Home About us Contact
|
Home About us Contact | ||
|
|
||
Likely Factor (likely + factor)
Selected AbstractsChanges in abundance of Vespula germanica and V. vulgaris in EnglandECOLOGICAL ENTOMOLOGY, Issue 1 2001Michael E. Archer Summary 1. Thirteen time series, varying from 17 to 27 years, of the abundance of Vespula germanica and V. vulgaris from lowland England are examined. The time series depend on either spring queens and workers taken in Malaise or suction traps, or collected colonies. 2. During the late 1970s and early 1980s, the abundance of V. germanica declined abruptly but that of V. vulgaris did not. 3. During the early 1980s, the 2-year cycle of annual abundance of V. vulgaris changed to a nearly perfectly damped pattern of annual abundances. 4. The most likely factor causing these population changes was the increased use of pesticides acting directly by killing the wasps and indirectly by reducing their food resources. 5. The difference in response of the two species to increased pesticide use may be related to a difference in foraging ability. [source] Does the diapause experience of bumblebee queens Bombus terrestris affect colony characteristics?ECOLOGICAL ENTOMOLOGY, Issue 1 2000M. Beekman Summary 1. Bumblebee colonies show much variation in the number of workers, drones, and queens produced. Because this variation prevails even when colonies are kept under identical conditions, it does not seem to be caused by extrinsic factors but rather by differences between founding queens. 2. The most likely factor that could cause differences between queens is diapause. Although colonies are raised under standardised conditions, the queens often experience diapause of different length. If there are costs associated with diapause that influence post-diapause reproduction, the diapause history of the queens could affect colony characteristics. 3. Here, several colony characteristics are compared: number of first and second brood workers; total number of workers, drones, and queens; energy spent on sexuals; sex ratio; rate of worker production; time to emergence of first reproductive; and colony lifetime. Colonies were used where the queens experienced a diapause treatment of 0 (nondiapause queens), 2, and 4 months. 4. Although no proof was found for the existence of costs associated with diapause, the colony characteristics of nondiapause queens were significantly different from those of diapause queens. Colonies of nondiapause queens produced the lowest number of workers but the highest number of young queens. 5. It is argued that these nondiapause colonies are more time-constrained than diapause colonies because nondiapause colonies produce two generations within the same season and should therefore be more efficient in producing sexual offspring. 6. Moreover, nondiapause colonies should rear a more female-biased sex ratio because they can be certain of the presence of males produced by other (diapause) colonies. [source] Ecological factors drive differentiation in wolves from British ColumbiaJOURNAL OF BIOGEOGRAPHY, Issue 8 2009Violeta Muñoz-Fuentes Abstract Aim, Limited population structure is predicted for vagile, generalist species, such as the grey wolf (Canis lupus L.). Our aims were to study how genetic variability of grey wolves was distributed in an area comprising different habitats that lay within the potential dispersal range of an individual and to make inferences about the impact of ecology on population structure. Location, British Columbia, Canada , which is characterized by a continuum of biogeoclimatic zones across which grey wolves are distributed , and adjacent areas in both Canada and Alaska, United States. Methods, We obtained mitochondrial DNA control region sequences from grey wolves from across the province and integrated our genetic results with data on phenotype, behaviour and ecology (distance, habitat and prey composition). We also compared the genetic diversity and differentiation of British Columbia grey wolves with those of other North American wolf populations. Results, We found strong genetic differentiation between adjacent populations of grey wolves from coastal and inland British Columbia. We show that the most likely factor explaining this differentiation is habitat discontinuity between the coastal and interior regions of British Columbia, as opposed to geographic distance or physical barriers to dispersal. We hypothesize that dispersing grey wolves select habitats similar to the one in which they were reared, and that this differentiation is maintained largely through behavioural mechanisms. Main conclusions, The identification of strong genetic structure on a scale within the dispersing capabilities of an individual suggests that ecological factors are driving wolf differentiation in British Columbia. Coastal wolves are highly distinct and representative of a unique ecosystem, whereas inland British Columbia grey wolves are more similar to adjacent populations of wolves located in Alaska, Alberta and Northwest Territories. Given their unique ecological, morphological, behavioural and genetic characteristics, grey wolves of coastal British Columbia should be considered an Evolutionary Significant Unit (ESU) and, consequently, warrant special conservation status. If ecology can drive differentiation in a highly mobile generalist such as the grey wolf, ecology probably drives differentiation in many other species as well. [source] Children making faces: the effect of age and prompts on children's facial composites of unfamiliar facesAPPLIED COGNITIVE PSYCHOLOGY, Issue 4 2008Carina B. Paine The police do not usually ask child witnesses (under 10-years) to construct facial composites, as it is believed that they could not create images of sufficient accuracy. The main aim of the current experiment was to evaluate whether this age limit is a suitable threshold by comparing composites made by children of age 6-, 8- and 10-years and adults. Additionally, as children's lack of vocabulary to describe faces was considered a likely factor, a technique based on visual prompts was devised to obtain facial descriptions, and compared to construction based on verbal prompting. The experiment involved participants' construction of composites, which were subsequently evaluated subjectively (ranking and rating tasks) and objectively (matching task). Although adults' and older children's composites were, on average, more accurate than those of the younger children, the results demonstrated that children from the age of 6-years were able to produce facial composites of an unfamiliar face. Copyright © 2007 John Wiley & Sons, Ltd. [source] Poster 1, Haemorrhagic bullae in a child with Henoch,Schönlein purpuraBRITISH JOURNAL OF DERMATOLOGY, Issue 6 2007S. Abdul-Ghaffar Henoch,Schönlein purpura (HSP) is one of the most common types of vasculitis in children. It usually presents with purpura, abdominal pain, arthralgia/arthritis and nephritis. The purpura seen in HSP is typically petechial or target-like and is the presenting sign in 50% of patients. Haemorrhagic bullae are rarely reported in children. We describe a 10-year-old boy who presented with a 1-week history of a petechial rash on his legs and buttocks, associated with abdominal pain and tender, swollen ankles and knees in May 2006. He had a history of a preceding upper respiratory tract infection. A clinical diagnosis of HSP was made at this stage. However, the rash became more extensive, involving his arms, shoulders and ears. Within 2 weeks, large tense haemorrhagic bullae developed on the lower legs, feet and hands. Urinalysis was positive for blood and protein but his blood pressure and renal function were normal. The rest of his investigations, including a full vasculitis screen, were normal. Because of the atypical bullae, a skin biopsy was performed. This showed leucocytoclastic vasculitis with IgA deposition consistent with HSP. The lesions improved with prednisolone, starting at 2 mg kg,1 daily, gradually reducing the dose over 3 months. Bullous HSP has been seen in up to 60% of adult patients but only in 2% of children. There have been only 11 reported cases of bullous HSP to date and the commonest sites were feet, ankles, legs and buttocks, suggesting that pressure is the most likely factor in its pathogenesis. This is an important observation as the presence of these atypical bullous lesions may pose a diagnostic challenge. [source] Autoimmune hepatitis after liver transplantation and other lessons of self-intoleranceLIVER TRANSPLANTATION, Issue 6 2002Albert J. Czaja MD Autoimmune hepatitis has been described as recurrent or de novo disease after transplantation. The legitimacy of these diagnoses and the bases for their occurrence are unknown. To better understand these aspects of allograft dysfunction, the purported pathogenic mechanisms of classical autoimmune hepatitis were reviewed and extrapolated to recurrent and de novo disease after transplantation. Loss of self-tolerance may relate to defects in the negative selection of autoreactive immunocytes and the clonal expansion of promiscuous lymphocytes that are cross-reactive to homologous antigens (molecular mimicry). Repopulation of the allograft with recipient antigen-presenting cells and the presence of primed promiscuous cytotoxic T cells within the recipient are likely factors for recurrent disease. Targets may be the same peptides that triggered the original disease, donor-derived class II antigens of the major histocompatibility complex, or homologous antigens associated with unidentified hepatotrophic viruses. De novo disease is probably due to similar mechanisms, but its predilection for children suggests that thymic dysfunction associated with cyclosporine treatment may be a factor. Corticosteroid therapy is effective in each condition. In conclusion, recurrent and de novo autoimmune hepatitis after transplantation are examples of self-intolerance. The mechanisms that perturb immunologic homeostasis in this human model of the classical disease must be studied more rigorously. [source] Radial growth responses to gap creation in large, old Sequoiadendron giganteumAPPLIED VEGETATION SCIENCE, Issue 4 2010Robert A. York Abstract Questions: Do large, old Sequoiadondron giganteum trees respond to the creation of adjacent canopy gaps? Do other co-occurring tree species and younger S. giganteum adjacent to gaps also respond? What are the likely factors affecting growth responses? Location: Mixed-conifer forests of the southern Sierra Nevada, California, USA. Methods: We measured the growth response of large, old S. giganteum trees (mean DBH=164 cm; ages estimated >1000 yr) to gap creation by coring trees and comparing growth after gap creation to growth before gap creation. We also measured young Abies concolor, Pinus lambertiana, and young S. giganteum. Gap-adjacent trees were compared with non-adjacent reference trees. Tree rings were analysed for carbon isotope discrimination and for longer-term growth trend correlations with climate. Results: Following gap creation gap-adjacent old S. giganteum grew more than reference trees. Abies concolor trees also exhibited a growth response to gap creation. No response was detected for young S. giganteum or P. lambertiana, although detection power was lower for these groups. There was no difference in carbon isotope discrimination response to gap creation between gap-adjacent and reference trees for old S. giganteum and radial growth was positively correlated with winter precipitation, but not growing season temperature. Conclusion: It is unclear what caused the growth release in old S. giganteum trees, although liberation of below-ground resources following removal of competing vegetation appears to be a significant contributor. Sequoiadondron giganteum, the third-longest lived and the largest of all species, remains sensitive to local environmental changes even after canopy emergence. Management activities that reduce vegetation surrounding individual specimen trees can be expected to result in increased vigor of even these very old and large trees. [source] | ||||||||||