scholarly journals Low marine food levels mitigate high migration costs in anadromous populations

2019 ◽  
Author(s):  
P. Catalina Chaparro-Pedraza ◽  
André M. de Roos
Keyword(s):  
Lower Energy ◽  
Fish Populations ◽  
Migratory Fish ◽  
Environmental Threats ◽  
Freshwater Streams ◽  
Risk Of Extinction ◽  
Ecological Success ◽  
Marine Food ◽  
Migration Costs ◽  
High Migration

AbstractMigratory fish populations, like salmon, have dramatically declined for decades. Because of their extensive and energetically costly breeding travel anadromous fish are sensitive to a variety of environmental threats, in particular infrastructure building in freshwater streams and food declines in the ocean. Here, we analyze the effects of these two threats combined. Unexpectedly, we find that low marine food availabilities favor, as opposed to threaten, the ecological success of endangered populations. This counterintuitive effect results from an aspect of individual energetics that individuals switching to higher food levels reach larger sizes with concomitant larger migration costs but have lower energy densities. Surprisingly, the decline of food levels in the ocean after the completion of dams may thus mitigate the risk of extinction of migratory fish populations. This highlights the need of a mechanistic understanding integrating individual energetics, life history, and population dynamics to accurately assess biological consequences of environmental change.

scholarly journals Optimal Fiscal Policy When Migration Is Feasible

2008 ◽  
Vol 8 (1) ◽  
Author(s):  
Filippo Occhino
Keyword(s):  
Fiscal Policy ◽  
Income Taxes ◽  
Public Expenditures ◽  
Fiscal Policies ◽  
High Productivity ◽  
Free Mobility ◽  
Optimal Fiscal Policy ◽  
Migration Costs ◽  
Limiting Case ◽  
High Migration

Abstract This paper investigates how the feasibility of migration affects governments' optimal fiscal policies. We assume that households migrate toward economies where their welfare is higher, governments choose taxes and public expenditures to maximize a weighted sum of the households' welfare, welfare is increasing in public expenditures, and only distortionary labor income taxes are available. In isolated economies, the optimal fiscal policy implies that some households are net fiscal contributors, while other households are net fiscal beneficiaries. When households can migrate, however, governments compete for the households which are net fiscal contributors, and modify the fiscal policy in their favor, lowering their taxes and net fiscal contribution, and increasing their welfare. The magnitude of the effect increases with the sensitivity of migration to welfare. In the limiting case of free mobility, all households are zero net fiscal contributors. As to the patterns of migration, the model predicts that, with high migration costs, all households migrate toward the same high-productivity countries, which benefits low-productivity households, whereas with low migration costs, households with different productivities migrate toward different countries, which benefits high-productivity households.

scholarly journals WEALTH CONSTRAINTS, MIGRANT SELECTION, AND INEQUALITY IN DEVELOPING COUNTRIES

2017 ◽  
Vol 23 (2) ◽  
pp. 535-567 ◽  
Author(s):  
Joaquín Naval
Keyword(s):  
Developing Countries ◽  
Technological Development ◽  
Wealth Inequality ◽  
Level Of Education ◽  
Migration Rates ◽  
Education Decisions ◽  
Advanced Stages ◽  
And Migration ◽  
Migration Costs ◽  
High Migration

This paper builds a theoretical framework for studying migration and education in developing countries. Migration and education decisions are affected by migrants' wealth constraints. Technology and migration costs determine the pattern of migration through level of education, income, and wealth inequality. The model predicts that in the first stages of technological development, migration rates increase, as does economic inequality over time, for high migration costs. At more advanced stages of development, migration rates and wealth inequality decline. I show that these predictions are in line with the data.

scholarly journals The ichthyofauna of the Rio Carinhanha basin, one of the main tributaries of the Rio São Francisco

2020 ◽  
Vol 51 (4) ◽  
pp. 31-44
Author(s):  
Gilberto Nepomuceno Salvador ◽  
Ruanny Casarim ◽  
Gustavo Ribeiro Rosa ◽  
Yuri Malta Caldeira ◽  
Paulo Santos Pompeu
Keyword(s):  
Endangered Species ◽  
Native Species ◽  
Catchment Area ◽  
Entire Length ◽  
Fish Populations ◽  
Migratory Fish ◽  
River Channels ◽  
Middle Section ◽  
Long Distance ◽  
Main River

The ichthyofauna of the Rio São Francisco basin is relatively well-documented. However, most of this knowledge is concentrated at the upper stretch of its catchment area. In this study, we compile a list of species encompassing almost the entire length of the Rio Carinhanha, an important tributary from upper-middle section of the Rio São Francisco, including a comprehensive diversity of environments. A total of 99 species from 8 orders and 27 families were recorded. Five species are considered non-native, six classifieds as long distance migrants, and three as vulnerable. The orders with the greatest richness of native species were Characiformes and Siluriformes. Characidae was the most represented family, followed by Loricariidae. The main river channels were the richest environments sampled, followed by floodplain lagoons, veredas, and streams. The Carinhanha basin has important lotic remnants, thus it has several migratory fish populations as well as endangered species. This study demonstrates the importance of cataloguing the still poorly explored tributaries of the upper-middle section of the Rio São Francisco basin.

scholarly journals Fertility, migration, and altruism

2020 ◽  
Vol 86 (3) ◽  
pp. 367-402
Author(s):  
Eli Berman ◽  
Zaur Rzakhanov
Keyword(s):  
Capital Investment ◽  
Empirical Test ◽  
Cultural Preservation ◽  
Birth Cohorts ◽  
Age At Migration ◽  
Intergenerational Altruism ◽  
Will Self ◽  
Migration Costs ◽  
Immigrant Selection ◽  
High Migration

AbstractMigration is a human capital investment in which parents bear costs and children share returns. Therefore, migrants from a population with heterogeneous intergenerational discount rates will self-select on intergenerational altruism. Intergenerational altruism and fertility are arguably linked, therefore immigrants might self-select on eventual fertility. Soviet Jews who migrated to Israel despite high migration costs averaged almost one child more than members of the same birth cohorts who migrated later, at lower cost. Distinguishing selection from treatment effects using mothers' age at migration, selection accounts for most of that difference (the proportion varies with specification), even with controls for religion and religiosity. Selection on fertility may have other explanations, including cultural preservation. To probe, we conduct an alternative empirical test of immigrant selection on altruism, finding that U.S. immigrants spend more time with grandchildren than do natives. Additionally, immigrant self-selection on fertility provides an alternative explanation for Chiswick's (1978, Journal of Political Economy86(5), 897–921) earnings-overtaking result.

scholarly journals Microzooplankton Communities in a Changing Ocean: A Risk Assessment

Diversity ◽  
2021 ◽  
Vol 13 (2) ◽  
pp. 82
Author(s):  
M. Celeste López-Abbate
Keyword(s):  
Global Change ◽  
Food Webs ◽  
Community Level ◽  
Global Trends ◽  
Individual Level ◽  
Environmental Threats ◽  
Risk Levels ◽  
Marine Food Webs ◽  
Marine Food ◽  
The Individual

Microzooplankton communities are fundamental components of marine food webs and have the potential to impact the functioning of carbon pumps. The identification of common responses of microzooplankton to global change has been challenging due to their plasticity and complex community-level interactions. However, accumulating research is providing new insights on the vulnerability of this group to different climate and other human-related hazards. Here, the current and future risk levels of microzooplankton associated with global change are assessed by identifying prevailing hazards, exposure, sensitivity, natural adaptability, and observed impacts based on available evidence. Most documented hazards for the survival and yield of microzooplankton are ocean warming, acidification, deoxygenation, and coastal eutrophication. Overall, heterotrophic protists are expected to respond and adapt rapidly to global trends. Fast growing, mixotrophy, wide internal stoichiometry, and their capacity to track optimal environmental conditions by changing species’ range distribution are among the most important traits that shape their high adaptability to global change. Community-level responses to warming, however, are predicted to be amplified in polar and subpolar regions. At the individual level, the highest risk is associated with the sensitivity to deoxygenation since microzooplankton, especially ciliates, are known to reduce metabolic rates under hypoxic episodes; however, vulnerable species can be readily replaced by specialized taxa from a similar functional type. Microzooplankton seem to act as functional buffers of environmental threats, thus conferring stability, in terms of community connectedness to marine food webs and ecosystems against external disturbances.

scholarly journals Preventing overexploitation of migratory fish stocks: the efficacy of marine protected areas in a stochastic environment

2009 ◽  
Vol 66 (9) ◽  
pp. 1919-1930 ◽  
Author(s):  
Christopher D. West ◽  
Calvin Dytham ◽  
David Righton ◽  
Jonathan W. Pitchford
Keyword(s):  
Protected Areas ◽  
Marine Protected Areas ◽  
Environmental Stochasticity ◽  
Fish Populations ◽  
Stochastic Environment ◽  
Migratory Fish ◽  
Deterministic Analysis ◽  
Fish Stocks ◽  
Harvest Control Rule ◽  
Stable Equilibria

Abstract West, C. D., Dytham, C., Righton, D., and Pitchford, J.W. 2009. Preventing overexploitation of migratory fish stocks: the efficacy of marine protected areas in a stochastic environment. – ICES Journal of Marine Science, 66: 1919–1930. Marine protected areas (MPAs) have been widely proposed for protecting overexploited fish populations. It has been suggested that fisheries may be enhanced by spillover of individuals from MPAs into fishing grounds. However, traditional spillover studies fail to account for the seasonal migrations of many populations. Most fisheries models also fail to include the stochasticity inherent in marine environments explicitly. Here we assess MPA efficacy using a simple population model simulating the migration of fish populations between a spawning ground MPA and a fishery. Including realistic environmental stochasticity in our model allows the population to deviate from, and shift between, positive stable equilibria, something that is impossible in a deterministic analysis. This deviation may result in population collapse in cases where deterministic analysis predicts population persistence. We show that, although effective at low migration levels, the ability of MPAs to protect stocks from collapse generally decreases as migration increases. However, an MPA provides greater protection and greater expected fisheries yield than a system without an MPA, irrespective of migration level. Combining MPAs with a harvest control rule may further increase protection and yield. We therefore argue that MPAs can play a role in the protection of migratory species.

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