Overpopulation is a major cause of biodiversity loss and smaller human populations are necessary to preserve what is left
Introduction
Human overpopulation is a major driver of biodiversity loss and a key obstacle to fairly sharing habitat and essential resources with other species (Crist, 2019). Yet those concerned to further conservation, including conservation scientists, rarely advocate for smaller human populations (exceptions include Foreman and Carroll, 2014; Driscoll et al., 2018). Speaking out about population matters can be challenging, but failure to address the root causes of biodiversity loss will doom conservationists' efforts (Shragg, 2015; Diaz et al., 2019). Successfully conserving Earth's remaining biodiversity requires challenging growth and addressing the excessive size of human populations and human economies, which are intimately connected. In what follows, we show that overpopulation is a major factor causing biodiversity loss (Section 2) and that population decreases open exciting possibilities for ecological restoration (Section 3). We discuss research opportunities to clarify how human demographic changes help or hinder conservation efforts (Section 4). We also argue that conservation biologists should actively promote smaller human populations, since they are necessary to preserve biodiversity (Section 5).
Section snippets
Overpopulation and biodiversity loss
The concept of human overpopulation, once common, is now rarely used in the scientific literature (Götmark et al., 2021). Here we stipulate that overpopulation exists where 1) people are displacing wild nature so thoroughly that they are extinguishing numerous species; 2) people are degrading ecosystems so thoroughly that future human generations likely will have a hard time living decent lives; and (3) one or both of these environmental catastrophes cannot be avoided without significantly
Population decreases open up ecological restoration possibilities
Just as population increases clearly contribute to biodiversity losses, so population decreases can aid in restoring biodiversity. All else being equal, smaller human numbers opens more space for wild species. One sees this particularly clearly in Europe, densely populated, but also the first continent to end humanity's modern population explosion. Europe's overall population has stabilized in recent years and its rural population has declined 20 % since 1960, contributing to extensive
Research opportunities
The evidence summarized in 2 Overpopulation and biodiversity loss, 3 Population decreases open up ecological restoration possibilities shows the need for a research agenda that explores the connection between human numbers and biodiversity preservation more rigorously and systematically. First, research is needed into how important population growth and overpopulation are in driving biodiversity loss, particularly compared to other factors (Rust and Kehoe, 2017). While the research cited in
Advocacy needs
Overall, few papers in the conservation biology literature analyze the role overpopulation plays in biodiversity loss. But even those that do usually do not recommend policies to end or reverse population growth. Of the 30 studies cited in Section 2 that report a negative impact of excessive population on biodiversity, only three of them directly advocate stabilizing or reducing human numbers (Estrada, 2017; Crist et al., 2017; Qiu et al., 2018). Similarly, none of the papers and reports cited
Conclusion
During the past hundred years, Homo sapiens' population increased from 2 billion to nearly 8 billion and the United Nations (2019) projects an increase of 3 billion more by 2100, unless steps are taken to reduce this population growth. Ignoring this projected increase means ignoring a major driver of the unfolding biodiversity crisis; accepting current bloated human numbers as an appropriate status quo means accepting a biologically impoverished planet. A scientific, evidence-based conservation
Declaration of competing interest
The authors hereby declare no conflict of interest involved in the writing or publication of this article. Philip Cafaro's work was supported by the endowment of the Philosophy Department, Colorado State University. Pernilla Hansson's work was supported by a grant from the GAIA Initiative for Earth - Human Balance.
References (125)
What drives land take and urban land expansion? A systematic review
Land Use Policy
(2018)Restoration, reintroduction, and rewilding in a changing world
Trends Ecol. Evol.
(2016)- et al.
Use of human rights to meet the unmet need for family planning
Lancet
(2012) - et al.
Population growth and climate change: addressing the overlooked threat multiplier
Sci. Total Environ.
(2020) - et al.
Management, scientific approach, and practice: a comment on Corlett
Trends Ecol. Evol.
(2017) - et al.
Aging human populations: good for us, good for the Earth
Trends Ecol. Evol.
(2018) Parks protect forest cover in a tropical biodiversity hotspot, but high human population densities can limit success
Biol. Conserv.
(2018)Effects of human population, area, and time on non-native plant and fish diversity in the United States
Biol. Conserv.
(2001)The social and environmental influences of population growth rate and demographic pressure deserve greater attention in ecological economics
Ecol. Econ.
(2020)Ecological economics for humanity's plague phase
Ecol. Econ.
(2020)
Road networks predict human influence on Amazonian bird communities
Rural abandonment and landscape evolution in the central region of Portugal
Building the Prairie
Impact of population growth on the planet
Bringing large mammals back: large carnivores in Europe
Global warming policy: is population left out in the cold?
Science
Odessa: city population
Just population policies for an overpopulated world
Ecol. Citizen
Reducing human numbers and the size of our economies is necessary to avoid a mass extinction and share Earth justly with other species
Philosophia
Policy-based population projections for the European Union: a complementary approach
Comp. Popul. Stud.
The potential environmental impacts of EU immigration policy: future population numbers, greenhouse gas emissions and biodiversity preservation
J. Popul. Sustain.
Establishment and growth of a new Dalmatian pelican Pelecanus crispus colony in central Greece
Acta Ornithol.
Recovery of large carnivores in Europe's modern human-dominated landscapes
Science
The Importance of Human Reproductive Health and Rights for Cheetah Conservation
Connecting landscape-scale ecological restoration and tourism: stakeholder perspectives in the great plains of North America
J. Sustain. Tour.
One Child: Do We Have a Right to More?
Should We Control World Population?
Abundant Earth: Toward an Ecological Civilization
The interaction of human population, food production, and biodiversity protection
Science
Protecting half the planet and transforming human systems are complementary goals
Front. Conserv. Sci.
Action Plan for the Dalmatian Pelican Pelecanus crispus in Europe
The global food-energy-water nexus
Rev. Geophys.
Time and the Generations: Population Ethics for a Diminishing Planet
Wildlife Comeback in Europe: The Recovery of Selected Mammal and Bird Species: Final Report to Rewilding Europe
Pervasive human-driven decline of life on earth points to the need for transformative change
Science
An ecoregion-based approach to protecting half the terrestrial realm
Bioscience
A global deal for nature: guiding principles, milestones, and targets
Sci. Adv.
Agricultural intensification and the collapse of Europe's farmland bird populations
Proc. R. Soc. B
A biodiversity-crisis hierarchy to evaluate and refine conservation indicators
Nat. Ecol. Evol.
One-dimensional ecology
Bull. At. Sci.
Danube delta: endangered landscapes programme
Reintroduction efforts see long absent kulan return to the Danube delta
Nine population strategies to stop short of 9 billion
Removing Barriers to Family Planning, Empowering Sustainable Environmental Conservation: A Background Paper and Call for Action
Impending extinction crisis of the world's primates: why primates matter
Sci. Adv.
Population on 1 January by age group, sex and NUTS 3 region
Barbarian hordes: the overpopulation scapegoat in international development discourse
Third World Q.
Man Swarm: How Overpopulation Is Killing the Wild World
The effect of human population size on the breeding bird diversity of urban regions
Biodivers. Conserv.
A Hundred Year Database for Integrated Environmental Assessments
Cited by (23)
Modeling multi-scale relationships between wilderness area changes and potential drivers: Evidence from the southeast coastal area of China
2024, Journal for Nature ConservationThermal stress-stimulated ZnO toxicity inhibits reproduction of freshwater crustacean Daphnia magna
2024, Environmental PollutionFewer people would help preserve biodiversity: A response to Hughes et al. (2023)
2023, Biological Conservation