Today—May 17, 2019—is Endangered Species Day, a day where conservation efforts to protect the United States’ endangered species and their habitats are recognized and observed.
On this day, we should also cast our view wider, as scientists at the Smithsonian Institute have done in proposing a “demographic safe space” for Asian elephants and, ultimately, for other large, slow-breeding species.
“Critical thresholds in so-called vital rates—such as mortality and fertility among males and females of various ages—can signal an approaching population collapse before numbers drop below a point of no return,” said Dr. Shermin de Silva, president and founder of Trunks & Leaves, an organization dedicated to the conservation of Asian elephants. “We propose that conservation efforts for Asian elephants and other slow-breeding megafauna be aimed at maintaining their ‘demographic safe space’; that is, the combination of key vital rates that support a non-negative growth rate.”
These key vital rates governing population growth, the researchers found, are a better indicator of a species’ viability than short-term trends in population size and distribution.
“History bears this out,” de Silva said. “Genomic studies of the last mammoths isolated on Wrangel Island—between Russia and Alaska—have shown that although they were able to persist for thousands of years beyond the extinction of mainland populations with just 300 individuals, they had accumulated numerous genetic mutations that may have eventually contributed to their extinction.”
In other words, a population of animals can continue to reproduce even though they become “biologically unviable” long before they disappear from the face of the earth.
With that in mind, the researchers turned their gaze to mammoths’ descendants, the elephants.
Asian elephants are classified as “endangered” under the IUCN Red List because populations are thought to have declined by at least 50 percent in less than a century. Not only that, but Asian elephants breed very slowly; most cows produce just one calf in six years or more. There are fewer than 500,000 of them alive today.
While African elephants face extinction due to the horrific practice of killing them just to get their ivory tusks, the vast majority of Asian elephants don’t have tusks. The problem they face is habitat destruction, followed by illegal trade in live animals and parts.
“Habitat loss can create something known as ‘extinction debt’ by slowing down birth rates and increasing mortality rates. For slow-breeding, long-lived species, even incremental changes make a big difference, but their longevity can obscure the risk of extinction,” de Silva said.
Asian elephants aren’t the only megafauna that could benefit from “demographic safe space.” Giraffes, rhinos, Bactrian camels, and eastern gorillas could also benefit from modeling the interaction between vital rates. Data for these species in the wild is scarce, but, the authors of the study suggest, there is an urgent need to get that data.
“Rather than rely on simple population counts or estimates of near-term extinction probability, we urge that conservation resources for slow-breeding megafauna also be invested in identifying demographic tipping points and how to maintain populations within their safe spaces,” de Silva concluded.
Photo: Two Asian elephants in a river in Thailand. Credit: Shutterstock