In 2019, the majority of French people between the ages of ** and **, ** percent, believed in the theory of a collapse of civilization. On a population scale, ** 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.

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.

Species' geographic ranges and climatic niches are likely to be increasingly mismatched due to rapid climate change. If a species' range and niche are out of equilibrium, then population performance should decrease from high-latitude "leading" range edges, where populations are expanding into recently ameliorated habitats, to low-latitude "trailing" range edges, where populations are contracting from newly unsuitable areas. Demographic compensation is a phenomenon whereby declines in some vital rates are offset by increases in others across time or space. In theory, demographic compensation could increase the range of environments over which populations can succeed and forestall range contraction at trailing edges. An outstanding question is whether range limits and range contractions reflect inadequate demographic compensation across environmental gradients, causing population declines at range edges. We collected demographic data from 32 populations of the scarlet monkeyflower (Erythranthe cardinalis) spanning 11˚ latitude in western North America and used integral projection models to evaluate population dynamics and assess demographic compensation across the species' range. During the 5-year study period, which included multiple years of severe drought and warming, population growth rates decreased from north to south, consistent with leading-trailing dynamics. Southern populations at the trailing range edge declined due to reduced survival, growth, and recruitment, despite compensatory increases in reproduction and faster life history characteristics. These results suggest that demographic compensation may only delay population collapse without the return of more favorable conditions or the contribution of other buffering mechanisms such as evolutionary rescue.

Theory predicts that the approach of catastrophic thresholds in natural systems (e.g., ecosystems, the climate) may result in an increasingly slow recovery from small perturbations, a phenomenon called critical slowing down. We used replicate laboratory populations of the budding yeast Saccharomyces cerevisiae for direct observation of critical slowing down before population collapse. We mapped the bifurcation diagram experimentally and found that the populations became more vulnerable to disturbance closer to the tipping point. Fluctuations of population density increased in size and duration near the tipping point, in agreement with the theory. Our results suggest that indicators of critical slowing down can provide advance warning of catastrophic thresholds and loss of resilience in a variety of dynamical systems.

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...

In small isolated populations, genetic drift is expected to increase chance fixation of partly recessive, mildly deleterious mutations, reducing mean fitness and inbreeding depression within populations and increasing heterosis in outcrosses between populations. We estimated relative effective sizes and migration among populations and compared mean fitness, heterosis, and inbreeding depression for eight large and eight small populations of a perennial plant on the basis of fitness of progeny produced by hand pollinations within and between populations. Migration was limited, and, consistent with expectations for drift, mean fitness was 68% lower in small populations; heterosis was significantly greater for small (mean = 70%, SE = 14) than for large populations (mean = 7%, SE = 27); and inbreeding depression was lower, although not significantly so, in small (mean = )0.29%, SE = 28) than in large (mean = 0.28%, SE = 23) populations. Genetic drift promotes fixation of deleterious mutations in small populations, which could threaten their persistence. Limited migration will exacerbate drift, but data on migration and effective population sizes in natural populations are scarce. Theory incorporating realistic vari- ation in population size and patterns of migration could better predict genetic threats to small population persistence.

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 pr...

Details on the brown bear deaths reported in the Cantabrian populations, from 1977 to 2020. (XLSX)

Summary on mortality based on the data compiled by Palomero et al (2021) [21]. Data are available in Table 2, page 16 of the referenced publication. (XLSX)

Continuous progress in empirical population genetics based on whole genome polymorphism data requires the theoretical analysis of refined models in order to interpret the evolutionary history of populations with adequate accuracy. Recent studies focus prevalently on the aspects of demography and adaptation, whereas age-structure (e.g. in plants via the maintenance of seed banks) has attracted less attention. Germ banking, i.e. seed or egg dormancy, is a prevalent and important life-history trait in plants and invertebrates, which buffers against environmental variability and modulates species extinction in fragmented habitats. Within this study, we investigate the combined effect of germ banking and time-varying population size on the neutral coalescent, and particularly derive the allele frequency spectrum under some simplifying assumptions. We then perform an ABC analysis using two simple demographic scenarios - a population expansion and an instantaneous decline. We demonstrate the appreciable influence of seed banks on the estimation of demographic parameters depending on the germination rate with biases scaled by the square of the germination rate. In the more complex case of a population bottleneck, which comprises an instantaneous decline and an expansion phase, ignoring information on the germination rate denies reliable estimates of the bottleneck parameters via the allelic spectrum. In particular, when seeds remain in the bank over several generations, recent expansions may remain invisible in the frequency spectrum, whereas ancient declines leave signatures much longer than in the absence of seed bank.

Diversity is expected to increase the resilience of ecosystems. Nevertheless, highly diverse ecosystems have collapsed, as did Lake Victoria’s ecosystem of cichlids or Caribbean coral reefs. We try to gain insight to this paradox, by analyzing a simple model of a diverse community where each competing species inflicts a small mortality pressure on an introduced predator. High diversity strengthens this feedback and prevents invasion of the introduced predator. After a gradual loss of native species, the introduced predator can escape control and the system collapses into a contrasting, invaded, low-diversity state. Importantly, we find that a diverse system that has high complementarity gains in resilience, whereas a diverse system with high functional redundancy gains in resistance. Loss of resilience can display early-warning signals of a collapse, but loss of resistance not. Our results emphasize the need for multiple approaches to studying the functioning of ecosystems, as managing an ecosystem requires understanding not only the threats it is vulnerable to but also pressures it appears resistant to.

Population growth and declining per capita Arable Land in China.

According to the theory of compensatory dynamics, depleted populations should recover when the threat responsible for their decline is removed because per capita population growth is assumed to be highest when populations are at their smallest viable sizes. Yet, many seriously depleted fish populations have failed to recover despite threat mitigation. Atlantic cod (Gadus morhua) off Newfoundland despite thirty years of dramatically reduced fishing mortality and numerous fishery closures has not recovered suggesting that drivers other than fishing regulate the growth of collapsed fish populations, inhibiting or preventing their recovery. Here, using Bayesian inference, we show strong evidence of Allee effects in a south Newfoundland cod population, based on data on recruitment and spawning stock biomass. We infer the Allee-effect threshold, below which recovery is impaired. We demonstrate the necessity of data at low population sizes to make inferences about the nature of low-abundance d...

Ongoing environmental changes alter how natural selection shapes animal migration. Understanding how these changes play out theoretically can be done using evolutionary game theoretic (EGT) approaches, such as looking for evolutionarily stable strategies. Here, we first describe historical patterns of how EGT models have explored different drivers of migration. We find that there are substantial gaps in both the taxa (mammals, amphibians, reptiles, insects) and mechanisms (mutualism, interspecific competition) included in past EGT models of migration. Although enemy interactions, including parasites, are increasingly considered in models of animal migration, they remain the least studied of factors for migration considered to date. Furthermore, few papers look at changes in migration in response to perturbations (e.g. climate change, new species interactions). To address this gap, we present a new EGT model to understand how infection with a novel parasite changes host migration. We find three possible outcomes when migrants encounter novel parasites: maintenance of migration (despite the added infection cost), loss of migration (evolutionary shift to residency) or population collapse, depending on the risk and cost of getting infected, and the cost currency. Our work demonstrates how emerging infection can alter animal behaviour such as migration.This article is part of the theme issue ‘Half a century of evolutionary games: a synthesis of theory, application and future directions’.

In recent years, in order to cope with the increasing trend of population aging, the Chinese government has constantly adjusted the family planning policy, continuously tracked and evaluated the actual effect of the birth policy adjustment, and the prediction and analysis of future births have important theoretical value and practical significance.The adjustment of the birth policy is of great significance for achieving long-term balanced population development. This paper assesses the net effect of fertility policy adjustments on Chinas birth and fertility rates by constructing a DID model using panel data collected from 31 provinces, autonomous regions and municipalities over the period 2005-2021. The study shows that the fertility policy adjustment does not significantly increase the birth and fertility rates in China, and the findings are confirmed by robustness tests using various methods. Heterogeneity analysis shows that the implementation of the comprehensive two-child policy is more pronounced in the central region. Further, a mechanistic and causal analysis reveals that fertility policy changes did not significantly increase peoples willingness to have children, nor did they affect many other factors that influence households fertility decisions. Finally, a GM (1, 1) grey forecast model is used to forecast the births in each province and municipality in the next five years, and it is concluded that the births in China will continue to show a declining trend. This paper argues that a supportive policy system for fertility should be established, public childcare and elderly care services should be optimised, and a favourable fertility climate and conditions should be created in order to improve fertility levels in China.

In recent years, in order to cope with the increasing trend of population aging, the Chinese government has constantly adjusted the family planning policy, continuously tracked and evaluated the actual effect of the birth policy adjustment, and the prediction and analysis of future births have important theoretical value and practical significance.The adjustment of the birth policy is of great significance for achieving long-term balanced population development. This paper assesses the net effect of fertility policy adjustments on Chinas birth and fertility rates by constructing a DID model using panel data collected from 31 provinces, autonomous regions and municipalities over the period 2005-2021. The study shows that the fertility policy adjustment does not significantly increase the birth and fertility rates in China, and the findings are confirmed by robustness tests using various methods. Heterogeneity analysis shows that the implementation of the comprehensive two-child policy is more pronounced in the central region. Further, a mechanistic and causal analysis reveals that fertility policy changes did not significantly increase peoples willingness to have children, nor did they affect many other factors that influence households fertility decisions. Finally, a GM (1, 1) grey forecast model is used to forecast the births in each province and municipality in the next five years, and it is concluded that the births in China will continue to show a declining trend. This paper argues that a supportive policy system for fertility should be established, public childcare and elderly care services should be optimised, and a favourable fertility climate and conditions should be created in order to improve fertility levels in China.

In recent years, in order to cope with the increasing trend of population aging, the Chinese government has constantly adjusted the family planning policy, continuously tracked and evaluated the actual effect of the birth policy adjustment, and the prediction and analysis of future births have important theoretical value and practical significance.The adjustment of the birth policy is of great significance for achieving long-term balanced population development. This paper assesses the net effect of fertility policy adjustments on Chinas birth and fertility rates by constructing a DID model using panel data collected from 31 provinces, autonomous regions and municipalities over the period 2005-2021. The study shows that the fertility policy adjustment does not significantly increase the birth and fertility rates in China, and the findings are confirmed by robustness tests using various methods. Heterogeneity analysis shows that the implementation of the comprehensive two-child policy is more pronounced in the central region. Further, a mechanistic and causal analysis reveals that fertility policy changes did not significantly increase peoples willingness to have children, nor did they affect many other factors that influence households fertility decisions. Finally, a GM (1, 1) grey forecast model is used to forecast the births in each province and municipality in the next five years, and it is concluded that the births in China will continue to show a declining trend. This paper argues that a supportive policy system for fertility should be established, public childcare and elderly care services should be optimised, and a favourable fertility climate and conditions should be created in order to improve fertility levels in China.