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Population Growth (population + growth)
Kinds of Population Growth Terms modified by Population Growth Selected AbstractsTHE EFFECT OF COUNTY-LEVEL PRISON POPULATION GROWTH ON CRIME RATES,CRIMINOLOGY AND PUBLIC POLICY, Issue 2 2006TOMISLAV V. KOVANDZIC Research Summary: Prior macro-level studies examining the impact of prison population growth on crime rates have produced widely varying results. Studies using national-level time series data find large impacts of prison growth on crime, whereas those using state panel data find more modest ones. Critics of the former studies maintain that the estimates are implausibly large, arguing that the effects are instead due to analysts' inability to control for potential confounding factors. Conversely, critics of the latter studies argue that they underestimate the total impacts of imprisonment by failing to account for potential free-riding effects. This study uses panel data for 58 Florida counties for 1980 to 2000 to reexamine the link between prison population growth and crime. Unlike previous studies, we find no evidence that increases in prison population growth covary with decreases in crime rates. Policy Implications: Our findings suggest that Florida policymakers carefully weigh the costs and benefits of their continued reliance on mass incarceration against the potential costs and benefits of alternatives. If the costs of mass incarceration do not return appreciable benefits, i.e., a reduction in crime, it is time to reconsider our approach to crime and punishment. Other research offers evidence of crime prevention programs operating inside the criminal justice system and in communities that hold promise for reducing crime; our findings indicate that policymakers carefully consider these options as a way to achieve their goals. [source] CAUSES OF MORTALITY IN CALIFORNIA SEA OTTERS DURING PERIODS OF POPULATION GROWTH AND DECLINEMARINE MAMMAL SCIENCE, Issue 1 2003JamesA. Abstract Elevated mortality appears to be the main reason for both sluggish growth and periods of decline in the threatened California sea otter population. We assessed causes of mortality from salvage records of 3,105 beach-cast carcasses recovered from 1968 through 1999, contrasting two periods of growth with two periods of decline. Overall, an estimated 40%-60% of the deaths were not recovered and 70% of the recovered carcasses died from unknown causes. Nonetheless, several common patterns were evident in the salvage records during the periods of population decline. These included greater percentages of (1) prime age animals (3,10 yr), (2) carcasses killed by great white shark attacks, (3) carcasses recovered in spring and summer, and (4) carcasses for which the cause of death was unknown. Neither sex composition nor the proportion of carcasses dying of infectious disease varied consistently between periods of population increase and decline. The population decline from 1976 to 1984 was likely due to incidental mortality in a set-net fishery, and the decline from 1995 to 1999 may be related to a developing live-fish fishery. Long-term trends unrelated to periods of growth and decline included a decrease in per capita pup production and mass/length ratios of adult carcasses over the 31-yr study. The generally high proportion of deaths from infectious disease suggests that this factor has contributed to the chronically sluggish growth rate of the California sea otter population. [source] The Complexity of Population Growth: Reply to Pletscher and SchwartzCONSERVATION BIOLOGY, Issue 6 2001Paul Phifer No abstract is available for this article. [source] The Tyranny of Population GrowthCONSERVATION BIOLOGY, Issue 6 2000Daniel H. Pletscher No abstract is available for this article. [source] Population Growth and the Environment in Africa: Local Informal Institutions, the Missing Link,ECONOMIC GEOGRAPHY, Issue 2 2002Valentina Mazzucato Abstract: Population and environment debates regarding Africa, whether Malthusian or Boserupian in nature, focus on population levels as the driving force behind the relationship between environment and society. This article argues, instead, that how people adjust to their rise in numbers is more important than are population levels. It focuses on the role of local informal institutions, such as land tenure systems, but also on customs, norms, and networks, and their change over time in mediating the relationship between people and the environment. The article is based on fieldwork conducted between 1995 and 1998 in the Sahelian and Sudano-Sahelian zones of Africa, as well as on a review of colonial documents pertaining to the area written in the first half of the twentieth century. The article concludes that adaptations made to local, informal institutions within the past century have enabled an environmentally sustainable land use within the context of a rising population and growing scarcity of natural resources. [source] Logistic Population Growth in the World's Largest CitiesGEOGRAPHICAL ANALYSIS, Issue 4 2006Gordon F. Mulligan This article demonstrates that recent population growth in the world's largest cities has conformed to the general parameters of the logistic process. Using data recently provided by the United Nations, logistic population growth for 485 million-person cities is analyzed at 5-year intervals during 1950,2010, with the UN projections for 2015 adopted as upper limits. A series of ordinary least-squares regression models of increasing complexity are estimated on the pooled data. In one class of models, the logarithms of population proportions are specified to be linear in time, which is the standard approach, but in a second class of models those proportions are specified as being quadratic. The most complex models control logistic growth estimates for (i) city-specific effects (e.g., initial population), (ii) nation-specific effects (e.g., economic development, age distribution of population), and (iii) global coordinates (for unobserved effects). Moreover, the results are segregated according to each city's membership in four different growth clubs, which was an important finding of previous research. [source] Economic Impacts of Technology, Population Growth And Soil Erosion At Watershed Level: The Case Of the Ginchi in EthiopiaJOURNAL OF AGRICULTURAL ECONOMICS, Issue 3 2004B.N. Okumu A dynamic bio-economic model is used to show that, without technological and policy intervention, soil loss levels, income and nutrition could not be substantially or sustainably improved in a highland area of Ethiopia. Although cash incomes could rise by more than 40% over a twelve-year planning period, average per ha soil losses could be as high as 31 tonnes per ha. With the adoption of an integrated package of new technologies, however, results show the possibility of an average two-and-a-half-fold increase in cash incomes and a 28% decline in aggregate erosion levels even with a population growth rate of 2.3%. Moreover, a minimum daily calorie intake of 2000 per adult equivalent could be met from on-farm production with no significant increases in erosion. However, higher rates of growth in nutritional requirements and population introduce significant strains on the watershed system. From a policy perspective, there is a need for a more secure land tenure policy than currently prevailing to facilitate uptake of the new technology package, and a shift from the current livestock management strategy to one that encourages livestock keeping as a commercial enterprise. It would also imply a shift to a more site-specific approach to land management. [source] On Population Growth and Technological Change: Selectivity Bias in Historical AnalysisJOURNAL OF AGRICULTURAL ECONOMICS, Issue 3 2000Jean-Paul Chavas This paper investigates the relationship between population growth and technological change. After an historical overview of the evolution of world population, alternative models of population growth are examined. They include a Malthusian model, a model of endogenous technological change, and a model of population growth that allows for switching regimes between Malthusian resource limitation and endogenous technological change. The regime-switching model stresses the potential for a biased interpretation of historical data. While there is strong empirical evidence supporting endogenous technical change, it is argued that the Malthusian scenario should not be overlooked even if the odds of facing it are low. [source] On the Tasks of a Population Commission: A 1971 Statement by Donald RumsfeldPOPULATION AND DEVELOPMENT REVIEW, Issue 3 2003Article first published online: 20 APR 200 In its most familiar form, analytic assessment of the impact of demographic change on human affairs is the product of a decentralized cottage industry: individual scholars collecting information, thinking about its meaning, testing hypotheses, and publishing their findings. Guidance through the power of the purse and through institutional design that creates and sustains cooperating groups of researchers can impose some order and coherence on such spontaneous activity. But the sum total of the result may lack balance and leave important aspects of relevant issues inadequately explored. Even when research findings are picked up by the media and reach a broader public, the haphazardness of that process helps further to explain why the salience of population change to human welfare and its importance in public policymaking are poorly understood. The syndrome is not unique to the field of population, but the typically long time-lags with which aggregate population change affects economic and social phenomena make it particularly difficult for the topic to claim public attention. A time-tested, if less than fool-proof remedy is the periodic effort to orchestrate a systematic and thorough examination of the causes, consequences, and policy implications of demographic processes. Because the most potent frame for policymaking is the state, the logical primary locus for such stocktaking is at the country level. The Commission on Population Growth and the American Future was a uniquely ambitious enterprise of this sort. The Commission was established by the US Congress in 1970 as a result of a presidential initiative. Along with the work of two earlier British Royal Commissions on population, this US effort, mutatis mutandis, can serve as a model for in-depth examinations conducted at the national level anywhere. Chaired by John D. Rockefeller 3rd, the Commission submitted its final report to President Richard M. Nixon in March 1972. The background studies to the report were published in seven hefty volumes; an index to these volumes was published in 1975. Reproduced below is a statement to the Commission delivered on April 14, 1971 by Donald Rumsfeld, then Counsellor to President Nixon and in charge of the Office of Economic Opportunity. (Currently, Mr. Rumsfeld serves as US Secretary of Defense.) The brief statement articulates with great clarity the objectives of the Commission and the considerations that prompted them. The text originally appeared in Vol. 7 (pp. 1-3) of the Commission's background reports, which contains the statements at public hearings conducted by the Commission. National efforts toward comprehensive scientific reviews of population issues have their analogs at the international level. Especially notable on that score were the preparatory studies presented at the 1954 Rome and 1965 Belgrade world population conferences. The world population conferences that took place in Bucharest in 1974, in Mexico City in 1984, and in Cairo in 1994 were intergovernmental and political rather than scientific and technical meetings, but they also generated a fair amount of prior research. The year 2004 will break the decadal sequence of large-scale international meetings on population, and apart from the quadrennial congresses of the IUSSP, which showcase the voluntary research offerings of its members, none is being planned for the coming years. A partial substitute will be meetings organized by the UN's regional economic and social commissions. The first of these took place in 2002 for the Asia-Pacific region; the meetings for the other regions will be held in 2003-04. The analytic and technical contribution of these meetings, however, is expected to be at best modest. National efforts of the type carried out 30 years ago by the Commission on Population Growth and the American Future would be all the more salutary. [source] The Effects of Supraoptimal Temperatures on Population Growth and Cortical Patterning in Tetrahymena pyriformis and Tetrahymena thermophila: A ComparisonTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2001JOSEPH FRANKEL ABSTRACT. In this investigation, we compare the multiplication rates and morphogenetic responses of the two most studied Tetrahymena species, T. pyriformis and T. thermophila, at supraoptimal temperatures. Although the upper temperature limits differ greatly in the two species, the pattern of growth responses to high temperature is for the most part similar, with some differences in detail. The transient recovery of cell division at the highest temperature that allows cell division, characteristic of T. pyriformis, is observed in a less distinct form in T. thermophila. Moreover, there is a remarkable difference in developmental response, with drastic abnormalities in patterning of oral structures during the transient recovery of cell division in T. pyriformis, and far more limited abnormalities under similar conditions in T. thermophila. The abnormalities result from spatial disorder in the alignment and orientation of basal body pairs within the early oral primordium, followed by failures in the realignment that normally occurs as oral structures (membranelles and undulating membrane) mature. Both the initial spatial disorder and the failures in realignment are far more severe in T. pyriformis than in T. thermophila. [source] Population growth of Daphnia magna under multiple stress conditions: Joint effects of temperature, food, and cadmiumENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2006Evelyn H. W. Heugens Abstract Aquatic organisms in the field often are exposed to combinations of stress factors of variousorigins. Little is known of the interaction between different types of stressors; hence, the predictability of their joint effects is low. Therefore, the present study analyzed the joint effects of temperature, food, and cadmium on the population growth rate of the water flea Daphnia magna. The results revealed that temperature, food, and cadmium, as well as their interactions, were important factors that influenced life-history parameters and, as a consequence, the population growth rate of D. magna. In general, population growth rate increased at high temperature and food level but decreased when cadmium was present. The positive effect of temperature on population growth rate was smallest at limiting food levels. Negative effects of cadmium on the growth rate were enhanced at elevated temperatures, whereas high food levels protected the daphnids from adverse effects of cadmium. To avoid over- or underestimation regarding the toxicity of substances to field populations, results of standard toxicity tests should be applied in a location-specific way. [source] Impact of the post-World War II generation on intensive care needs in NorwayACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 4 2010J. H. LAAKE Background: A high birth rate during the first two decades following World War II has increased the proportion of elderly people in present-day society and, consequently, the demand for health-care services. The impact on intensive care services may become dramatic because the age distribution of critically ill patients is skewed towards the elderly. We have used registry data and population statistics to forecast the demand for intensive care services in Norway up until the year 2025. Methods: Data collected by the Norwegian intensive care registry (NIR), showing the age distribution in Norwegian intensive care units (ICU) during the years 2006 and 2007, were used with three different Norwegian prognostic models of population growth for the years 2008,2025 to compute the expected increase in intensive care unit bed-days (ICU bed-days). Results: The elderly were overrepresented in Norwegian ICUs in 2006,2007, with patients from 60 to 79 years of age occupying 44% of ICU bed-days. Population growth from 2008 to 2025 was estimated to be from 11.1 to 26.4%, depending on the model used. Growth will be much larger in the age group 60,79 years. Other factors kept unchanged, this will result in an increase in the need for intensive care (ICU bed-days) of between 26.1 and 36.9%. Conclusion: The demand for intensive care beds will increase markedly in Norwegian hospitals in the near future. This will have serious implications for the planning of infrastructure, education of health care personnel, as well as financing of our health care system. [source] A MODEL LIFE TABLE FOR BOTTLENOSE DOLPHINS (TURSIOPS TRUNCATUS) FROM THE INDIAN RIVER LAGOON SYSTEM, FLORIDA, U.S.A.MARINE MAMMAL SCIENCE, Issue 4 2003Megan K. Stolen Abstract Data gathered from 220 stranded bottlenose dolphins (Tursiops truncatus) in the Indian River Lagoon system, Florida, were used to derive a life table. Survivorship curves were fit to the data using Siler's competing-risk model and a maximum likelihood approach. Population growth was estimated to be between r= 0.0 and 0.046 based on the observed numbers of stranded dolphins. Variance in survival rates was estimated using an individual-based, age-structured population projection model. We estimate that the overall annual mortality rate for this population was 9.8% per year. Sex-specific differences in survivorship were apparent with females outliving males. The overall mortality curve resembles that of other large mammals, with high calf mortality and an exponentially increasing risk of senescent mortality. The inclusion of live-capture removals of individuals from this population did not significantly affect the estimation of survival parameters for most age classes. [source] Which traits promote persistence of feral GM crops?OIKOS, Issue 1 2005Part 2: implications of metapopulation structure Transgenes may spread from crops into the environment via the establishment of feral populations, often initiated by seed spill from transport lorries or farm machinery. Locally, such populations are often subject to large environmental variability and usually do not persist longer than a few years. Because secondary feral populations may arise from seed dispersal to adjacent sites, the dynamics of such populations should be studied in a metapopulation context. We study a structured metapopulation model with local dispersal, mimicking a string of roadside subpopulations of a feral crop. Population growth is assumed to be subject to local disturbances, introducing spatially random environmental stochasticity. Our aim is to understand the role of dispersal and environmental variability in the dynamics of such ephemeral populations. We determine the effect of dispersal on the extinction boundary and on the distribution of persistence times, and investigate the influence of spatially correlated disturbances as opposed to spatially random disturbances. We find that, given spatially random disturbances, dispersal slows down the decline of the metapopulation and results in the occurrence of long-lasting local populations which remain more or less static in space. We identify which life history traits, if changed by genetic modification, have the largest impact on the population growth rate and persistence times. For oilseed rape, these are seed bank survival and dormancy. Combining our findings with literature data on transgene-induced life history changes, we predict that persistence is promoted by transgenes for oil-modifications (high stearate or high laurate) and, possibly, for insect resistence (Bt). Transgenic tolerance to glufosinate herbicide is predicted to reduce persistence. [source] What limits the spread of two congeneric butterfly species after their reintroduction: quality or spatial arrangement of habitat?ANIMAL CONSERVATION, Issue 6 2009F. Van Langevelde Abstract Population growth and spread of recently reintroduced species is crucial for the success of their reintroduction. We analysed what limits the spread of two congeneric butterfly species Maculinea teleius and Maculinea nausithous, over 10 years following their reintroduction. During this time, their distributions appeared to be limited to a few sites although it was thought that more suitable habitats were available. Thus, we question, does the quality or the spatial arrangement of their habitat limit their spread? Although adult individuals of both species can select high-quality plots, we show that selection of suitable plots in the area of reintroduction is spatially constrained. A low colonization probability of unoccupied distant plots of high quality was found for both species. The abandonment of occupied plots in Ma. teleius was also found to be dependent on the distance to occupied plots. We conclude that the spatial distribution of the two species during the 10 years following reintroduction was limited by the spatial arrangement of their habitat, rather than by the availability of high-quality plots. The spatial constraints in movement can explain observed source,sink structures when female butterflies deposit their eggs on low-quality plots. We conclude that although these species have very similar life histories, they require different approaches to their conservation due to subtle differences in adult habitat use and movement. Conservation of Ma. teleius should concentrate on improving local habitat quality, whereas conservation of Ma. nausithous is predicted to be more effective by creating a spatial network of suitable habitat plots, such as along road verges. [source] Population growth and mass mortality of an estuarine fish, Acanthopagrus butcheri, unlawfully introduced into an inland lakeAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2009Kimberley Smith Abstract 1.In 2006, two periods of hypoxia resulted in the death of approximately 35 tonnes of black bream (Acanthopagrus butcheri) in Lake Indoon, a small inland lake in Western Australia. 2.Acanthopagrus butcheri was the first fish species to be recorded in this lake, along with the mosquitofish (Gambusia holbrooki) which was also observed during sampling in 2006. Acanthopagrus butcheri appears to have been introduced to Lake Indoon between 1998 and 2003 and formed a self-sustaining population. It is believed to have been deliberately introduced for the purpose of creating a recreational fishery, despite the existence of substantial penalties for illegal translocation of fish in Western Australia. 3.Recent human-induced environmental changes, including rising groundwater and salinization, have probably aided the establishment of both species in Lake Indoon. The importance of salinity to recruitment success by A. butcheri was indicated by the presence of only two age classes in 2006, with estimated recruitment dates coinciding with the years of highest recorded salinity in the lake. 4.The ,fish kills' provided an opportunity to examine aspects of A. butcheri biology in a relatively low salinity environment which is atypical for this estuarine species. In particular, the recruitment period in Lake Indoon was delayed until autumn/winter, rather than spring/summer as seen in other populations. Biological responses in Lake Indoon have implications for natural populations living in estuaries with modified salinity regimes. 5.The ecological, social and economic impacts potentially arising from the introduction of fish to Lake Indoon, which is an important migratory bird habitat and a recreational amenity for local residents and tourists, illustrate the complexities of fish translocation and the need for rigorous assessment before stocking to identify potential costs and benefits. Copyright © 2008 John Wiley & Sons, Ltd. [source] The direct and indirect impacts of population growth and economic development on maize (Zea mays L.) diversity in highland GuatemalaAREA, Issue 1 2009Michael K Steinberg This paper discusses the impacts of population growth and economic development on maize diversity in highland Guatemala. In the context of this discussion, economic development specifically refers to the recent expansion of the non-traditional agricultural exports (NTAEs). Population growth and economic development (i.e. NTAEs) are linked because as land has become scarce in highland Guatemala, due to the poor distribution of land resources and rapid population growth over the past 50 years, many farmers have turned to non-traditional economic strategies such as new crops that produce more income per unit of land. These new crops have improved the economic conditions of many farming families, but it has come at a cost regarding the maintenance of local maize varieties and household food security. [source] Using Population Count Data to Assess the Effects of Changing River Flow on an Endangered Riparian PlantCONSERVATION BIOLOGY, Issue 4 2006DIANE M. THOMSON análisis de viabilidad poblacional; gestión ribereña; método de difusión; presas; riesgo de extinción Abstract:,Methods for using simple population count data to project extinction risk have been the focus of much recent theoretical work, but few researchers have used these approaches to address management questions. We analyzed 15 years of census data on the federally endangered endemic riparian plant Pityopsis ruthii (Small) with the diffusion approximation (DA). Our goals were to evaluate relative extinction risk among populations in two different watersheds (in Tennessee, U.S.A.) and potential effects of variation in managed river flow on population dynamics. Populations in both watersheds had high projected risks of extinction within 50 years, but the causes of this risk differed. Populations of P. ruthii on the Hiwassee River had higher initial population sizes but significantly lower average growth rates than those on the Ocoee River. The only populations with low predicted short-term extinction risk were on the Ocoee. Growth rates for populations on both rivers were significantly reduced during periods of lower river flow. We found only marginal evidence of a quadratic relationship between population performance and flow. These patterns are consistent with the idea that low flows affect P. ruthii due to growth of competing vegetation, but the degree to which very high flows may reduce population growth is still unclear. Simulations indicated that populations were most sensitive to growth rates in low-flow years, but small changes in the frequency of these periods did not strongly increase risk for most populations. Consistent with results of other studies, DA estimates of extinction risk had wide confidence limits. Still, our results yielded several valuable insights, including the need for greater monitoring of populations on the Hiwassee and the importance of low-flow years to population growth. Our work illustrates the potential value of simple methods for analyzing count data despite the challenges posed by uncertainty in estimates of extinction risk. Resumen:,Los métodos que utilizan datos de conteos simples de la población para proyectar el riesgo de extinción han sido el foco reciente de mucho trabajo teórico, pero pocos investigadores han utilizado estos métodos para responder preguntas de gestión. Analizamos 15 años de datos de censos de la planta ribereña, endémica y federalmente en peligro Pityopsis ruthii (Small) mediante el método de difusión. Nuestras metas fueron evaluar el riesgo de extinción de poblaciones en dos cuencas hidrológicas distintas y con dos efectos potenciales de la variación del flujo de agua sobre la dinámica de la población. Las poblaciones en ambas cuencas tenían alto riesgo de extinción proyectado a 50 años, pero las causas de este riesgo difirieron. Las poblaciones de P. ruthii en el Río Hiwassee tuvieron poblaciones iniciales más grandes, pero tasas de crecimiento significativamente menores, que las poblaciones en el Río Ocoee. Las únicas poblaciones con bajo riesgo de extinción pronosticado estaban en el Ocoee. Las tasas de crecimiento de las poblaciones en ambos ríos se redujeron significativamente durante períodos de bajo flujo en el río. Sólo encontramos evidencia marginal de la relación cuadrática entre el funcionamiento de la población y el flujo. Estos patrones son consistentes con la idea de que los bajos flujos afectan a P. ruthii debido al crecimiento de vegetación competitiva, pero aun no es claro el grado en que flujos muy grandes pueden reducir el crecimiento poblacional. Las simulaciones indicaron que las poblaciones son más sensibles a las tasas de crecimiento en años con bajo flujo en los ríos, pero pequeños cambios en la frecuencia de esos períodos no aumentaron el riesgo en la mayoría de las poblaciones. Consistentemente con los resultados de otros estudios, las estimaciones del riesgo de extinción mediante el método de difusión tienen amplios límites de confianza. Aun así, nuestros resultados aportaron varios conocimientos valiosos, incluyendo la necesidad de mayor monitoreo de las poblaciones en el Hiwassee y la importancia para el crecimiento poblacional de los años con bajo flujo. Nuestro trabajo ilustra el valor potencial de métodos sencillos de análisis de datos de conteo a pesar de los retos impuestos por la incertidumbre en las estimaciones del riesgo de extinción. [source] Matrix Models as a Tool for Understanding Invasive Plant and Native Plant InteractionsCONSERVATION BIOLOGY, Issue 3 2005DIANE M. THOMSON competencia; invasión biológica; plantas invasoras; modelo matricial; perturbación Abstract:,Demographic matrix models are an increasingly standard way to evaluate the effects of different impacts and management approaches on species of concern. Although invasive species are now considered among the greatest threats to biodiversity, matrix methods have been little used to explore and integrate the potentially complicated effects of invasions on native species. I developed stage-structured models to assess the impacts of invasive grasses on population growth and persistence of a federally listed (U.S.A.) endemic plant, the Antioch Dunes evening primrose (Oenothera deltoides subsp. howellii [Munz] W. Klein). I used these models to evaluate two frequently made assumptions: (1) when rare plant populations decline in invaded habitats, invasive species are the cause and (2) invasive plants suppress rare plants primarily through direct resource competition. I compared two control and two removal matrices based on previous experimental work that showed variable effects of invasive grasses on different life-history stages of O. deltoides. Matrix analysis showed that these effects translated into substantial changes in population growth rates and persistence, with control matrices predicting a mean stochastic population growth rate (,) of 0.86 and removal matrices predicting growth rates from 0.92 to 0.93. Yet even the most optimistic invasive removal scenarios predicted rapid decline and a probability of extinction near one in the next 100 years. Competitive suppression of seedlings had much smaller effects on growth rates than did lowered germination, which probably resulted from thatch accumulation and reduced soil disturbance. These results indicate that although invasive grasses have important effects on the population growth of this rare plant, invasion impacts are not solely responsible for observed declines and are likely to be interacting with other factors such as habitat degradation. Further, changes in the disturbance regime may be as important a mechanism creating these impacts as direct resource competition. My results highlight the value of demographic modeling approaches in creating an integrated assessment of the threats posed by invasive species and the need for more mechanistic studies of invasive plant interactions with native plants. Resumen:,Los modelos demográficos matriciales son una forma cada vez más utilizada para evaluar los efectos de diferentes impactos y métodos de gestión sobre las especies en cuestión. Aunque actualmente se considera a las plantas invasoras entre las mayores amenazas a la biodiversidad, los modelos matriciales han sido poco utilizados para explorar e integrar los efectos potencialmente complicados de las invasiones sobre las especies nativas. Desarrollé modelos estructurados por etapas para evaluar los impactos de pastos invasores sobre el crecimiento poblacional y la persistencia de una especie de planta endémica, enlistada federalmente (E.U.A.), Oenothera deltoides ssp. howellii [Munz] W. Klein. Utilicé estos modelos para evaluar dos suposiciones frecuentes: (1) cuando las poblaciones de plantas raras declinan en hábitats invadidos, las especies invasoras son la causa y (2) las plantas invasoras suprimen a las plantas raras principalmente mediante la competencia directa por recursos. Comparé dos matrices de control y dos de remoción con base en trabajo experimental previo que mostró efectos variables de los pastos invasores sobre las diferentes etapas de la historia de vida de O. deltoides. El análisis de la matriz mostró que estos efectos se tradujeron en cambios sustanciales en las tasas de crecimiento y persistencia de la población, las matrices de control predijeron una tasa media de crecimiento poblacional estocástica (,) de 0.86 y las matrices de remoción predijeron tasas de crecimiento de 0.92-0.93. Aun los escenarios más optimistas de remoción de invasores predijeron una rápida declinación y una probabilidad de extinción en 100 años cerca de uno. La supresión competitiva de plántulas tuvo mucho menor efecto sobre las tasas de crecimiento que la disminución en la germinación, que probablemente resultó de la acumulación de paja y reducción en la perturbación del suelo. Estos resultados indican que, aunque los pastos invasores tienen efectos importantes sobre el crecimiento poblacional de esta planta rara, los impactos de la invasión no son los únicos responsables de las declinaciones observadas y probablemente están interactuando con otros factores como la degradación del hábitat. Más aun, los cambios en el régimen de perturbación pueden ser un mecanismo tan importante en la creación de estos impactos como la competencia directa por recursos. Mis resultados resaltan el valor del enfoque de los modelos demográficos para la evaluación integral de las amenazas de especies invasoras y la necesidad de estudios más mecanicistas de las interacciones de plantas invasoras con plantas nativas. [source] THE CRIMINOGENIC EFFECTS OF IMPRISONMENT: EVIDENCE FROM STATE PANEL DATA, 1974,2002CRIMINOLOGY AND PUBLIC POLICY, Issue 3 2007LYNNE M. VIERAITIS Research Summary: The heavy reliance on the use of incarceration in an attempt to address the crime problem has resulted in a dramatic growth in the number of state prisoners over the past 30 years. In recent years, however, a growing concern has developed about the impact that large numbers of offenders released from prison will have on crime rates. Using a state panel data set for 46 states from 1974 to 2002, this study demonstrates that although prison population growth seems to be associated with statistically significant decreases in crime rates, increases in the number of prisoners released from prison seem to be significantly associated with increases in crime. Because we control for changes in prison population levels, we attribute the apparent positive influences on crime that seem to follow prison releases to the criminogenic effects of prison. Policy Implications: Policy makers should continue to serve the public interest by carefully considering policies that are designed to reduce incarceration rates and thus assuage the criminogenic effects of prison. These policies may include changes in sentencing, changes in probation and/or parole practices, or better funding of reentry services prerelease and postrelease. [source] THE EFFECT OF COUNTY-LEVEL PRISON POPULATION GROWTH ON CRIME RATES,CRIMINOLOGY AND PUBLIC POLICY, Issue 2 2006TOMISLAV V. KOVANDZIC Research Summary: Prior macro-level studies examining the impact of prison population growth on crime rates have produced widely varying results. Studies using national-level time series data find large impacts of prison growth on crime, whereas those using state panel data find more modest ones. Critics of the former studies maintain that the estimates are implausibly large, arguing that the effects are instead due to analysts' inability to control for potential confounding factors. Conversely, critics of the latter studies argue that they underestimate the total impacts of imprisonment by failing to account for potential free-riding effects. This study uses panel data for 58 Florida counties for 1980 to 2000 to reexamine the link between prison population growth and crime. Unlike previous studies, we find no evidence that increases in prison population growth covary with decreases in crime rates. Policy Implications: Our findings suggest that Florida policymakers carefully weigh the costs and benefits of their continued reliance on mass incarceration against the potential costs and benefits of alternatives. If the costs of mass incarceration do not return appreciable benefits, i.e., a reduction in crime, it is time to reconsider our approach to crime and punishment. Other research offers evidence of crime prevention programs operating inside the criminal justice system and in communities that hold promise for reducing crime; our findings indicate that policymakers carefully consider these options as a way to achieve their goals. [source] Changing household responses to drought in Tharaka, Kenya: vulnerability, persistence and challengeDISASTERS, Issue 2 2008Thomas A. Smucker Drought is a recurring challenge to the livelihoods of those living in Tharaka District, Kenya, situated in the semi-arid zone to the east of Mount Kenya, from the lowest slopes of the mountain to the banks of the Tana River. This part of Kenya has been marginal to the economic and political life of Kenya from the colonial period until the present day. A study of more than 30 years of change in how people in Tharaka cope with drought reveals resilience in the face of major macro-level transformations, which include privatisation of landownership, population growth, political decentralisation, increased conflict over natural resources, different market conditions, and environmental shifts. However, the study also shows troubling signs of increased use of drought responses that are incompatible with long-term agrarian livelihoods. Government policy needs to address the challenge of drought under these new macro conditions if sustainable human development is to be achieved. [source] Elevated dominance of extrafloral nectary-bearing plants is associated with increased abundances of an invasive ant and reduced native ant richnessDIVERSITY AND DISTRIBUTIONS, Issue 5 2009Amy M. Savage Abstract Aim, Invasive ants can have substantial and detrimental effects on co-occurring community members, especially other ants. However, the ecological factors that promote both their population growth and their negative influences remain elusive. Opportunistic associations between invasive ants and extrafloral nectary (EFN)-bearing plants are common and may fuel population expansion and subsequent impacts of invasive ants on native communities. We examined three predictions of this hypothesis, compared ant assemblages between invaded and uninvaded sites and assessed the extent of this species in Samoa. Location, The Samoan Archipelago (six islands and 35 sites). Methods, We surveyed abundances of the invasive ant Anoplolepis gracilipes, other ant species and EFN-bearing plants. Results,Anoplolepis gracilipes was significantly more widely distributed in 2006 than in 1962, suggesting that the invasion of A. gracilipes in Samoa has progressed. Furthermore, (non- A. gracilipes) ant assemblages differed significantly between invaded and uninvaded sites. Anoplolepis gracilipes workers were found more frequently at nectaries than other plant parts, suggesting that nectar resources were important to this species. There was a strong, positive relationship between the dominance of EFN-bearing plants in the community and A. gracilipes abundance on plants, a relationship that co-occurring ants did not display. High abundances of A. gracilipes at sites dominated by EFN-bearing plants were associated with low species richness of native plant-visiting ant species. Anoplolepis gracilipes did not display any significant relationships with the diversity of other non-native ants. Main conclusions, Together, these data suggest that EFN-bearing plants may promote negative impacts of A. gracilipes on co-occurring ants across broad spatial scales. This study underscores the potential importance of positive interactions in the dynamics of species invasions. Furthermore, they suggest that conservation managers may benefit from explicit considerations of potential positive interactions in predicting the identities of problematic invaders or the outcomes of species invasions. [source] Range-wide patterns of greater sage-grouse persistenceDIVERSITY AND DISTRIBUTIONS, Issue 6 2008Cameron L. Aldridge ABSTRACT Aim, Greater sage-grouse (Centrocercus urophasianus), a shrub-steppe obligate species of western North America, currently occupies only half its historical range. Here we examine how broad-scale, long-term trends in landscape condition have affected range contraction. Location, Sagebrush biome of the western USA. Methods, Logistic regression was used to assess persistence and extirpation of greater sage-grouse range based on landscape conditions measured by human population (density and population change), vegetation (percentage of sagebrush habitat), roads (density of and distance to roads), agriculture (cropland, farmland and cattle density), climate (number of severe and extreme droughts) and range periphery. Model predictions were used to identify areas where future extirpations can be expected, while also explaining possible causes of past extirpations. Results, Greater sage-grouse persistence and extirpation were significantly related to sagebrush habitat, cultivated cropland, human population density in 1950, prevalence of severe droughts and historical range periphery. Extirpation of sage-grouse was most likely in areas having at least four persons per square kilometre in 1950, 25% cultivated cropland in 2002 or the presence of three or more severe droughts per decade. In contrast, persistence of sage-grouse was expected when at least 30 km from historical range edge and in habitats containing at least 25% sagebrush cover within 30 km. Extirpation was most often explained (35%) by the combined effects of peripherality (within 30 km of range edge) and lack of sagebrush cover (less than 25% within 30 km). Based on patterns of prior extirpation and model predictions, we predict that 29% of remaining range may be at risk. Main Conclusions, Spatial patterns in greater sage-grouse range contraction can be explained by widely available landscape variables that describe patterns of remaining sagebrush habitat and loss due to cultivation, climatic trends, human population growth and peripherality of populations. However, future range loss may relate less to historical mechanisms and more to recent changes in land use and habitat condition, including energy developments and invasions by non-native species such as cheatgrass (Bromus tectorum) and West Nile virus. In conjunction with local measures of population performance, landscape-scale predictions of future range loss may be useful for prioritizing management and protection. Our results suggest that initial conservation efforts should focus on maintaining large expanses of sagebrush habitat, enhancing quality of existing habitats, and increasing habitat connectivity. [source] Invasion of Agave species (Agavaceae) in south-east Spain: invader demographic parameters and impacts on native speciesDIVERSITY AND DISTRIBUTIONS, Issue 5-6 2004Ernesto I. Badano ABSTRACT Several mechanisms have been proposed to explain the success of invasive species in new environments. A species may become invasive when a new site provides the potential for positive rates of population growth. This may be the case of several Agave species introduced to Spain in the 1940s. In this paper we document factors that promote large increases of populations of these species, and their effects on native plant communities in two sites of SE Spain. Results showed higher rhizome and bulbil production, and higher establishment rates by agaves in sandy soils than in clay soils. In their native habitats, agaves have low establishment rates and sandy soils are rare. This suggests that sandy soils are an opportunity which releases the clonal reproduction of Agave. The effects of agaves on the physiological performance and reproduction of native species were negative, positive or neutral, depending on the size and rooting depth of neighbours. Assemblages of native species growing within Agave stands had lower diversity than non-invaded sites. Our data show that Agave stands have positive growth rates in SE Spain, and suggest that sandy soils are a niche dimension enhancing the invasion in these new habitats. [source] Mutualism as a constraint on invasion success for legumes and rhizobiaDIVERSITY AND DISTRIBUTIONS, Issue 3 2001Matthew A. Parker Abstract Because hereditary symbiont transmission is normally absent in the mutualism of legume plants and root-nodule bacteria (rhizobia), dispersing plants may often arrive at new habitats where mutualist partners are too rare to provide full benefits. Factors governing invasion success were explored by analysing a system of two coupled pairwise competition models: a legume invader competing with a resident non-mutualistic plant, and a rhizobial population competing with a resident population of nonsymbiotic bacteria. The non-linear dependence of benefits on partner abundance in this mutualism creates the possibility of two alternative population size equilibria, so that a threshold density can exist for invasion. If legumes and rhizobia exceed a critical population size, both species achieve rapid population growth, while if initial densities of both species are below their respective thresholds, they remain rare and are thus vulnerable to extinction in the presence of competitors. Overall, the results indicate that legumes may often fail at colonization attempts within habitats where mutualist partners are scarce. Data on legume prevalence in island floras and rates of geographical spread by legume weeds are consistent with this inference. Predictive insights about invasiveness may emerge from comparative research on key traits identified by the model, especially the shape of the function determining the number of nodules formed at low rhizobial density. [source] Heroin users in Australia: population trendsDRUG AND ALCOHOL REVIEW, Issue 1 2004C. YALÇIN KAYA Senior Lecturer Abstract The aim of this paper is to identify certain important population trends among heroin users in Australia for the period 1971 , 97, such as: population growth, initiation, i.e. the number who were initiated to heroin in a given year, and quitting, i.e. the number that quit using heroin. For this purpose, we summarize and extract relevant characteristics from data from National Drug Strategy Household Survey (NDSHS 1998) conducted in Australia in 1998. We devise a systematic procedure to estimate historical trends from questions concerning past events. It is observed from our findings that the size of the heroin user population in Australia is in a sharp increase, especially from the early 1980s onwards. The general trend obtained for the period 1971 , 97 is strikingly similar to that obtained by Hall et al. (2000) for the dependent heroin user population in Australia, even though their study was based on different datasets and a different methodology. In our reconstruction of the time history we also detect a levelling-off prior to 1990. Initiation is also observed to be on a sharp increase. The latter trend is accompanied by a similar trend of quitting, perhaps indicating a relatively short heroin use career. A sharp decrease in both initiation and quitting is observed after 1990. In conclusion, in the case of the trend in the population of heroin users a high rate of growth has been identified that is consistent with the existing literature. In the process, we demonstrated that even a static survey such as NDSHS 1998 can, sometimes, be used to extract historical (dynamic) trends of certain important variables. [source] Effects of nitrogen deposition on the interaction between an aphid and its host plantECOLOGICAL ENTOMOLOGY, Issue 1 2008CARALYN B. ZEHNDER Abstract 1.,Anthropogenic increases in nitrogen deposition are impacting terrestrial ecosystems worldwide. While some of the direct ecosystem-level effects of nitrogen deposition are understood, the effects of nitrogen deposition on plant,insect interactions and on herbivore population dynamics have received less attention. 2.,Nitrogen deposition will potentially influence both plant resource availability and herbivore population growth. If increases in herbivore population growth outstrip increases in resource availability, then increases in the strength of density dependence expressed within the herbivore population would be predicted. Alternatively, if plant resources respond more vigorously to nitrogen deposition than do herbivore populations, a decline in the strength of density dependence would be expected. No change in the strength of density dependence acting upon the herbivore population would suggest equivalent responses by herbivores and plants. 3.,A density manipulation experiment was performed to examine the effect of nitrogen deposition on the interaction between a host plant, Asclepias tuberosa, and its herbivore, Aphis nerii. Aphid maximum per capita growth rate (Rmax), carrying capacity (K), and the strength of density dependence were measured under three nitrogen deposition treatments. The effect of nitrogen deposition on the relationship among these three measures of insect population dynamics was explored. 4.,Simulated nitrogen deposition increased aphid per capita population growth, plant foliar nitrogen concentrations, and plant biomass. Nitrogen deposition caused Rmax and K to increase proportionally, leading to no overall change in the strength of density dependence. In this system, potential changes in the negative feedback processes operating on herbivore populations following nitrogen deposition appear to be buffered by concomitant changes in resource availability. [source] Demographic analysis of continuous-time life-history modelsECOLOGY LETTERS, Issue 1 2008André M. De Roos Abstract I present a computational approach to calculate the population growth rate, its sensitivity to life-history parameters and associated statistics like the stable population distribution and the reproductive value for exponentially growing populations, in which individual life history is described as a continuous development through time. The method is generally applicable to analyse population growth and performance for a wide range of individual life-history models, including cases in which the population consists of different types of individuals or in which the environment is fluctuating periodically. It complements comparable methods developed for discrete-time dynamics modelled with matrix or integral projection models. The basic idea behind the method is to use Lotka's integral equation for the population growth rate and compute the integral occurring in that equation by integrating an ordinary differential equation, analogous to recently derived methods to compute steady-states of physiologically structured population models. I illustrate application of the method using a number of published life-history models. [source] Antagonistic effects of seed dispersal and herbivory on plant migrationECOLOGY LETTERS, Issue 3 2006Mark Vellend Abstract The two factors that determine plant migration rates , seed dispersal and population growth , are generally treated independently, despite the fact that many animals simultaneously enhance plant migration rate via seed dispersal, and decrease it via negative effects of herbivory on population growth. Using extensive empirical data, we modelled the antagonistic effects of seed dispersal and herbivory by white-tailed deer on potential migration rates of Trillium grandiflorum, a forest herb in eastern North America. This novel antagonistic interaction is illustrated by maximum migration rates occurring at intermediate, but low herbivory (< 15%). Assuming herbivory < 20% and favourable conditions for population growth during post-glacial migration, seed dispersal by deer can explain rates of migration achieved in the past, in contrast to previous models of forest herb migration. However, relatively unfavourable conditions for population growth and increasingly intense herbivory by deer may compromise plant migration in the face of present and future climate change. [source] | ||||||||||||||||||||||||||||||||||||||||||||||