Anthropogenic and climatic drivers of population densities in an African
savanna ungulate community
Abstract
Many ungulate species in Africa range in habitats that vary in type and
quality over space and time, but ongoing environmental change is
substantially altering their habitats. Identifying key environmental
variables that regulate ungulate population densities can guide
management actions for effective conservation. We studied the local
population density responses of a community of sympatric ungulate
species in the Tarangire Ecosystem of northern Tanzania, to a suite of
environmental factors that vary over space and time, to quantify
population trends, determine the primary environmental correlates of
densities, and identify covariation in densities among species. We
estimated seasonal densities of five commonly detected species (impala,
dik-dik, Grant’s gazelle, eland, and waterbuck) based on 7 years of
distance-sampling data from 41 replicate surveys of 237 line transects.
We systematically analyzed the effects of spatial, seasonal, and annual
environmental covariates on variation in transect species-specific
densities across space and time. Despite large fluctuations in climatic
factors, we documented more spatial than temporal variation in four of
the five species, suggesting that spatial heterogeneity may provide some
buffer against temporal variation in the environment. Protection of
sufficient habitats and water sources should allow ungulates to respond
to a temporally changing world by moving across space. Further,
among-species covariation patterns identified two potential ungulate
guilds (impala—dik-dik—waterbuck; eland—grant’s gazelle) that
should aid in developing efficient and coordinated management actions.