Tracking Elephants and Dung Beetles in Gabon
October 25, 2019
African forest elephants – the world’s largest remaining frugivores – are ecological engineers that create and maintain forest habitat by eating and spreading seeds across wide areas of land. But what happens when elephants and their habitat are threatened? How does this affect forest composition and the plant, animal and insect life in these elephants’ native Afrotropical forests?
Last spring, undergraduate Alina Xiao ’21 (Biology) and doctoral student Anna Nordseth (Ecology) received a Bass Connections Student Research Award to evaluate how African forest elephants facilitate seed dispersal and whether elephant dung protects seeds from forest predators. Their research continues the work of the Mega-gardeners of Tropical Forests project team, which examined how African forest elephants affect seed dispersal by tracking and modeling gut passage time, or the time between seed ingestion and defecation. Their project is mentored by John Poulsen.
This summer, Nordseth and Xiao traveled to Ivindo National Park in Gabon to continue tracking gut passage time, identify seed predators and survival rates and evaluate whether elephant dung provides seeds with protection from exposure and predation. Recently, Xiao shared this update:
Elephants, Dung Beetles, and Seed Dispersal in Ivindo National Park
By Alina Xiao
Defaunation, or the local and global extinction of animals due to increasing anthropogenic (i.e. human) activities, has become a pervasive conservation concern over the last few decades. In the tropics, the rate of species loss is among the highest in the world. While many studies examine the effects of hunting, bushmeat trade, and the expansion of human settlement on medium- to large-bodied vertebrates, limited research is available on how the loss of these vertebrates influences invertebrate communities in understory habitats.
In Afrotropical forests, dung beetles (Scarabaeoidea) provide crucial ecological services such as nutrient cycling, soil aeration and secondary seed dispersal, and are significant contributors in shaping plant community structures. By rolling, burying or dwelling inside dung, dung beetles move seeds, reduce seeds’ risk of being eaten or attacked by pathogens and often facilitate germination and seedling recruitment. However, the diet composition of dung beetles necessitates their dependence on other vertebrate species. In central Africa, dung beetles have been recorded as highly prevalent and active, but research on their distribution and activity following severe defaunation is lacking.
In the summer of 2019, I travelled to Gabon with Anna Nordseth (Ph.D. in Ecology) to evaluate the cascading effects of defaunation on dung beetle populations near five villages in Makokou. It has always been my dream to study African forest elephants and conduct field research in central Africa.
I still remember how the experience began: At 2:30 a.m., I woke up to the sounds of elephants at the Ipassa Research Station inside Ivindo National Park. I followed the noise of branches breaking to the far side of the porch. There I sat, listened and watched. From just about 10 meters away, I saw the elephants walk across that small patch of grass to re-enter the forest. I watched the dream I had carried for so many years become real right in front of my eyes.
Although the actual work and logistics were even more challenging than I expected, this research experience was one of the most exhilarating and fulfilling I have had. To obtain the bait for the dung beetles, we followed the trails of African forest elephants (Loxodonta cyclotis) and collected fresh elephant dung near the Ivindo National Park, where our Bass Connections team previously studied gut passage time (GPT) – the time between seed ingestion and defecation – and seed dispersal by forest elephants.
For each of the five village sites, we set up two kilometer transects from the village edge to the inner forest. We placed pitfall traps using the collected elephant dung at 100 meters, one kilometer and two kilometers from the village. After 48 hours, we collected the trap contents, and counted, measured and classified all dung beetles.
After this summer, I feel even more energized and inspired to keep pursuing research. Now, we are working to analyze the data we collected in Gabon. Findings from this project will help us better understand the abundance and richness of dung beetle communities and the relationship of the dung beetle to seed dispersal and defaunation.