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Reduced Effect (reduced + effect)
Selected AbstractsIncreased rainfall variability and reduced rainfall amount decreases soil CO2 flux in a grassland ecosystemGLOBAL CHANGE BIOLOGY, Issue 2 2005Christopher W. Harper Abstract Predicted climate changes in the US Central Plains include altered precipitation regimes with increased occurrence of growing season droughts and higher frequencies of extreme rainfall events. Changes in the amounts and timing of rainfall events will likely affect ecosystem processes, including those that control C cycling and storage. Soil carbon dioxide (CO2) flux is an important component of C cycling in terrestrial ecosystems, and is strongly influenced by climate. While many studies have assessed the influence of soil water content on soil CO2 flux, few have included experimental manipulation of rainfall amounts in intact ecosystems, and we know of no studies that have explicitly addressed the influence of the timing of rainfall events. In order to determine the responses of soil CO2 flux to altered rainfall timing and amounts, we manipulated rainfall inputs to plots of native tallgrass prairie (Konza Prairie, Kansas, USA) over four growing seasons (1998,2001). Specifically, we altered the amounts and/or timing of growing season rainfall in a factorial combination that included two levels of rainfall amount (100% or 70% of naturally occurring rainfall quantity) and two temporal patterns of rain events (ambient timing or a 50% increase in length of dry intervals between events). The size of individual rain events in the altered timing treatment was adjusted so that the quantity of total growing season rainfall in the ambient and altered timing treatments was the same (i.e. fewer, but larger rainfall events characterized the altered timing treatment). Seasonal mean soil CO2 flux decreased by 8% under reduced rainfall amounts, by 13% under altered rainfall timing, and by 20% when both were combined (P<0.01). These changes in soil CO2 flux were consistent with observed changes in plant productivity, which was also reduced by both reduced rainfall quantity and altered rainfall timing. Soil CO2 flux was related to both soil temperature and soil water content in regression analyses; together they explained as much as 64% of the variability in CO2 flux across dates under ambient rainfall timing, but only 38,48% of the variability under altered rainfall timing, suggesting that other factors (e.g. substrate availability, plant or microbial stress) may limit CO2 flux under a climate regime that includes fewer, larger rainfall events. An analysis of the temperature sensitivity of soil CO2 flux indicated that temperature had a reduced effect (lower correlation and lower Q10 values) under the reduced quantity and altered timing treatments. Recognition that changes in the timing of rainfall events may be as, or more, important than changes in rainfall amount in affecting soil CO2 flux and other components of the carbon cycle highlights the complex nature of ecosystem responses to climate change in North American grasslands. [source] Depression, depressive symptoms and mortality in persons aged 65 and over living in the community: a systematic review of the literatureINTERNATIONAL JOURNAL OF GERIATRIC PSYCHIATRY, Issue 6 2001Pedro Saz Abstract Background No recent attempt has been made to synthesize information on mortality and depression despite the theoretical and practical interest in the topic. Our objective was to estimate in the older population the influence on mortality of depression and depressive symptoms. Methods Data sources were: Medline, Embase, personal files and colleagues' records. Studies were considered if they included a majority of persons aged ,,65 years at baseline either drawn from a total community sample or drawn from a random sample from the community. Samples from healthcare facilities were excluded. Effect sizes were extracted from the papers; if they were not included in the published papers, effect sizes were calculated if possible. No attempt was made to contact authors for missing data. Results We found 21 reports on 23 cohorts using depression diagnosis. For 15 of these, odds ratios were pooled using the Greenland method based on confidence intervals (CIs), giving an estimated odds ratio for mortality with depression of 1.73 (95% CI 1.53 to 1.95). A fixed effects meta-regression of these studies suggested that longer follow-up predicted smaller effect sizes (log odds ratios ,0.096 per year (95% CI ,0.179 to ,0.014)). There is a weak suggestion of a reduced effect of depression on mortality for women. We were unable to pool effect sizes from the 17 studies using symptom totals and scales, or from eight studies of specific symptoms. Conclusions The studies show that diagnosed depression in community-resident older people is associated with increased mortality. The picture for sex differences is still unclear. Copyright © 2001 John Wiley & Sons, Ltd. [source] Group breeding dramatically increases reproductive success of yearling but not older female scrubwrens: a model for cooperatively breeding birds?JOURNAL OF ANIMAL ECOLOGY, Issue 3 2001Robert D. Magrath Summary 1,Many studies of cooperatively breeding birds have found no effect of group size on reproductive success, contrary to predictions of most adaptive hypotheses. A model is proposed for variation in group-size effects: group size has a reduced effect on success when conditions for breeding are good, such as in good environmental conditions or in groups with older breeders. This hypothesis is tested with a case study of white-browed scrubwrens Sericornis frontalis and a review of the literature. 2,The scrubwren is a cooperatively breeding passerine with male helpers. Previous analyses revealed no effect of group size on reproductive success, but those analyses were restricted to groups with older females (Magrath & Yezerinac 1997). Here 7 years' data are used to contrast the effect of group size on reproductive success for yearling and older females. 3,Yearling females breeding in groups had more than double the seasonal reproductive success than those breeding in pairs, even after controlling for territory quality. However, group size still had no effect on the reproductive success of older females. Yearling females tended to survive better in groups, but older females tended to survive better in pairs, emphasizing this pattern. 4,Yearlings breeding in pairs were more likely to be found on poor-quality territories than those breeding in groups, exaggerating the already-strong effect of group size on yearling success. Older females were not affected significantly by territory quality. 5,Group size, territory quality and female age affected different components of seasonal reproductive success. Group size increased the success of individual nesting attempts, while both territory quality and female age affected the length of the breeding season, and thus the number of breeding attempts. 6,A sample of the literature on cooperative breeders shows that group size has a larger effect on reproductive success in poorer conditions, caused either by younger, inexperienced breeders or poorer environmental conditions. Scrubwrens therefore illustrate a widespread pattern, which provides an explanation for much of the variation in group-size effects among and within species. Clearly single estimates of group-size effects for species can be inadequate to test ideas about the evolution of cooperative breeding. [source] Depth-dependent swimbladder compression in herring Clupea harengus observed using magnetic resonance imagingJOURNAL OF FISH BIOLOGY, Issue 1 2009S. M. M. Fässler Changes in swimbladder morphology in an Atlantic herring Clupea harengus with pressure were examined by magnetic resonance imaging of a dead fish in a purpose-built pressure chamber. Swimbladder volume changed with pressure according to Boyle's Law, but compression in the lateral aspect was greater than in the dorsal aspect. This uneven compression has a reduced effect on acoustic backscattering than symmetrical compression and would elicit less pronounced effects of depth on acoustic biomass estimates of C. harengus. 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