The common hippopotamus (Hippopotamus
amphibius), or hippo, is a large, mostly herbivorous mammal in sub-Saharan
Africa, and one of only
two extant species in the family Hippopotamidae, the other being the pygmy
hippopotamus (Choeropsis
liberiensis or Hexaprotodon liberiensis). The name comes from the ancient Greek for "river horse" (ἱπποπόταμος). After
the elephant and rhinoceros, the common hippopotamus is the third-largest type
of land mammal and the
heaviest extant artiodactyl.
The
hippopotamus is considered very aggressive and has frequently been reported as
charging and attacking boats. Small boats can be capsized by hippos and
passengers can be injured or killed by the animals or drown. In one case in
Niger, a boat was capsized by a hippo and 13 people were killed. As
hippopotamuses will often engage in raiding nearby crops if the opportunity
arises, humans may also come in conflict with them on these occasions, with
potential for fatalities on both sides.
Notwithstanding
its aggressive nature, do you know that the hippo plays a significant role in
the food chain? Let me share the following story with you, for that matter:
The common hippopotamus can spend
up to 16 hours a day immersed in rivers and lakes. Lumbering out of the water
at night, these herbivores graze on tropical grasses and consume 80 to 100
pounds in one meal. Now, a new study shows the ecological importance of
hippopotamus-vectored subsidies.
By daybreak,
having eaten their fill, they return to their daytime resting area to rest,
digest and, eventually, eliminate. This natural process results in millions of
tons of hippo dung entering Africa's aquatic ecosystems every year.
However, as
distasteful as that might seem, the hippos' deposits actually serve an
important ecological function. A new study by UC Santa Barbara's Douglas
McCauley and colleagues reveals that the organic matter produced by hippos is a
source of nutrition for a variety of river fish and aquatic insects. The
researchers' findings appear today in the journal Ecosphere.
"The
ecological importance of hippopotamus-vectored subsidies has been widely
speculated, but we use tools from chemistry to directly demonstrate that these
hippo nutrients are being directly picked up and used by aquatic animals,"
said McCauley, an assistant professor in UCSB's Department of Ecology, Evolution
and Marine Biology.
"Ecologists are really interested in how materials and energy flow across ecosystems, and here is a very clear boundary -- aquatic versus terrestrial," he added. "These two worlds are clearly distinct, but our
research shows
that wildlife such as hippos build important connections across these ecosystem
gaps. Our study confirms that hippos are bringing a part of terrestrial ecology
-- nutrients and energy -- into this other domain of rivers."
McCauley's team
found that some species of river fish -- both in their native habitat of
Kenya's Ewaso Ng'iro River and in the laboratory -- fed on the nutrients from
hippo dung. The scientists were able to use stable isotopes, a class of natural
chemical markers, to trace the flow of organic matter through the food
pipeline, from the back end of the hippo to the tissue of river fish and
insects. The results demonstrate that these aquatic consumers absorb nutrients
from hippo dung as part of their diet.
An additional
discovery showed that the importance of the hippo as a food source is
contingent on the conditions of the river. For example, the researchers found
that the uptake of nutrients from hippo-vectored organic matter was most
pronounced during periods of low river flow, which were caused by seasonal
changes in rainfall.
"When the
river is high, it seems to be diluting a lot of the material that the hippos
are bringing in and the animals in the river just can't get to it quickly
enough," McCauley explained. "And when it's dry, these materials
concentrate in these pools and the animals are able to make better use of
them."
These findings
are important not only because they characterize the importance of hippos in
the river food web but also because rivers in East Africa are changing rapidly.
"Climate change and regional development are certainly changing river
flow," McCauley said.
"With
hippo populations declining in Africa and water regimes changing rapidly, it is
critically important that we understand more about the ecological role of hippos,"
he added. "The linkages that we highlight in our research illustrate that
the fate of the hippo is intimately linked to the fate of whole food webs and
to the functioning of entire ecosystems."
Source:
http://www.en.wikipedia.org/wiki/Hippopotamus
http://www.sciencedaily.com/releases/2015/04/150414130528.htm.
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