Human Life Expectancy Linked to Number of Invasive and Endangered Species

As human life expectancy increases, so do the number of invasive and endangered birds and mammals, according to researchers at the University of California, Davis.

Published in the journal Ecology and Society, the study included a total of 100 countries accounting for roughly 87 percent of the world's population, 43 percent of global GDP and 74 percent of the Earth's land area. The researchers examined a combination of 15 social and ecological variables, including tourism, GDP, water stress and political stability, and then analyzed their correlations with invasive and endangered birds and mammals.

Based on the results, the researchers determined that human life expectancy was the greatest predictor of global invasions and extinctions.

"It's not a random pattern," said lead author Aaron Lotz, a postdoctoral scholar in the Department of Wildlife, Fish and Conservation Biology when the study was conducted. "Out of all this data, that one factor -- human life expectancy -- was the determining factor for endangered and invasive birds and mammals."

New Zealand, the United States and the Philippines exhibited the highest percentages of endangered and invasive birds, the researchers found. African countries, in contrast, had the lowest percentage of invasive and endangered birds and mammals. The researchers attributed this latter finding to the fact that these nations have very little international trade, limiting the venues of biological invasion.

New Zealand had the highest percentage of all endangered and invasive species combined, which the scientists report is largely the result of a lack of native terrestrial mammals. According to the study, in the past 700 to 800 years since the country was colonized, it has undergone a massive invasion by non-native species, spurring a significant loss in biodiversity.

"Some studies have this view that there's wildlife and then there's us," Lotz said. "But we're part of the ecosystem. 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."