A new study by researchers from the National Evolutionary Synthesis Center in Durham, North Carolina, US, has revealed how reproductive speed prevents large grazing animals such as deer and antelope, that are regularly hunted by humans, from becoming extinct.
The study revealed that though habitat loss and living in a limited geographic area does pose significant risks for extinction of a species, but under pressures of hunting, it's reproductive speed with which they proliferate that really matters; the slower the reproductive cycle, the higher the risk of extinction for large grazing animals, said evolutionary biologist Samantha Price, a postdoctoral fellow at the National Evolutionary Synthesis Center in Durham, North Carolina.
According to her, this key variable also explains, for example, why the American bison was nearly wiped out in just a few years of intense hunting pressure, with relatively slight habitat change, compared to the white-tailed deer that continued to grow in large numbers despite hunting and suburban sprawl.
"The bison nurses its young for 283 days on average; the deer just 80," said Price in her study, which appears online in the May 16 issue of the journal Proceedings of the Royal Society B.
As part of her study, Price did a complex statistical analysis of 144 species of hoofed mammals, including pigs, llamas, cattle, sheep, goats and antelopes, combining a global list of threatened species with data on hunting, land use and the animals' reproductive rates.
She found that where hunting isn't a factor, habitat loss is the biggest issue. But whether the threat comes from hunting or habitat destruction, extinctions are "all human-caused at some level".
The worst-case scenario, she said, is where humans are expanding into an area and changing its habitat, and hunting the indigenous animals as they go.
"Three areas of the world - West Africa, Indonesia and Malaysia, and South America - are "hot spots" for hunting, and many species in these areas are threatened. The poorer the country, the greater the threat," she said.
According to her, regional military conflicts also turn up the heat on species, as people in strife-torn areas increasingly turn to "bush meat," including hoofed animals, to supplement their diets.
"Since these are large, plant-eating animals, they have a significant effect on the local ecology. These animals help disperse plant seeds through their manure and keep plant growth in check. You can completely change the ecosystem without knowing it if you hunt these animals to extinction," Price said.