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Multiple Years (multiple + year)
Selected AbstractsCombining data from multiple years or areas to improve variogram estimationENVIRONMETRICS, Issue 6 2007John F. Walter III Abstract A requirement for geostatistical prediction is estimation of the variogram from the data. Often low sample size is a major impediment to elucidating a variogram even for a highly autocorrelated spatial process. This paper presents a methodology for improving variogram estimation when samples exist from multiple years or regions sharing a similar process for generating spatial autocorrelation. Such samples may come from annual monitoring programs for natural resources or from multiple geologic regions. As each set of samples contains some information on the spatial autocorrelation, combining information through the construction of a combined variogram cloud and binning to obtain a common variogram improves the estimation of the variogram. In both simulations and in real datasets of oyster abundance the method proposed here reduces the likelihood of failing to obtain a variogram from a set of samples and improves the efficiency of variogram estimation. In practice, the benefits obtained by estimating an otherwise elusive variogram generally outweigh the costs of using a slightly incorrect variogram model if different sampling stanzas are combined when they do not share the same spatial autocorrelation. Copyright © 2007 John Wiley & Sons, Ltd. [source] Mapping sea bird densities over the North Sea: spatially aggregated estimates and temporal changesENVIRONMETRICS, Issue 6 2005Edzer J. Pebesma Abstract In the Dutch sector of the North Sea, sea bird densities are recorded bi-monthly by using airborne strip-transect monitoring. From these data we try to estimate: (i) high-resolution spatial patterns of sea bird densities; (ii) low-resolution spatial-average bird densities for large areas; and (iii) temporal changes in (i) and (ii), using data on Fulmaris glacialis as an example. For spatial estimation, we combined Poisson regression for modelling the trend as a function of water depth and distance to coast with kriging interpolation of the residual variability, assuming spatial (co)variances to be proportional to the trend value. Spatial averages were estimated by block kriging. For estimating temporal differences we used residual cokriging for two consecutive years, and show how this can be extended to analyse trends over multiple years. Approximate standard errors are obtained for all estimates. A comparison with a residual simple kriging approach reveals that ignoring temporal cross-correlations leads to a severe loss of statistical accuracy when assessing the significance of temporal changes. This article shows results for Fulmaris glacialis monitored during August/September in 1998 and 1999. Copyright © 2005 John Wiley & Sons, Ltd. [source] NUPTIAL GIFTS AND THE EVOLUTION OF MALE BODY SIZEEVOLUTION, Issue 3 2002Kenneth M. Fedorka Abstract In many insect systems, males donate nuptial gifts to insure an effective copulation or as a form of paternal investment. However, if gift magnitude is both body size-limited and positively related to fitness, then the opportunity exists for the gift to promote the evolution of large male size. In the striped ground cricket, Allonemobius socius, males transfer a body size-limited, somatic nuptial gift that is comprised primarily of hemolymph. To address the implications of this gift on male size evolution, we quantified the intensity and direction of natural (fecundity) and sexual (mating success) selection over multiple generations. We found that male size was under strong positive sexual selection throughout the breeding season. This pattern of selection was similar in successive generations spanning multiple years. Male size was also under strong natural selection, with the largest males siring the most offspring. However, multivariate selection gradients indicated that gift size, and not male size, was the best predictor of female fecundity. In other words, direct fecundity selection for larger gifts placed indirect positive selection on male body size, supporting the hypothesis that nuptial gifts can influence the evolution of male body size in this system. Although female size was also under strong selection due to a size related fecundity advantage, it did not exceed selection on male size. The implications of these results with regard to the maintenance of the female-biased size dimorphic system are discussed. [source] Effects of acidification on the breeding ecology of a stream-dependent songbird, the Louisiana waterthrush (Seiurus motacilla)FRESHWATER BIOLOGY, Issue 11 2008ROBERT S. MULVIHILL Summary 1.,We compared breeding ecology of the Louisiana waterthrush (Seiurus motacilla) on acidified and circumneutral streams in the Appalachian Highlands of Southwestern Pennsylvania from 1996 to 2005. 2.,Headwater streams impacted by acid mine drainage and/or acidic precipitation showed reduced pH (range 4.5,5.5) compared to four circumneutral streams (pH c. 7). Acid-sensitive taxa, including most mayflies (Ephemeroptera), were almost completely absent from acidified streams, whereas several acid-tolerant taxa, especially stonefly (Plecoptera) genera Leuctra and Amphinemura, were abundant. 3.,Louisiana waterthrush breeding density (c. 1 territory km,1) was significantly reduced on acidified streams compared to circumneutral streams (>2 territories km,1). Territories on acidified streams were almost twice as long as on circumneutral streams. Territories usually were contiguous on circumneutral streams, but they were often disjunct on acidified streams. Breeding density declined on one acidified stream that we studied over a 10-year period. 4.,Clutch initiation was significantly delayed on acidified streams, on average by 9 days in comparison to circumneutral streams, and first-egg dates were inversely related to breeding density. Birds nesting along acidified streams laid smaller clutches, and nestlings had shorter age-adjusted wing lengths. Stream acidity had no effect on nest success or annual fecundity (fledglings/female). However, the number of young fledged km,1 was nearly twice as high on circumneutral streams as on acidified streams. 5.,Acidified streams were characterized by a younger, less site-faithful breeding population. Individuals were less likely to return multiple years to breed, allowing inexperienced breeders to settle on acidified streams. Pairing success was lower on acidified streams, and we observed four cases of waterthrushes emigrating from territories on acidified streams to nearby circumneutral streams in the following year. 6.,We conclude that acidified headwaters constitute lower quality habitat for breeding Louisiana waterthrush. However, breeding birds can apparently compensate for reduced prey resources to fledge young on acidified streams by increasing territory size, foraging in peripheral non-acidified areas, and by provisioning young with novel prey. [source] Seasonal mortality and the effect of body size: a review and an empirical test using individual data on brown troutFUNCTIONAL ECOLOGY, Issue 4 2008Stephanie M. Carlson Summary 1,For organisms inhabiting strongly seasonal environments, over-winter mortality is thought to be severe and size-dependent, with larger individuals presumed to survive at a higher rate than smaller conspecifics. Despite the intuitive appeal and prevalence of these ideas in the literature, few studies have formally tested these hypotheses. 2We here tested the support for these two hypotheses in stream-dwelling salmonids. In particular, we combined an empirical study in which we tracked the fate of individually-marked brown trout across multiple seasons and multiple years with a literature review in which we compiled the results of all previous pertinent research in stream-dwelling salmonids. 3We report that over-winter mortality does not consistently exceed mortality during other seasons. This result emerged from both our own research as well as our review of previous research focusing on whether winter survival is lower than survival during other seasons. 4We also report that bigger is not always better in terms of survival. Indeed, bigger is often worse. Again, this result emerged from both our own empirical work as well as the compilation of previous research focusing on the relationship between size and survival. 5We suggest that these results are not entirely unexpected because self-sustaining populations are presumably adapted to the predictable seasonal variation in environmental conditions that they experience. [source] Publicly funded medical savings accounts: expenditure and distributional impacts in Ontario, CanadaHEALTH ECONOMICS, Issue 10 2008Jeremiah Hurley Abstract This paper presents the findings from simulations of the introduction of publicly funded medical savings accounts (MSAs) in the province of Ontario, Canada. The analysis exploits a unique data set linking population-based health survey information with individual-level information on all physician services and hospital services utilization over a four-year period. The analysis provides greater detail along three dimensions than have previous analyses: (1) the distributional impacts of publicly funded MSAs across individuals of differing health statuses, incomes, ages, and current expenditures; (2) the impact of differing degrees of risk adjustment for MSA contributions; and (3) the impact of MSA funding over multiple years, incorporating year-to-year variation in spending at the individual level. In addition, it analyses more plausible designs for publicly funded MSAs than the existing studies. Government uses information available from year t,,,1 to allocate its budget for year t in a manner that is ex ante fiscally neutral for the public sector: the government first withholds funds equal to expected catastrophic insurance payments under the MSA plan, and then allocates only the balance to individual MSA accounts. The government captures the savings associated with reduced health-care utilization under MSAs and we examine deductibles that vary by income rather than by current health-care expenditures. The impacts on public expenditures under these designs are more modest than in the previous studies and under plausible assumptions MSAs are predicted to decrease public expenditures. MSAs, however, are also predicted to have unavoidable negative distributional consequences with respect to both public expenditures and out-of-pocket spending. Copyright © 2007 John Wiley & Sons, Ltd. [source] The Tax Incidence of Lotteries: Evidence from Five StatesJOURNAL OF CONSUMER AFFAIRS, Issue 2 2000ANN HANSEN The nature of revenue generation for state-sponsored lotteries has been an issue of public debate for quite some time. Although most studies have found lotteries to have a regressive tax incidence, several have concluded otherwise. Unfortunately, the vast majority of academic studies address this concern by examining the tax incidence of only one state's lottery and/or by using only one time period's data. In addition, many assessments of the tax impact of lotteries fail to consider other demographic variables that may influence purchase patterns and, thus, be of interest to policymakers. To remedy this, the current paper assesses the incidence of the lottery excise tax for five states using county level data spanning multiple years. Also assessed are changes in incidence across demographic groups as the lotteries matured. Lottery tax incidence is assessed with multiple regression estimates of the income elasticity of demand for lottery products. The predominant finding is that the lottery tax for these states had a regressive incidence. Otherwise, few consistencies in either change in lottery tax incidence or purchase patterns across demographic variables were found. [source] Analyzing and interpreting NSSE dataNEW DIRECTIONS FOR INSTITUTIONAL RESEARCH, Issue 141 2009Pu-Shih Daniel Chen Drawing on their experience, current and former NSSE research analysts offer helpful tips and recommendations for institutional researchers on how to analyze student engagement data, including ways to work with multiple years of results and interpret effect sizes. [source] The course and correlates of high hospital utilization in sickle cell disease: Evidence from a large, urban Medicaid managed care organization,AMERICAN JOURNAL OF HEMATOLOGY, Issue 10 2009C. Patrick Carroll Although most patients with sickle cell disease (SCD) are hospitalized infrequently and manage painful crises at home, a small subpopulation is frequently admitted to emergency departments and inpatient units. This small group accounts for the majority of health care expenses for patients with SCD. Using inpatient claims data from a large, urban Medicaid MCO for 5 consecutive years, this study sought to describe the course of high inpatient utilization (averaging four or more admissions enrolled per year for at least 1 year) in members with a diagnosis of SCD and a history of hospitalizations for vaso-occlusive crisis. High utilizers were compared with the other members with SCD on demographics, medical and psychiatric comorbidity, and use of other health care resources. Members who were high utilizers had more diagnostic mentions of sickle cell complications than low utilizers. However, the pattern of high inpatient utilization was likely to moderate over successive years, and return to the pattern after moderation was uncommon. Despite this, a small subpopulation engaged in exceptional levels of inpatient utilization over multiple years. Am. J. Hematol., 2009. © 2009 Wiley-Liss, Inc. [source] Behavioral responses to tooth loss in wild ring-tailed lemurs (Lemur catta) at the Beza Mahafaly Special Reserve, MadagascarAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2009James B. Millette Abstract Severe dental wear and tooth loss is often assumed to impede the processing, breakdown, and energetic conversion of food items, thereby negatively impacting individual health, reproduction, and survival. Ring-tailed lemurs at the Beza Mahafaly Special Reserve demonstrate exceptionally high frequencies of severe dental wear and antemortem tooth loss, yet often survive multiple years with these impairments. To test the hypothesis that these lemurs mitigate tooth loss through behavioral adjustments, we collected 191 h of observational data from 16 focal subjects, eight without tooth loss and eight with between 3% and 44% loss. These data indicate dentally-impaired ring-tailed lemurs show compensatory behaviors consistent with the demands of living in a social group. During early afternoon (12:00,14:30 h) individuals with loss showed trends towards higher frequencies of foraging and grooming, while individuals without loss rested significantly more often. Individuals with >10% loss (n = 7) showed higher frequencies of feeding, foraging, and grooming, and lower frequencies of resting during this period than individuals with <10% loss (n = 9). Individuals with tooth loss maintained relatively higher levels of feeding and foraging throughout the day. These individuals licked tamarind fruit at higher frequencies, likely spending more time softening it before ingestion. These individuals did not demonstrate longer feeding bouts overall, although bouts involving tamarinds were significantly longer. Individuals with marked toothcomb wear engaged in higher rates of certain types of allogrooming, demonstrating that social behaviors are used to compensate for reduced grooming efficiency. These data have implications for interpreting behavioral responses to dental impairment in the fossil record. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source] Survival rates for a declining population of bottlenose dolphins in Doubtful Sound, New Zealand: an information theoretic approach to assessing the role of human impactsAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 6 2009Rohan J. C. Currey Abstract 1.The bottlenose dolphins of Doubtful Sound, New Zealand are a declining population at the southern limit of the species' range, exposed to impacts from tourism and habitat modification. Patterns in apparent annual survival were analysed from photographic resightings of naturally marked adults (1990 to 2008) and calves within the first year of life (1994 to 2008) using capture-recapture models. 2.The most parsimonious model for adults provided a time-invariant, sex-invariant estimate of survival (,a(1990,2008)=0.9374; 95% CI: 0.9170,0.9530), marginally lower than prior estimates for wild bottlenose dolphins. 3.The most parsimonious model for calves indicated a significant time-variant decline in survival from an estimate similar to other populations (,c(1994,2001)=0.8621; 95% CI: 0.6851,0.9473) to a current estimate that is, to our knowledge, the lowest recorded for free-ranging bottlenose dolphins (,c(2002,2008)=0.3750; 95% CI: 0.2080,0.5782). 4.Information theoretic evidence ratios suggested that observed patterns in calf survival were 22 times more likely to be explained by a decline coincident with the opening of a second tailrace tunnel for a hydroelectric power station than by a decline in any other year or across multiple years. 5.Projections using an age-structured stochastic population model indicated that the current level of calf survival was unsustainable (population decline: 100% of model runs; population extinction: 41.5% of model runs) and was a key factor in the observed population decline in Doubtful Sound. Copyright © 2008 John Wiley & Sons, Ltd. [source] A baseline biological survey of the proposed Taputeranga Marine Reserve (Wellington, New Zealand): spatial and temporal variability along a natural environmental gradientAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 2 2009Anjali Pande Abstract 1.Four macroalgal, four macroinvertebrate and eight fish species were surveyed at eight sites (three inside, five outside the proposed reserve) over three years before the establishment of the Taputeranga Marine Reserve (MR) on Cook Strait (Wellington, New Zealand). This baseline data set was used to estimate temporal and spatial variability in size and abundance of these taxa, and will be used to quantify taxon-specific changes in size and abundance once the MR is established. 2.Statistically significant differences in size and/or abundance were observed for many taxa among the sites. These differences are consistent with the existence of a natural environmental gradient from the west (entrance to Cook Strait) to the east (Wellington Harbour). This gradient highlights the importance of conducting a pre-reserve baseline survey at multiple sites and over multiple years to better understand the conservation or fisheries benefits that MRs are expected to deliver. 3.Two macroalgal, one macroinvertebrate, and six fish species showed statistically significant seasonal variation in abundance. Subsequent multi-taxa monitoring needs to include a seasonal component to capture this natural variability. 4.This multi-site and multi-year data set represents one of the most comprehensive and robust baseline data sets available anywhere in the world. It will be used to quantify the ecological changes associated with a newly established full no-take marine reserve. Ongoing monitoring will enhance understanding of the sizes and abundances of key taxa, allow a detailed determination of the conservation effects of reserve establishment, and inform management decisions for Wellington's south coast. Copyright © 2008 John Wiley & Sons, Ltd. [source] Spatial distribution and prediction of seed production by Eucalyptus microcarpa in a fragmented landscapeAUSTRAL ECOLOGY, Issue 1 2010PETER A. VESK Abstract Woodlands worldwide have been greatly modified by clearing for agriculture, and their conservation and restoration requires understanding of tree recruitment processes. Seed production is one possible point of recruitment failure, and one that the spatial arrangement of trees may affect. We sampled 118 Eucalyptus microcarpa (Myrtaceae) trees to compare and analyse the determinants of seed production in this dominant tree of modified, fragmented temperate grassy woodlands, which extend over much of southeastern Australia. Fecundity was estimated as the seed crop measured on leaf mass and whole tree bases and was compared between categories of tree configuration. We also modelled fecundity using boosted regression trees, a new and flexible tool. Fecundity on a leaf mass basis was predominantly influenced by environmental factors (topographic ,wetness', slope, soil type), rather than by local tree density and configuration. Fewer seed per unit leaf mass were produced on flat and topographically wet sites, reflecting poor tolerance of waterlogging by E. microcarpa. By contrast, whole tree fecundity was little influenced by environmental factors. Local tree density and configuration did influence whole tree fecundity, which was high in solitary and woodland-spaced trees and reduced under high local density. We found little evidence for reduced fecundity of E. microcarpa in solitary trees. This points to the importance of scattered trees as sources of seed for tree recruitment and for natural regeneration of landscape level tree cover. Considerable uncertainty remains in modelled seed supply, and may be reduced with sampling across multiple years and greater environmental and spatial domains. [source] Evaluating combined land conservation benefits from perennial pasture: lucerne (Medicago sativa L.) for management of dryland salinity and herbicide resistance in Western Australia,AUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 2 2009Graeme J. Doole The inclusion of perennial pasture phases in cropping rotations has been widely promoted throughout Australia for reducing the incidence of dryland salinity. To a lesser extent, they have also been promoted to enhance the management of herbicide-resistant weeds. No previous economic analysis of perennial pasture has considered both of these benefits. This study combines a dynamic linear programming model to estimate the magnitude of salinity-related benefits and a complex simulation model to assess the economics of herbicide-resistance management. We present a case study of the perennial pasture lucerne (Medicago sativa L.) in the Wheatbelt of Western Australia, where the weed annual ryegrass (Lolium rigidum Gaudin) is resistant to multiple herbicide groups. Sequences incorporating lucerne are the most profitable land use at the standard set of parameter values if (i) annual ryegrass is resistant to all selective herbicides, (ii) the water table is so shallow (approximately < 3.5 m deep) that frequent rotation with perennials is required to avert soil salinisation, (iii) sheep production is highly profitable, or (iv) there is a combination of less extreme cases. The value of perennial pasture is sufficient under these circumstances to overcome its high establishment cost and the displacement of multiple years of crop. Consideration of dryland salinity and herbicide resistance are about equally important in evaluating the economics of lucerne; neither should be neglected. [source] | ||||||||||||||||