Population’s effects on biodiversity: evidence from recent scientific literature

By The Overpopulation Project | 11 July 2023
The Overpopulation Project

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A lot of great scientific work has been done lately on population and biodiversity, spanning all areas of the globe. A new study from TOP describes this work and summarizes its main lessons.

Earlier this year, Phil, Pernilla and Frank released A Bibliography of Recent Scientific Work on Population and Biodiversity Conservation as a TOP working paper. A revised and expanded version has now been published by the Indian Journal of Population and Development as Population Effects on Biodiversity and Climate Change: Evidence from Recent Scientific Literature, 2010-2022, adding several dozen new citations suggested by researchers working in this area.

The new publication presents its 154 studies, each providing significant analyses of the impact of human numbers on biodiversity, in a more useful framework than the working paper. Each entry is listed twice: once by geographical area and once in one of eight analytic categories: ecological restoration, deforestation, protected areas, warnings and policy recommendations, agriculture and biodiversity, large multi-author syntheses, defaunation, and general biodiversity loss.

Population Effects on Biodiversity and Climate Change makes six key findings regarding this recent literature.

  1. Much recent work has been done on population and biodiversity; more than in previous decades. Although there remains ideological resistance to writing about population matters, the obvious, ongoing failure of conservation efforts that ignore the fundamental drivers of biodiversity loss seems to have tipped the scales. Just as biologists are coming to recognise continued economic growth is incompatible with biodiversity conservation, they now are documenting the ways through which excessively large populations harm biodiversity.
  1. Population growth and high population densities are important drivers of deforestation, defaunation, and general biodiversity loss. It is striking that studies exploring the importance of population growth as a driver of biodiversity loss, and the importance of high population density as an impediment to conservation success, nearly always find their effects compelling. Many studies find population impacts as dominant in determining conservation success, particularly when paired with per capita resource consumption or the proportion of the landscape in protected areas. The rest reliably find an important effect of human population, whether focused on preserving birds, mammals, fishes, insects, or plants.

  1. Smaller human numbers and lower human population densities increase chances to establish protected areas (PAs) and increase the effectiveness of PAs in preserving biodiversity. There are many reasons for this. More people make it harder to establish protected areas. They also increase poaching in and near PAs; decrease support for existing PAs; undermine connectivity between PAs; and increase harvesting of essential resources in PAs. Increasing the size, number and effectiveness of PAs is necessary for preserving the remaining biodiversity on the planet. The biodiversity benefits of smaller human populations are, therefore, clear.
  1. Decreasing human populations foster success in ecological restoration as they open up new areas as candidates for restoration and make such efforts more likely to succeed. The decreasing extractive economic opportunities associated with depopulation may increase willingness among local residents to try new approaches to living with wildlife.

  1. Larger populations increase agriculture demand and hence lead to the conversion of forests, wetlands, and other biodiverse ecosystems for agricultural use. In this way, population growth fuels a leading cause of biodiversity loss through agricultural (and aquacultural) conversion. Similarly, population growth increases urban development, which is another important cause of habitat loss and habitat degradation leading to significant biodiversity loss.
  1. Since large human populations cause biodiversity loss while small populations foster biodiversity protection, future human numbers will play an important role in building our capacity to preserve biodiversity going forward. This is true at all scales, from the local to the global. Studies from many parts of the world suggest this for particular taxa and for preserving biodiversity in general. The present review suggests that growing numbers of conservation biologists are making this connection explicit and are willing to advocate policies to curb or reduce human numbers.

To summarise, the published scientific literature on human population’s effects on biodiversity suggests that continued human population growth and high population densities are major causes of biodiversity loss, and, therefore, smaller human populations are necessary to preserve the biodiversity that is left on the planet.

Reprinted with permission from Frank Götmark – Project leader of The Overpopulation Project (TORP); Professor, Animal ecology and Conservation Biology, University of Gothenburg.

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