Anticipating critical transitions in spatially extended systems is a key topic of interest to ecologists. Gradually declining metapopulations are an important example of a spatially extended biological system that may exhibit a critical transition. Theory for spatially extended systems approaching extinction that accounts for environmental stochasticity and coupling is currently lacking. Here, we develop spatially implicit two-patch models with additive and multiplicative forms of environmental stochasticity that are slowly forced through population collapse, through changing environmental conditions. We derive patch-specific expressions for candidate indicators of extinction and test their performance via a simulation study. Coupling and spatial heterogeneities decrease the magnitude of the proposed indicators in coupled populations relative to isolated populations, and the noise regime and the degree of coupling together determine trends in summary statistics. This theory may be readily applied to other spatially extended ecological systems, such as coupled infectious disease systems on the verge of elimination.

In 2019, the majority of French people between the ages of 50 and 64, 69 percent, believed in the theory of a collapse of civilization. On a population scale, 65 percent of French people in total adhered to collapsological theories. Collapsology is a current of thought that theorizes and studies the possibility of a collapse of post-industrial society due to climate disruption caused by global warming.

In 2024, the total population of Spain was around 48.38 million people. By 2029, it was forecast to grow up to 50.76 million inhabitants.

Population of Spain While Spain’s fertility rate has been relatively decreasing over the past decade, its year-over-year population growth has been increasing continuously since 2016. The collapse of the job and real estate markets may have led the Spanish to postpone having (more) kids or to migrate to other countries in search of a more stable economy, while inflow of migrates has increased . This theory is supported by data on the average age of Spain’s inhabitants; a look at the median age of Spain’s population from 1950 up until today shows that the Spanish get older on average – perhaps due to the aforementioned factors.

Economic recovery Speaking of Spain’s economy, economic key factors suggest that the country is still recovering from the crisis. Its gross domestic product (GDP) was in admirable shape prior to the collapse, but it still has not returned to its former glory. Only recently has Spain reported actual GDP growth since 2008. Nevertheless, during 2020 and the COVID-19 pandemic, Spain's GDP had a decrease of more than 11 percent. This in turn, led to an increase of the country’s unemployment rate after years of slowly but surely decreasing following an alarming peak of 26 percent in 2013. Future perspectives are, however, somewhat brighter, as GDP is forecast to maintain a positive growth rate at least until 2029, even exceeding two percentage points in 2025.

Despite growing concerns regarding increasing frequency of extreme climate events and declining population sizes, the influence of environmental stochasticity on the relationship between population carrying capacity and time-to-extinction has received little empirical attention. While time-to-extinction increases exponentially with carrying capacity in constant environments, theoretical models suggest increasing environmental stochasticity causes asymptotic scaling, thus making minimum viable carrying capacity vastly uncertain in variable environments. Using empirical estimates of environmental stochasticity in fish metapopulations, we showed that increasing environmental stochasticity resulting from extreme droughts was insufficient to create asymptotic scaling of time-to-extinction with carrying capacity in local populations as predicted by theory. Local time-to-extinction increased with carrying capacity due to declining sensitivity to demographic stochasticity, and the slope of this...

Population genetic theory related to the consequences of rapid population decline is well-developed, but there are very few empirical studies where sampling was conducted before and after a known bottleneck event. Such knowledge is of particular importance for species restoration, given links between genetic diversity and the probability of long-term persistence. To directly evaluate the relationship between current genetic diversity and past demographic events, we collected genome-wide single nucleotide polymorphism data from pre-bottleneck historical (c.1906) and post-bottleneck contemporary (c.2014) samples of Pinzón giant tortoises (Chelonoidis duncanensis; n=25 and 149 individuals, respectively) endemic to a single island in the Galapagos. Pinzón giant tortoises had a historically large population size that was reduced to just 150-200 individuals in the mid 20th century. Since then, Pinzón’s tortoise population has recovered through an ex situ head-start program in which eggs or pre-emergent individuals were collected from natural nests on the island, reared ex situ in captivity until they were 4-5 years old, and subsequently repatriated. We found that the extent and distribution of genetic variation in the historical and contemporary samples was very similar, with the latter group not exhibiting the characteristic genetic patterns of recent population decline. No population structure was detected either spatially or temporally. We estimated an effective population size (Ne) of 58 (95% CI = 50-69) for the post-bottleneck population; no pre-bottleneck Ne point estimate was attainable (95% CI = 39-infinity) likely due to the sample size being lower than the true Ne. Overall, the historical sample provided a valuable benchmark for evaluating the head-start captive breeding program, revealing high retention of genetic variation and no skew in representation despite the documented bottleneck event. Moreover, this work demonstrates the effectiveness of head-starting in rescuing the Pinzón giant tortoise from almost certain extinction.

1.Emerging and invasive pathogens can have long-lasting impacts on susceptible wildlife populations, including localised collapse and extirpation. Management of threatening disease is of widespread interest and requires knowledge of spatiotemporal patterns of pathogen spread.

2.Theory suggests disease spread often occurs via two patterns: homogenous mixing and travelling waves. However, high resolution empirical data demonstrating localised (within population) disease spread patterns are rare.

3.This study examined the spread of sarcoptic mange (aetiological agent Sarcoptes scabiei) in a population of bare-nosed wombats (Vombatus ursinus), and investigated whether pathogen spread occurred by homogenous mixing or a travelling wave.

4.Using seven years of population surveys and four years of disease severity surveys, we show that mange was first detected in the east of a wombat population in northern Tasmania, and progressed westward as a travelling wave. Wombat mortality rates reached 100% behind the wave, with a 94% decline in overall wombat abundance within the park.

5.Synthesis and applications. Globally distributed pathogens may have severe impacts on susceptible host species. This is the first study to quantify population level impacts of sarcoptic mange upon bare-nosed wombats, showing a wave of mange disease which resulted in a dramatic population decline. Successful management of the spread of this and similar pathogens may hinge on the capacity to establish transmission barriers at local or between-population scales.

Much of Argentina's modern society and culture is rooted in the Spanish Empire's colonization of the region in the 16th century, along with the influx of European migration to the country around the turn of the twentieth century. There are records of human presence in the region dating back to the paleolithic period (3.3 million to 9,650 BCE) and the Incan Empire is known to have extended into the region before Columbus' arrival in the Americas in 1492; however most of this culture and civilization was wiped out by Europeans in the 1500s. During Spanish colonization, the majority of Argentina was a part of the Viceroyalty of the Río de la Plata (which also included territories in modern-day Chile, Bolivia, Paraguay and Uruguay) and was still economically bound to the Spanish crown. With a population of just 0.5 million in 1800, a combination of mass migration (particularly from Southern Europe) and high birth rates have helped Argentina's population grow above 45 million over the past two centuries.

Independence, Immigration and the Gold rush The age of enlightenment and revolutions in Europe inspired a longing in the region for independence, and Napoleon's invasion of Spain in 1808 was the catalyst for the Spanish Empire's downfall in the Americas, with Argentinian independence declared in 1816. The Spanish military was then defeated in mid 1800s, but for the majority of the next century there was little political or economic stability in the region, with several small-scale civil wars between the different Argentinian states. Starting with the government of Julio Argentino Roca in 1880, ten consecutive federal governments actively pursued a liberal economic policy which led to a massive wave of state-promoted European immigration; so much so that the number of migrants received by Argentina in that period was second only to the United States worldwide. This immigration led to the rejuvenation and reinvention of Argentinian society and economy to such an extent, that by 1908 the country had the seventh largest economy in the world. This in turn led to further immigration and higher standards of living. It is also worth noting that the Tierra del Fuego gold rush that started around 1883 and lasted to around 1906 also contributed greatly to immigration. Unfortunately, Argentina was unable to retain it's acquired economic might; it failed to develop industrially at the same speed as the rest of the world, and the Great Depression of 1929 set in motion an economic decline that contributed to much civil and political unrest.

The impact of Perón, and modern Argentina
The election of Juan Perón in 1946 proved to be a defining point in Argentina's history; Perón was a demagogue who imprisoned (and reportedly tortured) his rivals and critics, and whose isolationist policies and radical spending contributed to severe inflation. With the death of Perón's extremely popular wife, Eva Duarte, in 1952, his popularity declined and he was eventually exiled following a coup in 1955. Despite this exile, Perón returned in 1973 and re-assumed the presidency, until his death in 1974, where he was the succeeded by his third wife. Peron's political philosophy, known as "Peronism", is a mixture of right wing nationalist and left wing populist theories; although Peronism has developed greatly over time, its core belief system is the foundation of Argentina's largest party, the Justicialist Party (although they have become increasingly left wing since the Kirchner administrations).

With the expulsion of Perón in 1955, Argentina's trend of military coups and failed governments continued, and the country faced further economic instability. Despite all of this, medical advancements and improvements to quality of life across the globe helped Argentina's mortality rate to decline, and the population grew at a faster rate than ever before. In April 1982, Argentine forces invaded the British territory of the Falkland Islands, leading to a ten week war between the nations, that ended with Argentina's surrender in June. The war had a relatively small death toll, but contributed to riots in Buenos Aires, which helped to topple the military dictatorship and established the current democratic system. Following a severe recession that began in 2001, President Néstor Kirchner assumed office in 2003, and his wife took over from 2007 to 2015; during the Kirchner administrations, more than eleven million people were lifted out of poverty, and Argentina's economy grew in stature to become one of the Group of Twenty.

50 year Projected Urban Growth scenarios. Base year is 2000. Projected year in this dataset is 2050.

By 2020, most forecasters agree, California will be home to between 43 and 46 million residents-up from 35 million today. Beyond 2020 the size of California's population is less certain. Depending on the composition of the population, and future fertility and migration rates, California's 2050 population could be as little as 50 million or as much as 70 million. One hundred years from now, if present trends continue, California could conceivably have as many as 90 million residents. Where these future residents will live and work is unclear. For most of the 20th Century, two-thirds of Californians have lived south of the Tehachapi Mountains and west of the San Jacinto Mountains-in that part of the state commonly referred to as Southern California. Yet most of coastal Southern California is already highly urbanized, and there is relatively little vacant land available for new development. More recently, slow-growth policies in Northern California and declining developable land supplies in Southern California are squeezing ever more of the state's population growth into the San Joaquin Valley. How future Californians will occupy the landscape is also unclear. Over the last fifty years, the state's population has grown increasingly urban. Today, nearly 95 percent of Californians live in metropolitan areas, mostly at densities less than ten persons per acre. Recent growth patterns have strongly favored locations near freeways, most of which where built in the 1950s and 1960s. With few new freeways on the planning horizon, how will California's future growth organize itself in space? By national standards, California's large urban areas are already reasonably dense, and economic theory suggests that densities should increase further as California's urban regions continue to grow. In practice, densities have been rising in some urban counties, but falling in others.

These are important issues as California plans its long-term future. Will California have enough land of the appropriate types and in the right locations to accommodate its projected population growth? Will future population growth consume ever-greater amounts of irreplaceable resource lands and habitat? Will jobs continue decentralizing, pushing out the boundaries of metropolitan areas? Will development densities be sufficient to support mass transit, or will future Californians be stuck in perpetual gridlock? Will urban and resort and recreational growth in the Sierra Nevada and Trinity Mountain regions lead to the over-fragmentation of precious natural habitat? How much water will be needed by California's future industries, farms, and residents, and where will that water be stored? Where should future highway, transit, and high-speed rail facilities and rights-of-way be located? Most of all, how much will all this growth cost, both economically, and in terms of changes in California's quality of life? Clearly, the more precise our current understanding of how and where California is likely to grow, the sooner and more inexpensively appropriate lands can be acquired for purposes of conservation, recreation, and future facility siting. Similarly, the more clearly future urbanization patterns can be anticipated, the greater our collective ability to undertake sound city, metropolitan, rural, and bioregional planning.

Consider two scenarios for the year 2100. In the first, California's population would grow to 80 million persons and would occupy the landscape at an average density of eight persons per acre, the current statewide urban average. Under this scenario, and assuming that 10% percent of California's future population growth would occur through infill-that is, on existing urban land-California's expanding urban population would consume an additional 5.06 million acres of currently undeveloped land. As an alternative, assume the share of infill development were increased to 30%, and that new population were accommodated at a density of about 12 persons per acre-which is the current average density of the City of Los Angeles. Under this second scenario, California's urban population would consume an additional 2.6 million acres of currently undeveloped land. While both scenarios accommodate the same amount of population growth and generate large increments of additional urban development-indeed, some might say even the second scenario allows far too much growth and development-the second scenario is far kinder to California's unique natural landscape.

This report presents the results of a series of baseline population and urban growth projections for California's 38 urban counties through the year 2100. Presented in map and table form, these projections are based on extrapolations of current population trends and recent urban development trends. The next section, titled Approach, outlines the methodology and data used to develop the various projections. The following section, Baseline Scenario, reviews the projections themselves. A final section, entitled Baseline Impacts, quantitatively assesses the impacts of the baseline projections on wetland, hillside, farmland and habitat loss.

Migration is expected to benefit individuals through exposure to higher quality forage and reducing predation rates more than non-migratory conspecifics. Previous studies of partially migratory ungulates (with migrant and resident individuals) have focused on bottom–up factors regulating resident and migrant segments, yet differential predation between strategies could also be a density-dependent regulatory mechanism. Our study tested for density-dependence in mortality, as well as mechanisms of bottom–up or top–down regulation in the resident and migrant portions of the partially migratory Ya Ha Tinda elk population. We tested for density dependence in adult female and juvenile survival rates, and then discriminated between predator- and food-regulation hypotheses by testing for density-dependence amongst mortality causes for adult female elk. Notably, the population declined almost 70% from near previously published estimates of carrying capacity over 10 years, providing ideal conditions to test for density dependence. In contrast to predictions, we found only weak support for density dependence in adult survival and juvenile survival. We also found few differences between migrant and resident elk in adult or juvenile survival, though juvenile survival differences were biologically significant. Predation by humans and grizzly bears was density dependent, but similar between migratory strategies. Predation by wolves was the leading known cause of mortality, yet remained constant with declining elk density equally for both migrant and resident elk, indicating wolf predation was density-independent. Instead of being strongly regulated by food or predation, instead, we found adult female survival was driven by density-independent predation and climatic factors. The few differences between migratory strategies suggest equivalent fitness payoffs for migrants and residents. This population is being limited by density-independent predation leading to declines of both migratory strategies. Our results challenge classical predator–prey theory, and call for better integration between predator–prey and migration theory.

The Plague of Justinian was an outbreak of bubonic plague that ravaged the Mediterranean and its surrounding area, between 541 and 767CE. It was likely the first major outbreak of bubonic plague in Europe, and possibly the earliest pandemic to have been recorded reliably and with relative accuracy. Contemporary scholars described the symptoms and effects of the disease in detail, and these matched descriptions of the Black Death and Third Pandemic, leading most historians to believe that this was bubonic plague. It was also assumed that the plague originated in sub-Saharan Africa, before making its way along the Nile to Egypt, and then across the Mediterranean to Constantinople. In 2013, scientists were able to confirm that Justinian's Plague was in fact Yersinia pestis (the bacteria which causes bubonic plague), and recent theories suggest that the plague originated in the Eurasian Steppes, where the Black Death and Third Pandemic are also thought to have originated from, and that it was brought to Europe by the Hunnic Tribes of the sixth century. Plague of Justinian The pandemic itself takes its name from Emperor Justinian I, who ruled the Byzantine Empire (or Eastern Roman Empire) at the time of the outbreak, and who actually contracted the disease (although he survived). Reports suggest that Constantinople was the hardest hit city during the pandemic, and saw upwards of five thousand deaths per day during the most severe months. There are a multitude of sources with differing estimates for the plague's death toll, with most ranging between 25 and 100 million. Until recently, scholars assumed that the plague killed between one third and 40 percent of the world's population, with populations in infected regions declining by up to 25 percent in early years, and up to 60 percent over two centuries. The plague was felt strongest during the initial outbreak in Constantinople, however it remained in Europe for over two centuries, with the last reported cases in 767. Pre-2019 sources vary in their estimates, with some suggesting that up to half of the world's population died in the pandemic, while others state that it was just a quarter of the Mediterranean or European population; however most of them agree that the death toll was in the tens of millions. Historians have also argued about the plague's role in the fall of the Roman Empire, with opinions ranging from "fundamental" to "coincidental", although new evidence is more aligned with the latter theories. Challenging theories As with the recent studies which propose a different origin for the disease, one study conducted by researchers in Princeton and Jerusalem calls into question the accuracy of the death tolls estimated by historians in the 19th and 20th centuries. In 2019, L. Mordechai and M. Eisenberg published a series of papers suggesting that, although the plague devastated Constantinople, it did not have the same impact as the Black Death. The researchers argue that modern historians have taken a maximalist approach to the death tolls of the pandemic, and have applied the same models of distribution to Justinian's Plague as they believe occurred during the Black Death; however there is little evidence to support this. They examine the content and number of contemporary texts, as well archaeological, agricultural and genetic evidence which shows that the plague did spread across Europe, but did not seem to cause the same societal upheaval as the Black Death. It is likely that there will be further investigation into this outbreak in the following years, which may shed more light on the scale of this pandemic.

pone.0236872.t005 - Will colleges survive the storm of declining enrollments? A computational model

Individuals that disperse farther than other individuals are more likely to be on the frontlines of spreading populations and may be more likely to mate with one another as a consequence of their spatial proximity. Over generations, this process—known as spatial sorting—can produce patterns of increasing dispersal ability from a population’s core towards the spreading front. By contrast, when the spread of a population is limited by the availability of suitable habitat, theory predicts that range boundaries can select against more dispersive phenotypes and produce patterns of decreasing dispersal capacity towards population margins. In a common garden study of invasive kudzu bugs (Megacopta cribraria)—which are limited by the availability of hostplants in their southern and western margins—I show that midrange individuals fly 49% farther than individuals in the core and 37% farther than individuals at margins. This result highlights that other processes, such as maternal effects or selection at range boundaries, may create more complicated patterns of dispersal ability across landscapes than predicted by models of spatial sorting alone.

Methods

These data are from a common garden study of kudzu bug flight performance, as measured on flight mills (see methods). Each row describes measurements from a single individual and includes characteristics associated with the site from which it was collected.

There are two datasets: (1) a complete dataset with all flights, including individuals that did not fly, and (2) a reduced dataset, which excludes non-flying insects and those that flew two rotations or less.