Long-Term Population Trends in Savannah Herbivores

Abstract

African savannah ecosystems support the largest remaining assemblages of large-bodied wild herbivores on Earth, yet long-term population trends for most savannah herbivore species remain poorly characterised beyond a handful of well-monitored flagship species and protected areas. Declines outside protected areas have been severe across the continent -- estimated at 60-80% for many species since the 1970s -- while some populations within large protected areas have remained stable or increased, creating a highly heterogeneous continental picture inadequately captured by range-wide assessments. This study synthesises the most comprehensive long-term population trend database for African savannah herbivores yet assembled, compiling systematic count data from 247 sites across 18 African countries spanning 1970-2022 (52-year series), covering 38 herbivore species from impala (Aepyceros melampus) to African elephant (Loxodonta africana). Mean annual population change across all species and sites was -2.84% (95% CI: -3.47 to -2.21%), consistent with halving of abundance approximately every 24 years at this rate. Protected area status was the strongest predictor of population trend (partial R2 = 0.54; p < 0.001): species inside well-managed protected areas showed mean +0.84% per year; species outside showed -4.84% per year -- a 5.68% annual divergence. Rainfall variability (ENSO-linked) and lion density explained significant additional variance in short-term population fluctuations, while hunting pressure and settlement expansion predicted the long-term negative trends outside protected areas.