Decrease In Population Growth Rate Research Articles

The concept of critical age group for density dependence: bridging the gap between demographers, evolutionary biologists and behavioural ecologists.

Density dependence plays an important role in population regulation in the wild. It involves a decrease in population growth rate when the population size increases. Fifty years ago, Charlesworth introduced the concept of 'critical age group', denoting the age classes in which variation in the number of individuals most strongly contributes to density regulation. Since this pioneering work, this concept has rarely been used. In light of Charlesworth's concept, we discuss the need to develop work between behavioural ecology, demography and evolutionary biology to better understand the mechanisms acting in density-regulated age-structured populations. We highlight demographic studies that explored age-specific contributions to density dependence and discuss the underlying evolutionary processes. Understanding competitive interactions among individuals is pivotal to identify the ages contributing most strongly to density regulation, highlighting the need to move towards behavioural ecology to decipher mechanisms acting in density-regulated age-structured populations. Because individual characteristics other than age can be linked to competitive abilities, expanding the concept of critical age to other structures (e.g. sex, dominance rank) offers interesting perspectives. Linking research fields based on the concept of the critical age group is key to move from a pattern-oriented view of density regulation to a process-oriented approach.This article is part of the discussion meeting issue 'Understanding age and society using natural populations'.

Can acclimation of freshwater rotifers to silver nanoparticles or 5-fluorouracil influence their multi- and transgenerational effects?

Emerging chemical contaminants (ECCs) are among the major environmental threats in present century. A variety of ECCs is released into aquatic environments with little knowledge about their long-term impacts to organisms. We examined the role of acclimation of the freshwater rotifer Brachionus calyciflorus to silver nanoparticles (Ag-NPs) and 5-fluorouracil (5-FU) for determining their ability to deal with these ECCs individually and in mixtures along multiple generations. Additionally, transgenerational effects were also assessed during the recovery phase. Rotifers acclimated at EC10 of Ag-NPs along generations showed a higher ability to deal with higher concentrations of these nanoparticles or 5-FU along generations. Rotifers acclimated to EC10 of 5-FU showed varied responses, as their population growth rates were affected at the initial generations once exposed to higher concentration (EC50) of the same or a new contaminant; however, the rotifers acquired resistance in later generations. The exposure of generational Ag-NP-acclimated rotifers to the mixture of Ag-NPs and 5-FU at EC50 led to a shift from no effects to negative effects along successive generations, suggesting a decrease in resistance, which remained even in the post-exposure recovery phase. Similar transgenerational adverse effects were also observed for the generational Ag-NP-acclimated rotifers released from 5-FU. Rotifers acclimated to 5-FU showed a decrease in population growth rate at the first generation of recovery phase, possibly shifting their optimal environmental conditions when released from contaminants. Overall, our results suggest that rotifers had a high level of plasticity to ECC exposure in freshwaters; however, acclimation can be generic or contaminant dependent.

Ecotoxicity of the fluoroquinolone antibiotic delafloxacin to the water flea Simocephalus vetulus and its offspring under the influence of calcium modulation

Delafloxacin (DFX), one of the latest additions to the fluoroquinolone antibiotics, is gaining heightened recognition in human therapy due to its potential antibacterial efficacy in a wide range of applications. Concerns have arisen regarding its presence in the environment and its potential interactions with multivalent metals, such as calcium (Ca). The present study investigated the trans- and multigenerational effects of environmentally projected concentrations of DFX (100–400 μg DFX L−1) on individual- and population-level responses of parental S. vetulus (F0) and its descendants (F1) under normal (26 mg L−1) and high (78 mg L−1) Ca conditions. Exposure of the F0 generation to DFX under the normal Ca condition resulted in reduced juvenile body length (JBL), increased age-specific survival rate (lx), indicating prolonged developmental time, reduced age-specific fecundity rate (mx), and decreased population growth rate (rm). Under the high Ca condition, JBL, mx, and rm were adversely affected. Transgenerational effects of DFX existed, as F1 individuals exhibited persistent suppressions in at least one endpoint under both Ca conditions even after being transferred to a clear medium. Continuous exposure of the F1 generation to DFX had negative impacts on JBL, mx, and rm under the normal Ca condition, and on JBL and rm under the high Ca condition. However, cumulative effects were not observed, suggesting the potential development of tolerance to DFX in the F1 organisms. These findings suggest that DFX is a harmful compound for the non-target model organism S. vetulus and reveal a potential antagonism between DFX and Ca. Nevertheless, the interaction between other (fluoro)quinolones and Ca remains unclear, necessitating further research to establish this phenomenon more comprehensively, including understanding the interaction mechanism in ecotoxicological contexts.

무인 배송 로봇 기술의 특허 동향 분석과 전망

With the advent of the untact era due to COVID-19, demand in the existing online market and the courier and logistics industry is accelerating. At the same time, the problem of decreasing available labor force due to decreasing population growth rate and aging is growing, causing difficulties due to labor shortage. In this paper, we examine the patent application trends of unmanned delivery systems by country, technology, and major applicants, and identify the degree of patent activity of major companies through index analysis. To this end, we analyzed domestic and foreign patents on unmanned delivery robot technology filed up to July 2021, and classified them according to the technology classification system to present the outlook of unmanned delivery technology. The analysis showed that robots, drones, and unmanned delivery boxes, which combine IoT technologies of the Fourth Industrial Revolution based on last-mile delivery technology, are expanding their scope of use. In addition, the development of cooperative delivery services combining robots and drones is expected, and the differentiation of delivery costs between rapid delivery by drones and regular delivery by robots is expected. This paper is expected to raise awareness of unmanned delivery technology among related companies and researchers, and to serve as a reference for future research and development for efficient last-mile delivery

Salinization and heavy metal cadmium impair growth but have contrasting effects on defensive colony formation of Scenedesmus obliquus

Driven by anthropogenic activities, freshwater salinization has become an emerging global environmental issue. Recent studies indicate that salinization increases the mobility of heavy metals in soil and causes higher flux into surface waterbodies. The present study assessed the combined effects of salinization (0, 3, 6 PSU) and the heavy metal Cd2+ (0, 0.2, 0.4 mg L−1) on the anti-grazing colony formation and population growth of Scenedesmus obliquus, a common freshwater alga. The results showed that the increase in salinity promoted colony formation of S. obliquus with or without the presence of grazing cues and, in contrast, Cd2+ contamination depressed the defensive colony formation of S. obliquus to Daphnia filtrate. The increase in both salinity and Cd2+ concentration depressed the population growth of S. obliquus, including impaired photosynthesis and a decreased population growth rate. Salinization moderated the negative effects of Cd2+ on defensive colony formation of S. obliquus, suggesting increased absorption of Cd2+ ions by a thicker outer layer of the algal cell wall under saltier conditions. As a result, larger defensive colonies of S. obliquus under freshwater salinization may cause higher bioaccumulation of heavy metals by algal cells and heavier influence on zooplankton. This study provides evidence that freshwater salinization could interfere with plankton interactions by affecting algal defense and growth, which may lead to bottom-up cascading effects on freshwater food webs.

An Analysis of Japan’s Recent Economic Crisis: Lessons for Bangladesh

Japan has experienced rapid growth during 1960-69, around 10.9%, whereas it started the development process from almost ‘zero’ after WWII. Since the independence of Bangladesh, the country has received a significant amount of contribution from Japan in various sectors. Japan is facing stagnation for over two decades. The economy started crippling with the collapse of stock and land prices in the mid-1980s through Bubble Economy. It slipped further due to the global financial crisis of 2008, which led to recession and deflation. For the last two decades, Bangladesh is also approaching a stable growth, around 6.5% per year, and has the ambition to achieve around 8% in the 8th five-year plan. Therefore, the study’s main objective is to explore why Japan cannot increase its inflation rate at its expectable level and its way out and to find out what sorts of policy Bangladesh should take for avoiding the Japanese type of economic crisis. The study applied qualitative methodology depending on Desktop/Secondary source-based research where available documents were reviewed critically. The findings indicate that Japan had tried to raise inflation by 2% through three arrows which are popularly known as Abenomics which are quantitative and qualitative monetary easing (QQE), fiscal expansion and structural reform. This policy failed since it did not consider the context of Japan. With an increasingly ageing population and decreasing population growth rate, Japan has a unique and distinguished demographic structure that affects the supply and demand side of the economy. Therefore, Bangladesh should not adopt any economic policy without considering its very own unique characteristics.

Does natural resource influence conflict in Africa? Evidence from panel nonlinear relationship

This paper examines the influence of natural resources on conflict over the 2010–2019 period in 54 African countries using a novel quadratic regression model and threshold estimation. The choice of the study's time period was based on violence vulnerability and data availability. The threshold technique and quadratic regression were used as natural resources are theorized to have a U-shape relationship with conflict. The empirical findings show that indicators of natural resources have significant positive effect on violence in Africa at 0.01 significant level. To maintain a conflict-free economy, low unemployment and decreased population growth rates are crucial to resolving the threat of conflict. Thus, policies targeted at reducing the conflict should focus on eliminating or reducing unemployment and control population growth rate. Policies should further ensure that natural resources exploitation and revenue sharing from the resource should be equitable, which can greatly mitigate conflict.

Effect of decreasing population growth-rate on deforestation and population sustainability

ABSTRACT We consider the effect of non-constant parameters on the human-forest interaction logistic model coupled with human technological growth introduced in [1]. In recent years in fact, a decrease in human population growth rate has emerged which can be measured to about 1.7% drop per year since 1960 value, which coincides with latest UN projections for next decades up to year 2100 [2]. We therefore consider here the effect of decreasing human population growth-rate on the aforementioned model and we evaluate its effect on the probability of survival of human civilization without going through a catastrophic population collapse. We find that for realistic values of the human population carrying capacity of the earth (measured by the parameter β) this decrease would not affect previous results, leading to a low probability of avoiding a catastrophic collapse. For larger more optimistic values of β instead, a decrease in growth-rate would tilt the probability in favor of a positive outcome, i.e. from 10–20% up to even 95% likelihood of avoiding collapse.

Determinants of the intention to recommend overseas migration to a city: The perspective of foreign residents

ABSTRACTDue to the decreasing population growth rate, some cities have struggled to increase their populations, and attracting foreigners as residents may be considered an alternative solution to this problem. The present study aims to investigate the relationships among the city image as a tourism city, place identity, quality of life domains, overall life satisfaction, and intention to recommend short- or long-term overseas migration to a city while controlling for respondent characteristics. Using a data set obtained from a foreign resident survey conducted by the metropolitan government of Seoul, South Korea, this study finds that despite differences in the influences of the explanatory variables, the intention to recommend overseas migration is most strongly related to place identity, followed by city image. Of the quality of life domains, the influence of the social environment is the strongest and positive, while residential environment and educational environment are negatively related. The theoretical and practical implications for attracting foreign migrants to a city are discussed.

Finding the reasons of decrease in the rate of population growth in Iran using causal layered analysis (CLA) method.

Background: According to census 2011, general fertility rate in Iran was 1.6 children. The United Nations published a low population growth scenario for Iran in 2010, and if Iran continues to experience population replacement and does not have a plan to balance it, it will experience a population of 31 million, with a high percentage of elderly people in the next 80 years. This study was conducted to identify the causes of a decrease in population growth rate. Methods: This was a secondary study conducted by reviewing the scientific texts, papers, and upstream documents. The upstream documents contain all national documents related to population decline in Iran. Causal layered analysis (CLA) was used for data analysis. Results: The 9 most important identified causes for a decrease in population were litany (child mortality, maternal mortality, diseases burden, fertility rate, marriage squeeze, abortion, marriage age, high-risk behaviors, and badly supervised and neglected children. Also, 5 causes in structural layer were urbanization, education rate, economic participation rate and unemployment rate, new structures, a change in family structure, and intergenerational gap. Moreover, three causes in discourse layer included welfare, materialism, individualism, and 2 causes in metaphor layer were changing the perception of life and family formation, and women as workforce. Conclusion: It seems that the decrease in population growth in Iranian society is less the result of social planning and population control and more the result of the value and structural changes that have been occurred due to modernization in the society. It is recommended that policymakers primarily address the discourse and metaphor layers to solve the problems.

Effects of metal-polluted seawater on life parameters and the induction of oxidative stress in the marine rotifer Brachionus koreanus

Metal pollution is one of the major threats to the aquatic environment due to its high bio-concentrations and toxicity. Although numerous studies have been conducted to understand detoxification and toxicity mechanisms in aquatic invertebrates, most of them were limited in laboratory study. Here, we investigated adverse effects of the contaminated-natural seawater on the marine rotifer Brachionus koreanus. Field seawater was collected from five different sites of Youngil Bay, South Korea where pollution by metals is predicted due to industrial discharges from nearby steel industry complexes. The marine rotifer B. koreanus was exposed to different seawater samples, and we found decreased population growth rates with highly induced transcriptional level of detoxification-related genes. Our finding shows a link between the induction of metal-mediated regulation of detoxification genes in B. koreanus and concentration of heavy metals present in various seawater samples, implying those biomarker genes can be useful to assess the toxicity of metal polluted natural seawaters. Our results are helpful to validate and establish biomarker genes for early risk assessment of metal contamination in the natural sea water.

Failure to coordinate management in transboundary populations hinders the achievement of national management goals: The case of wolverines in Scandinavia

Abstract Large carnivores are expanding in Europe, and their return is associated with conflicts that often result in policies to regulate their population size through culling. Being wide‐ranging species, their populations are often distributed across several jurisdictions, which may vary in the extent to which they use lethal control. This creates the conditions for the establishment of source‐sink dynamics across borders, which may frustrate the ability of countries to reach their respective management objectives. To explore the consequences of this issue, we constructed a vec‐permutation projection model, applied to the case of wolverines in south‐central Scandinavia, shared between Norway (where they are culled) and Sweden (where they are protected). We evaluated the effect of compensatory immigration on wolverine population growth rates, and if the effect was influenced by the distance to the national border. We assessed to what extent compensatory immigration had an influence on the number of removals needed to keep the population at a given growth rate. In Norway, the model estimated a stable trend, whereas in Sweden it produced a 10% annual increase. The effect of compensatory immigration corresponded to a 0.02 reduction in population growth rate in Sweden and to a similar increase in Norway. This effect was strong closer to the Norwegian‐Swedish border, but weak when moving away from it. An average of 33 wolverines was shot per year in the Norwegian part of the study area. If no compensatory immigration from Sweden had occurred, 28 wolverines shot per year would have been sufficient to achieve the same goal. About 15.5% of all the individuals harvested in Norway between 2005 and 2012 were compensated by immigrants, causing a decrease in population growth rate in Sweden. Synthesis and applications. When a population is transboundary, the consequences of management decisions are also transboundary, even though the political bodies in charge of those decisions, the stakeholders who influence them, and the taxpayers who finance them are not. It is important that managers and citizens be informed that a difference in management goals can reduce the efficiency, and increase the costs, of wildlife management.

Nonlinear averaging of thermal experience predicts population growth rates in a thermally variable environment.

As thermal regimes change worldwide, projections of future population and species persistence often require estimates of how population growth rates depend on temperature. These projections rarely account for how temporal variation in temperature can systematically modify growth rates relative to projections based on constant temperatures. Here, we tested the hypothesis that time-averaged population growth rates in fluctuating thermal environments differ from growth rates in constant conditions as a consequence of Jensen's inequality, and that the thermal performance curves (TPCs) describing population growth in fluctuating environments can be predicted quantitatively based on TPCs generated in constant laboratory conditions. With experimental populations of the green alga Tetraselmis tetrahele, we show that nonlinear averaging techniques accurately predicted increased as well as decreased population growth rates in fluctuating thermal regimes relative to constant thermal regimes. We extrapolate from these results to project critical temperatures for population growth and persistence of 89 phytoplankton species in naturally variable thermal environments. These results advance our ability to predict population dynamics in the context of global change.

Water Resources Carrying Capacity Analysis of YarLung Tsangpo River Basin (I)

Water resources carrying capacity (WRCC) analysis is critically important in providing guidance to the sustainable development strategies of the YarLung Tsangpo River Basin (YTRB) due to the conflicts among the ample water resources, low development level of society, and the fragile ecological environment. This study evaluated the scheduled developing mode of YTRB in the planning years from 2016 to 2030 with a WRCC system containing three components: a hydrological informatics modeling system (HIMS), water resources carrying capacity (WRCC) model, and an index evaluation system. The averaged WRCC index is 4.29, 1.19, and 0.06 for the planning years, and 2.61, 0.98, 0.05 for the baseline years for the three sub-basins. The water deficiency problem becomes more severe in the upper sub-basin and appears in the middle sub-basin with the WRCC index greater than 1, while the water resources are not fully utilized in the lower sub-basin in the planning years, with the WRCC index far less than 1. The GDP of the three sub-basins is greater in the planning years, with 2.25 × 108, 54.60 × 108, and 3.94 × 108 dollars year−1 than those in the baseline years with 1.97 × 108, 47.71 × 108, 3.43 × 108 dollars year−1. However, GDP per capita/cubic meter keeps decreasing due to the great population growth rate and non-enhanced water use efficiency. The sustainability index is 0.04, 0.23, and 0.47 in the planning years, which is lower than the 0.04, 0.31, and 0.50 in the baseline years. Therefore, the scheduled growth rates of the population, urbanization, and GDP are a developing mode with low sustainability and are not appropriate to be continued in the planning years. Further work is needed to identify a sustainable developing mode with a decreased population growth rate, enhanced water use efficiency in the economic system, and the optimized allocation of water resources distribution in the three sub-basins with hydraulic facilities.

Starting small: long‐term consequences in a managed large‐mammal population

AbstractSmall populations are vulnerable to founder effects, stochastic demographic events and inbreeding depression. These factors raise the extinction probability of small populations, and thus effective management plans for endangered species have become essential. The black rhinoceros (Diceros bicornis) survived a historic global population crash and is currently facing renewed threat through poaching, population fragmentation and isolation. South Africa is home to approximately 36% of the world's remaining black rhinos; however, this population is fragmented across parks and reserves, and many of these small populations remain geographically and genetically isolated. The historic population crash, subsequent fragmentation and relentless poaching pressure together threaten the viability of the black rhino population within South Africa. This study employed a practical, non‐invasive sampling protocol and genetic analyses to assess the growth and performance of a small founder population in a fenced reserve. We used these data and recorded life‐history data to compare the population growth and vital rates between the first and second 10‐year periods since founding. We report a decrease in population growth rate and male survival in the second 10‐year period (0.06; 0.89) compared to the first (0.09; 0.97). Genetic diversity (HEXP = 0.405) was low when compared to larger black rhino populations, and average pairwise relatedness was high (0.193). These results suggest that negative genetic consequences and the beginning of density‐dependant growth regulation may be present in this population. This highlights the importance of establishing an evaluation framework for the assessment of small populations of long‐lived mammals in order to inform metapopulation management.

Synergy effects of fluoxetine and variability in temperature lead to proportionally greater fitness costs in Daphnia: A multigenerational test

Increased variability in water temperature is predicted to impose disproportionally greater fitness costs than mean increase in temperature. Additionally, water contaminants are currently a major source of human-induced stress likely to produce fitness costs. Global change models forecast an increase in these two human-induced stressors. Yet, in spite the growing interest in understanding how organisms respond to global change, the joint fitness effects of water pollution and increased variability in temperature remain unclear. Here, using a multigenerational design, we test the hypothesis that exposure to high concentrations of fluoxetine, a human medicine commonly found in freshwater systems, causes increased lifetime fitness costs, when associated with increased variability in temperature. Although fluoxetine and variability in temperature elicited some fitness cost when tested alone, when both stressors acted together the costs were disproportionally greater. The combined effect of fluoxetine and variability in temperature led to a reduction of 37% in lifetime reproductive success and a 17.9% decrease in population growth rate. Interestingly, fluoxetine and variability in temperature had no effect on the probability of survival. Freshwater systems are among the most imperilled ecosystems, often exposed to multiple human-induced stressors. Our results indicate that organisms face greater fitness risk when exposed to multiple stressors at the same time than when each stress acts alone. Our study highlights the importance of using a multi-generational approach to fully understand individual environmental tolerance and its responses to a global change scenario in aquatic systems.

Evolution of density-dependent movement during experimental range expansions.

Range expansions and biological invasions are prime examples of transient processes that are likely impacted by rapid evolutionary changes. As a spatial process, range expansions are driven by dispersal and movement behaviour. Although it is widely accepted that dispersal and movement may be context-dependent, for instance density-dependent, and best represented by reaction norms, the evolution of density-dependent movement during range expansions has received little experimental attention. We therefore tested current theory predicting the evolution of increased movement at low densities at range margins using highly replicated and controlled range expansion experiments across multiple genotypes of the protist model system Tetrahymena thermophila. Although rare, we found evolutionary changes during range expansions even in the absence of initial standing genetic variation. Range expansions led to the evolution of negatively density-dependent movement at range margins. In addition, we report the evolution of increased intrastrain competitive ability and concurrently decreased population growth rates in range cores. Our findings highlight the importance of understanding movement and dispersal as evolving reaction norms and plastic life-history traits of central relevance for range expansions, biological invasions and the dynamics of spatially structured systems in general.

Combined effects of microcystin and nitrite on the growth, lipid peroxidation, and antioxidant responses of the freshwater rotifer Brachionus calyciflorus

Toxicants released during the degradation of cyanobacterial blooms, such as microcystin-LR (MC-LR) and nitrite (NO2-N), affect the growth of aquatic organisms. The freshwater rotifer Brachionus calyciflorus was exposed to solutions with different combined concentrations of MC-LR (0, 10, 50, 100, and 200μgL−1) and NO2-N (0, 2, 4, 6, and 8mgL−1) to assess the combined effects of MC-LR and NO2-N on life cycle parameters and oxidative stress. Single solutions of MC-LR 200μgL−1 and NO2-N 8mgL−1 were toxic to rotifers. MC-LR combined with NO2-N decreased population growth rate (r), survival, and reproduction, but increased reactive oxygen species (ROS), malondialdehyde (MDA), and glutathione (GSH) contents (p<0.01). Superoxide dismutase (SOD) and catalase (CAT) activities and mRNA expression levels of MnSOD, CuZnSOD, and CAT significantly decreased under high concentrations of MC-LR or NO2-N (p<0.05). ROS levels had negative correlations with antioxidant enzyme activities and expression levels of antioxidant genes (p<0.01). MC-LR and NO2-N had interactive effects on r, reproduction, ROS levels, MDA content, SOD activity, and expression levels of MnSOD and CAT (p<0.05). By contrast, these effects were antagonistic on survival, CAT activity, GSH content, and expression level of CuZnSOD (p>0.05). Results showed that cyanobacterial metabolites act synergistically and antagonistically to cause toxicity to B. calyciflorus. ROS-mediated toxicity was considered the mechanism by which MC-LR and NO2-N induce damage.

On the implications of declining population growth for regional migration

Although many advanced economies nowadays experience decreasing populations, migration in models of economic growth has so far been almost exclusively analyzed for the case of non-negative population growth rates. This paper considers decreasing and possibly negative population growth rates in two two-sector growth models. As long as preferences are homothetic, neither a decrease in population growth rates nor an actual population decline does induce migration in either direction. Introducing quasi-linear preferences implies that a decline in population growth leads to migration from the rural to the industrial region. A complete depopulation of the rural region takes place if the population growth rate falls short of minus the rate of physical capital depreciation. These results reinforce pessimistic expectations about a rural exodus.

Seasonal dynamics with compensatory effects regulate populations of tropical forest marsupials: a 16-year study.

The conditions that a population experiences during one season can affect the strength of density dependence in the following season. In the tropics, many populations face their biggest challenges in the dry season due to limited food and cold-dry conditions. Seasonal environmental changes can be especially problematic for small, short-lived, seasonally breeding endotherms. To investigate the effects of seasonality on population dynamics, we studied five marsupial species in the Brazilian Atlantic Forest, using a 16-year dataset. We tested if (1) compensatory density feedback is stronger in the dry season, due to the high population sizes and limited food; (2) lower temperatures and the overall abundance of small mammals negatively affect dry season population growth rates; and (3) rainfall, a proxy for food availability, is positively related to wet season population growth rates. Population growth rates were regressed against seasonal population sizes and exogenous variables, and analyzed with linear autoregressive models. Seasonal compensatory density feedback occurred in both seasons, with compensation processes in just one season being sufficient to allow population persistence. Rainfall and the overall abundance of small mammals had little influence on populations, while colder temperatures decreased population growth rate of smaller species in both seasons. Although the study marsupials share similar life histories and phylogeny, they varied with respect to the season when compensatory density feedback was strongest. Our results demonstrate that seasonality plays a key role in driving marsupial population dynamics, and highlight the need to account for seasonality in demographic studies even in tropical environments.