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Linear Decline (linear + decline)
Selected AbstractsTHE CHANGE IN QUANTITATIVE GENETIC VARIATION WITH INBREEDINGEVOLUTION, Issue 12 2006Josh Van Buskirk Abstract Inbreeding is known to reduce heterozygosity of neutral genetic markers, but its impact on quantitative genetic variation is debated. Theory predicts a linear decline in additive genetic variance (VA) with increasing inbreeding coefficient (F) when loci underlying the trait act additively, but a nonlinear hump-shaped relationship when dominance and epistasis are important. Predictions for heritability (h2) are similar, although the exact shape depends on the value of h2 in the absence of inbreeding. We located 22 published studies in which the level of genetic variation in [source] Forced depression of leaf hydraulic conductance in situ: effects on the leaf gas exchange of forest treesFUNCTIONAL ECOLOGY, Issue 4 2007T. J. BRODRIBB Summary 1Recent work on the hydraulic conductance of leaves suggests that maximum photosynthetic performance of a leaf is defined largely by its plumbing. Pursuing this idea, we tested how the diurnal course of gas exchange of trees in a dry tropical forest was affected by artificially depressing the hydraulic conductance of leaves (Kleaf). 2Individual leaves from four tropical tree species were exposed to a brief episode of forced evaporation by blowing warm air over leaves in situ. Despite humid soil and atmospheric conditions, this caused leaf water potential (,leaf) to fall sufficiently to induce a 50,74% drop in Kleaf. 3Two of the species sampled proved highly sensitive to artificially depressed Kleaf, leading to a marked and sustained decline in the instantaneous rate of CO2 uptake, stomatal conductance and transpiration. Leaves of these species showed a depression of hydraulic and photosynthetic capacity in response to the ,blow-dry' treatment similar to that observed when major veins in the leaf were severed. 4By contrast, the other two species sampled were relatively insensitive to Kleaf manipulation; photosynthetic rates were indistinguishable from control (untreated) leaves 4 h after treatment. These insensitive species demonstrate a linear decline of Kleaf with ,leaf, while Kleaf in the two sensitive species falls precipitously at a critical water deficit. 5We propose that a sigmoidal Kleaf vulnerability enables a high diurnal yield of CO2 at the cost of exposing leaves to the possibility of xylem cavitation. Linear Kleaf vulnerability leads to a relatively lower CO2 yield, while providing better protection against cavitation. [source] Prevalence and characteristics of older community residents with mild cognitive declineGERIATRICS & GERONTOLOGY INTERNATIONAL, Issue 2 2002Yoshinori Fujiwara Background:, Cognitive impairment is a major health issue, but epidemiological data on mild cognitive decline have been almost absent in Japan. Methods: Of all residents aged 65 years and over living in Yoita town, Niigata Prefecture, Japan in the year 2000 (n = 1673), 1544 participated in the interview survey held at community halls or at home (92.3% response). They underwent the Mini-Mental State Examination (MMSE) for assessment of cognitive function and answered questionnaires comprising socio-demographic, psychological, physical and medical, and social activity items. Higher-level functional capacities were evaluated with the Tokyo Metropolitan Index of Competence (TMIG-Index of Competence). According to subject's age and MMSE score, all subjects were classified into 3 groups: control (MMSE,>,1 SD below age-specific means), mild cognitive decline (MMSE,,,21 and ,,1 SD below age-specific means), and severe cognitive decline (MMSE,,,20), and compared various characteristics among these groups. Results: Mean MMSE score of the subjects showed a linear decline with advancing age. Among the participants, 232 (15.2%) were classified as mild cognitive decline. Compared with the controls, the subjects with mild cognitive decline reported poorer subjective health, more depressive moods, more history of stroke, more prevalence of basic activity of daily living (BADL) disability, and lower higher-level functional capacity, even after controlling for possible confounding factors. They also reported a low level of social activities: both participating in group activities and enjoying hobbies were less frequent. Their food intake pattern tended to be monotonous. Conclusions: Older persons with mild cognitive decline comprised a substantial proportion (15.2%) of the community-dwelling older population. In addition to lower cognitive function, they had lower levels of functional capacity and social activity. [source] Declining winter survival and fitness implications associated with latitudinal distribution in Norwegian Greylag Geese Anser anserIBIS, Issue 1 2006PIERRE A. PISTORIUS The Norwegian Greylag Goose Anser anser population has been increasing steadily over the past few decades, causing increasing nuisance in terms of agricultural crop damage. This, in combination with the importance of Greylags as a hunting target, has called for demographic estimates for the population to assist in management decisions. To this end, we analysed long-term mark,recapture data using Cormack,Jolly-Seber models embedded in program MARK to obtain survival estimates for the population. No sex-specific difference, or age effect on survival after juveniles had completed their first migration (3 months of age), was evident. Mean first-year survival was reported as 0.485 and annual survival of older birds as 0.700. On a monthly basis, survival in Greylags during summer and winter was very similar over the study period. A significant linear decline in winter survival from 0.909 to 0.807 was, however, apparent during the study period. Over the second half of the study (1994,2002), summer survival was about 3% lower than in the first half (1986,94) but no linear relationship was evident. We found a significant inverse relationship between Greylag survival during summer and latitudinal distribution in Norway. A similar relationship was evident between survival and annual bag numbers. The changes in adult survival observed in this study are likely to have had a substantial impact on the growth rate of the Norwegian Greylag population. [source] Competitive effects of grasses and woody plants in mixed-grass prairieJOURNAL OF ECOLOGY, Issue 4 2001Duane A. Peltzer Summary 1,Variation in the competitive ability of plant species may determine their persistence and abundance in communities. We quantified the competitive effects of grasses and woody plants in native mixed-grass prairie on the performance of transplant species and on resources. 2,We separated the effects of grasses, shrubs and intact vegetation containing both grasses and shrubs by manipulating the natural vegetation using selective herbicides to create four neighbourhood treatments: no neighbours (NN), no shrubs (NS), no grasses (NG) and all neighbours (AN). Treatments were applied to 2 × 2 m experimental plots located in either grass- or shrub-dominated habitats. The effects of grasses and shrubs on resource availability (light, soil moisture, soil available nitrogen) and on the growth of transplants of Bouteloua gracilis, a perennial tussock grass, and Elaeagnus commutata, a common shrub, were measured over two growing seasons. 3,Resource availability was two- to fivefold higher in no neighbour (NN) plots than in vegetated plots (NS, NG, AN) with grasses and shrubs having similar effects. Light penetration declined linearly with increasing grass or shrub biomass, to a minimum of about 30% incident light at 500 g m,2 shoot mass. Soil resources did not decline with increasing neighbour shoot or root mass for either grasses or shrubs, suggesting that the presence of neighbours was more important than their abundance. 4,Transplant growth was significantly suppressed by the presence of neighbours, but not by increasing neighbour shoot or root biomass, except for a linear decline in Bouteloua growth with increasing neighbour shoot mass in plots containing only shrubs. Competition intensity, calculated as the reduction in transplant growth by neighbours, was similar in both grass- and shrub-dominated habitats for transplants of Bouteloua, but was less intense in shrub-dominated habitats for the shrub Elaeagnus. Variation in the persistence and abundance of plants in communities may therefore be more strongly controlled by variation in the competitive effects exerted by neighbours than by differences in competitive response ability. [source] No evidence for optimal fitness at intermediate levels of inbreeding in Drosophila melanogasterBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 3 2009STEPHEN P. ROBINSON Optimal outbreeding theory predicts fitness benefits to intermediate levels of inbreeding. In the present study, we test for linear (consistent with inbreeding depression) and nonlinear (consistent with optimal outbreeding) effects of inbreeding on reproductive fitness in male and female Drosophila melanogaster. We found linear declines in fitness associated with increased inbreeding for egg-to-adult viability, but not the number of eggs laid or sperm competitive ability. Egg-to-adult viability was also lower in the progeny of inbred males and females mated to unrelated individuals. However, there was no evidence for optimal fitness at intermediate levels of inbreeding for any trait. The present study highlights the importance of considering biologically realistic levels of inbreeding and cross-generational effects when investigating the costs and benefits of mating with relatives. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 501,510. [source] | ||||||||||