Testing the effects of anthropogenic pressures on a diverse African herbivore community

Abstract

2020. Testing the effects of anthropogenic pressures on a diverse African herbivore community. Ecosphere 11(3):Abstract. Large herbivore communities around the world have declined steeply in recent decades.Although excessive bushmeat harvesting is thought to be the primary cause of herbivore declines in many ecosystems, the direct effects of anthropogenic pressures on large herbivore populations remain poorly described in most of the systems experiencing decline. To test the extent to which large herbivores are impacted by ecological and anthropogenic factors in a protected area (PA) thought to be experiencing human-caused decline, we fit distance sampling models to seven years of data from systematic groundbased surveys in Kafue National Park (KNP) to estimate the population densities and distributions of 10 species of large herbivores, and to test what factors affect these parameters. Population densities of the ten most abundant large herbivores in KNP were substantially lower than those reported for an ecologically similar PA with less poaching pressure. Low densities were consistent across species and areas, though there was ecologically important variation among species and size classes. Densities of larger-bodied herbivores were greatly depressed relative to smaller species. This pattern has direct and indirect effects on large carnivore populations, with broad implications for the ecotourism and trophy hunting industries. Statistically and methodologically rigorous methods to test the effects of anthropogenic and environmental variables on density and distribution exist, but are rarely applied to large herbivores. To quantify trends in herbivore populations and evaluate the effectiveness of conservation actions, our results show that distance sampling with stratified ground-based monitoring is an efficient and effective method. In the Greater Kafue Ecosystem (GKE), continued increases in resource protection are needed to facilitate the recovery of an economically and ecologically important large herbivore guild. More broadly, our results confirm that anthropogenic effects on large herbivore distribution and abundance can be strong over wide areas for all species (particularly the larger members of the guild), even in very large PAs.

Response of lion demography and dynamics to the loss of preferred larger prey

“…The GKE represents 13% of the Kavango‐Zambezi Transfrontier Conservation Area (KAZA TFCA, 520,000 km 2 ), which spans the borders of Angola, Botswana, Namibia, Zambia, and Zimbabwe. KNP is impacted by prey depletion, and densities of larger‐bodied herbivores are particularly depressed relative to smaller species (Vinks et al 2020b). Though the majority of our data was collected in KNP, some of our inferences likely also pertain to the entire GKE, most of which is facing more human pressure than our study site (Watson et al 2015, Overton et al 2017).…”

“…Central Zambia’s Greater Kafue Ecosystem (GKE), comprised of Kafue National Park (KNP) and surrounding Game Management Areas (GMAs), is a potential lion population stronghold, although prey depletion due to illegal offtake has already altered the diets of large carnivores, particularly lions, in this system (Midlane et al 2014, Creel et al 2018, Vinks et al 2020b). Notably, lions have switched their diet from less abundant, though preferred, larger prey to relatively more abundant smaller prey (Hayward and Kerley 2005, Creel et al 2018, Vinks et al 2020b).…”

“…Central Zambia’s Greater Kafue Ecosystem (GKE), comprised of Kafue National Park (KNP) and surrounding Game Management Areas (GMAs), is a potential lion population stronghold, although prey depletion due to illegal offtake has already altered the diets of large carnivores, particularly lions, in this system (Midlane et al 2014, Creel et al 2018, Vinks et al 2020b). Notably, lions have switched their diet from less abundant, though preferred, larger prey to relatively more abundant smaller prey (Hayward and Kerley 2005, Creel et al 2018, Vinks et al 2020b). As a consequence of low prey abundance and a switch to previously unpreferred prey, we would expect lions in this system to pay costs in the form of lower juvenile survival, constraints on reproduction, a lower carrying capacity, and (if severe) lower adult survival (Van Orsdol et al 1985, Gaillard et al 1998, Eberhardt 2002, VanderWaal et al 2009, Ferreira and Funston 2010).…”

“…Specifically, we fit mark–recapture models to data from intensive monitoring of known individual lions in KNP and parts of the surrounding GMAs between 2013 and 2018, providing precise estimates of population size and annual survival, while accounting for imperfect detection. We have previously used extensive data from ground‐based distance sampling (over the same period) to identify the drivers of large herbivore densities on this site (Vinks et al 2020b), presenting a unique opportunity to test whether the environmental and anthropogenic variables that predict prey density also predict lion survival. Similar data have been successfully used to guide conservation and management of lions in other systems (Loveridge et al 2007, 2016, Packer et al 2010, Rosenblatt et al 2014, Mweetwa et al 2018, Ferreira et al 2020), and by comparing our estimates of density, survival, and age structure to similar data from other populations, we further evaluate the consequences of prey depletion (Creel et al 2018).…”

Global extent and drivers of mammal population declines in protected areas under illegal hunting pressure

“…Therefore, due to their functional importance and growing threats, mammals are an excellent taxon to document hunting pressures and identify improved conservation strategies in PAs. Fortunately, the distribution changes of mammals brought about by hunting are broadly known [14,27]-but current research rarely focuses on PAs [8].…”