| dc.description.abstract | Seed dispersal by animals is important for maintaining healthy populations
of many tree species. The Janzen-Connell hypothesis, states that trees are under
selective pressures to the have their seeds dispersed away from the parent plant
and into an environment more suitable for growth. Seeds typically do not survive
underneath the parent plant for a myriad of reasons, including light and nutrient
limitations, and excessive predation. Large-seeded tree species are especially
affected by these factors because their seeds cannot be dispersed by abiotic factors,
such as wind. Trees with large seeds that can only be effectively dispersed by largebodied
animals are referred to as megafaunal syndrome species. African forest
elephant disperser effectiveness has been well studied. African savannah elephants
may fill a similar niche, although experimental data are few. African savannah
elephants have been suggested as critical seed dispersers, and may be the only
remaining organisms capable of effectively dispersing seeds of megafaunal
syndrome species.
I examined the effectiveness of savannah elephant dung as a protective
barrier for three tree species: Acacia tortilis, Tamarindus indica, and Balanites
aegyptiaca. Experimental treatments were established to measure the effect of dung
in protecting passed seeds. I also addressed the Janzen-Connell model. I predicted
that seeds in dung and seeds away from the parent tree would experience less
infestation than fresh seeds. Simple linear regression was used to determine daily
removal and infestation rates. Two-way analysis of variance was used to compare
time in days and treatment and their interaction. Multiple comparisons using a
Tukey's test of honest significant differences were made to check for true
differences between paired treatments from the ANOVA. Finally, loglinear analysis
was used to test for differences among infestation of seeds at different distances
from adult conspecific trees.
In January 2013, ants or termites in Experiment 1 likely removed passed
seeds in dung. Fresh seeds experienced similar levels of removal. Chi-square
analysis of data supported my hypothesis and revealed differences in beetle
emergence between passed and fresh seeds. In support of my prediction, in October
2013, seeds in dung experienced less beetle infestation than fresh seeds in
Experiment 2. Seeds at distances greater than five meters experienced less beetle
infestation than seeds underneath conspecific trees in Experiment 3. This study was
the first to experimentally address post-dispersal seed fate for megafaunal
syndrome species by savannah elephants. It creates a link between disperser
effectiveness of forest and savannah elephants, and provides foundation for further
examining savannah elephants as seed dispersers of megafaunal syndrome species. | |
