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44-624: In 2011, it had a population of 355,320 and the population density was 61.63/km. This county has a total area of 5,765 km (2,226 sq mi). The North side of the county is occupied by the mountains from the Southern Carpathians group: the Făgăraș Mountains in the east with heights over 2,200 m (7,200 ft), and the Lotru Mountains in the west with heights over 2,000 m (6,600 ft). They are separated by

88-579: A large part of the current Vâlcea County; however the territories situated to the east of the Olt River in the current county were not part of the historical county. The county was bordered to the north by Sibiu County , to the east by the counties of Argeș and Olt , to the south by Romanați County , and to the west by the counties of Dolj and Gorj . The county was in 1930 divided into five administrative districts ( plăși ): By 1938, there were six districts, four previous and two new ones resulting from

132-451: A little less than the land area of Puerto Rico , 8,868 square kilometres (3,424 sq mi). Although the arithmetic density is the most common way of measuring population density, several other methods have been developed to provide alternative measures of population density over a specific area. Allee effect The Allee effect is a phenomenon in biology characterized by a correlation between population size or density and

176-414: A population exhibiting a strong Allee effect will have a critical population size or density under which the population growth rate becomes negative. Therefore, when the population density or size hits a number below this threshold, the population will be destined for extinction without any further aid. A strong Allee effect is often easier to demonstrate empirically using time series data, as one can pinpoint

220-501: A population is unlikely to result in species extinction because the escalating costs to find the last few individuals will exceed the fixed price one achieves by selling the individuals on the market. However, when rare species are more desirable than common species, prices for rare species can exceed high harvest costs. This phenomenon can create an "anthropogenic" Allee effect where rare species go extinct but common species are sustainably harvested. The anthropogenic Allee effect has become

264-452: A population will experience a reduced overall growth rate at higher density and increased growth rate at lower density. In other words, individuals in a population would be better off when there are fewer individuals around due to a limited amount of resources (see logistic growth ). However, the concept of the Allee effect introduced the idea that the reverse holds true when the population density

308-475: A standard approach for conceptualizing the threat of economic markets on endangered species. However, the original theory was posited using a one dimensional analysis of a two dimensional model. It turns out that a two dimensional analysis yields an Allee curve in human exploiter and biological population space and that this curve separating species destined to extinction vs persistence can be complicated. Even very high population sizes can potentially pass through

352-499: Is 53/km (140/sq mi). This includes all continental and island land area, including Antarctica . However, if Antarctica is excluded, then population density rises to over 58 per square kilometre (150/sq mi). The European Commission's Joint Research Centre (JRC) has developed a suite of (open and free) data and tools named the Global Human Settlement Layer (GHSL) to improve the science for policy support to

396-450: Is a measurement of population per unit land area. It is mostly applied to humans , but sometimes to other living organisms too. It is a key geographical term. Population density is population divided by total land area , sometimes including seas and oceans, as appropriate. Low densities may cause an extinction vortex and further reduce fertility. This is called the Allee effect after

440-959: Is a reduction in fitness of the species through the process of genetic drift , as well as inbreeding depression . This overall fitness decrease of a species is caused by an accumulation of deleterious mutations throughout the population. Genetic variation within a species could range from beneficial to detrimental. Nevertheless, in a smaller sized gene pool, there is a higher chance of a stochastic event in which deleterious alleles become fixed ( genetic drift ). While evolutionary theory states that expressed deleterious alleles should be purged through natural selection, purging would be most efficient only at eliminating alleles that are highly detrimental or harmful. Mildly deleterious alleles such as those that act later in life would be less likely to be removed by natural selection, and conversely, newly acquired beneficial mutations are more likely to be lost by random chance in smaller genetic pools than larger ones. Although

484-499: Is around 8,000,000,000 and the Earth 's total area (including land and water) is 510,000,000 km (200,000,000 sq mi). Therefore, the worldwide human population density is approximately 8,000,000,000 ÷ 510,000,000 = 16/km (41/sq mi). However, if only the Earth's land area of 150,000,000 km (58,000,000 sq mi) is taken into account, then human population density

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528-405: Is given by the cubic growth model. where the population has a negative growth rate for 0 < N < A {\displaystyle 0<N<A} , and a positive growth rate for A < N < K {\displaystyle A<N<K} (assuming 0 < A < K {\displaystyle 0<A<K} ). This is a departure from

572-416: Is given by the reaction-diffusion model where When a population is made up of small sub-populations additional factors to the Allee effect arise. If the sub-populations are subject to different environmental variations (i.e. separated enough that a disaster could occur at one sub-population site without affecting the other sub-populations) but still allow individuals to travel between sub-populations, then

616-431: Is low. Individuals within a species often require the assistance of another individual for more than simple reproductive reasons in order to persist. The most obvious example of this is observed in animals that hunt for prey or defend against predators as a group. The generally accepted definition of Allee effect is positive density dependence, or the positive correlation between population density and individual fitness. It

660-430: Is sometimes referred to as "undercrowding" and it is analogous (or even considered synonymous by some) to " depensation " in the field of fishery sciences . Listed below are a few significant subcategories of the Allee effect used in the ecology literature. The component Allee effect is the positive relationship between any measurable component of individual fitness and population density. The demographic Allee effect

704-418: Is the positive relationship between the overall individual fitness and population density. The distinction between the two terms lies on the scale of the Allee effect: the presence of a demographic Allee effect suggests the presence of at least one component Allee effect, while the presence of a component Allee effect does not necessarily result in a demographic Allee effect. For example, cooperative hunting and

748-402: The 2020 Romanian local elections , consists of 32 counsellors, with the following party composition: Vâlcea County has two municipalities, nine towns and 78 communes as follows: Historically, the county was located in the southwestern part of Greater Romania , in the northeast part of the historical region of Oltenia . Its capital was Râmnicu Vâlcea . The interwar county territory comprised

792-631: The European Commission Directorate Generals and Services and as support to the United Nations system. Several of the most densely populated territories in the world are city-states , microstates and urban dependencies . In fact, 95% of the world's population is concentrated on just 10% of the world's land. These territories have a relatively small area and a high urbanization level, with an economically specialized city population drawing also on rural resources outside

836-802: The Olt River crossing the county from North to South. Its main affluents are the Lotru River in the North and the Olteț River in the South. The predominant industries in the county are: In the West of the county coal and salt are extracted. The area in the center of the county is well suited for fruit orchards, vineyards , and raising cattle. The South is better suited for growing cereals and vegetables. The main tourist destinations are: The Vâlcea County Council, renewed at

880-514: The Olt River valley — the most accessible passage between Transylvania and Muntenia . Along the Olt River valley there are smaller groups of mountains, the most spectacular being the Cozia Mountains  [ ro ] . Towards the South, the heights decrease, passing through the sub-carpathian hills to a high plain in the West side of the Wallachian Plain . The main river is

924-582: The logistic growth equation where After dividing both sides of the equation by the population size N, in the logistic growth the left hand side of the equation represents the per capita population growth rate, which is dependent on the population size N, and decreases with increasing N throughout the entire range of population sizes. In contrast, when there is an Allee effect the per-capita growth rate increases with increasing N over some range of population sizes [0,  N ]. Spatio-temporal models can take Allee effect into account as well. A simple example

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968-434: The Allee effect can also promote genetic diversity in expanding populations. These results counteract commonly held notions that the Allee effect possesses net adverse consequences. Reducing the growth rate of the individuals ahead of the colonization front simultaneously reduces the speed of colonization and enables a diversity of genes coming from the core of the population to remain on the front. The Allee effect also affects

1012-429: The Allee effect, which will increase the risk of population extinction. Whether or not demographic stochasticity can be considered a part of Allee effect is somewhat contentious however. The most current definition of Allee effect considers the correlation between population density and mean individual fitness. Therefore, random variation resulting from birth and death events would not be considered part of Allee effect as

1056-420: The ability to more easily find mates, both influenced by population density, are component Allee effects, as they influence individual fitness of the population. At low population density, these component Allee effects would add up to produce an overall demographic Allee effect (increased fitness with higher population density). When population density reaches a high number, negative density dependence often offsets

1100-988: The area, illustrating the difference between high population density and overpopulation . Deserts have very limited potential for growing crops as there is not enough rain to support them. Thus, their population density is generally low. However, some cities in the Middle East, such as Dubai , have been increasing in population and infrastructure growth at a fast pace. Cities with high population densities are, by some, considered to be overpopulated, though this will depend on factors like quality of housing and infrastructure and access to resources. Very densely populated cities are mostly in Asia (particularly Southeast Asia ); Africa's Lagos , Kinshasa , and Cairo ; South America's Bogotá , Lima , and São Paulo ; and Mexico City and Saint Petersburg also fall into this category. City population and especially area are, however, heavily dependent on

1144-407: The component Allee effects through resource competition, thus erasing the demographic Allee effect. Allee effects might occur even at high population density for some species. The strong Allee effect is a demographic Allee effect with a critical population size or density. The weak Allee effect is a demographic Allee effect without a critical population size or density. The distinction between

1188-472: The county's urban population was 31,909 inhabitants, comprising 94.8% Romanians, 1.3% Romanies, 1.0% Germans, 0.8% Jews, 0.7% Hungarians, as well as other minorities. From the religious point of view, the urban population was composed of 96.4% Eastern Orthodox, 1.4% Roman Catholic, 0.8% Jewish, 0.7% Lutheran, 0.3% Greek Catholic, as well as other minorities. Population density Population density (in agriculture : standing stock or plant density )

1232-547: The definition of "urban area" used: densities are almost invariably higher for the center only than when suburban settlements and intervening rural areas are included, as in the agglomeration or metropolitan area (the latter sometimes including neighboring cities). In comparison, based on a world population of 8 billion, the world's inhabitants, if conceptualized as a loose crowd occupying just under 1 m (10 sq ft) per person (cf. Jacobs Method ), would occupy an area of 8,000 square kilometres (3,100 sq mi)

1276-828: The field, they tend to be more commonly associated with the Allee effect concept. Nevertheless, mechanisms of Allee effect that are less conspicuous such as inbreeding depression and sex ratio bias should be considered as well. Although numerous ecological mechanisms for Allee effects exist, the list of most commonly cited facilitative behaviors that contribute to Allee effects in the literature include: mate limitation, cooperative defense, cooperative feeding, and environmental conditioning. While these behaviors are classified in separate categories, they can overlap and tend to be context dependent (will operate only under certain conditions – for example, cooperative defense will only be useful when there are predators or competitors present). Classic economic theory predicts that human exploitation of

1320-413: The fitness of the individuals within the population. This type of Allee effect will likely be more prevalent in monogamous species than polygynous species. Demographic and mathematical studies demonstrate that the existence of an Allee effect can reduce the speed of range expansion of a population and can even prevent biological invasions. Recent results based on spatio-temporal models show that

1364-423: The increased risk of extinction is not a consequence of the changing fates of individuals within the population. Meanwhile, when demographic stochasticity results in fluctuations of sex ratios, it arguably reduces the mean individual fitness as population declines. For example, a fluctuation in small population that causes a scarcity in one sex would in turn limit the access of mates for the opposite sex, decreasing

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1408-402: The individual sub-populations are more likely to go extinct than the total population. In the case of a catastrophic event decreasing numbers at a sub-population, individuals from another sub-population site may be able to repopulate the area. If all sub-populations are subject to the same environmental variations (i.e. if a disaster affected one, it would affect them all) then fragmentation of

1452-402: The long-term population persistence of several species with low genetic variation has recently prompted debate on the generality of inbreeding depression, there are various empirical evidences for genetic Allee effects. One such case was observed in the endangered Florida panther ( Puma concolor coryi ). The Florida panther experienced a genetic bottleneck in the early 1990s where the population

1496-402: The mean individual fitness (often measured as per capita population growth rate ) of a population or species. Although the concept of Allee effect had no title at the time, it was first described in the 1930s by its namesake, Warder Clyde Allee . Through experimental studies, Allee was able to demonstrate that goldfish have a greater survival rate when there are more individuals within

1540-431: The originally proposed Allee thresholds on predestined paths to extinction. Declines in population size can result in a loss of genetic diversity, and owing to genetic variation 's role in the evolutionary potential of a species, this could in turn result in an observable Allee effect. As a species' population becomes smaller, its gene pool will be reduced in size as well. One possible outcome from this genetic bottleneck

1584-405: The population is detrimental to the population and increases extinction risk for the total population. In this case, the species receives none of the benefits of a small sub-population (loss of the sub-population is not catastrophic to the species as a whole) and all of the disadvantages ( inbreeding depression, loss of genetic diversity and increased vulnerability to environmental instability) and

1628-587: The population size or density at which per capita growth rate becomes negative. Due to its definition as the positive correlation between population density and average fitness, the mechanisms for which an Allee effect arises are therefore inherently tied to survival and reproduction. In general, these Allee effect mechanisms arise from cooperation or facilitation among individuals in the species. Examples of such cooperative behaviors include better mate finding, environmental conditioning, and group defense against predators. As these mechanisms are more-easily observable in

1672-424: The reorganisation of the southwest part of the county: According to the 1930 census data, the county population was 246,713 inhabitants, ethnically divided as follows: 97.4% Romanians, 1.6% Romanies, 0.2% Germans, 0.2% Hungarians, 0.2% Jews, as well as other minorities. From the religious point of view, the population was 99.0% Eastern Orthodox, 0.4% Roman Catholic, 0.2% Jewish, as well as other minorities. In 1930,

1716-443: The scientist who identified it. Examples of the causes of reduced fertility in low population densities are: Population density is the number of people per unit of area, usually transcribed as "per square kilometer" or square mile, and which may include or exclude, for example, areas of water or glaciers. Commonly this is calculated for a county , city , country , another territory or the entire world . The world's population

1760-419: The spatial distribution of diversity. Whereas spatio-temporal models which do not include an Allee effect lead to a vertical pattern of genetic diversity (i.e., a strongly structured spatial distribution of genetic fractions), those including an Allee effect lead to a "horizontal pattern" of genetic diversity (i.e., an absence of genetic differentiation in space). A simple mathematical example of an Allee effect

1804-432: The tank. This led him to conclude that aggregation can improve the survival rate of individuals, and that cooperation may be crucial in the overall evolution of social structure. The term "Allee principle" was introduced in the 1950s, a time when the field of ecology was heavily focused on the role of competition among and within species. The classical view of population dynamics stated that due to competition for resources,

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1848-443: The timescale for this inbreeding depression is larger than of those more immediate Allee effects, it has significant implications on the long-term persistence of a species. Demographic stochasticity refers to variability in population growth arising from sampling random births and deaths in a population of finite size. In small populations, demographic stochasticity will decrease the population growth rate, causing an effect similar to

1892-438: The two terms is based on whether or not the population in question exhibits a critical population size or density . A population exhibiting a weak Allee effect will possess a reduced per capita growth rate (directly related to individual fitness of the population) at lower population density or size. However, even at this low population size or density, the population will always exhibit a positive per capita growth rate. Meanwhile,

1936-511: Was reduced to ≈25 adult individuals. This reduction in genetic diversity was correlated with defects that include lower sperm quality, abnormal testosterone levels, cowlicks, and kinked tails. In response, a genetic rescue plan was put in motion and several female pumas from Texas were introduced into the Florida population. This action quickly led to the reduction in the prevalence of the defects previously associated with inbreeding depression. Although

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