Breeding phenology in relation to NDVI variability in free-ranging African elephant

The phenology of reproduction is often correlated with resource availability and is hypothesized to be shaped by selective forces in order to maximize lifetime reproductive success. African elephants have the distinctive life history traits of a 22 month gestation and extended offspring investment, necessitating a long-term strategy of energy acquisition and reproductive expenditure to ensure successful offspring recruitment.
We investigated the relationship between the reproductive phenology of a wild elephant population and resource availability using remotely sensed Normalized Differential Vegetation Index (NDVI) data as a measure of time-specific primary productivity and hence forage quality.
The initiation of female elephants' 3+yr reproductive bout was dependent on conditions during the season of conception but timed so parturition occurred during the most likely periods of high primary productivity 22 months later. Thus, the probability of conception is linked to the stochastic variation in seasonal quality and the phenology of parturition is related to the predictable seasonality of primary productivity, indicating elephants integrate information on known current and expected future conditions when reproducing.
Juvenile mortality was not correlated with ecological variability, hence female fecundity rather than calf mortality appears to drive demographic processes in the study population.
Extreme climatic events, such as those associated with the El Niño-Southern-Oscillation (ENSO), acted to synchronize female fecundity in the population. This study suggests that the relationship between fecundity and ecological variability instigates the characteristic demographic fluctuations in elephant populations, rather than the mortality-driven fluctuations observed in many ungulate populations.