Mega-gardeners of Tropical Forests: Modeling Seed Dispersal by Forest Elephants (2018-2019)
Poaching is rapidly wiping out African forest elephants (Loxodonta cyclotis) from most of their historical range, leaving vast areas of elephant-free tropical forest. Elephants are ecological engineers that create and maintain forest habitat; the reduction of elephant populations will result in dramatic ecological changes in central African forests, including altered species composition, increased stem densities of small trees and lower abundance of large trees. This unintended experiment may help resolve whether differences between central African and neotropical forests are due to the destruction of megafauna in the neotropics thousands of years ago.
Despite the threat of extinction, African forest elephants remain understudied. We have limited knowledge of their ecological impacts on tropical forests, and most studies of forest elephants have been concentrated in a few protected areas.
Forest elephants primarily influence plant populations through seed dispersal and browsing of saplings and young trees, although they also incidentally prey on seeds and trample seedlings. This Bass Connections project focuses on one of the key uncertainties about how forest elephants affect forests, using a combination of new technologies to measure seed dispersal in the field and model how elephants influence forest composition, diversity and structure through this plant-animal interaction.
Patterns of seed dispersal by elephants depend on two key variables: how elephants move; and the average amount of time a seed spends in an elephant gut (gut passage time). Through collaboration with the Gabon Parks Agency, Duke researchers have nearly two years of data on hourly movements of 56 forest elephants. However, there are no existing data on the time it takes a seed to pass through a forest elephant’s gut. To overcome this data gap, the project team will conduct experiments in Gabon to estimate gut passage time in wild forest elephants for several plant species that vary in seed size. A principal aspect of this work is to develop and test four methods under consideration:
- Providing “external” seed species (a diet species that is not concurrently fruiting in the study are) for consumption by collared elephants, and then following the elephant to recover the dispersed seeds to estimate the time and distance of dispersal
- Embedding a colored plastic cylindrical head screw into the seeds of naturally occurring seeds, and following the elephants as in #1 to recover the dispersed seed and estimate gut passage time
- Embedding an iButton thermocouple that records temperature with time, into the seeds of fruits
- Using consumable radio tracking devices to map seed displacement distances.
With the gut passage time and seed displacement data, the team will be able to model forest elephant seed dispersal and evaluate the consequences of differences in dispersal patterns with sex, site and environmental variables for forest plant populations.
New method for determining role of forest elephants in seed dispersal; two publications (methods and results of gut passage and seed displacement experiments; seed dispersal patterns of forest elephants); data for a long-term project on effects of elephants on forest composition and structure; external grant proposals
Spring 2018 – Fall 2018
- Spring 2018: Meet weekly to discuss ideas and test experimental methods; form sub-teams responsible for sub-tasks (e.g., testing different gut passage field methods, developing statistical models of seed dispersal); work with engineers and biotechnicians to develop technology for experiments; test methods on captive savanna elephants at North Carolina Zoo
- Summer 2018: Work collaboratively in Gabon with project partners (mid-May through mid-August)
- Fall 2018: Meet weekly to analyze data and write up results; submit articles
/faculty/staff Team Members
Christopher William Beirne, Nicholas School of the Environment-Environmental Sciences and Policy*
Alan Gelfand, Arts & Sciences-Statistical Science
John Poulsen, Nicholas School of the Environment-Environmental Sciences and Policy*
Colin Rundel, Arts & Sciences-Statistical Science*
Justin Wright, Arts & Sciences-Biology*
/graduate Team Members
Graden Froese, Environment-PHD
Seokmin Kim, Master of Environmental Management, Ecosystem Science and Conservation
Amelia Meier, Environment-PHD
Taylor Minich, Master of Environmental Management, Ecosystem Science and Conservation, Forest Resource Management-MF
Chase Nunez, Environment-PHD
/undergraduate Team Members
Melissa Baldino, Biology (BS), Environmental Sci/Policy (AB2)
Lingrong Jin, Biology (BS), Statistical Science (AB2)
Julia Knorr, Environmental Sciences (BS), Global Health (AB2)