Unchecked human population growth and consumption are key drivers of the current threats facing wildlife and wild spaces. Understanding the evidence-backed consequences of human population growth and the barriers to working on this issue is important for developing and prioritizing solutions.
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Ament, J. M., Collen, B., Carbone, C., Mace, G. M., & Freeman, R. (2019). Compatibility between agendas for improving human development and wildlife conservation outside protected areas: Insights from 20 years of data. People and Nature, 1(3), 305–316. https://doi.org/10.1002/pan3.10041
What is the research about?
The study analyzes the connections among trends in human development and wildlife over time, specifically using bird and mammal population abundance trends. The analyses focused on low‐ and lower‐middle income countries to observe wildlife trends occurring simultaneously with human development. This also helps to avoid measuring signals of historical change, including the effects of extinction filters, which are when countries that have already experienced significant development and species loss don’t show an accurate representation of these correlations.
What are the key takeaways?
Results indicate negative relationships between human population growth and wildlife abundance, for both bird and mammals, across 298 wildlife populations in 33 countries. There was also a positive correlation between wildlife abundance trends with economic growth, suggesting that as countries develop environmental regulations improve and help place a higher priority on conservation. The potential unintended consequences and compatibility between the conservation and development agendas indicate a need to better coordinate these strategies.
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Arnocky, S., Dupuis, D., & Stroink, M. L. (2012). Environmental concern and fertility intentions among Canadian university students. Population and Environment, 34(2), 279–292. https://doi.org/10.1007/s11111-011-0164-y
What is the research about?
To better understand how individuals understand reduced fertility as a solution to environmental problems this study looked at two types of environmental concern: (1) concerns about humans’ role in affecting the natural environment and the importance of environmental protection (2) concerns with health risks due to pollution.
What are the key takeaways?
The results showed that that pollution-related health concern was related to lower fertility intention. Future research could investigate additional distinction between limiting one’s reproduction out of environmental concern for the world at large as compared with more self-oriented environmental concerns.
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Bar-On, Y. M., Phillips, R., & Milo, R. (2018). The biomass distribution on Earth. Proceedings of the National Academy of Sciences of the United States of America, 115(25), 6506–6511. https://doi.org/10.1073/pnas.1711842115
What is the research about?
This study presents a survey of the composition of living organisms in our world to help gain a better understanding of biological relationships and dynamics.
What are the key takeaways?
The biomass of humans is more than eight times that of wild mammals, and the biomass of poultry is almost three times that of wild birds. The combination of humans and livestock outweigh all vertebrates except for fish. Also, total plant biomass has been halved since the start of human civilization, which has consequences for carbon sequestration. This is partly due to human advances and associated impacts we’ve made with agriculture, livestock domestication and industry in order to support our growing population.
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Barnes, M. D., Craigie, I. D., Harrison, L. B., Geldmann, J., Collen, B., Whitmee, S., … Woodley, S. (2016). Wildlife population trends in protected areas predicted by national socio-economic metrics and body size. Nature Communications, 7:12747. https://doi.org/10.1038/ncomms12747
What is the research about?The study analyzes correlates of population change in 1,902 populations of birds and mammals from 447 protected areas globally.
What are the key takeaways?
Protected areas are maintaining populations of monitored birds and mammals within their boundaries. Indicators of greater human wealth and development were associated with more positive population trends. This could be due to more resource availability for protected area management and people in these populations being less likely to extract resources from the protected areas. Human-caused drivers of wildlife abundance change appear to have more influence than those drivers affecting ecological dimensions. Managing sociopolitical dimensions like wealth, development and corruption, instead of exclusively ecological dimensions like size, shape and age of protected area, is important to wildlife conservation in protected areas.
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Barrett, S., Dasgupta, A., Dasgupta, P., Neil Adger, W., Anderies, J., van den Bergh, J., … Wilen, J. (2020). Social dimensions of fertility behavior and consumption patterns in the Anthropocene.Proceedings of the National Academy of Sciences of the United States of America, 117(12), 6300–6307. https://doi.org/10.1073/pnas.1909857117
What is the research about?
This study looks at how decisions around family planning and consumption behaviors aren’t exclusively individual decisions but also influenced by social pressures. Our individual needs appear small but have major impacts in aggregate and over time, when these demands are ingrained as social norms due to competitive and conformist behavior.
What are the key takeaways?
Continued growth of fertility and per capita GDP is not sustainable. Technology is often touted as the solution to many of our environmental issues, but it has not been a cure-all for habitat destruction and biodiversity loss. Social change is an important part of the solution, along with policy changes. These are most effective at the local and national level, rather than regional and global level.
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Berger, J., Wangchuk, T., Briceño, C., Vila, A., & Lambert, J. E. (2020). Disassembled Food Webs and Messy Projections: Modern Ungulate Communities in the Face of Unabating Human Population Growth. Frontiers in Ecology and Evolution, 8:128. https://doi.org/10.3389/fevo.2020.00128
What is the research about?
This study reviews how human population growth and its related disruptions alter wildlife community dynamics and ecological relationships of ungulates now and in the future.
What are the takeaways?
Many formerly predictable patterns and processes have diminished, and ecological surprises are becoming more regular occurrences. Disturbed habitat and altered communities can still offer important contributions to biodiversity, but we must continue to protect what we still have. Scientists need to be more involved outside academic literature and to participate in policy direction, speaking out and outreach. It’s important to help the public understand the relevance of food webs, biodiversity and community composition to shape policy, motivate politicians and elected officials, and influence state and federal agencies.
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Bologna, M., & Aquino, G. (2020). Deforestation and world population sustainability: a quantitative analysis. Scientific Reports, 10(1), 1–9. https://doi.org/10.1038/s41598-020-63657-6
What is the research about?
This study presents an analysis of how current population growth trends will affect deforestation.
What are the key takeaways?
Human activities are responsible for driving climate change through water and air contamination (mostly greenhouse effect) and deforestation. Results of this study show that based on the current growth and consumption rates and best estimate of technological rate growth, we have very low probability, less than 10% in the most optimistic scenario, to survive without facing a catastrophic collapse. Our civilization’s best chance for survival is shifting away from a culture strongly ruled by economy.
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Bradshaw, C. J. A., Giam, X., & Sodhi, N. S. (2010). Evaluating the relative environmental impact of countries. PLoS ONE, 5(5), e10440. https://doi.org/10.1371/journal.pone.0010440
What is the research about?
This study ranks countries by their proportional (relative to resource availability) and total environmental impact focused on consumption, deforestation, pollution and biodiversity loss. Of 228 countries considered, 179 (proportional) and 171 (absolute) had sufficient data for correlations and ranking based on natural forest loss, habitat conversion, marine captures, fertilizer use, water pollution, carbon emissions and species threat. Those results were then compared to socioeconomic indicators: human population size, human population density, human population growth rate and wealth. These country rankings can provide a better understanding of which countries could improve on their environmental impact, along with countries that are doing especially well and may serve as models for policy change.
What are the key takeaways?
Countries with higher total human populations and densities had greater proportional environmental impact, and those with lower population growth rates had a slightly lower proportional environmental impact. However, overall wealth was the most important indicator of environmental impact. Improving environmental performance doesn’t fall exclusively on less-developed countries, but wealthier developed countries have plenty room for improvement, too.
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Bradshaw, C. J. A., & Di Minin, E. (2019). Socio-economic predictors of environmental performance among African nations. Scientific Reports, 9(1), 1–13. https://doi.org/10.1038/s41598-019-45762-3
What is the research about?
This study tested hypotheses looking at the socioeconomic predictors of ecosystem change and degradation for countries across Africa, hypothesizing that human density and economic development increase the likelihood of cumulative environmental damage.
What are the key takeaways?
Much of the research investigating environmental change has not focused on the wider socioeconomic conditions contributing to environmental degradation. Models indicate that increasing population density and overall economic activity are some of the strongest predictors of increased environmental degradation. The study suggests that dedicated family planning, to reduce population growth, and economic development that limits agricultural expansion are needed to support environmental sustainability.
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Brown, M. L., Donovan, T. M., Schwenk, W. S., & Theobald, D. M. (2014). Predicting impacts of future human population growth and development on occupancy rates of forest-dependent birds. Biological Conservation, 170, 311–320. https://doi.org/10.1016/j.biocon.2013.07.039
What is the research about?
This paper models predictions of how human development will affect several bird species in the northeastern United States.
What are the key takeaways?
97% of towns experienced reductions in the occupancy of species within their town borders. There were also declines in the probability of species occupying an area when development was predicted to increase. These types of predictive modeling studies are important for evaluating the environmental costs of development.
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Cardillo, M., Purvis, A., Sechrest, W., Gittleman, J. L., Bielby, J., & Mace, G. M. (2004). Human population density and extinction risk in the world’s carnivores. PLoS Biology, 2(7). https://doi.org/10.1371/journal.pbio.0020197
What is the research about?
This is a global-scale analysis of biological and external predictors of extinction risk among carnivores based on human population density.
What are the key takeaways?
Biology is a stronger predictor of extinction risk to carnivores than exposure to high-density human populations. However, biology interacts with human population density to determine extinction risk: Biological traits explain 80% of variation in risk for carnivore species with high levels of exposure to human populations, compared to 45% for carnivores generally. Inherent ecological and life-history traits determine how resilient populations can be when exposed to threats. The study demonstrates how a model predicting extinction risk based on biology can be combined with projected human population density to identify species that might move toward extinction faster than based on biology alone. Maintaining the stability of particularly susceptible species before they become threatened could be more cost-effective in the long term than attempts to rescue them from the brink of extinction after large declines occur.
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Cavicchioli, R., Ripple, W. J., Timmis, K. N., Azam, F., Bakken, L. R., Baylis, M., … Webster, N. S. (2019). Scientists’ warning to humanity: microorganisms and climate change. Nature Reviews Microbiology, 17(9), 569–586. https://doi.org/10.1038/s41579-019-0222-5
What is the research about?
This article provides a series of examples and consequences of how microorganisms affect climate change (such as production and consumption of greenhouse gases) but also how they will be affected by climate change and other human activities. Together they create a feedback loop that accelerates climate change, worsens pollution, threatens agriculture and increases the spread of disease.
What are the key takeaways?
Some of the consequences that are shown as directly connected to human population growth include the increasing spread of animal, human and crop pathogens and increasing antimicrobial resistance of microorganisms.
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Ceballos, G., Ehrlich, P. R., Barnosky, A. D., García, A., Pringle, R. M., & Palmer, T. M. (2015). Accelerated modern human-induced species losses: Entering the sixth mass extinction. Science Advances, 1(5), e1400253. https://doi.org/10.1126/sciadv.1400253
What is the research about?
The study assesses, using conservative assumptions, whether human activities are causing a mass extinction.
What are the key takeaways?
Even under conservative assumptions that minimize evidence of a burgeoning mass extinction, the average rate of vertebrate species loss over the last century is up to 100 times higher than the background rate. This analysis emphasizes that humans have started to destroy other species at an accelerating rate, initiating a mass extinction episode that has not been seen for 65 million years. Avoiding a true sixth mass extinction will require efforts much more drastic than what is already being done to prevent the loss of already threatened species and to reduce pressures on their populations, such as habitat loss, overexploitation for economic gain, and climate change.
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Ceballos, G., Ehrlich, P. R., & Dirzo, R. (2017). Biological annihilation via the ongoing sixth mass extinction signaled by vertebrate population losses and declines. Proceedings of the National Academy of Sciences of the United States of America, 114(30), E6089–E6096. https://doi.org/10.1073/pnas.1704949114
What is the research about?
This study demonstrates that the current mass extinction is even worse than previously thought. This is because this analysis includes not just the extinction of entire species but declines in ranges and individual populations.
What were the key takeaways?
In addition to global species extinctions, there are widespread population declines and extirpations. The study found that the rate of population loss in terrestrial vertebrates is extremely high — even in “species of low concern.” In this sample, comprising nearly half of known vertebrate species, 32% (8,851/27,600) are decreasing in population size and range. In the 177 mammals for which there were detailed data, all have lost 30% or more of their geographic ranges, and more than 40% of the species have experienced severe population declines (>80% range shrinkage).
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Crist, E., Mora, C., & Engelman, R. (2017). The interaction of human population, food production, and biodiversity protection. Science, 356(6335), 260–264. https://doi.org/10.1126/science.aal2011
What is the research about?
This paper reviews the various proposed solutions and feasibility of feeding the world’s population. While some recommendations, such as changes in diet and reducing food waste, would help, there is still a reliance on intensification that continues the cycle of environmental degradation. The absence of addressing population growth has also paved the way for this reliance on technological advances to improve well-being.
What are the key takeaways?
Tackling both population and consumption is necessary to undo the environmental damages that have been done. Human-rights solutions like gender equity, along with educating women and investing in improved universal family planning services, are key elements of slowing population growth. Intensification of agriculture isn’t enough to compensate for our food supply because current rates are already unsustainable.
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Ganivet, E. (2019). Growth in human population and consumption both need to be addressed to reach an ecologically sustainable future. Environment, Development and Sustainability, 22, 4979–4998. https://doi.org/10.1007/s10668-019-00446-w[SB1
What is the research about?
This paper gives an overview of how increasing human population growth continues to negatively affect biodiversity, how we can change perceptions about population, and various noncoercive solutions like education and increasing access to contraception.
What are the key takeaways?
The habitat destruction driven by agricultural land-use change for food production and urban expansion to support our growing population show no signs of slowing down. There is substantial evidence to refute the argument that population is no longer an issue or something we can afford to ignore. There are several countries that have successfully implemented noncoercive population policies involving contraception and education to reduce their fertility rates than can be looked to as examples.
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Marques, A., Martins, I. S., Kastner, T., Plutzar, C., Theurl, M. C., Eisenmenger, N., … Pereira, H. M. (2019). Increasing impacts of land use on biodiversity and carbon sequestration driven by population and economic growth. Nature Ecology and Evolution, 3(4), 628–637. https://doi.org/10.1038/s41559-019-0824-3
What is the research about?
This study assesses how socioeconomic activities affect biodiversity by looking at bird species richness and reduced carbon sequestration through land-use change.
What are the key takeaways?
Population growth and economic growth between 2000-2011 led to decreases in bird diversity and carbon sequestration. Increasing development and human population will continue to drive biodiversity and carbon sequestration loss. These losses are not always caused by the population of the region they occur in, as international trade complicates these relationships.
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McKee, J., Chambers, E., & Guseman, J. (2013). Human Population Density and Growth Validated as Extinction Threats to Mammal and Bird Species. Human Ecology, 41(5), 773–778. https://doi.org/10.1007/s10745-013-9586-8
What is the research about?
This study tested the hypothesis that human population growth and human population density are correlated with the number of threatened species. The study also aimed to establish whether this can be quantified for future population growth.
What are the key takeaways?
This is the first study to show that continued change in human population densities quantitatively relates to species biodiversity threats. Predictions about extinction threat in 2010 were strongly correlated with observed data. Human population growth was found to be statistically significant with the increase in number of threatened species. Countries that experience a decline in population had a decrease in the number of threatened species, which was due to recovery efforts, not extinction.
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Mora, C., & Sale, P. (2011). Ongoing global biodiversity loss and the need to move beyond protected areas: a review of the technical and practical shortcomings of protected areas on land and sea. Marine Ecology Progress Series, 434, 251–266. https://doi.org/10.3354/meps09214
What is the research about?
If protected areas are failing to protect biodiversity, support for conservation could be lost and we need to consider different solutions. This paper reviews the existing literature and data on the ability of protected areas to prevent the loss of biodiversity without additional actions that address stabilizing population growth and associated ecological demands.
What are the key takeaways?
We will not be able to slow down biodiversity loss without changing our current levels of consumption. Reducing human population growth and consumption is cited as the only scenario to effectively address the underlying causes of biodiversity loss. The authors call for prioritizing solutions that fulfill human needs and also protect human welfare, along with noting the effectiveness of advocating from social, economic and ecological perspectives.
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O’Bryan, C. J., Allan, J. R., Holden, M., Sanderson, C., Venter, O., Di Marco, M., … Watson, J. E. M. (2020). Intense human pressure is widespread across terrestrial vertebrate ranges. Global Ecology and Conservation, 21, e00882. https://doi.org/10.1016/j.gecco.2019.e00882
What is the research about?
This study assesses the extent of intense cumulative human pressures on the geographic range of more than 20,000 terrestrial vertebrate species. This included several metrics that illustrate the intense effects of a growing human population, such as more space for people (population density and built environments), more food to feed them (crop lands and pasture lands), and more systems to support them (roads, railways, electric infrastructure).
What are the key takeaways?
There is substantial scientific evidence pointing to the destructive effects of interacting threats on biodiversity, but many species lack information on their exposure to cumulative human pressures since most studies focus on specific individual threats. Results show that 85% (17,517) of the terrestrial vertebrate species assessed have over half of their range exposed to intense human pressure, with 16% (3,328) of the species being entirely exposed to this amount of pressure.
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O’Neill, B. C., Dalton, M., Fuchs, R., Jiang, L., Pachauri, S., & Zigova, K. (2010). Global demographic trends and future carbon emissions. Proceedings of the National Academy of Sciences of the United States of America, 107(41), 17521–17526. https://doi.org/10.1073/pnas.1004581107
What is the research about?
This study provided an assessment for how various scenarios of changes in demography could affect carbon dioxide emissions globally. This assessment took a more detailed approach that included population size, age structure and urbanization, which have been left out or oversimplified in previous analyses.
What are the key takeaways?
The results show that slowing population growth could provide 16-29% of the emissions reductions needed to stay below a 2 degree Celsius temperature increase. Population composition can also affect emissions, and aging can reduce emissions by up to 20% in developed countries. This analysis also suggest that improved family planning policies could help in certain regions (like the United States and developing regions other than China) that account for half of the total reductions that results from lower population growth.
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Scovronick, N., Budolfson, M. B., Dennig, F., Fleurbaey, M., Siebert, A., Socolow, R. H., … Wagner, F. (2017). Impact of population growth and population ethics on climate change mitigation policy. Proceedings of the National Academy of Sciences of the United States of America, 114(46), 12338–12343. https://doi.org/10.1073/pnas.1618308114
What is the research about?
This study looked at how future population is valued affects climate change mitigation decisions. Two approaches to valuing population were explored: increasing the number of people who are happy or increasing the average level of people’s happiness.
What are the key takeaways?
Whether lowering population growth entails overall improvements in wellbeing — rather than merely cost savings — depends on the ethical approach to valuing population. One way values additional people that increase the number of people who are happy over the climate damages and necessary mitigation costs and the other values a smaller population to avoid those costs. These considerations need to be discussed when deciding climate policy.
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Seto, K. C., Güneralp, B., & Hutyra, L. R. (2012). Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools. Proceedings of the National Academy of Sciences of the United States of America, 109(40), 16083–16088. https://doi.org/10.1073/pnas.1211658109
What is the research about?
This study provides forecasts of urban land-cover change and the effects on habitat in biodiversity hotspots and tropical carbon storage and biomass.
What are the key takeaways?
Urban land cover is expected to triple by 2030 from 2000 amounts if current trends in population density continue. Some of the highest rates in growth are predicted to happen in areas that were relatively undeveloped in 2000. Critical biodiversity hotspot habitat will be lost if these patterns continue. The long-term environmental impacts of infrastructure associated with sprawl and urbanization need to be considered when developing urbanization policies.
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Weinzettel, J., Hertwich, E. G., Peters, G. P., Steen-Olsen, K., & Galli, A. (2013). Affluence drives the global displacement of land use. Global Environmental Change, 23(2), 433–438. https://doi.org/10.1016/j.gloenvcha.2012.12.010
What is the research about?
This study seeks to better understand how international supply chains to final consumption impact the use of land and water by modeling agricultural, food, and forestry products while also including the land requirements of manufactured goods and services.
What are the key takeaways?
Increasing affluence is often suggested as a driver for the human impact on biologically productive areas and identified among the causes of biodiversity loss, but international trade complicates these relationships. The land and ocean area footprint of nations increased by a third for each doubling of income, with all variables analyzed on a per capita basis. This increase came largely from imports, which increased proportionally to income, demonstrating the disproportionate impact wealthier countries have because of higher consumption.
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Williams, J. N. (2013). Humans and biodiversity: Population and demographic trends in the hotspots. Population and Environment, 34(4), 510–523. https://doi.org/10.1007/s11111-012-0175-3
What is the research about?
This study seeks to quantify the amount of population growth occurring in biodiversity hotspots in order to understand and better mitigate habitat loss.
What are the key takeaways?
The population growth rate declined from 1.6% to 1.3% in biodiversity hotspots but the total population increased by 187 million people. These slower growth rates are the result of trends in decreasing fertility, aging populations and increased urbanization. The hotspots are mostly populated by younger people who haven’t entered their reproductive years or are in the early stages. This means that populations in these priority conservation areas will grow, despite declining birth rates. As a result, biodiversity conservation in these areas may face obstacles.
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