Biocomplexity of the Greater Serengeti: Humans in a Biologically Diverse Ecosystem

The Greater Serengeti Ecosystem (hereafter "the Serengeti") is a complex coupled human and natural system consisting of a network of diverse and intense trophic interactions played out over a heterogeneous landscape. Livestock and a species-rich assemblage of large mammalian herbivores, the most abundant of which migrate over a 12,000 square-km area each year, consume a high fraction of primary plant production. These herbivores sustain human populations and a rich assemblage of avian and mammalian carnivores. Moreover, humans, wild animals, and livestock are all vulnerable to a wide variety of infectious diseases.

Broad-scale heterogeneity in land use is superimposed on this dynamic landscape. The Serengeti National Park is a classic example of a protected area and ecotourism destination, while the adjacent Ngorongoro Conservation Area permits Maasai pastoralism, game reserves, (Maswa and Ikorongo) permit-controlled off-take of trophy species, and game-controlled areas (Grumeti) that permit all human activity except agriculture. The linkages between human and natural components of the Serengeti are so pervasive that human decision making may be the critical process governing the fate of the entire ecosystem. Pressure is mounting as human and animal populations converge on the western border of Serengeti National Park (SNP) and Mara Reserve.

To study the coupling of natural ecosystem functioning and human decision making in the greater Serengeti, this interdisciplinary research project will use four modeling approaches: (1) Process-rich, spatially explicit ecosystem simulation models will be developed to predict changes in plant and animal communities as well as human use of landscapes at different scales. (2) Agent-based models will incorporate individual decision-making rules in a spatially explicit environment. (3) Analytical models of community modules will explore interactions among five to ten key species. (4) Macro-ecological models will describe system patterns and processes as functions of major resource inputs, such as rainfall and soil nutrients. These models will explore emergent dynamics of the Serengeti at various organizational scales.

A large amount of Serengeti field data will be analyzed to parameterize the models and to assess their ability to explain past dynamics and current ecosystem trends. In addition, crucial new data on human activities and choices will be collected to understand the coupling of system dynamics between natural and human-dominated components. This blend of different modeling approaches and data syntheses will permit a unique integration of ecological and social sciences. The concept of ecosystem resilience/resistance will be directly related to the vulnerability of human societies. The theory of complex systems proposes that emergent properties can arise from relatively simple underlying mechanisms propagated in space and time.

The vulnerability of humans and sustainability of biodiversity in the Serengeti may be driven by a few critical constraints that operate independently of individual components. These constraints arise from fundamental laws/principles in psychology, biology, chemistry, and physics that constrain key biological processes and human decisions. Alternatively, complex systems may be sensitive to small differences in initial conditions and show a tendency to switch between alternative states. This sensitivity suggests that biodiversity and human welfare may be highly contingent on details such as individual behavior, the identity of the species participating, and the precise spatial arrangement of interactions among humans, plants, animals, and diseases.

The Serengeti provides a unique opportunity to test this hypothesis, because its component parts are so conspicuous and its dynamical patterns have been measured for 40 years. Finally, emergent system properties may be contingent on just a few critical components, which would imply that the Serengeti can be understood from networks of interaction among a few key species of plants/animals and humans. In addition to providing fundamental new knowledge, the project will provide insights and information of immediate value of managers and decision makers in the study region and many other locales. It also will provide valuable research and training opportunities for students and post-doctoral scholars, and it will facilitate international collaborations between U.S. and African scientists. This project is supported by an award resulting from the FY 2003 special competition in Biocomplexity in the Environment focusing on the Dynamics of Coupled Natural and Human Systems.