This was a presentation I created with the help of a classmate for a course called "Field Research in Savannah Ecology" while I was abroad in South Africa through Duke University and the Organization for Tropical Studies (Spring 2011). After carrying out a self designed research project, my partner and I presented our findings to the employees of Kruger National Park (the park where the research was conducted) as well as our professors and fellow classmates. I created all the images in this presentation using powerpoint.

1. Squirrels:
Predators or Dispersers of Marula Nuts?
Emma Alterman and Peter Macfarlane
Organization for Tropical Studies
May 2, 2011

2. Introduction Methods Results Discussion
Marula
(Sclerocarya birrea subsp. caffra)

3. Introduction Methods Results Discussion
Dispersal
Bottlenecks
Adult
Mortality
Fire Trap/
Browse
Establishment
Time

4. Introduction Methods Results Discussion
Dispersal
Bottlenecks
Adult
Mortality
Fire Trap/
Browse
Establishment
Time

5. Introduction Methods Results Discussion
Tree Squirrels
(Paraxerus cepapi subsp. cepapi)

6. Introduction Methods Results Discussion
Janzen-Connell Hypothesis
I=SeedsShadow
P=Probability of seedling survival because of lower predation

7. Introduction Methods Results Discussion
Our Goals

8. Introduction Methods Results Discussion
The Set Up
“Near” “Intermediate” “Far”

9. Introduction Methods Results Discussion
In the open
Under trees
In the bush

10. Introduction Methods Results Discussion
•Eaten
•Scatter-hoarded
•Moved
•Missing

11. Introduction Methods Results Discussion
Scatter-hoarding

12. Introduction Methods Results Discussion
UV Torch
Scatter-hoarding

13. Introduction Methods Results Discussion
12
Number of Marula Nuts
10
8
Untouched
6
Eaten
4
Scatter-Hoarded
Missing
2
0
Near Intermediate Far
Predation seen directly under the marula trees
Mix of eating, scatter-hoarding and unknowns

14. Introduction Methods Results Discussion
10
Number of Marula Nuts left untouched
9
8
7
6
5
4
3
2
1
0
Under Marula Trees Under Other Trees
Similar predation rates under marula and non-marula trees

15. Introduction Methods Results Discussion
10
Number of Marula Nuts left untouched
9
8
7
6
5
4
3
2
1
0
In the Bush On the Golf Course
Lower predation rates in the bush than on the golf course

16. Introduction Methods Results Discussion
40
35
30
25
20
15
10
Number of Marula Nuts
5
0
-4 0 4 8 12 16 20 24
Distance of Scatter-Hoarding (m)
Most nuts were scatter-hoarded close to the tree

17. Introduction Methods Results Discussion
Janzen-Connell Hypothesis
Critical Point?
“Near” “Intermediate” “Far”

18. Introduction Methods Results Discussion
Under Trees In The Open
Predation under marula and Fear predation
non-marula trees same Feel safest in the trees
-Trees as triggers

19. Introduction Methods Results Discussion
Under Trees In The Open
Predation under marula and Fear predation
non-marula trees same Feel safest in the trees
-Trees as triggers
But…
In The Bush
To much cover might make it
difficult for squirrels to find
nuts

20. Introduction Methods Results Discussion

21. Elephants!

22. Introduction Methods Results Discussion
Can travel 6km per day
Food in gut for up to 46 hours
Excreted food deposited far from source
Piles good foraging locations
Can be filled with up to 700 nuts

23. Introduction Methods Results Discussion

24. Introduction Methods Results Discussion
Nut found by squirrel
Scatter-hoarded near dung pile
Nut buried far away from parent
trees!

25. Introduction Methods Results Discussion
Why is this an effective
dispersal method?
Seed mortality in elephant gut very low
• Seed can travel far safely
Buried seeds protected from threats
• Risk of being burned
• Predation

26. Conclusions •Janzen-Connell holding true
for savannas
•Trees as triggers
•Marulas possibly dispersed
by 2 modes of zoochory

27. Thank you!

28. Thank you!
Questions?

29. References
• Alterman, E. B. Lind, and A. Martinez. 2011. Where are my nuts? The role of elephants and squirrels in marula (Sclerocarya birrea subsp. caffra) seed
dispersal. Organization for Tropical Studies report spring 2011. Skukuza, Mpumalanga Province, South Africa.
• Butchart, D. 2009. Wildlife of South Africa | A Photographic Guide. Struik Nature, Cape Town, SA.
• Davis, S. 2007. Endozoochory in Subtropical Thicket: comparing effects of species with different digestive systems on seed fate. MSc Thesis, Nelson
Mandela Metropolitan University, South Africa.
• Forget, P.M. 1990. Seed dispersal of Vouacapoua Americana (Caesalpiniaceae) by caviomorph rodents in French Guiana. Journal of Tropical Ecology
6:459-468.
• Forget, P.M. and S.B. Vander Wall. 2001. Scatter-hoarding rodents and marsupials: convergent evolution on diverging continents. Trends in Ecology &
Evolution. 16(2):65-67.
• Gallaher, K.S.L. 2010. Marula (Sclerocarya Birrea Subsp. Caffra) Dispersal by Mammals: Are Squirrels Seed Predators Or Seed Dispersers? BSc. Honors
Thesis. Botany Department University of Cape Town, Cape Town, SA.
• Helm, C.V., S.L. Scott, and E.T.F. Witkowski. 2011. Reproductive potential and seed fate of Sclerocarya birrea subsp. caffra (marula) in the low altitude
savannas of South Africa. South African Journal of Botany. in press.
• Jacobs, O.S. and R. Biggs. 2002. The status and population structure of the marula in the Kruger National Park. South African Journal of Wildlife
Research 32(1): 1–12.
• Janzen, D. 1970. Herbivores and the Number of Tree Species in Tropical Forests. The American Naturalist 104(940):501-528.
• Laorie, S.R., Van Aarde, R.J., and S.L. Pimm. 2009. Fences and artificial water affect African savannah elephant movement patterns. Biological
Conservation 142:3086–3098
• Midgley, J.J. and W.J. Bond. 2001. A synthesis of the demography of African acacias. Journal of Tropical Ecology 17:871–886.
• Rees, P. A. 1982. Gross assimilation efficiency and food passage time in the African elephant. African Journal of Ecology 20(3):193-198.
• Shackleton, C.M., J. Botha, P.L. Emanuel and S. Ndlovu. 2002. Inventory of Marula (Sclerocarya birrea subsp. caffra) Stocks and Fruit Yields in
Communal and Protected Areas of the Bushbuckridge Lowveld, Limpopo Province, South Africa. Department of Environmental Science, Rhodes
University, Grahamstown 6140, South Africa.
• Schmidt E., M. Lötter, W. McCleland. 2002. Trees and Shrubs of Mpumalanga and Kruger National Park. Jacana, Johannesburg, SA.
• Stuart, C. and T. Stuart. 2007 Field Guide to Mammals of Southern Africa. Fourth Edition Struik Piblishers, Cape Town, SA.
• van Wilgen, B.W., W.S.W. Trollope, H.C. Biggs, A.L.F. Potgieter, and B.H. Brockett. 2003. Fire as a Driver of Ecosystem Variability. Pp 149-170 in J.T.
du Toit, K.H. Rogers, and H.C. Biggs, editors. The Kruger Experience Ecology and Management of Savanna Heterogeneity. Island Press, Washington,
DC, USA.