Studying longer-term effects on elephants from poaching
Jane Wynyard, Colorado State University
September 17, 2021
See link
https://phys.org/news/2021-09-longer-term-effects-elephants-poaching.html
for photo.
Poaching has longer-term effects on elephant populations than originally
thought, according to a pair of studies published recently by researchers
at Colorado State University and Save the Elephants.
This new research shows that orphaned juvenile elephants have less chance
of survival in a herd, and that losing them has a significant impact on
population growth or decline.
Conservation efforts have traditionally been informed by macro-scale
research of populations, said George Wittemyer, lead author of a study
published in Ecosphere and a professor at CSU.
The research team analyzed how the survival of different age groups affect
elephant population trends. Because older male elephants tend to reproduce
more than younger ones, and older females are the leaders of family groups
and social units, conservation biologists long assumed that the older age
group was most important to population trends. But the study showed that's
not the case.
Research Teams Used 20 Years of Data
Wittemyer and colleagues from Save the Elephants examined 20 years of data
collected in Samburu National Reserve in northern Kenya and looked at how
mortality of elephants at different ages impacted populations.
Juvenile elephants who are just starting to become independent of their
parents are the most important to elephant population dynamics, said
Wittemyer.
"If they're surviving well, the population is pretty buffered from
decline," he said. "If they start to decline, then you're in deep trouble."
The data also showed that human activity—specifically, wounding or killing
elephants—decreased survival of all ages in a population.
"Even for calves, which we don't think of as being targeted by humans for
ivory, their survival was really strongly driven by human impact on the
population," Wittemyer said. "Human impacts dominate anything else going on
in the population in terms of affecting survival."
Wittemyer said if conservationists or governments want to implement more
targeted actions, they need to know which animals in the population are
driving increases or decreases, which is why these studies are important.
Orphans Left Behind Struggle to Survive
Jenna Parker, who recently received a doctoral degree in ecology from CSU,
was the lead author of a study published in Current Biology that showed
poaching adult elephants not only directly lowers population growth, but
indirectly lowers it as well through the lowered survival of their orphaned
offspring.
Parker is currently a postdoctoral researcher at the San Diego Zoo Wildlife
Alliance.
"For social populations, poaching has a larger impact than originally
thought, because you have to account for the orphans who are left behind
who struggle to survive because they don't have a mother," Parker said.
Parker and her research team examined 20 years of monitoring data collected
by Save the Elephants and compared survival of young elephants who were
orphaned by poaching with those who were not.
They found that orphans had lower survival probabilities, and that lowered
orphan survival further exacerbated declines in populations caused by
poaching. And when poaching was more frequent, the effect of orphan
survival on these populations was greater. Even orphans who were no longer
dependent on their mother's milk had a lower survival rate than their peers
with a living mother, the study found.
"The total impact of poaching is greater than was originally recognized,"
Parker said. "In populations that we think have undergone a lot of
poaching, even as the poaching slows, we still need to consider its
residual effects."
The two studies highlight the impacts of poaching on elephant behavior, and
in turn, on elephant demographics.
"Killing an elephant is not removing one elephant from a population;
killing an elephant has downstream effects on those elephants that are
bonded to it," Wittemyer said. "These papers give us high-resolution
information on elephant demographics that help us to better understand the
decline and recovery processes of elephant populations."
*More information: *Jenna M. Parker et al, Poaching of African elephants
indirectly decreases population growth through lowered orphan survival,
Current Biology (2021).
DOI: 10.1016/j.cub.2021.06.091
Journal information: Current Biology, Ecosphere
https://phys.org/news/2021-09-longer-term-effects-elephants-poaching.html