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622
result(s) for
"linear mixed-effects model"
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Long‐term phenological trends, species accumulation rates, aphid traits and climate: five decades of change in migrating aphids
2015
Aphids represent a significant challenge to food production. The Rothamsted Insect Survey (RIS) runs a network of 12·2‐m suction‐traps throughout the year to collect migrating aphids. In 2014, the RIS celebrated its 50th anniversary. This paper marks that achievement with an extensive spatiotemporal analysis and the provision of the first British annotated checklist of aphids since 1964. Our main aim was to elucidate mechanisms that advance aphid phenology under climate change and explain these using life‐history traits. We then highlight emerging pests using accumulation patterns. Linear and nonlinear mixed‐effect models estimated the average rate of change per annum and effects of climate on annual counts, first and last flights and length of flight season since 1965. Two climate drivers were used: the accumulated day degrees above 16 °C (ADD16) indicated the potential for migration during the aphid season; the North Atlantic Oscillation (NAO) signalled the severity of the winter before migration took place. All 55 species studied had earlier first flight trends at rate of β = −0·611 ± SE 0·015 days year⁻¹. Of these species, 49% had earlier last flights, but the average species effect appeared relatively stationary (β = −0·010 ± SE 0·022 days year⁻¹). Most species (85%) showed increasing duration of their flight season (β = 0·336 ± SE 0·026 days year⁻¹), even though only 54% increased their log annual count (β = 0·002 ± SE <0·001 year⁻¹). The ADD16 and NAO were shown to drive patterns in aphid phenology in a spatiotemporal context. Early in the year when the first aphids were migrating, the effect of the winter NAO was highly significant. Further into the year, ADD16 was a strong predictor. Latitude had a near linear effect on first flights, whereas longitude produced a generally less‐clear effect on all responses. Aphids that are anholocyclic (permanently parthenogenetic) or are monoecious (non‐host‐alternating) were advancing their phenology faster than those that were not. Climate drives phenology and traits help explain how this takes place biologically. Phenology and trait ecology are critical to understanding the threat posed by emerging pests such as Myzus persicae nicotianae and Aphis fabae cirsiiacanthoidis, as revealed by the species accumulation analysis.
Journal Article
Sensitivity of UK butterflies to local climatic extremes: which life stages are most at risk?
2017
1. There is growing recognition as to the importance of extreme climatic events (ECEs) in determining changes in species populations. In fact, it is often the extent of climate variability that determines a population's ability to persist at a given site. 2. This study examined the impact of ECEs on the resident UK butterfly species (n = 41) over a 37-year period. The study investigated the sensitivity of butterflies to four extremes (drought, extreme precipitation, extreme heat and extreme cold), identified at the site level, across each species' life stages. Variations in the vulnerability of butterflies at the site level were also compared based on three life-history traits (voltinism, habitat requirement and range). 3. This is the first study to examine the effects of ECEs at the site level across all life stages of a butterfly, identifying sensitive life stages and unravelling the role life-history traits play in species sensitivity to ECEs. 4. Butterfly population changes were found to be primarily driven by temperature extremes. Extreme heat was detrimental during overwintering periods and beneficial during adult periods and extreme cold had opposite impacts on both of these life stages. Previously undocumented detrimental effects were identified for extreme precipitation during the pupal life stage for univoltine species. Generalists were found to have significantly more negative associations with ECEs than specialists. 5. With future projections of warmer, wetter winters and more severe weather events, UK butterflies could come under severe pressure given the findings of this study.
Journal Article
The recovery of functional diversity with restoration
by
O'Brien, Sophie A.
,
Tylianakis, Jason M.
,
Dehling, D. Matthias
in
active
,
Biodiversity
,
ecological communities
2022
Ecological restoration aims at recovering biodiversity in degraded ecosystems, and it is commonly assessed via species richness. However, it is unclear whether increasing species richness in a site also recovers its functional diversity (FD), which has been shown to be a better representation of ecosystem functioning. We conducted a quantitative synthesis of 30 restoration projects and tested whether restoration improves FD. We compared actively and passively restored sites with degraded and reference sites with respect to four key measures of FD (functional richness, evenness, dispersion, and turnover) and two measures of species diversity (richness and evenness). We separately analyzed longitudinal studies (which monitor degraded, reference, and restored sites through time) and space-for-time substitutions (which compare at one point in time degraded and reference sites with restored sites of different ages). Space-for-time studies suggested that species diversity and FD improved over time. However, replicated longitudinal data showed no sustained benefits of active or passive restoration for FD measures, relative to degraded sites. This could suggest that the positive results in space-for-time designs may have been unreliable, but the relatively short duration of longitudinal studies suggests a need for longer-term longitudinal research to robustly demonstrate the absence of any effect. These differences across study designs may explain the variable results found in recent studies directly measuring the response of FD to restoration. We recommend that future assessments of ecological community dynamics include control sites in monitoring, to ensure that the consequences of treatments, including but not limited to restoration, are correctly partitioned from unassisted temporal changes.
Journal Article
The Impact of Sociodemographic Factors on Job Insecurity Among Obstetric Nurses Under the Low Fertility Background: A Linear Mixed-Effects Model Analysis and Targeted Intervention Strategies
2026
With the continuous decline in fertility rates in China, the demand for obstetric care services has decreased, posing severe challenges to the occupational security and mental health of obstetric nurses.
The purpose of this study is to explore the effects of demographic sociological variables of obstetrical nurses on sense of security under the background of low fertility rate, identify the key driving factors, and put forward intervention countermeasures based on the empirical results, in order to improve the professional survival status of obstetric nurses and stabilize the obstetric nursing team.
From April to May 2025, 406 obstetric nurses were recruited as the research subjects by using the two-stage sampling method and surveyed using a general information questionnaire and Job Insecurity Scale. Q-Q plots assessed data normality; normally distributed data were expressed as M±SD, with t-tests/ANOVA (SNK-q for pairwise comparisons).Under the premise of controlling the hospital agglomeration effect, the factors influencing the hospital agglomeration effect were analyzed by using the linear mixed effect model.
Obstetric nurses' total job insecurity score was 76.07±22.80, with 69.21% above the median (62.5). Linear mixed-effects model analysis showed significant differences (all P<0.05): secondary hospital nurses had higher job insecurity scores than tertiary hospital ones (β=12.55, 95% CI: 6.66~18.43); contracted nurses scored higher than staffed nurses (β=18.832, 95% CI: 13.254~24.409); those with monthly salary ≤4,000 yuan scored higher than ≥6,001 yuan (β=10.002, 95% CI: 2.891~17.113); nurses with 6-10 years of experience scored higher than ≤5 years (β=7.741, 95% CI: 1.829~13.653); team leaders scored lower than general nurses (β=-9.457, 95% CI: -16.245~-2.669). The model explained 26% of individual and 23% of hospital-level variance in job insecurity scores.
Obstetric nurses in Chongqing have relatively high job insecurity affected by hospital and individual factors. This study provides empirical support for a dual approach of \"optimizing hospital environment and precise individual empowerment\" to stabilize the team and ensure maternal-infant safety.
Journal Article
Effects of Size, Competition and Altitude on Tree Growth
by
Allen, Robert B.
,
Coomes, David A.
in
Altitude
,
Animal and plant ecology
,
Animal, plant and microbial ecology
2007
1. Understanding the factors influencing tree growth is central to forest ecology because of the significance of growth to forest structure and biomass. One of the simplest, yet most controversial growth models, proposed by Enquist and colleagues, predicts that stem-diameter growth scales as the one-third power of stem diameter. Recent analyses of large-scale data sets have challenged the generality of this theory and highlighted the influence of resource competition on the scaling of growth with size. 2. Here we explore the factors regulating the diameter growth of 3334 trees of mountain beech (Nothofagus solandri var. cliffortioides) growing in natural single-species forests in New Zealand. Maximum-likelihood modelling was used to quantify the influences of tree size, altitude, the basal area of taller neighbours (BL) and the basal area of all neighbours (BT) on growth. Our interpretation of the models assumed that taller neighbours compete for light whereas all neighbours compete for nutrients. 3. The regression analyses indicate that competition for light has a strong influence on the growth of small trees, whereas competition for nutrients affects trees of all sizes. These findings are consistent with experimental manipulation studies showing that competition for light and nutrients inhibits the growth of small mountain beech trees, and fertilizer application studies showing that nitrogen limits the growth of large trees. 4. Tree growth declined with altitude. The regression analyses suggest that the intensity of light competition also declines with altitude, when trees with similar BTand BLvalues were compared along the gradient. These results are consistent with observations that trees become stunted and have more open canopies at high altitudes. 5. Our study is the first to build the effects of competition and environment into Enquist's model of tree growth. We show that competitive interactions alter the scaling of mean growth rate with size, whereas altitude does not influence the scaling of potential growth rate with size.
Journal Article
Ecological drivers of taxonomic, functional, and phylogenetic diversity of bryophytes in an oceanic island
by
Collart, Flavien
,
Patiño, Jairo
,
Sim‐Sim, Manuela
in
alpha diversity
,
Anthropogenic factors
,
beta diversity
2024
Montane oceanic islands possess unique geographic and ecological attributes, rendering them valuable for assessing patterns and drivers of alpha and beta taxonomic, functional, and phylogenetic diversity along elevational gradients. Such comparisons of diversity facets can provide insights into the mechanisms governing community assembly on islands. Herein, we aimed to characterize taxonomic, functional, and phylogenetic bryophyte diversity on Madeira Island within and across areas at varying elevations. We also assessed how these diversity facets for the alpha and beta components relate to ecological and anthropogenic factors. We estimated and compared alpha and beta taxonomic, functional, and phylogenetic diversity using 80 plots of 0.5 m × 0.5 m across the whole elevational gradient of the island. We compiled trait databases and supplemented them with our own observations. Phylogenetic information was sourced from the Moss and Liverwort Tree of Life. To assess the impact of ecological and anthropogenic factors on the three facets, we applied linear mixed‐effects models and generalized dissimilarity models to alpha‐ and beta‐diversity matrices, respectively. All facets of diversity exhibited strong correlations within both mosses and liverworts, indicating a substantial congruence when alpha and beta are analyzed separately. The bryophyte groups categorized by the growth form demonstrated contrasting patterns, aligning with their distinctive ecological requirements. While a mid‐elevation peak emerged as a common pattern across the three facets of alpha diversity, beta diversity often displayed the opposite trend. Although the relative influence of environmental factors varied depending on the diversity facet and bryophyte grouping considered, we found that alpha and beta diversity of bryophytes are more influenced by climatic factors and the predominant type of vegetation than by anthropogenic factors. In the current context of global change, these results should be interpreted with caution, but they point to the resilience of bryophytes to survive in relatively well‐preserved natural microhabitats within anthropogenic landscapes. In this study on Madeira Island, we investigated patterns and drivers of alpha and beta taxonomic, functional, and phylogenetic diversity along elevational gradients. We found that alpha and beta diversity of bryophytes are more strongly influenced by climatic factors and the predominant type of vegetation than by anthropogenic factors. In this study on Madeira Island, we investigated patterns and drivers of alpha and beta taxonomic, functional, and phylogenetic diversity along elevational gradients. We found that alpha and beta diversity of bryophytes are more strongly influenced by climatic factors and the predominant type of vegetation than by anthropogenic factors.
Journal Article
Seeing the trees for the forest: drivers of individual growth responses to climate in Pinus uncinata mountain forests
by
Galván, Juan Diego
,
Gutiérrez, Emilia
,
Zuidema, Pieter
in
Animal and plant ecology
,
Animal, plant and microbial ecology
,
basal area
2014
Individual trees, not forests, respond to climate. Such an individual‐scale approach has seldom been used to retrospectively track the radial growth responses of trees to climate in dendrochronology. The aim of this study was to adopt this individual view to retrospectively assess tree sensitivity to climate warming, and to evaluate and compare the potential drivers of tree growth responses to climate acting at species, site and individual scales. Following a dendroecological framework, we sampled a network of 29 Pinus uncinata forests in NE Spain and obtained tree‐ring widths series from 642 trees. Individual features as northness, elevation, slope, basal area, sapwood area, tree height and tree age were used to evaluate the potential drivers of tree growth responses to climate. The analysed data set includes diverse ecological and biogeographical conditions. The tree growth responses to climate were assessed by relating growth indices to climatic variables using linear‐mixed effects models. Maximum November temperatures during the year prior to tree‐ring formation enhanced P. uncinata growth mainly in mid‐elevation sites, whereas at higher elevations growth was more dependent on the positive effect of warmer minimum May temperatures during the year of tree‐ring formation. Current June precipitation was the positive main climatic driver of growth in sites prone to water deficit such as the southernmost limit of the species distribution area or very steep sites. Elevation was the main factor controlling how much growth variability is explained by climate at the site and tree scales. Climate warming was more intense during the early 20th century, when the importance of elevation as an indirect modulator of growth declined as compared with the late 20th century. Synthesis. The individual‐scale approach taken in this study allowed detecting that trees growing at southern and low‐elevation sites were the most negatively affected by warm and dry summer conditions. Our results emphasize that both (i) an individual‐scale approach to quantify tree growth responses to climate and (ii) a detailed evaluation of the potential biotic and abiotic drivers of those individual responses are necessary to understand climate sensitivity of trees.
Journal Article
Simultaneous inference for misaligned multivariate functional data
by
Raket, Lars Lau
,
Olsen, Niels Lundtorp
,
Markussen, Bo
in
Analysis of covariance
,
Classification
,
Covariance
2018
We consider inference for misaligned multivariate functional data that represents the same underlying curve, but where the functional samples have systematic differences in shape. We introduce a class of generally applicable models where warping effects are modelled through non-linear transformation of latent Gaussian variables and systematic shape differences are modelled by Gaussian processes. To model cross-covariance between sample co-ordinates we propose a class of low dimensional cross-covariance structures that are suitable for modelling multivariate functional data. We present a method for doing maximum likelihood estimation in the models and apply the method to three data sets. The first data set is from a motion tracking system where the spatial positions of a large number of body markers are tracked in three dimensions over time. The second data set consists of longitudinal height and weight measurements for Danish boys. The third data set consists of three-dimensional spatial hand paths from a controlled obstacle avoidance experiment. We use the method to estimate the cross-covariance structure and use a classification set-up to demonstrate that the method outperforms state of the art methods for handling misaligned curve data.
Journal Article
Fifty years of natural succession in Swiss forest reserves: changes in stand structure and mortality rates of oak and beech
by
Wunder, Jan
,
Brang, Peter
,
Rohner, Brigitte
in
Akaike weight
,
Climate models
,
Deciduous forests
2012
Question: What are the drivers of structural changes and mortality in oak— beech forests over 50 yrs of natural succession? Location: Twelve unmanaged forest sites, comprising a large environmental gradient in the Swiss lowlands. Method: By using repeated inventory data from more than 17 600 individually tagged trees, the dynamics of oak—beech stands over the past 50 yrs were analysed. Generalized linear mixed-effects models were fitted to quantify annual mortality rates of oak and beech based on DBH, stand basal area, precipitation and slope. Results: Stand basal area increased, whereas tree density decreased over time. At most sites, the relative importance of oak decreased gradually compared to beech. Mortality increased over time for both oak and beech, but the increase was stronger for oak. Oak and beech mortality decreased with increasing DBH and tended to increase with precipitation. Additionally, oak mortality increased with stand basal area, whereas no such trend was found for beech. Conclusion: Our study indicates that mortality in Central European oak—beech forests is driven by a combination of stand structures (i.e. tree size and stand basal area) and climate. However, the influence of climate on oak mortality is comparably low. Increasing oak mortality with stand basal area is a plausible consequence of its lower relative competitiveness and higher demand for light. Thus, in forests developing towards higher stand basal area, the ecologically important oak is increasingly outcompeted by beech, unless competition is reduced through management or disturbances.
Journal Article
The Influence of Ozone on Net Ecosystem Production of a Ryegrass–Clover Mixture under Field Conditions
by
Švik, Marian
,
Grace, John
,
Juráň, Stanislav
in
Agricultural land
,
Agricultural production
,
Arable land
2021
In order to understand the effect of phytotoxic tropospheric ozone (O3) on terrestrial vegetation, we quantified the impact of current O3 concentration ([O3]) on net ecosystem production (NEP) when compared to the conditions of the pre-industrial era. We compared and tested linear mixed-effects models based on [O3] and stomatal O3 flux (Fsto). The managed ryegrass–clover (Lolium perenne and Trifolium pratense) mixture was grown on arable land in the Czech Republic, Central Europe. Values of [O3] and Fsto were measured and calculated based on resistance analogy, respectively, while NEP was calculated from eddy covariance CO2 fluxes. We found the Fsto-based model more precise when compared to measured NEP. High Fsto was found even at low [O3], while broad summer maximum of [O3] was not necessarily followed by significant NEP decline, due to low soil water content leading to a low stomatal conductivity and Fsto. Comparing to low pre-industrial O3 conditions, current levels of O3 resulted in the reduction of cumulative NEP over the entire growing season, up to 29.7 and 13.5% when the [O3]-based and Fsto-based model was applied, respectively. During the growing season, an O3-induced reduction of NEP ranged between 13.1% in May and 26.2% in July when compared to pre-industrial Fsto levels. Looking to the future, high [O3] and Fsto may lead to the reduction of current NEP by approximately 13.3% on average during the growing season, but may increase by up to 61–86.6% in autumn, indicating further O3-induced acceleration of the senescence. These findings indicate the importance of Fsto and its inclusion into the models estimating O3 effects on terrestrial vegetation. The interaction between environmental factors and stomatal conductance is therefore discussed in detail.
Journal Article