Natural Population Growth Rate Research Articles

Resistance of some canola cultivars to Myzus persicae (Hemiptera: Aphididae)

The green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), is an important insect pest of a canola crop Brassica napus L., in Ardabil, Iran. Host plant resistance is an essential component of the integrated management of M. persicae. In field experiments, the population density of M. persicae was higher on Zarfam and lower on Ebonite, Elite, Okapi, RGS003, and Opera among the 19 canola cultivars during 2008 and 2009. In a free-choice situation, the numbers of attracted aphids per plant was lowest on Opera (1.2). In the life table study, aphids reared on Opera had the shortest adult longevity (8.3 days), lowest numbers of progeny per female (15.4) and the lowest survival rate (62.5%) compared to the other five cultivars. The intrinsic rate of the natural increase (rm) and population growth rate (λ) were lowest on Opera and highest on Zarfam. The generation time (T) was shortest on Opera (11.7 d) and longest on RGS003 (13.1 d), whereas the doubling time (DT) was longest on Opera (3.58 d) and shortest on Zarfam (2.26 d). Our results clearly suggest that Opera was the highest resistant host among the tested cultivars and has the potential to be used in the integrated management of M. persicae.

Water shortage in Jordan — Sustainable solutions

The large environmental challenge that Jordan faces today is the scarcity of water. Definitely, water is the significant feature in the population/resource equation where water resources in Jordan are limited and the country's population has continued to rise. A high rate of natural population growth, combined with massive influxes of refugees, has transformed into an imbalance condition between population and water. Jordan's water resources are limited to support population in a sustainable manner. The situation has been intensified by the fact that Jordan shares most of its surface water resources with neighboring countries; their control on water has partially disallowed Jordan of its fair share of water. Current use of water already exceeds its renewable supply. The deficit is covered by the unsustainable practice of overdrawing highland aquifers, resulting in lowered water tables and declining water quality.This paper focuses on the water shortage in Jordan, the primarily evaluation of this problem and the solution is contemplate. A true foundation of sustainable water solution requires awareness upon the part of the population, and a number of governmental and non-governmental organizations are actively involved in educating the populace about water shortage. The more essential and “doable” elements of a sustainable water solutions were discussed in this research, these elements are standing under, the development of new supplies of water, water harvesting, desalination, reuse of wastewater in the agricultural sector and reduction of water demands.Moreover, this article presents specific recommendations addressing water resource shortage in the kingdom and highlighting the importance of conservation of water and discussing the basics of sustainable solution.

Persistence of mobile species in marine protected areas

A central goal of many marine protected areas is ensuring the persistence of fish populations, which depends on the life history characteristics and movement patterns of individual species. While previous studies have focused on species where adults are sedentary, the current study examines an age-structured diffusion model for a one-species system in a single spatial dimension. We define persistence as a positive growth rate for small populations and determine conditions that will yield a positive growth rate. We find that the minimum fraction of habitat needed to be off-limits to fishing depends on two dimensionless parameters representing the net birth rate in the reserve, measured in the time it takes to move the length of the habitat, and the net death rate in the fished area, in that same time. Of the two parameters, natural population growth rate has a larger impact on reserve size than the net death rate due to fishing, although their ratio is useful for determining reserve size. These results suggest that reserves are appropriate for mobile species having at least one of several qualities: (1) small movement rates, (2) high birth rates relative to fishing rates or (3) large habitat sizes.

Site-specific vulnerability assessment for debris flows: Two case studies

Here the vulnerability is defined as the potential total maximum losses due to a debris flow damaging event for a specific debris flow fan. The vulnerability is classified into property vulnerability and population vulnerability. Assessment indexes include the assets of buildings, traffic facilities, lifeline works, personal properties, and land resources for property vulnerability; age, education, and wealth of the inhabitants, natural population growth rate, and population density for population vulnerability. The vulnerability is expressed as the sum of the transformed values of the losses of property and population. Two study cases with post-fact damages by historic debris flow events in Sichuan of SW China are presented.

Vasectomy of older bulls to manage elephant overpopulation in Africa: a proposal

This article is a proposal based on literature, it provides a concept that still requires on the ground investigation and implementation. When it was initially presented at the EMOA symposium in 2004 vascetomy had not yet performed on a bull elephant, but since tht time the opertion has been carried out several times in South Africa. The article reviews the advantages of male sterilization over that of females and looks at the 'general, technical, sex-related and financial aspects of the vascetomy of elephant bulls'. It appears that after dominant bulls are selected, treatment of less that 2% of the elephants would stabilize a population in parks with a natural population growth rate. Analysis suggests that for parks with 100 to 300 elephants, occasional vasectomy of a dominant bull would provide an effective elepahnt family planning tool.

Temporal Autocorrelation Can Enhance the Persistence and Abundance of Metapopulations Comprised of Coupled Sinks

In spatially heterogeneous landscapes, some habitats may be persistent sources, providing immigrants to sustain populations in unfavorable sink habitats (where extinction is inevitable without immigration). Recent theoretical and empirical studies of source-sink systems demonstrate that temporally variable local growth rates in sinks can substantially increase average abundance of a persisting population, provided that the variation is positively autocorrelated--in effect, temporal variation inflates average abundance. Here we extend these results to a metapopulation in which all habitat patches are sinks. Using numerical studies of a population with discrete generations (buttressed by analytic results), we show that temporal variation and moderate dispersal can jointly permit indefinite persistence of the metapopulation and that positive autocorrelation both lowers the magnitude of variation required for persistence and increases the average abundance of persisting metapopulations. These effects are weakened--but not destroyed--if variation in local growth rates is spatially synchronized and dispersal is localized. We show that the inflationary effect is robust to a number of extensions of the basic model, including demographic stochasticity and density dependence. Because ecological and environmental processes contributing to temporally variable growth rates in natural populations are typically autocorrelated, these observations may have important implications for species persistence.

Strategic development plan for integrated water resources management in Lake Manyara sub-basin, North-Eastern Tanzania

This paper reports that the core problem in the water resources management of the Lake Manyara sub-basin in north-eastern Tanzania is unsustainable utilization and management of natural resources. The subsequent effects observed in the sub-basin are natural resource use conflicts, poverty, low productivity, overcrowding, high siltation in rivers and lakes, degraded environment, decreased river flows, polluted water sources, etc. In order to establish strategies to arrest this situation, a strategic planning process has been used as a tool involving key stakeholders in the basin at various levels. Policy making officials at the district level i.e. planning officers, agricultural officers, water engineers and natural resources officers and grass root level experiences of respective wards in the basin were established through involving Ward executive officers. Water users of the key sectors in the basin were equally involved which included hotels, tented camps, irrigators and livestock keepers. Institutions working in natural resources management in the areas also participated including NGOs. The main causes leading to unsustainable utilization and management of natural resources were established as poverty, environment degradation, poor governance, weak enforcement of conservation laws, conflicting policies, inadequate experts at all levels, inadequate information on natural resources, high natural population growth rate, high immigration rates, high livestock population in comparison to land carrying capacity, political interference in implementation, limited water resources and lack of basin wide institution managing the natural resources in the basin. Various strategic objectives were identified by stakeholders and respective strategies, activities and verifiable indicators mapped for implementation. Stakeholders having owned the process and articulated the strategies themselves showed commitment and readiness to cooperate in the implementation of the plan.

Extinction risk to bird populations caused by DDT exposure

The impact of toxic chemicals on wild animals and plants can be quantified in terms of the enhanced risk of population extinction. To illustrate a method for doing this, we estimated such impact for two bird species: herring gull ( Larus argentatus) in Long Island, NY, and sparrowhawk ( Accipiter nisus) in eastern England, when they were exposed to DDT ( p, p ′-dichlorodiphenyltrichloroethane) and its metabolites (called DDTs). The method we used is based on a formula of the mean time to population extinction derived for a stochastic differential equation (the canonical model). The intrinsic rate of natural population growth was estimated from an exponentially growing population, and the intensity of the environmental fluctuation was estimated from the magnitude of population size fluctuation. The effect of exposure to DDTs in reducing the population growth rate was evaluated based on an age-structured population model, by assuming that age-specific fertility is density-dependent and sensitive to DDTs exposure, but age-specific survivorship is not. The results are expressed in terms of the risk equivalent––the decrease in carrying capacity K that causes the same enhancement of extinction risk as chemical exposure at a given level. The risk equivalent can be used in mitigation banking.

Correlates of growth in juvenile three‐spined sticklebacks: potential predictors of growth rates in natural populations

Abstract ‐ The possibility of using indices to quantitatively predict short‐term growth rates of juvenile three‐spined sticklebacks (Gasterosteus aculeatus L.) was assessed. A range of weight‐specific growth rates (GW) was obtained in experiments with individual sticklebacks fed enchtraeid worms at different daily rations over 21 days. There was a strong, positive correlation between GW and the RNA : DNA ratio in white muscle (r2 = 0.90) and lipid concentration (as percentage dry weight) of the carcass (r2 = 0.92). There were smaller, but significant correlations between GW and the percentage of dry matter in the carcass (r2 = 0.67), and the residuals from the weight–length relationship (r2 = 0.49). Regressions relating growth to RNA : DNA ratio and lipid concentration offer a means of estimating short‐term growth rates in natural populations. A test of such predictions using the results from a 56‐day experiment on stickleback growth suggested that predictions from percentage lipid were biased and inefficient, while predictions from the RNA : DNA ratio were unbiased but inefficient. Predictions from percentage lipid were higher than from the RNA : DNA ratio.

Site-specific debris flow vulnerability assessment

Debris flow vulnerability is the potential maximum losses in people, property and materials due to potential debris flow damaging phenomenon for a specified area and during a reference period, which is measured on a scale of 0 (0%) to 1 (100%). Debris flow vulnerability is related to the huge and complex socioeconomic and environmental system, which is mainly classified into two categories of property and population. The property index includes the assets of building, transportation infrastructure, lifeline, personal property, and land resources. Site-specific debris flow vulnerability is a complex-function of the property index. The population index includes the age, education level, wealth situation, natural growth rate of population, and population density. Site-specific debris flow vulnerability is a sum-production-function of the property index. Monetary unit is used to measure the property value, while the value of person may not be simply measured by money. Thus the property index and population index with different units cannot be directly added. In this paper, the transformation functions have successfully provided identical scale and dimensionless expression for both the indexes of property and of population, which make the vulnerability possibly to be expressed synthetically as the sum of the values of property and population. Mathematically debris flow vulnerability is computed by the square root of the half sum of the transformed values of property index and population index.

Extinction risk to herring gull populations from DDT exposure

The impact of toxic chemicals on wild animals and plants can be quantified in terms of the enhanced risk of population extinction. To illustrate the method, we estimated it for herring gull (Larus argentatus) populations in Long Island (NY, USA) exposed to DDT (p,p'-dichlorodiphenyltrichloroethane) and its metabolites (abbreviated as DDTs) with a strong biomagnification effect. The method is based on a formula of the mean time to population extinction derived for a stochastic differential equation (the canonical model). The intrinsic rate of natural population growth was estimated from the doubling time of an exponentially growing population and the intensity of the environmental fluctuation from the magnitude of population size fluctuation. The effect of exposure to DDTs in reducing the population growth rate was evaluated based on an age-structured population model by assuming that age-specific fertilities (including chick survivorship) are density dependent and sensitive to DDTs exposure but age-specific survivorships are not. The results are expressed in terms of the risk equivalent-the decrease in the carrying capacity K that causes the same enhancement of extinction risk as chemical exposure at a given level. The high concentration reported in Long Island in the 1960s corresponds to the equivalent loss of carrying capacity by 42.5% when K is 100 (the number of breeding females), and coefficient of variation (CV) = 0.2 (sigma2 = 0.0298) [corrected]. Risk equivalent allows us to compare different risk factors and is useful in mitigation banking.

A study of deep-sea natural microbial populations and barophilic pure cultures using a high-pressure chemostat.

Continuous cultures in which a high-pressure chemostat was used were employed to study the growth responses of (i) deep-sea microbial populations with the naturally occurring carbon available in seawater and with limiting concentrations of supplemental organic substrates and (ii) pure cultures of copiotrophic barophilic and barotolerant deep-sea isolates in the presence of limiting carbon concentrations at various pressures, dilution rates, and temperatures. We found that the growth rates of natural populations could not be measured or were extremely low (e.g., a doubling time of 629 h), as determined from the difference between the dilution rate and the washout rate. A low concentration of supplemental carbon (0.33 mg/liter) resulted in positive growth responses in the natural population, which resulted in an increase in the number of cells and eventually a steady population of cells. We found that the growth responses to imposed growth pressure by barophilic and barotolerant pure-culture isolates that were previously isolated and characterized under high-nutrient-concentration conditions were maintained under the low-nutrient-concentration limiting conditions (0.33 to 3.33 mg of C per liter) characteristic of the deep-sea environment. Our results indicate that deep-sea microbes can respond to small changes in substrate availability. Also, barophilic microbes that are copiotrophic as determined by their isolation in the presence of high carbon concentrations and their preference for high carbon concentrations are versatile and are able to compete and grow as barophiles in the low-carbon-concentration oligotrophic deep-sea environment in which they normally exist.

Sex expression and growth rates in natural populations of the desert soil crustal mossSyntrichia caninervis

The low elevation Mojave Desert cryptobiotic crust is dominated by the mossSyntrichia caninervis. In 16 populations of this moss, stem height and population were significantly associated with sex expression, with longer stems expressing sex more frequently and producing more perichaetia. The above-ground age of stems ranged up to 10 years, with a mean growth rate across populations of 0.36 mm year−1. The overall stem sex ratio, as a proportion of the total number of stems, was 0.30♀: 0♂: 0.70 non-expressing. The probability of expressing sex in a given season was 0.09. The absence of sexual reproduction (no sporophytes) and likely absence of the male sex from the area indicate that the non-expressing plants are female individuals. The slow growth rates, low rates of sex expression, absence of male plants, and absence of sexual reproduction in this crustal species may help explain why re-establishment of mosses on desert soils can take decades.

Growth lines within the beak microstructure of the octopus Octopus vulgaris Cuvier, 1797

Octopus vulgaris Cuvier, 1797 is commercially the most important species in the central-eastern Atlantic cephalopod fishery. The estimation of growth parameters in wild octopus populations is essential to management of the fishery. As there are problems with methods based on length-frequency modal analyses for describing growth from field data and there is a lack of age determination techniques for octopod species, estimation of the growth rates of natural populations is currently difficult. The present work describes the use of beaks to determine the age of O. vulgaris, using a new method based on a sample of beaks from 25 animals caught in the area in 1993. After sectioning different planes of the beaks embedded in resin blocks, they were analysed to select the best with which to observe growth increments. The sagittal plane (from outer to inner) revealed a pattern of increments of similar width in the internal rostral area of all the beaks analysed that are possibly related to the age of the animal. Th...

Distribution of chromosome length variation in natural isolates of Escherichia coli.

Large-scale variation in chromosome size was analyzed in 35 natural isolates of Escherichia coli by physical mapping with a restriction enzyme whose sites are restricted to rDNA operons. Although the genetic maps and chromosome lengths of the laboratory strains E. coli K12 and Salmonella enterica sv. Typhimurium LT2 are highly congruent, chromosome lengths among natural strains of E. coli can differ by as much as 1 Mb, ranging from 4.5 to 5.5 Mb in length. This variation has been generated by multiple changes dispersed throughout the genome, and these alterations are correlated; i.e., additions to one portion of the chromosome are often accompanied by additions to other chromosomal regions. This pattern of variation is most probably the result of selection acting to maintain equal distances between the replication origin and terminus on each side of the circular chromosome. There is a large phylogenetic component to the observed size variation: natural isolates from certain subgroups of E. coli have consistently larger chromosome, suggesting that much of the additional DNA in larger chromosomes is shared through common ancestry. There is no significant correlation between genome sizes and growth rates, which counters the view that the streamlining of bacterial genomes is a response to selection for faster growth rates in natural populations.

Prospects for fertility reduction and projections for future population growth in Kenya

In 1979 Kenya's annual rate of natural population growth was 3.8%. Data from the1989 Kenya Demographic and Health Survey indicate that significant decreases in fertility levels were experienced during the 1980s. Factors associated with conditions supportive of high fertility in Kenya are discussed, and progress toward attaining significant fertility reduction thresholds during the 1980s is assessed. Findings from recent fertility surveys are presented, and 1969–1989 national level family planning data are evaluated. Four population projections for 1985–2025 are presented and analyzed. One projection is based on official government growth targets; two are based on estimates provided by the United Nations and the Population Reference Bureau, and a fourth projection is based on the assumption that Kenya will attain an annual natural population growth rate of less than 1% by the year 2025. Each projection assumes that fertility declines will be experienced. Kenya's prospects for reducing the annual population growth rate to 1% within the next sixty years and a cost-sharing development policy are addressed briefly in the concluding section. Recent data suggest that Kenya will probably not complete the demographic transition before the year 2050, but Kenya should continue to move through the transition stage.

The Chinese single-child family programme and population psychology.

Following the Chinese population explosion in the early 1950s and late 1960s, the implementation of the single-child family planning programme in the 1970s caused a drastic decline in the natural growth rate of population in China. In this paper demographic data are presented to show population growth at various periods in Chinese history. The socio-psychological effects and problems encountered in the administration of the Chinese single-child family policy in recent decades are discussed. A population cycle caused by the abrupt change in population may last for 60 to 80 years until the mid-21st century. Around A.D. 2010 when there will be about equal number of children and old people in the Chinese society, a dilemma betweenparental investment and successor's investment may occur. The long-term consequence of the single-child family policy would be an aged society with more elders than children in society. A support system must therefore be designed as a mechanism to keep the Chinese three generation family system intact to care for the old. Grandparenting is suggested as a means to maintain inter-dependence in the family to cope with the dynamics of the changing inter-generation patterns. Classical Confucian ideology is considered important to maintain the traditional Chinese social institutions and ethical values.

Population growth and the demographic transition in Kenya.

This paper focuses on patterns of population growth in Kenya. The historical pattern of population growth from the close of the nineteenth century to 1992 is explored in the first two major sections. Estimates of the annual rate of natural population growth have not exceeded 2.5 per cent prior to 1960. Since 1960 the annual natural population growth rate has increased from 3 per cent in 1962 to 3.8-3.9 per cent for the 1977-1990 period. The rate has fallen slightly to 3.6 per cent for 1992, and data from the 1989 Kenya Demographic and Health Survey indicate that the total fertility rate declined significantly during the 1980s. The applicability of demographic transition theory to the study of population growth and development in Kenya is addressed in the third section. A fourstage model grounded in the work of Petersen, Caldwell and Chesnais is developed and applied to Kenya. Kenya is observed to have passed through the underdeveloped stage characterised by increasing birth and death rates and entered the transition/developing stage during the 1980s. Issues concerning the prospects of substantial continued reductions in the fertility level are addressed in the concluding section.

Population pressure, intensification of agriculture, and rural-urban migration

Low rates of labor absorption in rural areas with relatively low population density, such as Sub-Saharan Africa, are usually explained by poor natural conditions, mainly infertile tropical soil. I offer an explanation based on the extensive techniques of land use emplopyed in low density areas. I incorporate the intensity of land use as a parameter in a standard two-sector model to show that the rate of labor absorption (defined as the rate of natural population growth in the rural areas minus the rate of rural-urban migration) is positively correlated with the intensity of the technique of cultivation. An empirical section employs cross-section data from Iran to illustrate and confirm the relationships derived from the model.

Demographic findings relevant for health care planning and evaluation collected through a malaria control project in the Kivu Mountains, Zaire

Population studies were conducted in the margin of a community based malaria control programme in the Katana Health zone, in the Eastern part of Zaire. The reported findings are based on prospective registration of vital events from March 1986 through February 1987. At mid term 28.083 people were covered. The age and sex structure of the population was typical for tropical Africa, apart from an excess of males to females after the age of 64. The mean age at marriage was 21.2 years for women and 25.6 years for men. 89% of women did not complete a single year of formal education. The crude fertility rate was 250‰ and total fertility 8.3 children. The infant mortality rate and the child mortality quotients attained 130‰ and 183‰ respectively. The crude death rate was 23 per 1000 and the natural population growth rate 31‰. Due to a net out-migration of 28‰ the zone's population remained, however, virtually stable. The latter observation questions the purported role of demographic pressure as a key determinant of the region's slow socio-economic development. The other findings provide valuable baseline and background information for planning and evaluating health-related activities.