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What Happens When Forest Elephants Are Wiped Out in an Ecosystem?
As go the
elephants, so go the trees. That’s the message of a new study published in the
May 2013 issue of Forest Ecology and Management that found more than a dozen
elephant-dependent tree species suffered catastrophic population declines in
new plant growths after forest elephants were nearly extirpated from their
ecosystems. The fruit-bearing trees all rely on forest elephants as their
primary means of seed distribution, a process known as megafaunal dispersal
syndrome.
The study was
conducted in Salonga National Park in the Democratic Republic of the Congo, a
region where more than 98 percent of the forest elephants (Loxodonta cyclotis) have been
killed by poachers over the past few decades. “As an ecologist studying
plant–animal interactions, I was really worried about elephant survival and the
plants that had coexisted with them for a million years,” says the paper’s lead
author, David Beaune, a research associate with the
Biogeoscience Laboratory at the University of Burgundy in France and the Max
Planck Institute for Evolutionary Anthropology in Germany. “I started to assess
the trees that required elephants for seed dispersal, and I became increasingly
worried with time when I did not find any evidence of new growths. We decided
then to study if those plant species were able to survive without their seed
dispersal partner, the elephant.”
Elephants, with their massive
appetites, play two key roles for many of these trees. For one thing, forest
elephants roam over large swaths of land, spreading seeds far and wide via
their dung. For another, previous research has shown that seeds that have been
softened by an elephant’s stomach acids tend to germinate at a much faster rate
than seeds that have not. This dual relationship allows fruit trees with no
other dispersal partners to ensure reproduction.
The researchers conducted their
study at the LuiKotale Research Site, where data on medicinal plants has been
actively collected since 2002. They found that 18 different elephant-dependent
tree species at that location had dropped in productivity; 14 of those species
were not producing enough new trees for to replace the old ones as they die
off, a process known as self-replacement.
The loss of these
trees could have wide-ranging ecological effects. “These trees also feed many
herbivores and frugivores such as bats, birds, insects and other mammals,”
Beaune says. “Consequently, the loss of these tree species can affect them.”
For example, chimpanzees and bonobos in certain forest areas rely on the fruit
of one of the elephant-dependent trees, Irvingia gabonensis, for months at
a time. (Bonobos also play an important seed-dispersal role, which Beaune and
his fellow researchers are studying.)
Human populations could also
suffer, Beaune says, as many of these trees have long been used for traditional
medicine. “Local people have barely any access to Western medicine,” he says.
“They rely on traditional use of plants such as these trees that have not yet
revealed all their secret molecules to modern science.”
At least one of the
tree species mentioned in the study, Autranella congolensis, is already listed as critically
endangered due to habitat loss. Efforts could be taken to preserve and protect
it and the other tree species, but would such efforts be effective if elephants
are not part of the equation? “This is a big issue in conservation biology,”
Beaune says. “The protection of an area is useless if the ecological
functionality is not maintained. In the case of Autranella congolensis,
imagine a special reserve dedicated to their conservation which contains big,
healthy adult trees and no elephants! The conservation plan could be severely
compromised.”
In their paper Beaune and his
co-authors recommend that artificial nurseries be established to preserve some
of these tree species as well as call for increased law enforcement to protect
forest elephants and reintroduction programs to bring them back.
Elephants are about as
charismatic as endangered megafauna get and therefore are an emotional issue
for a lot of people. Plants rarely engender as much passion. Even if they did,
it might not be enough. “Unfortunately the sole emotional value of a species
hardly helps them to survive our strange era,” Beaune says.
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