International Research Fellowship Program: Ecological Consequences of Large-Herbivore Declines under Different Rainfall Regimes

Pringle Robert M, Stanford CA

Investigators

Abstract

0852961 Pringle This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twenty-four-month research fellowship by Dr. Robert M. Pringle to work with Dr. Fabian Haas at the International Centre for Insect Pathology and Ecology (CIPE), with Dr. Charles Warui at the National Museums of Kenya, and with Dr. M. Kinnaird at the Mpala Research in Kenya. Recent studies suggest that large mammalian herbivores may be ?strong interactors? whose removal will precipitate major changes in biological communities. This project aims to document and explain the short-term (2-3 year) responses of plant and invertebrate communities to the exclusion of ungulate herbivores in a Kenyan savanna, and also to examine how these responses are contingent upon variability in rainfall. This is being done using a unique experiment with four 1-ha treatments: total exclusion (removal of all herbivores larger than 4-kg hares), exclusion of all herbivores larger than 6-kg dik-diks, exclusion only of megaherbivores (elephants and giraffes), and unfenced control (all animals present). These treatments are each replicated three times at three levels of a natural rainfall gradient. Project personnel are testing four specific hypotheses. I: Herbivore exclusion alters the palatability of individual plants, enhances recruitment, reduces species evenness, and increases structural complexity at the habitat level. II: Via these effects on plants, herbivore exclusion leads to increased total biomass of both herbivorous and carnivorous arthropods. III: Indirect responses of individual arthropod species vary, but depend on (a) diet breadth and host-plant preference, (b) foraging strategy, and (c) predation vulnerability. IV: The strength of both direct and indirect effects is negatively correlated with rainfall. Humans are reducing large-herbivore populations worldwide, and climate change promises dramatic changes in precipitation patterns. Yet nobody knows how these changes will affect biodiversity and ecological function in iconic landscapes such as African savannas and the Yellowstone ecosystem. Generating this knowledge will reveal fundamental truths about how large mammals influence ecological dynamics and how these influences are modulated by environmental context. It will also provide a basis for predicting the consequences of large-mammal declines and extinctions in a rapidly changing world. To date, measurements of responses to large-mammal removal have been idiosyncratic and opportunistic, and the mechanisms offered to explain underlying the responses are often speculative. Moreover, the few exclusion experiments conducted in species-rich ungulate guilds have mostly been ?all or none,? meaning that the effects of particular species or subgroups cannot be identified, whereas our sequential size-based exclusion approach will isolate these effects. Finally, this experiment is the first to combine large-herbivore exclusion with replication across multiple levels of an environmental gradient, which is consistent with recent calls for ecologists to address the context-dependence of species interactions. In terms of developing human capital and international collaboration, this project supports five full-time research assistants from local communities in rural Kenya. Their employment provides them with valuable, transferable skills (identification of native Kenyan biodiversity, data entry and computer training, management and teamwork experience). These men are also from different ethnic groups and religions in a region torn (as recently as January, 2008) by ethnic strife; working together cements bonds that overcome ethnic differences. Local people and their children will be taken on guided tours of the experimental facilities, allowing them to interact with biodiversity in an educational setting, which will promote environmental stewardship in the region. This project also involves collaboration among three research institutions in Kenya (as well as three universities in the US and Canada) that have long operated separately; this collaboration will build intra- and international partnerships and capacity that will facilitate future joint endeavors. The project also lays a foundation for future work on the poorly known invertebrates of this region. Lastly, the conservation and management implications of the work will be disseminated in short essays for non-scientific audiences to be published both in local Kenyan media and on the worldwide web.