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

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.

by The Overpopulation Project

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.
A forest road in the Amazon jungle in Belterra, Pará, Brazil. This forest was studied by Ahmed et al. (2014) to show the negative impact of road networks on Amazonian bird communities. Photo: cropped from Freitas et al. (2019)
  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.
A satoyama landscape near Aikawa on Sado island, Japan. The island has experienced continuous depopulation and one of the results is a shift in value orientations and transition to more nature friendly agriculture. This type of agriculture can benefit animals such as the endangered toki, or Japanese crested ibis (Nipponia nippon), whose only remaining habitat in Japan is Sado. Photo: Peter Matanle (2017)
  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.

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

  1. While I agree, I find this too simplistic and one-sided. Overall global decline in population and consumption would be a net positive, but it hasn’t happened yet, and what we’ve seen from local depopulation sometimes is only deceivingly positive.

    Like Japan, my country, Italy, has seen a decline in population in certain rural areas. Overall I would say it’s often a good thing locally, since marginal and fragile ecosystems have rested and reforested, BUT:

    – we’re substituting and importing from abroad what we aren’t producing ourselves anymore. “Extractive industries” don’t end, they merely relocate. Someone should look at the overall impact of ceasing local production and switching to imports, and it’ probably negative (e.g. cutting a tree behind your home vs importing gas or plastic, shearing your own sheep vs wearing synthetic imported clothes, importing soy from the Amazon instead of cutting hay, glyphosate-treated Canadian wheat vs our own etc)

    – similarly, people who have left and moved to the cities have destroyed nature around urban settlements, and increased their overall consumption. They’ve also kept many rural homes as property

    – some types of biodiversity have been lost this way (e.g. meadow species)

    – not having local governance is risky; rewilding, like I always say, should be natural and not imposed. Many rural dwellers feel they have lost political clout by losing numbers, and policies have been imposed on them by the more numerous city dwellers. The impact has been very negative on both people and biodiversity (see the point above, also things like hydropower in “depopulated” valleys, tourism which can be worse than traditional activities…) If rural inhabitants are not represented and ruled over, this creates an incentive to increase population again

  2. Hi Gaia, thanks for comments, some problems always remain and need to be solved. Note, the content of all these papers is very broad, and we feel it is important to make clear how much population growth (also linked to growth in consumption) has reduced biodiversity, all these species that we share this planet with… Ethical aspects are central, otherwise we would have no good compass for conservation work. Of course, due to all people, with all wishes, it is not going to be easy to repair the damages we have caused on many types of ecosystems. Rewilding initiatives not under law probably work best as national populations decreases, like in Japan, South Korea, the Baltic countries, etc. Perhaps Japan may be the most important ‘test case’. But legally protected areas generally have strong support among citizens in most countries, and produce value also through tourism.

    Rewilding is (one) part of nature restoration, for which the EU parliament just passed a new initiative. It will probably be handled differently depending on country within the EU. See news here
    https://www.theguardian.com/world/2023/jul/12/eu-passes-nature-restoration-law-vote-meps

    Frank

    1. It is an extraordinarily complicated situation. I follow the Italian farming lobbies and when I see what they lobby for, sometimes I agree, sometimes I am horrified.
      It’s the same when I talk to rural dwellers. Sometimes I think they are unfairly ignored and their legitimate interests overlooked; sometimes it maddens me that they don’t realise how wasteful and outsized their lifestyle is.
      We need to speak to each other, about everything, all the time, or resentment will breed and we’ll end up, at the very best, like the Netherlands.

    2. As for the EU, if they are not willing to both reduce overall population and stop aiming for economic growth, they can pass all the laws in the world to protect nature, it’s only going to cause more conflict.
      I’ve seen the effects on the ground of their policies and they are very rarely positive.

      1. You are right in that most of the EU farmland support goes to the big farms, paid per hectare if I remember correct. But here in Sweden, with respect to nature conservation work, EU is a positive thing! The law surrounding Natura2000 is strong, and without EU support to rural farmland conservation actions (e.g. semi-natural pastures), much less of that would have existed here. EU pays half, the Swedish state pays half. Without the EU, even less than half would probably have existed. Much of forest, lakes etc are both nature reserves (about 5000) and Natura 2000 at the same time, law+law. Moreover, EU species protection (eg nesting birds) by Natura 2000 is very strong (eg for woodpecker). Recently, it turned out that EU may prohibit clear-cutting while birds are nesting.

        Frank

  3. You have a few sober scientists, let’s call them undertakers, writing up the bleeding-obvious relationship between the eight billion humans and the world rape of biodiversity.

    Then you have the thundering herd of scientists, lost their minds over United Nations Net Zero. Which wasn’t even a thing, ten years ago. That’s what’s so wonderfully handy about “green activists” for social justice. They almost render the Koch Brothers superfluous.

  4. Frank, I don’t know about Sweden and I don’t have a hard time believing things work well in your country. Italy on the other hand is very corrupt; it’s not just about the money going to big farms and intensive animal farming, which happens everywhere, but also things like money for “pasture” being taken by criminals and mafia, just to name one. Crazy bureaucracy to “plant” woodland, money given for totally questionable things like grazing donkeys in the forest (why??), etc. Some nature protection works, but I’ve personally seen a “restored” woodland on degraded farmland, in our low lying plains, in itself a good thing, which was mulched with… plastic! No one comes look how the money is spent, so they can do whatever.
    It’s not 100% fair to blame the EU, because we all can see things working differently in other EU countries (even just Austria, right here), but being in the EU doesn’t help, either.
    I’ve written a whole book on agricultural subsidies, but unfortunately it’s only available in Italian. It’s one of the worst policies you can imagine and I think they should be scrapped altogether. Let farmers be farmers, I say, without any subsidy, and protect nature with separate laws.
    If look at the whole picture, and not just a few laws here and there, I’d say the whole thing is mostly a farce. We are not really protecting anything, we’re just importing from somewhere else and appeasing the worst lobbies, such as intensive animal farming.

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