Invaders generally show better individual performance than non-invaders and, therefore, vital rates (survival, growth, fecundity) could potentially be used to predict species invasiveness outside their native range. Comparative studies have usually correlated vital rates with the invasiveness status of species, while few studies have investigated them in relation to population growth rate. Here, I examined the influence of five vital rates (plant establishment, survival, growth, flowering probability, seed production) and their variability (across geographic regions, habitat types, population sizes and population densities) on population growth rate (?) using data from 37 populations of an invasive, iteroparous herb (Lupinus polyphyllus) in a part of its invaded range in Finland. Variation in vital rates was often related to habitat type and population density. The performance of the populations varied from declining to rapidly increasing independently of habitat type, population size or population density, but differed between regions. The population growth rate increased linearly with plant establishment, and with the survival and growth of vegetative individuals, while the survival of flowering individuals and annual seed production were not related to ?. The vital rates responsible for rapid population growth varied among populations. These findings highlight the importance of both regional and local conditions to plant population dynamics, demonstrating that individual vital rates do not necessarily correlate with ?. Therefore, to understand the role of individual vital rates in a species ability to invade, it is necessary to quantify their effect on population growth rate.
Costs of reproduction are expected to vary with environmental conditions thus influencing selection on life-history traits. Yet, the effects of habitat conditions and climate on trade-offs among fitness components remain poorly understood. For 2-5 years, we quantified costs of experimentally increased reproduction in two populations (coastal long-season vs. inland short-season) of two long-lived orchids that differ in natural reproductive effort (RE; 30 vs. 75% fruit set). In both species, survival costs were found only at the short-season site, whereas growth and fecundity costs were evident at both sites, and both survival and fecundity costs declined with increasing growing season length and/or summer temperature. The results suggest that the expression of costs of reproduction depend on the local climate, and that climate warming could result in selection favouring increased RE in both study species.
Rasch models provide a framework for measurement and modelling latent variables. Having measured a latent variable in a population a comparison of groups will often be of interest. For this purpose the use of observed raw scores will often be inadequate because these lack interval scale properties. This paper compares two approaches to group comparison: linear regression models using estimated person locations as outcome variables and latent regression models based on the distribution of the score.
Meteorological conditions and air pollution in urban environments have been associated with general population and elderly mortality, showing seasonal variation.
This study is designed to evaluate the relationship between apparent temperature (AT) and air pollution (PM2.5) vs. mortality in elderly population of Metro Vancouver.
Statistical analyses are performed on moving sum daily mortality rates vs. moving average AT and PM2.5 in 1-, 2-, 3-, 5-, and 7-day models for all seasons, warm temperatures above 15?C, and cold temperatures below 10?C.
Approximately 37% of the variation in all-season mortality from circulatory and respiratory causes can be explained by the variation in 7-day moving average apparent temperature (r??=?0.37, p
Cites: Environ Monit Assess. 2006 Aug;119(1-3):425-3916741816
Cites: J Air Waste Manag Assoc. 2006 Jun;56(6):709-4216805397
In this work we extend approximate aggregation methods to deal with a very general linear time discrete model. Approximate aggregation consists in describing some features of the dynamics of a general system in terms of the dynamics of a reduced system governed by a few global variables. We present a time discrete model for a structured population (i.e., the population is subdivided in subpopulations) in which we can distinguish two processes of a general nature and whose corresponding time scales are very different from each other. We transform the general system to make the global variables appear and obtain the reduced system. These global variables are, for each subpopulation, a certain linear combination of the corresponding state variables. We show that, under quite general conditions, the asymptotic behavior of the reduced system can be known in terms of the corresponding behavior for the reduced system. The general method is applied to aggregate a multiregional Leslie model in which the demographic process is supposed to be fast with respect to migration.
To compare rates of fatal drug-related overdose death (OD) cases--a major harm outcome of illicit substance use--in the two provinces of British Columbia (BC) and Ontario, and the two largest municipalities in those provincial jurisdictions, namely the cities of Vancouver and Toronto, between 1992 and 2004.
Provincial coroners' data of drug-related OD cases for the provincial jurisdictions of BC and Ontario, and the municipal jurisdictions of Vancouver and Toronto, are descriptively presented and compared.
After drastic increases in the initial part of the observation period, OD rates in BC have been declining; moreover, due to major reductions of OD cases in Vancouver, the ratio of OD cases between Vancouver and the province of BC has fallen considerably. Conversely, OD rates in Ontario have remained stable at low levels, whereas Toronto has seen a slight decline in such rates during the observation period.
The recent establishment and expansion of treatment and harm reduction interventions may have influenced the decline of ODs in BC, yet similar interventions in Ontario did not have a similar effect, perhaps due to different patterns of illicit drug use. OD rates in jurisdictions across Canada need to be monitored and analyzed to inform evidence-based policy development.
Forests play a key role in the carbon balance of terrestrial ecosystems. One of the main uncertainties in global change predictions lies in how the spatiotemporal dynamics of forest productivity will be affected by climate warming. Here we show an increasing influence of climate on the spatial variability of tree growth during the last 120 y, ultimately leading to unprecedented temporal coherence in ring-width records over wide geographical scales (spatial synchrony). Synchrony in growth patterns across cold-constrained (central Siberia) and drought-constrained (Spain) Eurasian conifer forests have peaked in the early 21st century at subcontinental scales (~ 1,000 km). Such enhanced synchrony is similar to that observed in trees co-occurring within a stand. In boreal forests, the combined effects of recent warming and increasing intensity of climate extremes are enhancing synchrony through an earlier start of wood formation and a stronger impact of year-to-year fluctuations of growing-season temperatures on growth. In Mediterranean forests, the impact of warming on synchrony is related mainly to an advanced onset of growth and the strengthening of drought-induced growth limitations. Spatial patterns of enhanced synchrony represent early warning signals of climate change impacts on forest ecosystems at subcontinental scales.
A study designed to test the effects of delay between crime and lineup on identification accuracy produced an unusually high rate of correct rejection from target-absent, simultaneous lineups (J. E. Dysart, 1999). Examining the procedures indicated that one question included in a preidentification questionnaire differed from those used previously. The question asked witnesses if they believed they would be able to correctly reject a target-absent lineup. An experiment (N = 138) was conducted to explore the impact of preidentification questions, including this new question, on witness accuracy. Results revealed that asking witnesses these questions, prior to viewing the lineup, significantly increased correct rejections of target-absent simultaneous lineups.
Some countries have regulations against using a cellular telephone while driving. We used ecologic analysis to evaluate cellular telephone use and motor vehicle collisions in a city without such regulations.
We studied locations in Toronto, Ontario (n = 75) that were hazardous (total collisions = 3,234) and tested whether increases in collision rates from 1984 to 1993 correlated with increases in telephone usage over the same time interval.
Locations with the largest increases in collision rates tended to have the smallest increases in estimated cellular telephone usage. Yet extreme assumptions about potential protective effects from cellular telephones failed to explain the magnitude observed.
The effects of cellular telephones on driving ability are small relative to the biases in ecologic analysis. Claims from industry, which argue that cellular telephones are not dangerous based on ecologic analysis, can be misleading in the policy debate about whether to regulate cellular telephone use while driving.