Long-term data reveal fitness costs of anthropogenic prey depletion for a subordinate competitor, the African wild dog (Lycaon pictus)

Within carnivore guilds, dominant competitors (e.g., lions, Panthera leo)
are limited primarily by the density of prey, while subordinate
competitors (e.g., African wild dogs, Lycaon pictus) have been
limited by the density of dominant competitors. Historically, the fitness
and population density of subordinate competitors have not been
tightly linked to prey density. However, populations of large
herbivores have declined substantially across sub-Saharan Africa due
to human impacts, and where prey depletion is severe, fitness
costs for competitive subordinates may begin to outweigh the
benefits of competitive release. Using long-term intensive
monitoring of African wild dogs in Zambia’s Luangwa Valley
Ecosystem (LVE), we tested the effects of prey depletion on
survival and reproduction. Our study area included four contiguous regions
that varied in protection, prey density, and lion density. We fit
Bayesian Cormack-Jolly-Seber and closed-capture models to
estimate effects on survival and population density, and
generalized linear models to estimate effects on reproductive
success. We found that the LVE is a stronghold for wild dogs,
with an estimated median density of 4.0 individuals/100 km2. Despite this
high density, survival and reproduction differed among regions, and both
components of fitness were substantially reduced in the region
with the lowest prey density. Anthropogenic prey depletion
is becoming an important limiting factor for African wild dogs.
If prey depletion (or any other form of habitat degradation)
becomes severe enough that its fitness costs outweigh the benefits
of competitive release, such changes can fundamentally alter the
balance between limiting factors for competitively subordinate
species.