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Marula Dispersal

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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 ...

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.

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Marula Dispersal Marula Dispersal Presentation Transcript

  • Squirrels:Predators or Dispersers of Marula Nuts? Emma Alterman and Peter Macfarlane Organization for Tropical Studies May 2, 2011
  • Introduction Methods Results Discussion Marula (Sclerocarya birrea subsp. caffra)
  • Introduction Methods Results DiscussionDispersal Bottlenecks Adult Mortality Fire Trap/ Browse Establishment Time
  • Introduction Methods Results DiscussionDispersal Bottlenecks Adult Mortality Fire Trap/ Browse Establishment Time
  • Introduction Methods Results Discussion Tree Squirrels (Paraxerus cepapi subsp. cepapi)
  • Introduction Methods Results Discussion Janzen-Connell HypothesisI=SeedsShadowP=Probability of seedling survival because of lower predation
  • Introduction Methods Results Discussion Our Goals
  • Introduction Methods Results Discussion The Set Up “Near” “Intermediate” “Far”
  • Introduction Methods Results Discussion In the open Under trees In the bush
  • Introduction Methods Results Discussion •Eaten •Scatter-hoarded •Moved •Missing
  • Introduction Methods Results Discussion Scatter-hoarding
  • Introduction Methods Results DiscussionUV Torch Scatter-hoarding
  • 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
  • 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 TreesSimilar predation rates under marula and non-marula trees
  • 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
  • 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
  • Introduction Methods Results Discussion Janzen-Connell Hypothesis Critical Point? “Near” “Intermediate” “Far”
  • 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
  • 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
  • Introduction Methods Results Discussion
  • Elephants!
  • Introduction Methods Results Discussion Can travel 6km per day Food in gut for up to 46 hoursExcreted food deposited far from source Piles good foraging locations Can be filled with up to 700 nuts
  • Introduction Methods Results Discussion
  • Introduction Methods Results Discussion Nut found by squirrel Scatter-hoarded near dung pile Nut buried far away from parent trees!
  • Introduction Methods Results Discussion Why is this an effective dispersal method?Seed mortality in elephant gut very low • Seed can travel far safelyBuried seeds protected from threats • Risk of being burned • Predation
  • Conclusions •Janzen-Connell holding true for savannas •Trees as triggers •Marulas possibly dispersed by 2 modes of zoochory
  • Thank you!
  • Thank you! Questions?
  • 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.