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Is There a Link Between Biodiversity Loss and Economic Inequality?

Publié le 1 juin, 2008 | Pas de commentaires

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By examining economic distribution in various countries, can we better understand the impact these countries have on their indigenous plant and animal species? Recent research suggests that we can1. A consideration of income inequality may improve our ability to predict how much of the flora and fauna in a given country is threatened with extinction, suggesting that economic distribution has an important effect on how we interact with the broader ecosystems upon which our societies depend2.

Dan McKay, Biodiversity, 2007
Certains droits réservés.

The Earth’s biodiversity is in a constant state of change: populations of some organisms increase while others decline, and new species evolve while others become extinct. In recent decades, however, the balance between the generation of new species and the extinction of others has been greatly altered. Species extinctions are 100 to 1000 times more frequent now than they were at any point in time since the last mass extinction 65 million years ago2. Although there is still some debate over the causes of that pre-historic event, we know that current trends are brought about primarily by human activity2. These rapid extinctions are likely to harm human welfare by undermining the stability of the ecosystems that we depend on for food, climate regulation, and other benefits3.

The human activities that are most responsible for biodiversity loss are the destruction and degradation of habitat, the over-harvesting of species, the introduction of invasive species, and pollution2. Although these factors are relatively well understood, it is often difficult to determine their underlying social and economic causes. Why is it that certain societies degrade more habitats and exploit species less sustainably than others? Many have tried to answer this question, with many of the proposed answers focusing on the density of a society’s human population and its economic wealth4. It has frequently been suggested that a society with more people and greater economic activity will extract more resources from the environment and produce more waste. However, human societies of similar population density and wealth can be structured very differently. The impact that a society has on the biodiversity of the surrounding ecosystems may be better understood by examining the distribution of wealth among members of that society1.

How does inequality in a society affect the diversity of other species?

There are opposing theoretical viewpoints on the nature of the relationship between socio-economic inequality and its environmental impact. One of the first scholars to consider the issue, Mancur Olson, suggests that greater inequality could be beneficial for the environment. He proposes that the smaller a group in control of a certain resource is, the greater that group’s incentive and ability would be to manage the resources well 5. To illustrate this perspective, consider how a large amount of Europe’s forested land was protected from deforestation because it had historically been preserved as hunting grounds for the wealthy nobility 6. Garrett Hardin, in his famous paper “The Tragedy of the Commons,” lends support to this idea by arguing that the resources to which all members of a community have equal and open access are doomed to over-exploitation and degradation 7.

Another body of literature, however, argues that the theory put forward in the “Tragedy of the Commons” is an over-simplification, and that Hardin does not pay sufficient attention to the ability of people to establish systems and institutions to collectively manage their environment 8. When the importance of collective action is considered, the relationship between inequality and how a society interacts with its environment may be very different. Groups that are more equal tend to be more effective at acting together for mutual benefit because there is a greater overlap of priorities between individuals. Social cohesion may be stronger overall 9. In unequal societies, powerful groups are able to profit from resource extraction and degradation, while insulating themselves from the environmental costs. Weaker groups are often more vulnerable to environmental damage; however, they will have less ability to protect their interests 10.

A relationship between equality and social functioning has been demonstrated in the environment and other fields. Epidemiological work has empirically shown that unequal societies fare worse than egalitarian ones when various health issues are measured 11. Recently, a pattern of correlation between economic inequality and biodiversity loss has been shown to exist among countries, as well as among states within the United States. This correlation was not linear, but rather became even more pronounced at higher levels of economic inequality 12. Our study builds upon this research by taking a larger set of countries, testing how well we can predict biodiversity loss using different sets of socio-economic variables, and then testing to see if the inclusion of economic inequality improves our predictions in a meaningful way.

How biodiversity is measured

As an indicator of biodiversity in each country, we use IUCN (International Union for Conservation of Nature) Red Lists 13. These provide data on the number of species of plants and animals in each country, and identifies the number of those that are threatened with extinction 14. By taking the proportion of the species that are threatened, we can estimate the status of biodiversity as a whole in a given country. The IUCN also provides information on how many species are endemic—that is to say, species that can only be found in the country in question. This is important to consider when measuring trends in biodiversity because species that are found exclusively in a given country are, in general, more likely to be at risk of extinction than species that are more widespread. We would therefore expect countries with many endemic species to have a higher proportion of threatened species. For this reason, when we used economic inequality and other socio-economic data to predict biodiversity loss, we also took into account the proportion of endemic species in each country.

How socio-economic indicators are measured

A set of four simple indicators is used in our study to characterize societies and their economies. Population is measured as density (the number of inhabitants per unit of area) so that it is more indicative of the human pressure on the land 15. The level of economic activity is represented by gross domestic product (GDP) per capita, which is the total value of all economic transactions in a country per year divided by the population 16. Inequality in society is represented by income inequality, for which data is more relatively available than for other options such as the distribution of assets or of power 17. Finally, a measure of environmental governance is used in order to quantify how efficiently a society uses its natural resources 18. Together, these variables are similar to those used by the IPAT framework developed by Ehrlich and Holdren 19. The IPAT framework posits the idea that a society’s impact (I) on the environment is a function of its population (P), its affluence (A), and the kind of technology (T) predominant in its economy.

Figure 1
Upper Map: Percentage of Species Threatened by Country13
Lower Map: Income Inequality by Country17,20
(Maps created by author)

How time-lags in environmental effects are considered

Biodiversity loss is not an instantaneous process. For example, if large-scale logging severely reduces forest cover in a country, species will not immediately become extinct. Rather, their populations will experience a state of decline, and may become endangered or extinct only years later. To account for this time-lag between human activity and measurable impacts on biodiversity, our study uses human population density, GDP, and inequality data from a series of five-year periods between 1975 and 1999 and compares the results. These periods show relatively similar patterns; however, data from the five-year period from 1980 to 1984 were the strongest predictors of biodiversity status in 2007.

Comparing different hypotheses

We tested four different hypotheses of what determines biodiversity loss. These hypotheses were that the most important predictor was either (a) population density alone, (b) GDP per capita alone, (c) population density plus GDP per capita combined 21, or (d) environmental governance. We ran each of these four models both with and without economic inequality included 22. This allowed us to see if considering economic inequality improves our ability to predict biodiversity loss in a meaningful way 23.

Two key conclusions arose from the comparison of these models. The first was that the size of the economy is a better predictor of biodiversity loss than either population density or environmental governance. The best of the aforementioned models was the one that included only GDP per capita. It outperformed models (a) and (d) by a wide margin. Surprisingly, however, higher GDP was associated with a lower proportion of threatened species. This is the opposite of what we would expect if we were to assume that more intense economic activity would lead to negative pressures upon non-human species.

The second important conclusion from this testing is that economic inequality is a strong predictor of biodiversity loss. In all four models, adding the variable of inequality significantly improved our prediction of biodiversity loss, and in three of the four—the exception being the environmental governance model—the term itself was statistically significant. In all the models, inequality was associated with higher levels of threatened species. The relationship was quite strong. The results of the best performing model—GDP and inequality—suggests that an increase in economic inequality equivalent to the increase that occurred in the United States between 1990 and 1997 would be associated with a ten percent increase in the proportion of the species threatened 24.


The loss of biodiversity is one of the most serious environmental problems we face today, particularly because it is irreversible. In the words of biologist E. O. Wilson:

The one process now going on that will take millions of years to correct is the loss of genetic and species diversity by the destruction of natural habitats. This is the folly our descendants are least likely to forgive us 25.

Although we generally understand the direct natural processes behind current extinction rates, our understanding of their underlying socio-economic drivers is still weak and needs to be improved in order for us to more effectively combat future biodiversity loss. To simply consider the magnitude of human economic activity as a predictor of our impact on plant and animal species is insufficient. We must also focus on how socio-economic benefits are shared, suggesting that if societies can achieve a more equitable distribution of their resources, they will be taking a step towards easing the harm they are doing to other species.


1. The relationship between inequality and biodiversity is examined further in a study written by my colleagues and myself: Holland, T., Peterson, G.D., and Gonzalez, A. “Economic inequality and biodiversity loss: a cross-national survey” (in preparation).
2. Millenium Ecosystem Assessment. Ecosystems and Human Well-Being: Biodiversity Synthesis. 2005. [on line] http://www.maweb.org (last accessed: 18 May 2008).
3. Chapin, F.S., Zavaleta, E.S., Eviner, V.T., Naylor, R.L., Vitousek, P.M., Reynolds, H.L., Hooper, D.U., Lavorel, S., Sala, O.E., Hobbie, S.E., Mack, M.C., Diaz, S. “Consequences of Changing Biodiversity.” Nature 405.234 (2000): 234-242; Tilman, D. “Causes, Consequences and Ethics of Biodiversity.” Nature 405.208 (2000): 208-211; Millenium Ecosystem Assessment (2005).
4. For example, see York, R., Rosa, E.A., and Dietz, T. “Footprints on the Earth: The Environmental Consequences of Modernity.” American Sociological Review 68.2 (2003): 279-300. Also see references given in footnotes 15 and 16 below.
5. Olson, M. The Logic of Collective Action: Public Goods and the Theory of Groups. Cambridge, MA: Harvard University Press, 1965.
6. Williams, M. Deforesting the Earth: from prehistory to global crisis – an abridgement. Chicago: University of Chicago Press, 2006.
7. Hardin, G. “The Tragedy of the Commons.” Science 162 (1968): 1243-1248.
8. Dietz, T., Ostrom, E., and Stern, P. “The Struggle to Govern the Commons.” Science 302 (2003): 1907-1912; Klooster, D. “Institutional Choice, Community, and Struggle: A Case Study of Forest Co-Management in Mexico.” World Development. 28.1 (2000): 1-20.
9. Ostrom, E. Governing the commons: the evolution of institutions for collective action. New York: Cambridge University Press, 1990; Ostrom, E. “Reformulating the Commons.” in Protecting the Commons: a framework for resource management in the Americas. Eds. Burger, J., Ostrom, E., Norgaard, R.B., Policansky, D., Goldstein, B.D. Washington DC: Island Press, 2001.
10. Boyce, J. “Inequality as a Cause of Environmental Degradation.” Ecological Economics 11.3 (1994): 169-178.
11. For a review, see Wilkinson, R.G. and Pickett, K.E. “Income Inequality and Population Health: A Review and Explanation of the Evidence.” Social Science & Medicine 62.7 (2006): 1768-1784.
12. Mikkelson, G., Gonzalez, A., and Peterson, G.D. “Economic Inequality Predicts Biodiversity Loss.” Public Library of Science One 2.5 (2007) [on line] http://www.plosone.org/article/fetchArticle.action?articleURI=info:doi/10.1371/journal.pone.0000444 (last accessed: 18 May 2008).
13. IUCN (International Union for Conservation of Nature). Red List of Threatened Species. 2007. [on line] http://www.iucnredlist.org/info/stats (last accessed: 18 May 2008).
14. The IUCN’s measure of threat to a particular species is established at a global level, not a national one. Data on whether or not a species is threatened in a particular country does not exist on a broad scale, and so we must use information on the global status of species., This poses a challenge for this analysis; however, this fact should not affect countries differentially and thus bias our results in one direction over the other. It will likely make any relationship between inequality and biodiversity loss more difficult to detect.
15. There has been a long-running debate on the effect of population density on the environment. Many authors have assumed that more people on the land implies more environmental pressure; however, others have countered that a larger population promotes more efficient use of resources, both out of necessity and because of greater human capacity. For presentations of the two opposing sides of this discussion, see Ehrlich, P. The Population Bomb. New York: Ballantine Books, 1968; and Bosserup, E. The Conditions of Agricultural Growth: The Economics of Agrarian Change under Population Pressure. New York: Aldine Publishing Co., 1965. A case study providing evidence for Bosserup’s position (that more people can be good for the environment) is Tiffen, M., M. Mortimore, and F. Gichuki. More People, Less Erosion: Environmental Recovery in Kenya. Chicester, UK: J. Wiley, 1994.
16. There is debate on the relationship between the size of an economy and environmental degradation. Some environmental indicators seem to deteriorate continuously as the economy grows, while others have shown evidence of improving above a certain economic threshold; the latter trend is referred to as the Environmental Kuznets Curve (EKC) hypothesis. Whether or not this is a reliable hypothesis is an interesting question; generally, the EKC seems to hold true for only a few specific environmental indicators, particularly those that are relatively localized and that can be controlled with technology rather than those that require reductions in consumption. For a good general review of the EKC discussion, see Stern, D. “The Rise and Fall of the Environmental Kuznets Curve.” World Development. 32.8 (2004): 1419-1431. In general, because of its cumulative nature—a species lost in early stages of economic development can not come back in later stages—and because of the lack of any easy “techno-fix,” it would be surprising if the EKC was a useful model for biodiversity.
17. Income inequality is measured using the Gini index. This is a measurement that ranges in theory from 0 to 100, where 0 is perfect equality (all individuals have identical income) and 100 is perfect inequality (one individual has all of the income). In practice, the index ranges from a low of 23 for Slovakia to a high of 59 for Brazil (1995-99 data).
18. Population density and GDP data were obtained from the World Resources Institute’s Earth Trends database [on line] http://earthtrends.wri.org (last accessed: 18 May 2008). Income inequality data comes from the Standardized Income Distribution Database (SIDD) of the Pitt (University of Pittsburgh) Inequality Project. [on line] http://www.pitt.edu/~inequal 18 May 2008. Environmental governance is a composite indicator from 2005 calculated by the Yale Environmental Performance Measurement Project. [on line] http://www.yale.edu/esi (last accessed: 18 May 2008).
19. Erlich, P. and J. Holdren. “Impact of Population Growth.” Science 171 (1971): 1212-1217.
20. Average of values between 1980-84. Data source: Pitt Inequality Project. [on line] http://www.pitt.edu/~inequal (last accessed: 18 May 2008).
21. By combining population density (number of people per unit area) with GDP per capita (economic activity per person) we created a model that quantifies the economic intensity per unit area. This could be thought of as the ‘economic footprint’ of a society.
22. Models were evaluated using ordinary least squares (OLS) multiple regression.
23. Whether or not the improvement to the model was “meaningful” was judged using a statistical tool called Aikike’s Information Criterion (AIC). AIC is used to determine which one in a group of models is the best at explaining a given data set. It takes into account two factors: the total explanatory power of the model, and the number of predictor variables in the model. The inclusion of more variables will always improve explanatory power, no matter how spurious the newly included variables may be. The AIC therefore penalizes models with more variables, and identifies models which are the most parsimonious (meaning that they explain the most variation in the indicator of interest while still remaining as simple as possible).
24. Between 1990 and 1997, the USA experienced a five-point increase in the Gini index, from 44 to 49.
25. Wilson, E. O. Biophilia. Cambridge, MA: Harvard University Press, 1984. 121.

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