis L.) sprayed with growth retardants and harvest aid chemicals.
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Assessing the stability of tree ranges and influence of disturbance in eastern US forests
Shifts in tree species ranges may occur due to global climate change, which in turn may be exacerbated
by natural disturbance events. Within the context of global climate change, developing techniques to
monitor tree range dynamics as affected by natural disturbances may enable mitigation/adaptation of
projected impacts. Using a forest inventory across the eastern U.S., the northern range margins of tree
distributions were examined by comparing differences in the 95th percentile locations of seedlings to
adults (i.e., trees) by 0.5° longitudinal bands over 5-years and by levels of disturbance (i.e., canopy gap
formation). Our results suggest that the monitoring of tree range dynamics is complicated by the limits
of forest inventory data across varying spatial/temporal scales and the diversity of tree species/environments
in the eastern U.S. The vast majority of tree and seedling latitudinal comparisons across measurement
periods and levels of disturbance in the study were not statistically different from zero (53 out of 60
comparisons). A potential skewing of ranges towards a northern limit was suggested by the stability of
northern margins of tree ranges found in this study and shifts in mean locations identified in previous
work. Only a partial influence of disturbances on tree range dynamics during the course of the 5-years
was found in this study. The results of this study underscore the importance of continued examination
of the role of disturbance in tree range dynamics and refined range monitoring techniques given future
forest extent and biodiversity implications.Keywords: Disturbance, Seedlings, Tree range retreat, Climate change, Tree species migration, Canopy gapsKeywords: Disturbance, Seedlings, Tree range retreat, Climate change, Tree species migration, Canopy gap
Preliminary archaeoentomological analyses of permafrost-preserved cultural layers from the pre-contact Yupâik Eskimo site of Nunalleq, Alaska : implications, potential and methodological considerations
Acknowledgements Site excavation and samples collection were conducted by archaeologists from the University of Aberdeen, with the help of archaeologists and student excavators from the University of Aberdeen University of Alaska Fairbanks and Bryn Mawr College, Kuskokwim Campus, College of Rural Alaska and residents of Quinhagak and Mekoryuk. This study is funded through AHRC grant to the project âUnderstanding Cultural Resilience and Climate Change on the Bering Sea through Yupâik Ecological Knowledge, Lifeways, Learning and Archaeologyâ to Rick Knecht, Kate Britton and Charlotta Hillderal (University of Aberdeen; AH/K006029/1). Thanks are due to Qanirtuuq Inc. and Quinhagak, Alaska for sampling permissions and to entomologists working at the CNC in Ottawa for allowing access to reference collections of beetles, lice and fleas. Yves Bousquet, Ales Smetana and Anthony E. Davies are specially acknowledged for their help with the identification of coleopteran specimens. Finally, we would also like to thank Scott Elias for useful comments on the original manuscript.Peer reviewedPublisher PD
A multilevel analytical framework for studying cultural evolution in prehistoric hunter-gatherer societies
Over the past decade, a major debate has taken place on the underpinnings of cultural changes in human societies. A growing array of evidence in behavioural and evolutionary biology has revealed that social connectivity among populations and within them affects, and is affected by, culture. Yet the interplay between prehistoric hunter-gatherer social structure and cultural transmission has typically been overlooked. Interestingly, the archaeological record contains large data sets, allowing us to track cultural changes over thousands of years: they thus offer a unique opportunity to shed light on longâterm cultural transmission processes
Artifact and Artifact Categorization: Comparing Humans and Capuchin Monkeys
International audienceWe aim to show that far-related primates like humans and the capuchin monkeys show interesting correspondences in terms of artifact characterization and categorization. We investigate this issue by using a philosophically-inspired definition of physical artifact which, developed for human artifacts, turns out to be applicable for cross-species comparison. In this approach an artifact is created when an entity is intentionally selected and some capacities attributed to it (often characterizing a purpose). Behavioral studies suggest that this notion of artifact is not specific to the human kind. On the basis of the results of a series of field observations and experiments on wild capuchin monkeys that routinely use stone hammers and anvils, we show that the notions of intentional selection and attributed capacity appear to be at play in capuchins as well. The study also suggests that functional criteria and contextualization play a fundamental role in terms of artifact recognition and categorization in nonhuman primates
Ethnographic understandings of ethnically diverse neighbourhoods to inform urban design practice
The aim of this paper is to inform urban design practice through deeper
understanding and analysis of the social dynamics of public outdoor
space in ethnically diverse neighbourhoods. We hypothesise that
findings from ethnographic research can provide a resource that
improves cultural literacy and supports social justice in professional
practice. The primary method is a meta-synthesis literature review of 24
ethnographic research papers, all of which explore some dimensions of
public open space use and values in UK urban contexts characterised by
ethnic and racial diversity. We summarise thematic understandings and
significance of neighbourhood places of shared activity, parks, spaces of
passing-by and of retreat. We evaluate the implications for intercultural
social dynamics, exploring the spatial and temporal dimensions of
conviviality and racism in public open space. We then argue that it is
possible to develop principles for urban design practice informed by this
work, and propose four for discussion: maximising straightforward
participation, legitimising diversity of activity, designing in micro-retreats
of nearby quietness and addressing structural inequalities of open space
provision. We conclude that ethnographic research can provide detailed
insights into the use of the public realm and also inform a more nuanced
understanding of outdoor sociality relevant for an increasingly diverse
society. The challenge is two-fold: for ethnographers to become less
cautious in engaging with decisions and priorities regarding how cities
change, and for urban designers to explicitly embed informed
understandings of difference into their broad desire for inclusive public space
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