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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. Let us help you with all your property needs! Hoedspruit Office Tel: 015 793 1686 / Cell: 082 205 4798 Email: [email protected] Shop 10, Pick n Pay Centre, Hoedspruit, 1380 HOEDSPRUIT KLASERIE CHRONICLE NO 38 025 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]. TLB to rent. Ideal for digging septic tanks, ash pits, pipelines and cable trenches. General road maintenance, opening of drains and rebuilding drain humps. Slasher also available. Contact Martin: [email protected] or 0835563271