IN 1981, NOTORIOUS
drug lord Pablo Escobar
imported four hippos from
Africa to his estate near
Medellín, Colombia. Af-
ter his death in 1993, the
herd meandered into the
nearby Magdalena River.
Ecologists estimate there
are now 65 to 80 swimming
around, and that number
could reach 800 by 2050.
Introducing new species
often causes environmen-
tal mishaps. Toads releasedto eat crop-loving beetles
took over Australia, and ivy
brought to the New World
for decoration has toppled
native trees. But some ecol-
ogists think these hippos
may have happened upon
a valuable role: 100,
years ago, semiaquatic
hoofed mammals roamed
South America, and Esco-
bar’s pets may be filling the
niche they left behind. Here
are four ways they’re shap-
ing their environment.OVERVIEWby GRACE WA D E / illustration by JACQUELINE OAKLEYhungry hungry
hippos
A/Forging paths
At a whopping 3,500 pounds
each, hippos’ bodies are able to
create trails through shallow
rivers, altering flow. This forms
stream-like waterways where
small fish can hide from preda-
tors. Their survival supports
a diverse ecosystem, which is
generally more resilient than
one with fewer species.D/Stomping around
The hooves of these chunky
beasts dredge up sediment
along waterbeds, resuspend-
ing organic matter that algae
living close to the surface can
feed on. All this stomping
also forms small, deep pools
where fish can find shelter
during the dry season when
the river level drops.C/Fueling fish
Hippopotamuses expel waste
while wading, and their poop
provides a feast for aquatic
microorganisms—and in turn a
boost for the fish that eat them.
But invasive animals never
come without complications;
waste can also prompt algae
blooms that drop oxygen levels,
killing swimmers en masse.B/Snacking on shrubs
In Africa, these ungulates’
hefty appetites keep grass
height in check, spurring new
growth. Fresh sprouts are
lower in fiber and higher in
nutrients like nitrogen, making
them the perfect snack for
smaller grazers like vicuna.
A similar, unconfirmed effect
may be at play in Colombia.12 WINTER 2020 / POPSCI.COMABCD