Contrasting the Effects of Native Versus Exotic Grazers in an East African Savanna: Establishment of the Whistling Thorn Tree (Acacia drepanolobium)

EPA Grant Number: FP916317
Title: Contrasting the Effects of Native Versus Exotic Grazers in an East African Savanna: Establishment of the Whistling Thorn Tree (Acacia drepanolobium)
Investigators: Goheen, Jacob R.
Institution: University of New Mexico
EPA Project Officer: Lee, Sonja
Project Period: January 1, 2004 through December 31, 2006
Project Amount: $103,292
RFA: STAR Graduate Fellowships (2004) RFA Text |  Recipients Lists
Research Category: Fellowship - Terrestrial Ecology and Ecosystems , Academic Fellowships , Ecological Indicators/Assessment/Restoration


The objective of my research is to address how different rangeland practices affect community dynamics in savanna ecosystems. Specifically, I am evaluating how the extirpation of native mammalian herbivores influences the establishment of the whistling thorn tree, Acacia drepanolobium. I have demonstrated previously that survival of Acacia seedlings is twice as high in areas where mammalian herbivores occur relative to areas where they are absent. This pattern results from the suppression of rodents and some insect taxa by large herbivores such as elephants (Loxodonta africana), zebra (Equus burchelli), and various species of antelope. Although inconspicuous, these smaller consumers are important seedling predators and therefore have stronger direct, negative impacts upon Acacia seedling survival than do their larger counterparts. Thus, mammalian herbivores can indirectly enhance Acacia seedling establishment by suppressing populations of smaller, more important seedling predators.


In continuing this research, I am disentangling the effects of native herbivores from those of exotic herbivores with regard to seed production and seedling establishment of Acacia. By virtue of differences in browsing behavior and effects upon seedling predators, I predict seed production and subsequent seedling establishment will be highest in areas where only exotic herbivores occur, and lower in areas where both native and exotic herbivores coexist. This research fills a critical gap in our knowledge with regard to brush encroachment in savanna ecosystems and, more generally, has direct implications for the conservation of rangelands worldwide.

Supplemental Keywords:

fellowship, community dynamics, savanna ecosystems, herbivores, Acacia drepanolobium, species survival, seed production, rangeland practices, whistling thorn tree, seedling survival,, RFA, Scientific Discipline, ENVIRONMENTAL MANAGEMENT, Ecosystem Protection/Environmental Exposure & Risk, Ecosystem/Assessment/Indicators, Ecosystem Protection, Resources Management, Ecological Effects - Environmental Exposure & Risk, Ecology and Ecosystems, Ecological Indicators, East African Savanna, rangeland, exotic grazers, whistling thorn tree, mammal, conservation, seed establishment, animal feeding operations, ecosystem impacts, ecological research

Relevant Websites:

2004 STAR Graduate Fellowship Conference Poster (PDF, 1p., 110KB, about PDF)

Progress and Final Reports:

  • 2004
  • 2005
  • Final