Overpopulation is a major cause of biodiversity loss and smaller human populations are necessary to preserve what is left

https://doi.org/10.1016/j.biocon.2022.109646Get rights and content

Highlights

  • Global biodiversity decline is driven in large part by excessive human populations.

  • Population decline opens up important opportunities for ecological restoration.

  • Further research is needed into how human demographic changes help or hinder conservation efforts.

  • Conservation biologists should advocate for smaller populations, in both less developed and more developed nations.

Abstract

Global biodiversity decline is best understood as too many people consuming and producing too much and displacing other species. Wild landscapes and seascapes are replaced with people, our domestics and commensals, our economic support systems, and our trash. Conservation biologists have documented many of the ways that human activity drives global biodiversity loss, but they generally neglect the role of overpopulation. We summarize the evidence for how excessive human numbers destroy and degrade habitats for other species, and how population decrease opens possibilities for ecological restoration. We discuss opportunities for further research into how human demographic changes help or hinder conservation efforts. Finally, we encourage conservation biologists to advocate for smaller populations, through improved access to modern contraception and explicit promotion of small families. In the long term, smaller human populations are necessary to preserve biodiversity in both less developed and more developed parts of the world. Whether the goal is to save threatened species, create more protected areas, restore degraded landscapes, limit climate disruption, or any of the other objectives key to preserving biodiversity, reducing the size of the human population is necessary to achieve it.

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.

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