Diet switching in wild African elephants in response to primary production: Evidence from time-specific stable isotope chronologies

Assessment of temporal variation in diet is fundamental to understanding animal population dynamics and long-term impacts of environmental change on niche relationships. Ratios of stable isotopes in progressively growing animal tissue can provide continuous records of diet, movement, and climatic environment. Using serially collected tail hairs from a wild African elephant family, we develop techniques to collate chronological isotope records from multiple hairs spanning a six year period to calculate real time diet chronologies. The proportion of grass (C4 plants) versus browse (C3 plants) in the diet is assessed using an isotope turnover pool model.  We use this information to assess the influence of primary production, measured from remotely sensed Normalized Differential Vegetation Index (NDVI) data, on the diet of this generalist herbivore.  Dietary switching from browse to grass is seen at increased levels of primary production, reaching a maximum of about 50 - 60 percent grass.  As the ecosystem dried out and productivity declined, elephants gradually switched to a primarily browse diet.  This study provides information on time specific dietary switching in elephants important to understanding and mitigating the ecological impacts of this keystone species.