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Elasticity Analyses (elasticity + analysis)

Distribution by Scientific Domains

Life Sciences	93%

Selected Abstracts

Rainfall effects on rare annual plants

JOURNAL OF ECOLOGY, Issue 4 2008
Jonathan M. Levine
Summary 1Variation in climate is predicted to increase over much of the planet this century. Forecasting species persistence with climate change thus requires understanding of how populations respond to climate variability, and the mechanisms underlying this response. Variable rainfall is well known to drive fluctuations in annual plant populations, yet the degree to which population response is driven by between-year variation in germination cueing, water limitation or competitive suppression is poorly understood. 2We used demographic monitoring and population models to examine how three seed banking, rare annual plants of the California Channel Islands respond to natural variation in precipitation and their competitive environments. Island plants are particularly threatened by climate change because their current ranges are unlikely to overlap regions that are climatically favourable in the future. 3Species showed 9 to 100-fold between-year variation in plant density over the 5,12 years of censusing, including a severe drought and a wet El Niño year. During the drought, population sizes were low for all species. However, even in non-drought years, population sizes and per capita growth rates showed considerable temporal variation, variation that was uncorrelated with total rainfall. These population fluctuations were instead correlated with the temperature after the first major storm event of the season, a germination cue for annual plants. 4Temporal variation in the density of the focal species was uncorrelated with the total vegetative cover in the surrounding community, suggesting that variation in competitive environments does not strongly determine population fluctuations. At the same time, the uncorrelated responses of the focal species and their competitors to environmental variation may favour persistence via the storage effect. 5Population growth rate analyses suggested differential endangerment of the focal annuals. Elasticity analyses and life table response experiments indicated that variation in germination has the same potential as the seeds produced per germinant to drive variation in population growth rates, but only the former was clearly related to rainfall. 6Synthesis. Our work suggests that future changes in the timing and temperatures associated with the first major rains, acting through germination, may more strongly affect population persistence than changes in season-long rainfall. [source]

Incorporating Uncertainty into Demographic Modeling: Application to Shark Populations and Their Conservation

CONSERVATION BIOLOGY, Issue 4 2002
Enric Cortés
I used age-structured life tables and Leslie matrices based on a prebreeding survey and a yearly time step applied only to females to model the demography of 41 populations from 38 species of sharks representing four orders and nine families. I used Monte Carlo simulation to reflect uncertainty in the estimates of demographic traits and to calculate population statistics and elasticities for these populations; I used correlation analysis to identify the demographic traits that explained most of the variation in population growth rates ( , ). The populations I examined fell along a continuum of life-history characteristics that can be linked to elasticity patterns. Sharks characterized by early age at maturity, short lifespan, and large litter size had high , values and short generation times, whereas sharks that mature late and have long lifespans and small litters have low , values and long generation times. Sharks at the "fast" end of the spectrum tended to have comparable adult and juvenile survival elasticities, whereas sharks at the "slow" end of the continuum had high juvenile survival elasticity and low age,zero survival ( or fertility ) elasticity. Ratios of adult survival to fertility elasticities and juvenile survival to fertility elasticities suggest that many of the populations studied do not possess the biological attributes necessary to restore , to its original level after moderate levels of exploitation. Elasticity analysis suggests that changes in juvenile survival would have the greatest effect on ,, and correlation analysis indicates that variation in juvenile survival, age at maturity, and reproduction account for most of the variation in ,. In general, combined results from elasticity and correlation analyses suggest that research, conservation, and management efforts should focus on these demographic traits. Resumen: Exploré los efectos de la incertidumbre en los caracteres demográficos en análisis demográficos de tiburones, un método no empleado con anterioridad para este taxón. Utilicé tablas de vida estructuradas por edades y matrices de Leslie basadas en evaluaciones pre-gestación y pasos de tiempo de un año aplicados solo a las hembras para modelar la demografía de 41 poblaciones de 38 especies de tiburones que representan cuatro órdenes y nueve familias. Utilicé la simulación de Monte Carlo para reflejar la incertidumbre en las estimaciones de caracteres demográficos y calcular las estadísticas y elasticidades poblacionales para estas poblaciones y el análisis de correlación para identificar los caracteres demográficos que explican la mayoría de la variación en las tasas de crecimiento poblacional ( , ). Las poblaciones examinadas caen dentro de un continuo de características de historias de vida que pueden estar vinculadas con los patrones de elasticidad. Los tiburones que maduran a temprana edad y tienen corta duración de vida y grupos grandes de crías tuvieron valores altos de , y tiempos generacionales cortos, mientras que los tiburones que maduran tarde y tienen una duración de vida larga y grupos pequeños de crías tienen valores bajos de , y tiempos generacionales largos. Los tiburones que se encuentran en el punto final "rápido" del espectro tendieron a tener elasticidades de supervivencia de adultos y juveniles comparables, mientras que los tiburones en el punto final "lento" del continuo tuvieron una alta elasticidad de supervivencia de juveniles y una baja elasticidad en supervivencia a la edad cero (o fertilidad ). Las proporciones de elasticidades de supervivencia de adultos y fertilidad y de elasticidades de supervivencia de juveniles y fertilidad sugieren que muchas de las poblaciones estudiadas no poseen los atributos biológicos necesarios para restaurar , a su nivel original después de niveles moderados de explotación. El análisis de elasticidad sugiere que en la supervivencia de juveniles se podría tener el efecto mayor de , y el análisis de correlación indica que la variación en la supervivencia de juveniles, la edad de maduración y reproducción explican la mayor parte de la variación en ,. En general, los resultados combinados de los análisis de elasticidad y correlación sugieren que los esfuerzos de investigación, conservación y manejo deberían enfocarse a estas características demográficas. [source]

Demographic models and the management of endangered species: a case study of the critically endangered Seychelles magpie robin

JOURNAL OF APPLIED ECOLOGY, Issue 5 2003
Ken Norris
Summary 1Demographic models are assuming an important role in management decisions for endangered species. Elasticity analysis and scope for management analysis are two such applications. Elasticity analysis determines the vital rates that have the greatest impact on population growth. Scope for management analysis examines the effects that feasible management might have on vital rates and population growth. Both methods target management in an attempt to maximize population growth. 2The Seychelles magpie robin Copsychus sechellarum is a critically endangered island endemic, the population of which underwent significant growth in the early 1990s following the implementation of a recovery programme. We examined how the formal use of elasticity and scope for management analyses might have shaped management in the recovery programme, and assessed their effectiveness by comparison with the actual population growth achieved. 3The magpie robin population doubled from about 25 birds in 1990 to more than 50 by 1995. A simple two-stage demographic model showed that this growth was driven primarily by a significant increase in the annual survival probability of first-year birds and an increase in the birth rate. Neither the annual survival probability of adults nor the probability of a female breeding at age 1 changed significantly over time. 4Elasticity analysis showed that the annual survival probability of adults had the greatest impact on population growth. There was some scope to use management to increase survival, but because survival rates were already high (> 0·9) this had a negligible effect on population growth. Scope for management analysis showed that significant population growth could have been achieved by targeting management measures at the birth rate and survival probability of first-year birds, although predicted growth rates were lower than those achieved by the recovery programme when all management measures were in place (i.e. 1992,95). 5Synthesis and applications. We argue that scope for management analysis can provide a useful basis for management but will inevitably be limited to some extent by a lack of data, as our study shows. This means that identifying perceived ecological problems and designing management to alleviate them must be an important component of endangered species management. The corollary of this is that it will not be possible or wise to consider only management options for which there is a demonstrable ecological benefit. Given these constraints, we see little role for elasticity analysis because, when data are available, a scope for management analysis will always be of greater practical value and, when data are lacking, precautionary management demands that as many perceived ecological problems as possible are tackled. [source]

Demography and population dynamics of Drosera anglica and D. rotundifolia

JOURNAL OF ECOLOGY, Issue 1 2004
J.-F. Nordbakken
Summary 1We studied demography and population dynamics of the sympatric perennial herbs Drosera anglica and D. rotundifolia on a boreal bog in SE Norway. Dry mass of 2872 D. anglica plants and 2467 D. rotundifolia plants (estimated from field morphological measurements) was used to classify plants into five species-specific size classes. Demographic changes within these two populations were followed from 1995 to 1999, and within segments (quartiles) along the water table gradient and the peat productivity gradient. 2Mortality was strongly size dependent, and varied between years, for both species; it was high for seedlings, low for the smallest mature rosettes and increased again for the largest mature rosettes. The proportion of fertile rosettes increased with increasing rosette size. Fecundity varied considerably between years, but little relative to gradient position. 3Growth rate (,) was > 1, except in the second year, when it fell to 0.572 for D. anglica and 0.627 for D. rotundifolia . For D. anglica small, but significant, differences were found between the two extremities of the water table gradient, and for D. rotundifolia between the second and the uppermost quartile. There was a tendency for D. anglica populations to have a lower growth rate in the most productive sites, whereas D. rotundifolia grew less on both low and high peat productivity. Elasticity analysis showed that stasis and size increase (primarily within mature stages) made major contributions to , for D. anglica in all years. 4The variance in population growth rate (var ,) was high between years, and higher for D. anglica than for D. rotundifolia , while the variance between quartiles along the two main gradients was low. Life-table response experiment (LTRE) analyses revealed that for both species, differences in probabilities of transitions within mature stages, and in growth to larger stages, contributed most to var ,. 5The effects of global warming are uncertain: drier growing seasons would affect Drosera populations negatively, while initially positive responses to a wetter climate may be balanced by competition from increased Sphagnum growth. [source]

Demography and reproductive strategies of a polycarpic perennial, Trillium apetalon (Trilliaceae)

PLANT SPECIES BIOLOGY, Issue 3 2001
MASASHI OHARA
Abstract To investigate the connection between demographic strategies and reproductive strategies of a polycarpic perennial herb, Trillium apetalon Makino, we conducted three studies. First, we monitored the fate of individuals and the flowering behavior of T. apetalon for 12 years and used a transition matrix model to analyze the demography of the population. The analysis revealed that it takes a long time for individuals to go through one-leaf stage in juveniles. Elasticity analysis showed that the survival of flowering individuals was a decisive factor in the dynamics of the population. Furthermore, we found that the average remaining lifetime of flowering individuals was high relative to the other three stages. Second, to elucidate the demographic consequences of organ preformation, we investigated the development of flower buds for future years. We observed three to six flower buds per rhizome, suggesting that flower buds for the next 3,6 years were ready in advance in this plant. Third, the results of breeding experiments clarified that although this species appears to have a substantial capacity for both inbreeding and outbreeding, inbreeding plays an important role in seed production, and that crossing experiments (direct cross-pollination and self pollination) yielded similar seed-ovule ratios to those obtained from open-pollinated individuals. Our three studies suggest that the adult survival and continuous flowering strategies of T. apetalon obtained from demographic analysis are closely interlinked with breeding systems and preformation of flower buds. [source]

Management and Recovery Options for Ural River Beluga Sturgeon

CONSERVATION BIOLOGY, Issue 3 2010
PHAEDRA DOUKAKIS
caviar; CITES; criadero; Mar Caspio; puntos de referencia; sobrepesca Abstract:,Management of declining fisheries of anadromous species sometimes relies heavily on supplementation of populations with captive breeding, despite evidence that captive breeding can have negative consequences and may not address the root cause of decline. The beluga sturgeon (Huso huso), a species threatened by the market for black caviar and reductions in habitat quality, is managed through harvest control and hatchery supplementation, with an emphasis on the latter. We used yield per recruit and elasticity analyses to evaluate the population status and current levels of fishing and to identify the life-history stages that are the best targets for conservation of beluga of the Ural River. Harvest rates in recent years were four to five times higher than rates that would sustain population abundance. Sustainable rates of fishing mortality are similar to those for other long-lived marine species such as sharks and mammals. Yield per recruit, which is maximized if fish are first harvested at age 31 years, would be greatly enhanced by raising minimum size limits or reducing illegal take of subadults. Improving the survival of subadult and adult females would increase population productivity by 10 times that achieved by improving fecundity and survival from egg to age 1 year (i.e., hatchery supplementation). These results suggest that reducing mortality of subadults and adult wild fish is a more effective conservation strategy than hatchery supplementation. Because genetics is not factored into hatchery management practices, supplementation may even reduce the viability of the beluga sturgeon. Resumen:,El manejo de pesquerías de peces anádromos en declinación a veces depende estrechamente de la suplementación de poblaciones mediante la reproducción en cautiverio, no obstante la evidencia de que la reproducción en cautiverio puede tener consecuencias negativas y no abordar la causa principal de la declinación. El esturión beluga (Huso huso), una especie amenazada por el mercado de caviar negro y por reducciones en la calidad del hábitat, es manejado mediante el control de la cosecha y suplementación de poblaciones, con énfasis en esta. Utilizamos análisis de producción por recluta y de elasticidad para evaluar el estatus de la población y los niveles de pesca actuales y para identificar las etapas de la historia de vida que son los mejores blancos para la conservación del beluga en el Río Ural. Las tasas de cosecha en años recientes fueron cuatro a cinco veces mayores que las tasas que sustentarían la abundancia de la población. Las tasas sustentables de mortalidad por pesca son similares a las de otras especies marinas longevas como tiburones y mamíferos. La producción por recluta, que es maximizada si los peces son cosechados a la edad de 31 años, podría incrementar significativamente elevando los límites de talla mínima o reduciendo la captura ilegal de subadultos. La mejora de la supervivencia de hembras subadultas y adultas incrementaría la productividad de la población 10 veces más que la mejora obtenida incrementando la fecundidad y supervivencia de huevo a 1 año de edad (i. e., suplementación de poblaciones mediante reproducción en cautiverio). Estos resultados sugieren que la reducción de la mortalidad de peces silvestres subadultos y adultos es una mejor estrategia de conservación que la suplementación. Debido a que la genética no es considerada en las prácticas de manejo en los criaderos, la suplementación incluso puede reducir la viabilidad del esturión beluga. [source]

Using Logistic Regression to Analyze the Sensitivity of PVA Models: a Comparison of Methods Based on African Wild Dog Models

CONSERVATION BIOLOGY, Issue 5 2001
Paul C. Cross
Standardized coefficients from the logistic regression analyses indicated that pup survival explained the most variability in the probability of extinction, regardless of whether or not the model incorporated density dependence. Adult survival and the standard deviation of pup survival were the next most important parameters in density-dependent simulations, whereas the severity and probability of catastrophe were more important during density-independent simulations. The inclusion of density dependence decreased the probability of extinction, but neither the abruptness nor the inclusion of density dependence were important model parameters. Results of both relative sensitivity analyses that altered each parameter by 10% of its range and life-stage-simulation analyses of deterministic matrix models supported the logistic regression results, indicating that pup survival and its variation were more important than other parameters. But both conventional sensitivity analysis of the stochastic model which changed each parameter by 10% of its mean value and elasticity analyses indicated that adult survival was more important than pup survival. We evaluated the advantages and disadvantages of using logistic regression to analyze the sensitivity of stochastic population viability models and conclude that it is a powerful method because it can address interactions among input parameters and can incorporate the range of parameter variability, although the standardized regression coefficients are not comparable between studies. Model structure, method of analysis, and parameter uncertainty affect the conclusions of sensitivity analyses. Therefore, rigorous model exploration and analysis should be conducted to understand model behavior and management implications. Resumen: Utilizamos la regresión logística como un método de análisis de sensibilidad par a un modelo de análisis de viabilidad poblacional de perros silvestres Africanos ( Lycaon pictus) y comparamos estos resultados con análisis de sensibilidad convencionales de modelos estocásticos y determinísticos. Coeficientes estandarizados de los análisis de regresión logística indicaron que la supervivencia de cachorros explicaba la mayor variabilidad en la probabilidad de extinción, independientemente de que el modelo incorporara la denso-dependencia. La supervivencia de adultos y la desviación estándar de la supervivencia de cachorros fueron los parámetros que siguieron en importancia en simulaciones de denso-dependencia, mientras que la severidad y la probabilidad de catástrofes fueron más importantes durante simulaciones denso-independientes. La inclusión de la denso dependencia disminuyó la probabilidad de extinción, pero ni la severidad ni la inclusión de denso-dependencia fueron parámetros importantes. Resultados de los análisis de sensibilidad relativa que alteraron cada parámetro en 10% de su rango y análisis de la simulación de etapas de vida de modelos matriciales determinísticos apoyaron los resultados de la regresión logística, indicando que la supervivencia de cachorros y su variación fueron más importantes que otros parámetros. Sin embargo, el análisis de sensibilidad convencional del modelo estocástico que cambiaron cada parámetro en 10% de su valor medio y el análisis de elasticidad indicaron que la supervivencia de adultos fue más importante que la supervivencia de cachorros. Evaluamos las ventajas y desventajas de utilizar la regresión logística para analizar la sensibilidad de modelos estocásticos de viabilidad poblacional y concluimos que es un método poderoso porque puede atender interacciones entre parámetros ingresados e incorporar el rango de variabilidad de parámetros, aunque los coeficientes de regresión estandarizada no son comparables entre estudios. La estructura del modelo, el método de análisis y la incertidumbre en los parámetros afectan las conclusiones del análisis de sensibilidad. Por lo tanto, se debe realizar una rigurosa exploración y análisis del modelo para entender su comportamiento y sus implicaciones en el manejo. [source]

Population viability and perturbation analyses in remnant populations of the Andean catfish Astroblepus ubidiai

ECOLOGY OF FRESHWATER FISH, Issue 2 2005
L. A. Vélez-Espino
Abstract ,Astroblepus ubidiai (Actinopterygii; Siluriformes), which is the only native fish of the highlands of the Province of Imbabura, Ecuador, was abundant in the past in the Imbakucha watershed and adjacent drainages but currently it is restricted to a few isolated refuges. Population viability analysis (PVA) was used to detect critical aspects in the ecology and conservation biology of this unique fish. The annual population growth rate (,) was estimated for six remnant populations of this Andean catfish using a deterministic matrix population model. Sensitivity and elasticity analyses complemented the PVA by providing constructive insights into vital rates affecting projections and extinction probabilities. Positive population growth rates were found in all the study populations. The high contributions of juvenile survival to the variance of , and its high elasticity indicated that A. ubidiai population dynamics are highly sensitive to the transition values of this vital rate, which can promptly respond to management or antagonistic perturbations. Allowing fish to survive until the age of first reproduction and permitting the successful reproduction of these individuals will facilitate positive population growth rates, however the very small areas of occupancy, small extent of occurrence and severe fragmentation may still contribute to the extinction risk. Resumen 1. Astroblepus ubidiai (Actinopterygii; Siluriformes), el único pez nativo de los altos Andes en la Provincia de Imbabura, Ecuador, era abundante en el pasado en la cuenca de Imbakucha y en las cuencas adyacentes, pero actualmente existe en unos cuantos refugios geográficamente aislados. 2. Un Análisis de Viabilidad Poblacional (AVP) fue necesario para detectar los aspectos críticos en la ecología y biología de conservación de la especie. La tasa anual de crecimiento poblacional (,) se estimó en seis poblaciones remanentes de este pez andino usando un modelo matricial de población. Análisis de sensitividad y elasticidad permitieron la complementación de interpretaciones derivadas del AVP mediante la facilitación de exploraciones constructivas de los efectos relativos de las tasas vitales en proyecciones demográficas y probabilidades de extinción. 3. Todas las poblaciones estudiadas presentaron tasas positivas de crecimiento poblacional a pesar de que factores determinísticos tales como la pérdida de hábitat y fragmentación han llevado la ocurrencia de esta especie a pequeños fragmentos. La alta contribución a la varianza de , y la alta elasticidad de la supervivencia juvenil indicaron que las dinámicas poblacionales de A. ubidiai son altamente sensibles a los valores de transición de esta tasa vital, la cual puede responder con facilidad a actividades de manejo o perturbaciones antagónicas. 4. Facilitando que los peces sobrevivan hasta la edad de primera reproducción y permitiendo la reproducción exitosa de estos individuos son condiciones determinantes para mantener tasas positivas de crecimiento. Sin embargo, aún existe la necesidad de confrontar el riesgo de extinción derivado de pequeñas áreas de ocupación, limitada extensión de ocurrencia, y fragmentación severa. En este artículo también se discute la manera en que el conocimiento de estas circunstancias específicas es esencial para tomar acciones efectivas de conservación. [source]

Population dynamics in Digitalis purpurea: the interaction of disturbance and seed bank dynamics

JOURNAL OF ECOLOGY, Issue 6 2007
NINA SLETVOLD
Summary 1Plant ecologists have long since realized that the persistence of many facultative biennial plants depends upon disturbance. However, we still have a limited knowledge of the population-level effects of disturbance, and the connection between adult and seed bank dynamics. 2Using data from a 3-year demographic study combined with experimental gap-opening in a large population of Digitalis purpurea, we parameterized stochastic transition matrix models in ,disturbed' vs. ,undisturbed' areas. We simulated different gap sizes (fraction of population that was disturbed) and temporal disturbance patterns (constant, random, regular and irregular return intervals) and evaluated the effects on population growth rate and seed bank dynamics. To explore seed bank importance we used two alternatives for seed bank survival rate (0.75/0.35) and three alternatives for seed bank recruitment fraction (0.9/0.5/0.1). 3Observed background recruitment levels were insufficient to ensure a positive population growth rate. Increased amounts of gap-opening led to higher growth rates, and population persistence was predicted at moderate disturbance levels if seed bank survival was high (0.75). 4Temporal disturbance pattern affected model results; random and interval scenarios resulted in lower population growth rates and higher extinction risks than constant scenarios of the same average disturbance level. Small and frequent disturbances led to considerably higher growth rates than large and rare disturbances. 5Stochastic elasticity analyses identified the seed bank as the most important life cycle stage with respect to population growth and persistence in most scenarios, and its relative impact was positively related to seed bank survival rate and negatively related to disturbance level. Variation in the recruitment fraction from seed bank vs. seed rain affected both population growth rate and elasticity patterns, indicating the large impact of spatial variation in seed bank density. 6Synthesis: Despite the existence of a large seed bank, our data suggest that recruitment may be locally seed-limited due to a patchy seed bank structure. Local population development may consequently differ widely from gap to gap. These results illustrate how spatial structures in both seed bank, adult population and gap formation interact to shape plant population dynamics, as well as the occurrence of microsite- vs. seed-limitation. [source]

Demography of American chestnut populations: effects of a pathogen and a hyperparasite

JOURNAL OF ECOLOGY, Issue 4 2004
ANITA L. DAVELOS
Summary 1Matrix models were used to evaluate the effect of chestnut blight infection on transition probabilities and population growth rates for American chestnuts. Disease-free, epidemic and recovering (i.e. pathogen infected with a double-stranded (ds) RNA hypovirus) populations were compared. 2Population growth rates (,) did not differ significantly over time or with disease status. However, predicted stable stage distributions differed between population types, with disease-free and recovering populations more similar to each other than either was to epidemic populations. 3Survival had the highest proportional contribution to population growth rates as revealed by elasticity analyses. However, reductions in stasis of the largest trees contributed most to reductions in population growth rate when comparing diseased with disease-free populations using LTRE. 4The presence of hypovirus reduces pathogen virulence, allowing individual American chestnut trees to increase in size. Where dsRNA has spread, chestnut populations in Michigan have attained population dynamics similar to those found in disease-free populations. 5Matrix models and life table response experiments can be used to detect important pathogen-mediated changes in the dynamics of host populations. [source]

Sensitivity analysis of transient population dynamics

ECOLOGY LETTERS, Issue 1 2007
Hal Caswell
Abstract Short-term, transient population dynamics can differ in important ways from long-term asymptotic dynamics. Just as perturbation analysis (sensitivity and elasticity) of the asymptotic growth rate reveals the effects of the vital rates on long-term growth, the perturbation analysis of transient dynamics can reveal the determinants of short-term patterns. In this article, I present a completely new approach to transient sensitivity and elasticity analysis, using methods from matrix calculus. Unlike previous methods, this approach applies not only to linear time-invariant models but also to time-varying, subsidized, stochastic, nonlinear and spatial models. It is computationally simple, and does not require calculation of eigenvalues or eigenvectors. The method is presented along with applications to plant and animal populations. [source]

Axial symmetric elasticity analysis in non-homogeneous bodies under gravitational load by triple-reciprocity boundary element method

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2009
Yoshihiro Ochiai
Abstract In general, internal cells are required to solve elasticity problems by involving a gravitational load in non-homogeneous bodies with variable mass density when using a conventional boundary element method (BEM). Then, the effect of mesh reduction is not achieved and one of the main merits of the BEM, which is the simplicity of data preparation, is lost. In this study, it is shown that the domain cells can be avoided by using the triple-reciprocity BEM formulation, where the density of domain integral is expressed in terms of other fields that are represented by boundary densities and/or source densities at isolated interior points. Utilizing the rotational symmetry, the triple-reciprocity BEM formulation is developed for axially symmetric elasticity problems in non-homogeneous bodies under gravitational force. A new computer program was developed and applied to solve several test problems. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Demographic models and the management of endangered species: a case study of the critically endangered Seychelles magpie robin

Population dynamics and stage structure in a haploid-diploid red seaweed, Gracilaria gracilis

JOURNAL OF ECOLOGY, Issue 3 2001
Carolyn Engel
Summary 1,Many red seaweeds are characterized by a haploid-diploid life cycle in which populations consist of dioecious haploid (gametophyte) and diploid (tetrasporophyte) individuals as well as an additional diploid zygote-derived sporangium (carposporophyte) stage. A demographic analysis of Gracilaria gracilis populations was carried out to explore and evaluate the population dynamics and stage structure of a typical haploid-diploid red seaweed. 2,Four G. gracilis populations were studied at two sites on the French coast of the Strait of Dover. Survival, reproduction and recruitment rates were measured in each population for up to 4 years. Eight two-sex stage-based population projection matrices were built to describe their demography. 3,All four populations were characterized by high survival and low recruitment rates. Population growth rates (,) were similar between populations and between years and ranged from 1.03 to 1.17. In addition, generation times were found to be as long as 42 years. 4,Sex and ploidy ratios were variable across populations and over time. Female frequencies ranged from 0.31 to 0.59 and tetrasporophyte frequencies from 0.44 to 0.63. However, in most cases, the observed population structures were not significantly different from the calculated stage distributions. 5,Eigenvalue elasticity analysis showed that , was most sensitive to changes in matrix transitions that corresponded to survival of the gametophyte and tetrasporophyte stages. In contrast, the contribution of the fertility elements to , was small. Eigenvector elasticity analysis also showed that survival elements had the greatest impact on sex and ploidy ratios. [source]

Modelling life history strategies with capture,recapture data: Evolutionary demography of the water skink Eulamprus tympanum

AUSTRAL ECOLOGY, Issue 4 2001
Simon P. Blomberg
Abstract Matrix population models, elasticity analysis and loop analysis can potentially provide powerful techniques for the analysis of life histories. Data from a capture,recapture study on a population of southern highland water skinks (Eulamprus tympanum) were used to construct a matrix population model. Errors in elasticities were calculated by using the parametric bootstrap technique. Elasticity and loop analyses were then conducted to identify the life history stages most important to fitness. The same techniques were used to investigate the relative importance of fast versus slow growth, and rapid versus delayed reproduction. Mature water skinks were long-lived, but there was high immature mortality. The most sensitive life history stage was the subadult stage. It is suggested that life history evolution in E. tympanum may be strongly affected by predation, particularly by birds. Because our population declined over the study, slow growth and delayed reproduction were the optimal life history strategies over this period. Although the techniques of evolutionary demography provide a powerful approach for the analysis of life histories, there are formidable logistical obstacles in gathering enough high-quality data for robust estimates of the critical parameters. [source]