9,306 research outputs found
Interactive effects of losing key grazers and ecosystem engineers vary with environmental context
No full textLoss of biodiversity may cause significant changes to ecosystem structure and functioning. Evidence from long-term in situ removal experiments is rare but important in determining the effects of biodiversity loss against a background of environmental variation. Limpets and mussels are thought to be important in controlling community structure on wave-exposed shores in the UK: limpets as key grazers, mussels as ecosystem engineers. A long-term factorial removal experiment revealed interactive effects that varied between 2 shores in SW England. At one site (Harlyn), removing limpets caused a significant shift in community structure, but where limpets were lost, the presence or absence of mussels made little difference. Where limpets were present, however, the removal of mussels changed the structure and variability of the community. At the other site (Polzeath), the loss of mussels caused significant changes in community structure, and limpets played a less important role. At Harlyn, fucoid algae were abundant throughout the year. There were fewer algae at Polzeath, and cover was dominated by the summer bloom of ephemerals. At Harlyn, the limpets played a major role in controlling algae, but their effects were mediated by the presence of mussels. Other grazers were not able to fulfil their role. At Polzeath, mussels were far more important, and ephemeral algae grew on them regardless of the presence or loss of limpets. These findings emphasise the need to assess spatial and temporal variation in the effects of biodiversity loss and the importance of interactive effects of loss of multiple species from different functional groups
Financial control of multinational operations. /By/ Edward C, Bursk, John Dearden, David P. Hawkins,.
No full textNew York, Financial Executives Research Foundation, (1971
Consequences of climate-driven biodiversity changes for ecosystem functioning of North European rocky shores
No full textWe review how intertidal biodiversity is responding to globally driven climate change,
focusing on long-term data from rocky shores in the British Isles. Physical evidence of warming
around the British Isles is presented and, whilst there has been considerable fluctuation, sea surface
temperatures are at the highest levels recorded, surpassing previous warm periods (i.e. late 1950s).
Examples are given of species that have been advancing or retreating polewards over the last 50 to
100 yr. On rocky shores, the extent of poleward movement is idiosyncratic and dependent upon life
history characteristics, dispersal capabilities and habitat requirements. More southern, warm water
species have been recorded advancing than northern, cold water species retreating. Models have
been developed to predict likely assemblage composition based on future environmental scenarios.
We present qualitative and quantitative forecasts to explore the functional consequences of changes
in the identity, abundance and species richness of gastropod grazers and foundation species such as
barnacles and canopy-forming algae. We forecast that the balance of primary producers and secondary
consumers is likely to change along wave exposure gradients matching changes occurring
with latitude, thereby shifting the balance between export and import of primary production.
Increases in grazer and sessile invertebrate diversity are likely to be accompanied by decreasing
primary production by large canopy-forming fucoids. The reasons for such changes are discussed in
the context of emerging theory on the relationship between biodiversity and ecosystem functioning.
KEY WORDS: Climate change · Intertidal · Range shifts · Biodiversity · Ecosystem functioning ·
Northeast Atlanti
Highly efficient low voltage electron emission from directly spinnable carbon nanotube webs
No full textAbstract not availablePejman Hojati-Talemi, Stephen C. Hawkins, Chi P. Huynh, George P. Simo
Hawkins Freda — Canada and immigration. Public policy and public concern
No full textC. Y. Hawkins Freda — Canada and immigration. Public policy and public concern. In: Population, 30ᵉ année, n°1, 1975. p. 175
Hawkins Freda — Canada and immigration. Public policy and public concern
No full textC. Y. Hawkins Freda — Canada and immigration. Public policy and public concern. In: Population, 30ᵉ année, n°1, 1975. p. 175
[Letter from P. C. Washington to T. N. Carswell - June 3, 1942]
No full textA letter addressed to Mr. T. N. Carswell, Chairman 24th Senatorial District Drys, from P. C. Washington, President, Jarvis Christian College, Hawkins, Texas, dated June 3, 1942. Washington advises that there is no course on alcoholic problems but facts are taught throughout the whole curriculum
Bayesian statistical process control for Phase I count type data
No full textCount data, most often modeled by a Poisson distribution, are common in statistical process control. They are traditionally monitored by frequentist c or u charts, by cumulative sum and by exponentially weighted moving average charts. These charts all assume that the in-control true mean is known, a common fiction that is addressed by gathering a large Phase I sample and using it to estimate the mean. "Self-starting" proposals that ameliorate the need for a large Phase I sample have also appeared. All these methods are frequentist, ie, they allow only retrospective inference during Phase I, and they have no coherent way to incorporate less-than-perfect prior information about the in-control mean. In this paper, we introduce a Bayesian procedure that can incorporate prior information, allow online inference, and should be particularly attractive for short-run settings where large Phase I calibration exercises are impossible or unreasonable
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