Human Population Size Research Articles

Shrub cover declined as Indigenous populations expanded across southeast Australia.

Wildfires in forests globally have become more frequent and intense because of changes in climate and human management. Shrub layer fuels allow fire to spread vertically to forest canopy, creating high-intensity fires. Our research provides a deep-time perspective on shrub fuel loads in fire-prone southeastern Australia. Comparing 2833 records for vegetation cover, past climate, biomass burning, and human population size across different phases of human occupation, we demonstrated that Indigenous population expansion and cultural fire use resulted in a 50% reduction in shrub cover, from approximately 30% from the early to mid-Holocene (12 to 6 thousand years ago) to 15% during the late to mid-Holocene (6 to 1 thousand years ago). Since the start of British colonization to the present, shrub cover has increased to the highest ever recorded (mean of 35% land cover), increasing the risk of high-intensity fires.

The Effects of Egg- and Substrate-Associated Microbiota on the Larval Performance of the Housefly, Musca domestica.

Increasing human population size and income growth are causing an increasing demand for food and feed. Insects are a more sustainable alternative to conventional animal source proteins, as they can convert waste and by-products from the agricultural industry into biomass for commercial feed for livestock and, potentially, serve as a food source for human consumption. Moreover, insects together with their microorganisms have been shown to play a pivotal role in the development of insects and in the breakdown of complex growth substrates, and are, therefore, closely tied to insect production. This study aims to determine if the removal of egg- and substrate-associated microorganisms impacts larval performance (growth, final biomass, and the survival rate) of M. domestica Linnaeus. Four treatments are tested: disinfected eggs and non-autoclaved substrate, non-disinfected eggs and autoclaved substrate, disinfected eggs and autoclaved substrate, and a control without any removal of microbiota. The results show a significant decrease in the final biomass of larvae subjected to the treatments with only disinfected eggs, only autoclaved substrate, and both compared to the control, and a significant decrease in survival rate for non-disinfected eggs and autoclaved substrate and disinfected eggs and autoclaved substrate compared to the control group. Moreover, larval growth shows a significant difference across days within all treatments. Together, this suggests that the microorganisms of housefly eggs and the growth substrate play an important role in biomass, which is critical in commercial insect production. Together this suggest, that more studies are needed to examine these parameters with respect to more commercially relevant substrates.

The effects of climate and population on human land use patterns in Europe from 22ka to 9ka ago

Between 22ka and 9ka ago, after the Last Glacial Maximum (LGM) and during the transition to the Holocene, mobile hunter-gatherer populations, differentiated by their stone tool assemblages, periodically dispersed and contracted across Europe. It is well understood that climate played an important role in human distributions and population sizes during the post-LGM Late Pleistocene and Early Holocene, but the question remains as to whether increasing population sizes drove early human dispersal. Here, using a spatiotemporal species distribution model to infer the fundamental and potential human climatic niche space of Late Upper Paleolithic, Final Paleolithic and Early Mesolithic Europe, and hypotheses derived from the Ideal Distribution Model, we test i) how changes in climate affected the size and extent of the projected potential human niche space, ii) for effects of changes in size of projected potential niche on regional human population sizes, iii) whether increasing human population sizes drove human dispersal into less climatically suitable habitats, and iv) whether populations associated with different high-order material culture groupings (macro-level technocomplexes) occupied different climatic spaces. We find that changes in climate correlate strongly with the size and extent of the projected potential human niche space, that increases in the projected human niche space correlate with increases in human population, that human population size is just beginning to become large enough to influence land use and dispersal patterns at the Pleistocene-Holocene transition, and that archaeological technocultural entities overlap in their fundamental climatic niche space. This overlap implies that changing tools forms cannot readily been seen as reflecting adaptations to changing climates.

Small populations of Palaeolithic humans in Cyprus hunted endemic megafauna to extinction.

The hypothesized main drivers of megafauna extinctions in the late Quaternary have wavered between over-exploitation by humans and environmental change, with recent investigations demonstrating more nuanced synergies between these drivers depending on taxon, spatial scale, and region. However, most studies still rely on comparing archaeologically based chronologies of timing of initial human arrival into naïve ecosystems and palaeontologically inferred dates of megafauna extinctions. Conclusions arising from comparing chronologies also depend on the reliability of dated evidence, dating uncertainties, and correcting for the low probability of preservation (Signor-Lipps effect). While some models have been developed to test the susceptibility of megafauna to theoretical offtake rates, none has explicitly linked human energetic needs, prey choice, and hunting efficiency to examine the plausibility of human-driven extinctions. Using the island of Cyprus in the terminal Pleistocene as an ideal test case because of its late human settlement (~14.2-13.2 ka), small area (~11 000 km2), and low megafauna diversity (2 species), we developed stochastic models of megafauna population dynamics, with offtake dictated by human energetic requirements, prey choice, and hunting-efficiency functions to test whether the human population at the end of the Pleistocene could have caused the extinction of dwarf hippopotamus (Phanourios minor) and dwarf elephants (Palaeoloxodon cypriotes). Our models reveal not only that the estimated human population sizes (n = 3000-7000) in Late Pleistocene Cyprus could have easily driven both species to extinction within < 1000 years, the model predictions match the observed, Signor-Lipps-corrected chronological sequence of megafauna extinctions inferred from the palaeontological record (P. minor at ~12-11.1 ka, followed by P. cypriotes at ~10.3-9.1 ka).

Nonnative pest establishment: Spatial patterns and public detection

Early detection of new pests can reduce their long-term impacts by enabling more rapid management response. Knowledge of pest establishment risk and background rates of detection (e.g., by the public) can help inform more cost-effective targeting of formal early detection survey programs. Here we quantify county-level locational attributes associated with pest establishment and detection by the public using data for 113 new pest incursions detected in the United States from 2010 through 2018. Aligning with expectations, we find a higher likelihood of new pest establishment in counties with higher human population numbers, nearer to ports (<250 km), and with amenable climate characteristics. Controlling for potential sample selection issues, we find that pests are less likely to be first detected by the public (e.g., homeowners, community members) versus by other sources (e.g., agency surveys, researchers, or agricultural operators) in counties with higher total crop sales values and lower human population number. The negative association between public detection and high agricultural values may reflect greater survey efforts by other sources (e.g., by agency surveillance programs, researchers, and agricultural operators) in high-value agricultural areas. The positive association between public detection and human population size may reflect larger numbers of public detectors (i.e., people) available to encounter the pests. Our models provide spatially explicit estimates of the likelihood of new pest establishment across U.S. counties and of the likelihood that an established pest would first be detected by the public. These estimates can serve as quantitative inputs to decision-support activities for new pest surveillance planning.

Understanding long-term human ecodynamics through the lens of ecosystem collapse

Most research on long-term human ecodynamics examines changes in the size and structure of human populations, often in relation to climate change. Here we offer an alternative perspective that draws on recent progress in conservation science, examining the causes and consequences of ecosystem collapse. We identify human actions that can cause abrupt transformation of ecosystems, in relation to key mechanisms and underlying theory. Such ecosystem collapse can in turn affect human societies by altering flows of ecosystem benefits to people. In this way, human ecodynamics can be understood by separately analysing the dynamics of social and ecological sub-systems, which are reciprocally linked. Ecosystem collapse represents a perturbation of these sub-systems, and provides insights into the mechanisms underlying their respective dynamics. We illustrate this approach through four case studies, which examine the spread of agriculture during the Holocene. Four key knowledge gaps emerge through consideration of these case studies: the linkages between social and ecological sub-systems, and how these change over time; the presence of feedbacks between these sub-systems; the relationships between local- and regional-scale collapse; and the relationships with ecological recovery. Increased research on ecosystem collapse could help clarify the relative influence of environmental degradation on societal dynamics, while providing insights into resilience and sustainability. Given the outstanding societal importance of ecosystem collapse, such research could also strengthen the relevance of historical sciences to the contemporary world.

A dataset of human capital-weighted population estimates for 185 countries from 1970 to 2100

We provide a novel dataset of human capital-weighted population size (HCWP) for 185 countries from 1970 to 2100. HCWP summarizes a population’s productive capacity and human capital heterogeneity in a single metric, enabling comparisons across countries and over time. The weights are derived from Mincerian earnings functions applied to multi-country census data on educational attainment. The model used to compute the returns to schooling accounts for the diminishing positive relative relationship between education and wages as the overall education of populations rises. The population weights are adjusted by a skills assessment factor representing differences in education quality across countries and years. HCWP is calculated by applying these adjusted human capital weights to population estimates and projections disaggregated by age, sex and education, spanning the period 1970–2020 and 2020–2100 for five Shared Socioeconomic Pathway scenarios. Validation analyses demonstrate the utility of the new HCWP data in explaining national income trends. As a more comprehensive population measure than basic size and age-sex indicators, HCWP enhances the power of statistical models aimed at the assessment of socioeconomic change impacts and forecasting.

The anthropocene biogeography of alien birds on islands: Drivers of their functional and phylogenetic diversities.

A branch of island biogeography has emerged to explain alien species diversity in the light of the biogeographic and anthropogenic context, yet overlooking the functional and phylogenetic facets. Evaluating alien and native birds of 407 oceanic islands worldwide, we built structural equation models to assess the direct and indirect influence of biotic, geographic, and anthropogenic contexts on alien functional diversity (FD) and phylogenetic diversity (PD). We found that alien taxonomic richness was the main predictor of both diversities. Anthropogenic factors, including colonization pressure, associated with classic biogeographical variables also strongly influenced alien FD and PD. Specifically, habitat modification and human connectivity markedly drove alien FD, especially when controlled by taxonomic richness, whereas the human population size, gross domestic product, and native PD were crucial at explaining alien PD. Our findings suggest that humans not only shape taxonomic richness but also other facets of alien diversity in a complex way.

Phase synchronization between culture and climate forcing.

Over the history of humankind, cultural innovations have helped improve survival and adaptation to environmental stress. This has led to an overall increase in human population size, which in turn further contributed to cumulative cultural learning. During the Anthropocene, or arguably even earlier, this positive sociodemographic feedback has caused a strong decline in important resources that, coupled with projected future transgression of planetary boundaries, may potentially reverse the long-term trend in population growth. Here, we present a simple consumer/resource model that captures the coupled dynamics of stochastic cultural learning and transmission, population growth and resource depletion in a changing environment. The idealized stochastic mathematical model simulates boom/bust cycles between low-population subsistence, high-density resource exploitation and subsequent population decline. For slow resource recovery time scales and in the absence of climate forcing, the model predicts a long-term global population collapse. Including a simplified periodic climate forcing, we find that cultural innovation and population growth can couple with climatic forcing via nonlinear phase synchronization. We discuss the relevance of this finding in the context of cultural innovation, the anthropological record and long-term future resilience of our own predatory species.

Evaluating the Status of Lost, Found and Sighted Non-Native Pet Bird Species in South Africa

The global increase in the pet trade and ownership of pet birds has heightened the introduction of emerging invasive vertebrate species. We analyzed online databases of lost, found, and sighted non-native pet bird reports in South Africa to evaluate non-native pet bird statuses, investigate geographic patterns, assess species trends, and determine the factors associated with lost pet birds. We identified a total of 1467 case reports representing 77 species across nine families from websites (n = 3) and Facebook pages (n = 13). Most reports of lost birds were within large cities, in populated provinces, including Gauteng, KwaZulu-Natal, and Western Cape. Psittacidae, Psittaculidae, and Cacatuidae were the most dominant families, with African grey (Psittacus erithacus), Cockatiel (Nymphicus hollandicus), and Rose-ringed parakeet (Psittacula krameri) among the top species reported as lost. Lower-priced species were commonly reported as lost, and there was no association between the species’ price and the likelihood of being found. In addition, we found a positive relationship between species reported as lost and the number of pet shops, human population size, species size, and docility. There was a sharp increase in lost cases from 2019 onwards; however, males were more frequently lost. Our findings highlight challenges in regulating and monitoring the pet ownership and trade of non-native pet birds and the need to address commonly kept species in conservation efforts. Online resources can be effective tools for passive surveillance of non-native pet bird species, especially potentially invasive ones.

Boreal forest cover was reduced in the mid-Holocene with warming and recurring wildfires

The hemi-boreal zone, marking North America’s southern boreal forest boundary, has evolved post-glaciation, hosting diverse ecosystems including mixed forests with savannas, grasslands, and wetlands. While human, climate, and fire interactions shape vegetation dynamics therein, specific influences remain unclear. Here we unveil 12,000 years of hemi-boreal zone dynamics, exploring wildfire, vegetation, climate, and human population size interactions at such long time scales. Postglacial biomass burning exhibited episodes of persistent elevated activity, and a pivotal shift around 7000 years ago saw the boreal forest transition to an oak-pine barren ecosystem for about 2000 years before reverting. This mid-Holocene shift occurred during a period of more frequent burning and a sudden uptick in mean annual temperatures. Population size of Indigenous peoples mirrored wildfire fluctuations, decreasing with more frequent burning. Anticipated increases of fire activity with climate change are expected to echo transformations observed 7000 years ago, reducing boreal forest extent, and impacting land use.

Net benefit of smaller human populations to environmental integrity and individual health and wellbeing.

The global human population is still growing such that our collective enterprise is driving environmental catastrophe. Despite a decline in average population growth rate, we are still experiencing the highest annual increase of global human population size in the history of our species-averaging an additional 84 million people per year since 1990. No review to date has accumulated the available evidence describing the associations between increasing population and environmental decline, nor solutions for mitigating the problems arising. We summarize the available evidence of the relationships between human population size and growth and environmental integrity, human prosperity and wellbeing, and climate change. We used PubMed, Google Scholar, and Web of Science to identify all relevant peer-reviewed and gray-literature sources examining the consequences of human population size and growth on the biosphere. We reviewed papers describing and quantifying the risks associated with population growth, especially relating to climate change. These risks are global in scale, such as greenhouse-gas emissions, climate disruption, pollution, loss of biodiversity, and spread of disease-all potentially catastrophic for human standards of living, health, and general wellbeing. The trends increasing the risks of global population growth are country development, demographics, maternal education, access to family planning, and child and maternal health. Support for nations still going through a demographic transition is required to ensure progress occurs within planetary boundaries and promotes equity and human rights. Ensuring the wellbeing for all under this aim itself will lower population growth and further promote environmental sustainability.

Deriving a zero-truncated modelling methodology to analyse capture–recapture data from self-reported social networks

Capture–recapture (CRC) is widely used to estimate the size (N) of hidden human populations (e.g., the homeless) from the overlap of sample units between two or more repeated samples or lists (a.k.a., capture occasions). There is growing interest in deriving CRC data from social-network data. The current paper hence explored if self-reported social networks (lists of social ties) submitted by participants from the target population could function as distinct capture occasions. We particularly considered the application of zero-truncated count distribution modelling to this type of data. A case study and follow-up simulation study focused on two methodological issues: (1) that a participant cannot be named in their own self-reported social network and hence cannot be named as many times as non-participants; and (2) positive dependence between being a participant and being named by (a social tie of) other participants. Regarding the latter, a further motivation of the simulation study was to consider the impact of using respondent-driven sampling to select participants, because all non-seed RDS participants are recruited as a social tie of another participant. Exponential random graph modelling was used to generate the simulation study’s target populations. Early comparison was also made to estimates of N from Successive Sampling.

Patterns of green space change and fragmentation in a rapidly expanding city of northern Ghana, West Africa

Green spaces such as forests, grasslands, and croplands (including gardens) can be found in urban environments. Although they benefit human and animal well-being, they have become threatened due to rapid urban growth and unplanned development. Yet, little attention has been given to studying the dynamics of urban green spaces in sub-Saharan Africa. In this study, we examined the dynamics of land use and land cover (LULC) change and fragmentation (especially, green spaces) within the second fastest urbanising city in Ghana, Tamale. In particular, we focused our analyses on its urban core (∼5 km radius around the city centre) due to its relevance to urban economy and society. Landsat data was used to estimate fragmentation metrics of past and future LULC changes in the study area from 1990 to 2052. We found clear patterns of green space decline and fragmentation within the urban core: i.e., green spaces became patchy over time and the pattern was expected to continue in the future. Additionally, we found the built-up class benefited from the decline of green spaces with the latter being significantly negatively correlated with human population size. Our investigation reveals that protected forests and tree plantations contributed to a significant proportion of available green spaces in the urban core. However, these areas were becoming increasingly threatened by forest reserve downsizing, indiscriminate activities (e.g., logging and encroachment), and sale of public lands to private developers, practices commonly associated with population growth. Hence, the enforcement of relevant local legislations (e.g., the 2016 Land Use and Spatial Planning Act [Act 925]) coupled with the integration of urban initiatives and policies that encourage green spaces are needed to ensure the sustainability of urban ecosystems for the well-being of humans and the environment.

Bee species richness through time in an urbanizing landscape of the southeastern United States.

Compared to non-urban environments, cities host ecological communities with altered taxonomic diversity and functional trait composition. However, we know little about how these urban changes take shape over time. Using historical bee (Apoidea: Anthophila) museum specimens supplemented with online repositories and researcher collections, we investigated whether bee species richness tracked urban and human population growth over the past 118 years. We also determined which species were no longer collected, whether those species shared certain traits, and if collector behavior changed over time. We focused on Wake County, North Carolina, United States where human population size has increased over 16 times over the last century along with the urban area within its largest city, Raleigh, which has increased over four times. We estimated bee species richness with occupancy models, and rarefaction and extrapolation curves to account for imperfect detection and sample coverage. To determine if bee traits correlated with when species were collected, we compiled information on native status, nesting habits, diet breadth, and sociality. We used non-metric multidimensional scaling to determine if individual collectors contributed different bee assemblages over time. In total, there were 328 species collected in Wake County. We found that although bee species richness varied, there was no clear trend in bee species richness over time. However, recent collections (since 2003) were missing 195 species, and there was a shift in trait composition, particularly lost species were below-ground nesters. The top collectors in the dataset differed in how often they collected bee species, but this was not consistent between historic and contemporary time periods; some contemporary collectors grouped closer together than others, potentially due to focusing on urban habitats. Use of historical collections and complimentary analyses can fill knowledge gaps to help understand temporal patterns of species richness in taxonomic groups that may not have planned long-term data.

A transformative poultry feed system: The impact of insects as an alternative and transformative poultry-based diet in sub-Saharan Africa

Abstract There is growing interest in the transformation of costly, unsustainable feed systems to help address malnutrition and food insecurity in sub-Saharan Africa (SSA). In the poultry production industry, dietary insect meals were identified as a possible solution to aid in transforming poultry feeds by replacing expensive and environmentally threatening protein feed ingredients including soyabean and fish meal. Hence, playing an important role in helping to feed the ever-growing human population size through the production of more poultry meat and meat products. The potential of edible insects as highly nutritious, cost-effective, and biofriendly alternative protein feed ingredient in poultry diets is currently one of the most trending topics in animal nutrition worldwide. This review will provide a recent overview of the utilisation of insect-based diets by poultry-producing farmers in SSA, to improve poultry production at low costs with little effect on climate change. Therefore, the perspectives of various farmers towards using insect-based diets in poultry production; recent findings on the effect of insect-based diets on poultry production and performance; benefits of insect-based poultry meat; adoption and awareness of insect farming; and opportunities and constrains of rearing insects for animal feeding in SSA were discussed. Hence, there is still a need to improve insect farming infrastructure, educating and training insect and poultry-producing farmers on insect rearing and marketing, enforcing laws and policies on insect farming operation, investing and conducting more research on local insects in poultry diets, as well as conserving wild insects and the environment in general.

Intentional creation of carbon-rich dark earth soils in the Amazon.

Fertile soil known as Amazonian dark earth is central to the debate over the size and ecological impact of ancient human populations in the Amazon. Dark earth is typically associated with human occupation, but it is uncertain whether it was created intentionally. Dark earth may also be a substantial carbon sink, but its spatial extent and carbon inventory are unknown. We demonstrate spatial and compositional similarities between ancient and modern dark earth and document modern Indigenous practices that enrich soil, which we use to propose a model for the formation of ancient dark earth. This comparison suggests that ancient Amazonians managed soil to improve fertility and increase crop productivity. These practices also sequestered and stored carbon in the soil for centuries, and we show that some ancient sites contain as much carbon as the above-ground rainforest biomass. Our results demonstrate the intentional creation of dark earth and highlight the value of Indigenous knowledge for sustainable rainforest management.

Biases in parasite biodiversity research: why some helminth species attract more research than others.

As the number of known and described parasite species grows every year, one might ask: how much do we actually know about these species beyond the fact they exist? For free-living taxa, research effort is biased toward a small subset of species based on their properties or human-centric factors. Here, using a large data set on over 2500 helminth parasite species described in the past two decades, we test the importance of several predictors on two measures of research effort: the number of times a species description is cited following its publication, and the number of times a species' name is mentioned in the scientific literature. Our analysis highlights some taxonomic biases: for instance, descriptions of acanthocephalans and nematodes tend to receive more citations than those of other helminths, and species of cestodes are less frequently mentioned in the literature than other helminths. We also found that helminths infecting host species of conservation concern receive less research attention, perhaps because of the constraints associated with research on threatened animals, while those infecting host species of human use receive greater research effort. Intriguingly, we found that species originally described by many co-authors subsequently attract more research effort than those described by one or few authors, and that research effort correlates negatively with the human population size of the country where a species was discovered, but not with its economic strength, measured by its gross domestic product. Overall, our findings reveal that we have conducted very little research, or none at all, on the majority of helminth parasite species following their discovery. The biases in study effort we identify have serious implications for future research into parasite biodiversity and conservation.

Antimicrobials and antimicrobial resistance genes in a one-year city metabolism longitudinal study using wastewater-based epidemiology

This longitudinal study tests correlations between antimicrobial agents (AA) and corresponding antimicrobial resistance genes (ARGs) generated by a community of >100 k people inhabiting one city (Bath) over a 13 month randomised monitoring programme of community wastewater. Several AAs experienced seasonal fluctuations, such as the macrolides erythromycin and clarithromycin that were found in higher loads in winter, whilst other AA levels, including sulfamethoxazole and sulfapyridine, stayed consistent over the study period. Interestingly, and as opposed to AAs, ARGs prevalence was found to be less variable, which indicates that fluctuations in AA usage might either not directly affect ARG levels or this process spans beyond the 13-month monitoring period. However, it is important to note that weekly positive correlations between individual associated AAs and ARGs were observed where seasonal variability in AA use was reported: ermB and macrolides CLR-clarithromycin and dmCLR-N-desmethyl clarithromycin, aSPY- N-acetyl sulfapyridine and sul1, and OFX-ofloxacin and qnrS. Furthermore, ARG loads normalised to 16S rRNA (gene load per microorganism) were positively correlated to the ARG loads normalised to the human population (gene load per capita), which indicates that the abundance of microorganisms is proportional to the size of human population and that the community size, and not AA levels, is a major driver of ARG levels in wastewater. Comparison of hospital and community wastewater showed higher number of AAs and their metabolites, their frequency of occurrence and concentrations in hospital wastewater. Examples include: LZD-linezolid (used only in severe bacterial infections) and AMX-amoxicillin (widely used, also in community but with very low wastewater stability) that were found only in hospital wastewater. CIP-ciprofloxacin, SMX-sulfamethoxazole, TMP-trimethoprim, MTZ-metronidazole and macrolides were found at much higher concentrations in hospital wastewater while TET-tetracycline and OTC-oxytetracycline, as well as antiretrovirals, had an opposite trend. In contrast, comparable concentrations of resistant genes were observed in both community and hospital wastewater. This supports the hypothesis that AMR levels are more of an endemic nature, developing over time in individual communities. Both hospital and community wastewater had AAs that exceeded PNEC values (e.g. CLR-clarithromycin, CIP-ciprofloxacin). In general, though, hospital effluents had a greater number of quantifiable AAs exceeding PNECs (e.g. SMX-sulfamethoxazole, ERY-erythromycin, TMP-trimethoprim). Hospitals are therefore an important consideration in AMR surveillance as could be high risk areas for AMR.

Waterfowl Wintering in Cities of Temperate Climatic Zone and Its Shaping Factors.

The dynamics of the population size and species diversity of wintering waterfowl was for the first time studied in 30 cities of Russia over eight years. The total population size increased by 35%. The species diversity was found to reach 32 species in total. The mallard Anas platyrhynchos dominated in all 30 cities. The cities grouped to form seven clusters significantly differing from each other by the total parameter set. The geographical location and climatic characteristics of a city are the main environmental conditions for both people and birds. The variance of the wintering waterfowl population size was determined to the extent of 93% by the area and human population size of the city; and 62% of the variance in species number was determined by the longitude, the average January temperature, and the human population size of the city (p < 0.001). The population size and species number of birds correlated with the "age" of the wintering place (p < 0.05). If the urbanization rate continues the same, the population size and species diversity are expected to grow further.