Print PageOver the past fifty years, research on the Serengeti ecosystem has revealed several regulatory processes that stabilize the system’s dynamics despite periodic disturbances such as disease epidemics and human predation. However, various components of the ecosystem have tracked apparently unpredictable climatic variation. Global climate teleconnections, such as El Niño Southern Oscillation (ENSO), are well established and affect primary productivity in semi-arid systems in East Africa and small mammal food webs in South America. We were interested if ecosystem dynamics in the Serengeti ecosystem could be explained by ENSO as measured by the Southern Oscillation Index (SOI). We addressed this question by incorporating abiotic (precipitation and temperature) and biotic data at three trophic levels: producers (vegetation productivity as measured through Normalized Difference Vegetation Index [NDVI]), consumers (wildebeest [Connochaetes taurinus], topi [Damaliscus lunatus], rodents) and secondary consumers (lion [Panthera leo], small carnivores, raptors). Relationships between individual variables were analyzed using linear regression. System level trophic connections and feedbacks were addressed using structural equation modeling (SEM). Maximum likelihood was used to estimate parameter values of standardized correlation coefficients for each causal link. Akaike information criteria scores were used to assess the plausibility of alternate SEMs.
Results/Conclusions
Ecosystem connections were derived from variation in SOI. The combined effect of SOI, rainfall and temperature were sufficient to explain major pathways in the food web, first through dry season rainfall, NDVI, wildebeest/topi recruitment and lion recruitment, and second through short-rains rainfall, rodent outbreaks and raptor abundance. SOI was positively related to rainfall in the dry season months (R2 = 0.14, n = 73, P = 0.001) and negatively related to short-rains rainfall (R2 = 0.18, n = 73, P < 0.001). The relationship of SOI with dry season rainfall was further improved with the addition of temperature (R2 = 0.19, P < 0.001). SOI-related rainfall patterns had contrasting effects on three trophic pathways while temperature played a secondary role, and these effects propagated to higher trophic levels. The consequence for the ecosystem is an alternation of the three pathways as SOI fluctuates. An emerging property for the system is that the contrasting responses to SOI events reduce the risk of stochastic variation for top carnivores in the food web, providing an additional stabilizing mechanism. Climate-change induced fluctuations of the SOI could alter the stability of the Serengeti ecosystem by changing the strength of alternate food web pathways.
