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Demographic Consequences (demographic + consequence)

Distribution by Scientific Domains

Life Sciences	90%

Selected Abstracts

Social, Economic and Demographic Consequences of Migration on Kerala

INTERNATIONAL MIGRATION, Issue 2 2001
K.C. Zachariah
Migration has been the single most dynamic factor in the otherwise dreary development scenario of Kerala during the last quarter of the last century. It has contributed more to poverty alleviation and reduction in unemployment in Kerala than any other factor. As a result of migration, the proportion of the population below the poverty line has declined by 12 per cent. The number of unemployed persons , estimated to be only about 13 lakhs in 1998 compared with 37 lakhs reported by the Kerala Employment Exchanges , has declined by over 30 per cent. Migration has caused nearly a million married women in Kerala to live away from their husbands. Most of these so-called "Gulf wives" experienced extreme loneliness to begin with, and were burdened with added family responsibilities to which they had not been accustomed when their husbands were with them. But over a period, and with a helping hand from abroad over the ISD, most came out of their early gloom. Their gain in autonomy, status, management skills and experience in dealing with the world outside their homes were developed the hard way and would remain with them for the rest of their lives for the benefit of their families and society. In the long run, the transformation of these million women will have contributed more to the development of Kerala society than all the temporary euphoria created by remittances and modern gadgetry. Kerala is dependent on migration for employment, subsistence, housing, household amenities, institution building, and many other developmental activities. The danger is that migration could cease, as shown by the Kuwait war of 1993, and repercussions could be disastrous for the State. Understanding migration trends and instituting policies to maintain the flow of migration is more important today than at any time in the past. Kerala workers seem to be losing out in international competition for jobs in the Gulf market. Corrective policies are needed urgently to raise their competitive edge over workers in competing countries in South and South-East Asia. Like any other industry, migration from Kerala needs periodic technological upgrading of workers. Otherwise, there is a danger that the State might lose the Gulf market permanently. The crux of the problem is Kerala workers' inability to compete with expatriates from other South and South-East Asian countries. The solution lies in equipping workers with better general education and job training. This study suggests a twofold approach. In the short run, the need is to improve the job skills of prospective emigrant workers. This could be achieved through ad hoc training programmes focussed on the job market in Gulf countries. In the long run, the need is to restructure the educational system, taking into consideration the future demand of workers not only in Kerala but also in potential destination countries all over the world, including the US and other developed countries. Kerala emigrants need not always be construction workers in the Gulf countries; they could also be software engineers in developed countries. [source]

Demographic consequences of unpredictability in fertility outcomes

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 2 2002
Paul Leslie
Child survival is probabilistic, but the unpredictability in family formation and completed family size has been neglected in the fertility literature. In many societies, ending the family cycle with too few or too many surviving offspring entails serious social, economic, or fitness consequences. A model of risk- (or variance-) sensitive adaptive behavior that addresses long-term fertility outcomes is presented. The model shows that under conditions likely to be common, optimal, risk-sensitive reproductive strategies deviate systematically from the completed family size that would be expected if reproductive outcome is were predictable. This is termed the "variance compensation hypothesis." Variance compensation may be either positive or negative, resulting in augmented or diminished fertility. Which outcome obtained is a function of identifiable social, economic, and environmental factors. Through its effect on fertility behavior, variance compensation has a direct bearing on birth spacing and completed fertility, and thereby on problems in demography and human population biology ranging from demographic transitions to maternal depletion and child health. Risk-sensitive models will be a necessary component of a general theory of fertility. Am. J. Hum. Biol. 14:168,183, 2002. © 2002 Wiley-Liss, Inc. [source]

Introduction Strategies Put to the Test: Local Adaptation versus Heterosis

CONSERVATION BIOLOGY, Issue 3 2004
PHILIPPINE VERGEER
exogamia; introducciones multi-fuente; introducciones uni-fuente; Succisa pratensis Abstract:,Plant biodiversity has declined seriously because of both habitat deterioration and habitat fragmentation. As a result, many species have been forced into small, fragmented, and isolated populations and are believed to suffer from higher extinction risks. Genetic reinforcement and the establishment of new populations are now widely used to prevent extinction. However, the genetic background of transplants may seriously affect the long-term success of these populations because increased genetic variation may reduce the risk of inbreeding or lead to better performance by restored heterozygosity levels (heterosis). Introduced transplants, however, may be poorly adapted to the new local conditions. We tested the initial success of alternative introduction strategies. We evaluated the potential for inbreeding, heterosis, and/or local adaptation after introduction of artificial populations of Succisa pratensis. We introduced individuals from local and distant artificial populations that were created from either small or large populations. We created the artificial populations with the same census population size but varying effective population sizes by adjusting the relatedness of individuals. We analyzed the demographic consequences of inbreeding, heterosis, and/or local adaptation of these artificial populations. Reduced performance after selfing was manifested by a reduction in seed production, seed weight, germination, and flowering percentage. Seed production, seed weight, flowering percentage, and number of flowerheads were negatively affected by small population size. Local adaptation increased biomass and flowering percentage for local individuals. Seed weight and seed production exhibited significant heterosis. Our results demonstrate that threatened populations can benefit from introduction and genetic reinforcement of individuals from related populations. Significant differences among the artificial populations for several measured performance components suggest that introduction or reinforcement is best achieved through material from a local population or, when unavailable, from several large populations. Resumen:,La biodiversidad de plantas ha declinado seriamente tanto por el deterioro como la fragmentación de hábitats. Como resultado, muchas especies han sido relegadas a poblaciones pequeñas, fragmentadas y aisladas cuyos riesgos de extinción se piensa que son mayores. El reforzamiento genético y el establecimiento de poblaciones nuevas se utilizan ampliamente en la actualidad para prevenir la extinción. Sin embargo, los antecedentes genéticos de transplantes pueden afectar seriamente el éxito de estas poblaciones a largo plazo debido a que el incremento en la variación genética puede reducir el riesgo de endogamia o puede conducir a un mejor rendimiento por lograr niveles de heterocigosidad restaurados (heterosis). No obstante, los trasplantes introducidos pueden adaptarse deficientemente a las nuevas condiciones locales. Probamos el éxito inicial de estrategias de introducción alternativas. Evaluamos el potencial de endogamia, heterosis y/o adaptación local después de la introducción de poblaciones artificiales de Succisa pratensis. Introdujimos individuos de poblaciones locales y de poblaciones artificiales distantes que fueron creadas a partir de poblaciones tanto pequeñas como grandes. Las poblaciones artificiales fueron creadas con el mismo tamaño poblacional censal pero variaron en tamaños poblacionales efectivos al ajustar la parentela de los individuos. Analizamos las consecuencias demográficas de la endogamia, heterosis y/o adaptación local de estas poblaciones artificiales. Después de la autofecundación se manifestó una reducción en el rendimiento por reducción en la producción y peso de semillas y en el porcentaje de germinación y floración. La producción y peso de semillas, el porcentaje de floración y el número de botones florales fueron afectados negativamente por el tamaño poblacional pequeño. La adaptación local incrementó la biomasa y el porcentaje de floración en individuos locales. El peso y producción de semillas mostró heterosis significativa. Nuestros resultados demuestran que las poblaciones amenazadas pueden beneficiarse de la introducción y del reforzamiento genético de individuos de poblaciones emparentadas. Las diferencias significativas entre las poblaciones artificiales en varios de los componentes de rendimiento medidos sugiere que la introducción o reforzamiento se logra mejor con material de una población local o, cuando no disponible, con material de varias poblaciones grandes. [source]

A comparison of sex ratio, birth periods and calf survival among Serengeti wildebeest sub-populations, Tanzania

AFRICAN JOURNAL OF ECOLOGY, Issue 4 2009
Vedasto G. NdibalemaArticle first published online: 31 AUG 200
Abstract Although adaptation and environmental conditions can easily predict demographic variation in most savannah ungulates, no study on demographic consequences arising from natural and anthropogenic factors among Serengeti wildebeest (Connochaetes taurinus) sub-populations in Tanzania has been carried out. Here, I report estimates of annual sex ratio, calf and yearling survival rate and birth seasonality between resident and migratory sub-populations to explore demographic patterns arising from the different age and sex structure. The results indicate significantly higher female-biased sex ratios in the resident and almost even sex ratios among individual migrants. The calf recruitment estimated as mother: offspring ratios indicate a more synchronous birth in the migrant than the resident sub-population. Also, birth seasonality in the migratory sub-population coincided with seasonal variability of rainfall and the timing of the birth peak was more variable in the migrants than the resident sub-population. The migratory sub-population had a higher annual proportional mean calf survival estimate (0.84) than that of the residents (0.44) probably due to higher mortality resulting from predation in the western corridor. However, the proportion of yearling survival estimates was much lower (0.31) in the migrants and relatively higher (0.39) in the residents. Different demographic outcomes resulting from environment, predation, movements and ecological factors including resource competition have conservation implications for the two sub-populations. Résumé Bien que l'adaptation et les conditions environnementales puissent facilement aider à prédire la variation démographique de la plupart des ongulés de savane, aucune étude n'a encore été réalisée sur les conséquences démographiques de facteurs naturels et anthropiques chez les sous-populations de gnous (Connochaetes taurinus) du Serengeti, en Tanzanie. Ici, je rapporte des estimations du sex-ratio annuel, du taux de survie des veaux et des jeunes d'un an et le caractère saisonnier des naissances entre des sous-populations résidentes et migratrices, pour explorer les schémas démographiques qui se dessinent à partir des différentes structures d'âge et de sexe. Les résultats indiquent un sex-ratio significativement biaisé en faveur des femelles chez les animaux résidents et un sex-ratio presque équilibré chez les individus migrateurs. Le recrutement des veaux estimé selon le rapport mère/progéniture indique des naissances plus synchrones chez la sous-population migratrice que chez la résidente. La saisonnalité des naissances chez la sous-population migratrice coïncidait avec la variabilité saisonnière des chutes de pluies, et le timing du pic des naissances était plus variable chez la sous-population migratrice que chez la résidente. La sous-population migratrice avait une espérance de vie annuelle proportionnelle des veaux plus élevée (0,84) que la résidente (0,44), probablement en raison de la plus forte mortalité causée par des prédateurs dans le corridor occidental. Cependant, les estimations de la proportion de jeunes d'un an survivants étaient beaucoup plus basses (0,31) chez les migrateurs et relativement plus hautes (0,39) chez les résidents. Les résultats démographiques différents des facteurs environnementaux, de la prédation, des déplacements et des facteurs écologiques, y compris la compétition pour les ressources, ont des implications pour la conservation des deux sous-populations. [source]

Detecting genetic structure in migrating bowhead whales off the coast of Barrow, Alaska

MOLECULAR ECOLOGY, Issue 10 2007
P. E. JORDE
Abstract We develop a general framework for analysing and testing genetic structure within a migratory assemblage that is based on measures of genetic differences between individuals. We demonstrate this method using microsatellite DNA data from the Bering-Chukchi-Beaufort stock of bowhead whales (Balaena mysticetus), sampled via Inuit hunting during the spring and autumn migration off Barrow, Alaska. This study includes a number of covariates such as whale ages and the time separation between captures. Applying the method to a sample of 117 bowhead whales, we use permutation methods to test for temporal trends in genetic differences that can be ascribed to age-related effects or to timing of catches during the seasons. The results reveal a pattern with elevated genetic differences among whales caught about a week apart, and are statistically significant for the autumn migration. In contrast, we find no effects of time of birth or age-difference on genetic differences. We discuss possible explanations for the results, including population substructuring, demographic consequences of historical overexploitation, and social structuring during migration. [source]

Insect herbivory declines with forest fragmentation and covaries with plant regeneration mode: evidence from a Mexican tropical rain forest

OIKOS, Issue 2 2010
Betsabé Ruiz-Guerra
The consequences of tropical forest fragmentation on herbivory are poorly understood. The limited evidence suggests that forest fragmentation can have positive, negative or neutral effects on herbivory. Inconsistencies may be partly explained by plant interspecific variation and differential responses related to plant life history. In this study we examined the effects of forest fragmentation and plant regeneration mode (shade-tolerant and light-demanding species) on sapling herbivory using a large sample of the community (97 species, representing 25% of the woody flora of the study site), and a subset of species shared by forest fragments and continuous forest. For the latter, we also analyzed the effects of species identity on variation in herbivory. Also, for the shared species we used two techniques to measure herbivory: standing herbivory (i.e. instantaneous, actual damage) and cumulative herbivory (i.e. damage, accumulated over time, on initially intact leaves). Insect herbivory was the predominant type of damage in the two forest types, and standing herbivory at both the community and the shared species level was significantly higher in continuous forest than in fragments. Considering shared species, both standing and cumulative herbivory were significantly higher in light-demanding than in shade-tolerant species. Cumulative herbivory also showed a significant interaction between forest fragmentation and plant regeneration mode, whereby a significant decline in herbivory in fragments was driven by reduced herbivory in shade-tolerant species, whereas for light-demanding species herbivory did not change significantly, due to contrasting species-specific responses. We conclude that tropical forest fragmentation reduces insect herbivory, but this depends on plant regeneration mode and species identity. These changes could have effects on plant regeneration and diversity in forest fragments via long-term demographic consequences. [source]

Winter commingling of populations of migratory species can cause breeding range underpopulation

OIKOS, Issue 12 2007
Alexander M. Mills
We build a model with large-scale demographic consequences for migratory species. The model operates where four elements co-occur, and we rely on empirical research using migratory birds to demonstrate them. First, breeding ranges have internal structure flowing from natal philopatry. Second, fecundity varies geographically. Third, populations of different breeding provenances commingle during winter. And fourth, a population-limiting carrying capacity operates during winter. In the absence of breeding season population-limitation, only the breeding population with maximum fecundity persists. Consequently, some potential breeding areas that offer suitable and productive habitat are bereft of breeding birds because of the interplay between the geographical fecundity gradient and the shared winter quarters. Where breeding season population-limitation also plays a role for at least one population, one (or more) breeding population becomes permanently depressed, resulting in a density well below the carrying capacity of the productive breeding habitat that is occupied. In either case, not all populations fare equally well, despite net positive breeding season productivity. Changes in winter carrying capacity, for example habitat degradation in winter quarters, can lead to uneven effects on geographically defined breeding populations, even though there has been no change in the circumstances of the breeding range. [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]

Patterns of male residency and intergroup transfer in gray-cheeked mangabeys (Lophocebus albigena)

AMERICAN JOURNAL OF PRIMATOLOGY, Issue 4 2005
William Olupot
Abstract We describe the movements and fates of 36 collared gray-cheeked male mangabeys (Lophocebus albigena) that resided in seven social groups in Kibale National Park, Uganda. The male mangabeys were captured, radiotagged, and then contacted regularly over a period of up to 8 years. Individuals varied considerably in how tightly they were associated with their groups. "Central" males were usually found in close spatial association with their own groups, but they sometimes visited others. "Peripheral" males were often found several hundred meters away from their own groups. Most adult males were characterized by repeated intergroup transfers, manifested as "visits" and "dispersals." Visits were transfers that did not result in mating. The visits were brief, and ranged from a few minutes to a few days before the male returned to his previous group, moved on to another group, or returned to solitary life. The term "dispersal" refers to a transfer that results in mating, after which the male remains in the new group. Young males began to drift away from their natal groups in early subadulthood, but the timing of first associations with estrous females in other groups was highly variable. Natal dispersers were generally solitary for a month or more, and at least half moved into nonadjacent groups. Secondary dispersal was common. After they immigrated, adult males remained in a group for a median of 19 months before they emigrated again, with the probability of departure being approximately constant in time. Secondary dispersal was usually made into an adjacent group and lasted less than 7 days. Emigration and immigration were not seasonal, and males emigrated singly and apparently independently; however, immigrations were clumped in time, and male dispersal contributed to considerable heterogeneity of group composition. L. albigena dispersal patterns are intermediate between those described for Papio baboons and forest Cercopithecus, and models that predict demographic consequences of dispersal for baboons can be refined to apply to mangabeys. Am. J. Primatol. 66:331,349, 2005. © 2005 Wiley-Liss, Inc. [source]

Impact of recreational power boating on two populations of northern map turtles (Graptemys geographica)

AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2010
G. Bulté
Abstract 1.Recreational power boating is growing in popularity in North America. This activity is known to have lethal and sub-lethal effects on aquatic wildlife and freshwater turtles may be particularly sensitive to this activity. 2.This study reports on patterns of traumatic injuries inflicted by powerboat propellers to northern map turtles (Graptemys geographica) from two sites differing in boat traffic intensity in Ontario, Canada. 3.The relative vulnerability of turtles was assessed, in light of seasonal patterns in boat traffic, as a function of sex- and age-specific movement patterns, habitat use, and basking behaviour obtained by radio-telemetry. Population viability analyses (PVA) were also conducted to evaluate the potential demographic consequences of mortality induced by powerboats. 4.The prevalence of propeller injuries was two to nine times higher in adult females than in adult males and juvenile females. Patterns of movement, habitat use, and aquatic basking indicated that adult females are more exposed to collisions with boats. PVA showed that boat-induced mortality in adult females could lead to rapid population extinction if the risk of mortality when hit by a boat is greater than 10%. 5.The results of this study showed that recreational power boating is a serious threat to northern map turtles, even under moderate boat traffic. The need to adopt measures restricting boat traffic in areas important to turtles is discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source]