共查询到20条相似文献,搜索用时 31 毫秒
1.
Robin E. Snyder 《Theoretical Ecology》2008,1(3):129-139
The ability of environmental variation to affect species coexistence is much studied, yet environmental variation is not always
important. I present an approximate calculation for the long-run growth rate of a species in the presence of spatially and
temporally correlated environmental variation. I then perform a factorial numerical experiment, varying the mean seed dispersal
distances, competition radii, and overwinter seed survival probabilities for two competing species for an array of variational
regimes, noting the effects on their long-run growth rates. I find, first, that purely spatial variation has a greater capacity
for influence than variation with a temporal component. Second, spatiotemporal variation can promote coexistence as strongly
as purely temporal variation or more so, given the right species traits. Third, if the environmental variation has a spatial
component, traits which enable species to become spatially segregated promote coexistence most strongly. That is, it is the
possibility of spatial segregation which gives spatial variation its large potential to promote coexistence.
相似文献
Robin E. SnyderEmail: |
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3.
Most parallel machines, such as clusters, are space-shared in order to isolate batch parallel applications from each other
and optimize their performance. However, this leads to low utilization or potentially long waiting times. We propose a self-adaptive
approach to time-sharing such machines that provides isolation and allows the execution rate of an application to be tightly controlled by the administrator.
Our approach combines a periodic real-time scheduler on each node with a global feedback-based control system that governs
the local schedulers. We have developed an online system that implements our approach. The system takes as input a target
execution rate for each application, and automatically and continuously adjusts the applications’ real-time schedules to achieve
those rates with proportional CPU utilization. Target rates can be dynamically adjusted. Applications are performance-isolated
from each other and from other work that is not using our system. We present an extensive evaluation that shows that the system
remains stable with low response times, and that our focus on CPU isolation and control does not come at the significant expense
of network I/O, disk I/O, or memory isolation.
相似文献
Peter A. DindaEmail: |
4.
Over the last 20 years, transfer of the management of natural resources to local populations has been a major trend in the
tropics. Many of these initiatives today incorporate the development of monitoring systems based on Criteria and Indicators
(C&I), used to gauge environmental, socio-economic, and institutional consequences over a long period of time. The design
of C&I at a local level involves combining scientific expertise with traditional ecological knowledge. There are numerous
methods of merging these two branches of knowledge and developing a local monitoring system. The difficulty lies in setting
up these local monitoring systems. A review of the literature available demonstrates that the handing over of monitoring systems
to local communities has rarely been successful. In almost every case study, when the donor agency initiating the process
withdrew, monitoring was either much less intensive or came to a complete stop. Despite this blatant deficiency local monitoring
systems constitute an almost compulsory component of any donor-funded program/project dealing with sustainable management
of natural resources. In our views, the real implementation of C&I by and for communities can only be achieved if there is
a genuine devolution of management power, including responsibilities and benefits, to local stakeholders. Unless they link
environmental changes to the communities’ own management decisions, formal participative monitoring systems will continue
to fail.
相似文献
Guillaume LescuyerEmail: |
5.
Alejandro Rosas 《Biology & philosophy》2008,23(4):555-566
Recent developments in evolutionary game theory argue the superiority of punishment over reciprocity as accounts of large-scale
human cooperation. I introduce a distinction between a behavioral and a psychological perspective on reciprocity and punishment
to question this view. I examine a narrow and a wide version of a psychological mechanism for reciprocity and conclude that a narrow version is clearly distinguishable from punishment, but inadequate for
humans; whereas a wide version is applicable to humans but indistinguishable from punishment. The mechanism for reciprocity
in humans emerges as a meta-norm that governs both retaliation and punishment. I make predictions open to empirical investigation
to confirm or disconfirm this view.
相似文献
Alejandro RosasEmail: |
6.
Beyond Population and Environment: Household Demographic Life Cycles and Land Use Allocation Among Small Farms in the Amazon 总被引:1,自引:0,他引:1
Stephen G. Perz Robert T. Walker Marcellus M. Caldas 《Human ecology: an interdisciplinary journal》2006,34(6):829-849
Most research featuring demographic factors in environmental change has focused on processes operating at the level of national or global populations. This paper focuses on household-level demographic life cycles among colonists in the Amazon, and evaluates the impacts on land use allocation. The analysis goes beyond prior research by including a broader suite of demographic variables, and by simultaneously assessing their impacts on multiple land uses with different economic and ecological implications. We estimate a system of structural equations that accounts for endogeneity among land uses, and the findings indicate stronger demographic effects than previous work. These findings bear implications for modeling land use, and the place of demography in environmental research.
相似文献
Marcellus M. CaldasPhone: +1-517-4327058Fax: +1-517-4321671 |
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8.
Sub-Antarctic Marion Island has had a permanent research station for 50 years and the islands Wandering Albatrosses have been intensively studied for 20 years. The reactions of breeding birds to approaches by a human on foot were recorded. Three response variables were calculated: intensity of vocal reaction (IVR), intensity of non-vocal reaction (INR) and overall response index (ORI). At 5 m from the nest, twice as many birds stood and/or vocalised as at 15 m. Nearest neighbour distance, age and gender did not explain individual variability of responses. Study colony birds had higher IVR scores than non-study colony birds; birds at colonies closest to the station had the highest ORI scores. A better breeding record was associated with lower IVR and ORI scores, but a causative relationship remains to be demonstrated. A minimum viewing distance of 25 m is recommended for breeding Wandering Albatrosses.
相似文献
Marienne S. de VilliersEmail: Fax: +27-21-6503434 |
John CooperEmail: |
Peter G. RyanEmail: |
9.
In this paper, we explore the role of reciprocity in the employment of restrictive measures in contexts of contagion. Reciprocity
should be understood as a substantive value that governs the use, level and extent of restrictive measures. We also argue
that independent of the role reciprocity plays in the legitimisation the use of restrictive measures, reciprocity can also
motivate support and compliance with legitimate restrictive measures. The importance of reciprocity has implications for how
restrictive measures should be undertaken when preparing and evaluating public health responses to contagion.
相似文献
A. M. ViensEmail: |
10.
Terry Harmer 《Cluster computing》2007,10(3):277-285
Gridcast is an R&D project investigating grid ideas and technologies in the broadcasting technical infrastructure. In this
paper I discuss the business and technical issues in building infrastructures to support broadcasters and outline the structure
of the Gridcast grid-based service oriented architecture for broadcasting playout support.
相似文献
Terry HarmerEmail: |
11.
Roger Sansom 《Biology & philosophy》2008,23(4):475-491
I show that gene regulation networks are qualitatively consistent and therefore sufficiently similar to linearly seperable
connectionist networks to warrant that the connectionist framework be applied to gene regulation. On this view, natural selection
designs gene regulation networks to overcome the difficulty of development. I offer some general lessons about their evolvability
that can be learned by examining the generic features of connectionist networks.
相似文献
Roger SansomEmail: |
12.
13.
With the increased complexity of platforms, the growing demand of applications and data centers’ servers sprawl, power consumption
is reaching unsustainable limits. The need to improved power management is becoming essential for many reasons including reduced
power consumption & cooling, improved density, reliability & compliance with environmental standards. This paper presents
a theoretical framework and methodology for autonomic power and performance management in e-business data centers. We optimize
for power and performance (performance-per-watt) at each level of the hierarchy while maintaining scalability. We adopt mathematically-rigorous
optimization approach to minimize power while meeting performance constraints. Our experimental results show around 72% savings
in power while maintaining performance as compared to static power management techniques and 69.8% additional savings with
both global and local optimizations.
相似文献
Mazin S. YousifEmail: |
14.
The link between international trade and the global distribution of invasive alien species 总被引:2,自引:0,他引:2
Michael I. Westphal Michael Browne Kathy MacKinnon Ian Noble 《Biological invasions》2008,10(4):391-398
Invasive alien species (IAS) exact large biodiversity and economic costs and are a significant component of human-induced,
global environmental change. Previous studies looking at the variation in alien species across regions have been limited geographically
or taxonomically or have not considered economics. We used a global invasive species database to regress IAS per-country on
a suite of socioeconomic, ecological, and biogeographical variables. We varied the countries included in the regression tree
analyses, in order to explore whether certain outliers were biasing the results, and in most of the cases, merchandise imports
was the most important explanatory variable. The greater the degree of international trade, the higher the number of IAS.
We also found a positive relationship between species richness and the number of invasives, in accord with other investigations
at large spatial scales. Island status (overall), country area, latitude, continental position (New World versus Old World)
or other measures of human disturbance (e.g., GDP per capita, population density) were not found to be important determinants
of a country’s degree of biological invasion, contrary to previous studies. Our findings also provide support to the idea
that more resources for combating IAS should be directed at the introduction stage and that novel trade instruments need to
be explored to account for this environmental externality.
相似文献
Michael I. WestphalEmail: |
15.
Timothy D. Baird Paul W. Leslie J. Terrence McCabe 《Human ecology: an interdisciplinary journal》2009,37(4):463-474
In this study, we examine the effect of Tarangire National Park (TNP) on local perceptions of risk and how these perceptions
may influence behavioral responses. Data were collected during 2004–2005 through household surveys and participatory risk
mapping (PRM) in eight villages east of TNP. By identifying and rank-ordering respondents’ perceived risks, PRM enhances understanding
of the nature and variation of risks faced within a population by distinguishing between the incidence and severity of subjective
risk perceptions. Results indicate that proximity to the park has a strong effect on the type and severity of perceived risks.
Within villages close to the park, however, behavioral response to perceived risks varies considerably. This study contributes
to an appreciation of how behavioral response to environmental and socioeconomic factors is mediated by human perception.
相似文献
Timothy D. BairdEmail: |
16.
The recent contribution by Jarmila Kukalová-Peck on Hennigian phylogenetics and hexapod limb evolution is critically evaluated.
相似文献
Michael S. Engel (Corresponding author)Email: |
17.
Studies on the effects of a variety of exogenous and anthropogenic environmental factors, including endocrine disruptors,
heavy metals, UV light, high temperature, and others, on marine organisms have been presented at the 2nd Bilateral Seminar
Italy–Japan held in November 2006. Reports were discussed in order to reveal the current situation of marine ecosystems, aiming
at evaluation and prediction of environmental risks.
相似文献
V. MatrangaEmail: |
18.
Jane E. Schultz 《Journal of bioethical inquiry》2007,4(2):93-102
In researching the biomedically-engineered drug Neulasta (filgrastim), a breast cancer patient becomes aware of the extent
to which knowledge about the development and marketing of drugs influences her decisions with regard to treatment. Time spent
on understanding the commercial interests of insurers and pharmaceutical companies initially thwarts but ultimately aids the
healing process. This first-person narrative calls for physicians to recognize that the alignment of commercial interests
transgresses the patient’s humanity.
相似文献
Jane E. SchultzEmail: |
19.
Fabien Marpeau Aditya Barua Krešimir Josić 《Journal of computational neuroscience》2009,26(3):445-457
The stochastic integrate and fire neuron is one of the most commonly used stochastic models in neuroscience. Although some
cases are analytically tractable, a full analysis typically calls for numerical simulations. We present a fast and accurate
finite volume method to approximate the solution of the associated Fokker-Planck equation. The discretization of the boundary
conditions offers a particular challenge, as standard operator splitting approaches cannot be applied without modification.
We demonstrate the method using stationary and time dependent inputs, and compare them with Monte Carlo simulations. Such
simulations are relatively easy to implement, but can suffer from convergence difficulties and long run times. In comparison,
our method offers improved accuracy, and decreases computation times by several orders of magnitude. The method can easily
be extended to two and three dimensional Fokker-Planck equations.
相似文献
Fabien MarpeauEmail: |
20.
Overintensification and subsidies have long made American commodity farmers the enemy of conservationists. Yet, environmental
conditions are improving in the Mississippi Delta where farmer-based groups, water management districts and conservation organizations
have improved environmental quality and redefined the role of agriculture in environmental preservation. This work is all
the more remarkable given the region’s deeply conservative politics that discourage regulation. This paper examines this mainstreaming
of environmental values in light of debates on the role of the state in fostering environmental subjectivities. Following
cultural examinations of the state, we caution that the presence or retreat of the state is insufficient to understanding
environmental subjectivities. Instead, an ethnographic focus is necessary to identify connections between the state and particular
human-environment relations. In the Delta, this focus shows that local environmentalism is consonant with a politics of unsustainability,
one that simultaneously advances radical ecological change and defense of the region’s social hierarchies.
相似文献
Eleanor E. ShoremanEmail: |