People are living longer these days. That’s good, right? For us, yes. For species at risk, not so much.
That’s the conclusion of a new study by biologists from the University of California, Davis. Advances in medicine and science now allow humans to live longer than ever before. Unfortunately, human longevity has a direct and decidedly negative effect on endangered and invasive species.
The UC Davis team looked at 15 social, economic and ecological variables to determine their correlation with invasive and endangered species. Although human longevity hasn’t typically been a factor in studies about human impact to the environment, it turns out to be “the key predictor of global invasions and extinctions.”
“It’s not a random pattern,” said the study’s lead author, Aaron Lotz. “Out of all this data, that one factor — human life expectancy — was the determining factor for endangered and invasive birds and mammals.”
The study reviewed data from from 100 countries, spanning 74 percent of the total land area of the earth. This data represented 87 percent of the world’s total population and 43 percent of the world’s gross domestic product (GDP). Biologists focused on the following factors:
- Per capita GDP
- Export-import ratio
- Life expectancy
- Adult literacy
- Pesticide regulation
- Political stability
- Female participation in national government
- Energy efficiency
- Agricultural intensity
- Water stress
- Wilderness protection
The results showed in no uncertain terms that the places where people lead the longest lives are also the places with the most endangered and invasive species.
Where is this effect most clearly demonstrated? In New Zealand, which has the highest percentage of endangered animals and birds, the largest number of invasive species, and one of the highest life expectancies of any place in the world.
Conversely, African countries represent 23 of the top 25 countries with the fewest invasive and endangered mammals and birds. They have a closed trade policy and don’t engage in international trade to the extent the rest of the world does. These facts limit the ability of invasive species to hitch a ride into this area and claim a foothold.
The study revealed some interesting facts:
- As the affluence of a country increased, as measured by the GDP per capita, so did the percentage of invasive mammals and birds in that location.
- As biodiversity and land area of a country increased, so did the percentage of endangered birds.
- 25 countries did not have any reported invasive bird species; 13 of those countries did not have invasive mammals either.
- Sweden, Finland, Trinidad and Tobago, Switzerland and Nicaragua had the smallest percentages of endangered mammals.
- Cuba, the Dominican Republic, Sri Lanka and India had the highest percentages of endangered mammals.
- Ireland, Togo, the United Kingdom, Guinea-Bissau and Norway had the smallest percentages of endangered birds.
- New Zealand, the Philippines, the United States, Indonesia and Japan had the highest percentages of endangered birds.
- The percentage of invasive and endangered birds and mammals within a country was best predicted by a model that included only life expectancy.
The study concluded that increased life expectancy “means that people live longer and affect the planet longer; each year is another year of carbon footprint, ecological footprint, use of natural resources, etc. The magnitude of this impact is increased as more people live longer.”
“Some studies have this view that there’s wildlife and then there’s us. But we’re part of the ecosystem,” said Lotz. “We need to start relating humans to the environment in our research and not leave them out of the equation. We need to realize we have a direct link to nature.”
Yet again, there’s evidence that humans are the problem. We need to start coming up with ways to be the solution.