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KLASERIE CHRONICLE NO 37
025
Savanna landscapers?
Looking at the seed dispersal service by elephants
Article by Katherine Bunney, photos by Michele Henley
A
series of extinction events 50 to 10 thousand
years ago wiped out the large animals (megafauna)
of Europe, non-tropical Asia, Australia, and the
Americas. While the age of large animals might have seen
its end on most continents, Africa and small patches of
tropical Asia remain the exception. Five genera of Africa’s
megafaunal community – the white rhinoceros, black
rhinoceros, giraffe, hippopotamus, and African elephant
still exist, while two genera – the Asian elephant and onehorned rhinoceros remain in Asia. Sadly, the megafauna
that survived are under serious threat and have been
eradicated from a large proportion of their historical
ranges. It is clear that we are losing our megafauna. What
is less clear is the consequences of such a loss.
Large herbivores shape plant communities through
physical disturbance such as pushing down trees,
herbivory and seed dispersal. The removal of large
herbivores such as the African elephant and rhinoceros
will lead to changes in the plant community that cascade
throughout the ecosystem. Our work at the Biological
Sciences Department at the University of Cape Town
(under the supervision of Professor William Bond and
in collaboration with Michelle Henley of Elephants Alive
South Africa) focuses on describing the role of the African
savanna elephant as a seed disperser to predict the
consequences of its decline on savanna tree species.
Seed dispersal by elephants
To date, elephant seed dispersal studies have largely
focused on African and Asian forest elephants. These
studies have firmly established forest elephants as
prolific seed dispersers, consuming more fruit than any
other large animal. African forest elephants are also the
principal, and in some cases sole, seed dispersal agent
for a number of large-fruited trees. An example of this
is Balanites wilsoniana, an upper-canopy forest tree
in Uganda. The fruit of this species is too large to be
swallowed by anything other than elephant, and where
elephants are absent these trees are in decline.
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KLASERIE CHRONICLE NO 38
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In contrast, African savanna elephants have been the
subject of far fewer seed dispersal studies. Like the
African forest elephants, they disperse large quantities of
seeds. Joseph Dudley found that in Hwange National Park,
Zimbabwe savanna elephants disperse over 2,000 seeds/
km² every day.
The fruits elephants eat
To work out what fruits are reliant on elephants for their
dispersal we compiled a database of all South African
tree species. We then used characteristics of the fruit
and seeds to identify those fruits that, owing to their
large size, could only be swallowed whole by elephants.
We identified between 30 and 40 species. Some of the
better-known examples are fruit from the marula tree, the
sausage tree and the torchwood tree. If you have seen
elephants feeding on the fruits of any trees within the
Associated Private Nature Reserves or Kruger National
Park I would be very interested to hear about it.
Spatial pattern of seed dispersal
It is exceedingly difficult to track the fate of individual
seeds in the field. Instead, we model this pattern
by combining information from how long seeds are
retained in an animal’s gut, with the movement patterns
of that animal in the wild. We measured elephant gut
retention times by feeding different-sized fruits and
seeds to sanctuary elephants at Elephant Whispers,
Hazyview. Finding the seeds entailed sifting through
mammoth quantities of dung – my mum and I sat among
piles of warm dung for four days to gauge this. Animal
movements on the other hand are studied in the field
by attaching GPS tracking collars on wild animals. Our
elephant movement data was obtained from the locations
of 38 radio-collared wild elephants (27 males and 11
females) in the APNR, as collected by Elephants Alive over
a period of eight years.
The findings
Our model predicts that half of all seeds consumed by
elephants are carried over 2,5km and distances of up
to 65km are sometimes reached – a remarkable feat!
These findings suggest the savanna elephant as the
longest distance land animal seed disperser that has
been investigated to date. We have shown that African
megafauna such as the savanna elephant have been
providing a vehicle for the long-distance movement of
seeds for millennia. Maintaining their ecological role as a
seed disperser is important for the conservation of largefruited trees in the savanna landscape.
For more information, contact Katherine Bunney at
[email protected].
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