Large predators can mitigate nutrient losses associated with off-site removal of animals from a wildlife reserve.

Abstract

Animals concentrate key nutrients in their bodies. In fenced wildlife reserves where nutrient input and/or retention is low, the off-site removal of animals may constitute a significant loss of nutrients for the ecosystem. Here we add wildlife capture and removal into the phosphorus (P) and calcium (Ca) budget for a 121,700 ha fenced game reserve located in the southern Kalahari. We then use faecal P concentrations from 11 mammal herbivores >10 kg as an indicator of potential nutrient stress in this system to investigate whether the implications of nutrient loss via off-site wildlife removal may be cause for concern. Finally, we assess the role of natural predation as a mechanism to minimise the need for wildlife removal and concomitant nutrient loss. During the period 2009-2018, mean loss of P and Ca via wildlife removal was 2.9 and 6.2 kg km^-2 year^-1, respectively. This compares to 1.0 and 2.1 kg km^-2 year^-1 of P and Ca added via the provision of mineral licks. If it is assumed that natural fluxes of these elements are in steady state, then anthropogenic activities have resulted in a net deficit of 18.5 kg/km² of P and 40.6 kg/km² of Ca over the decade. We found that dry season herbivore faecal P concentrations are close to or below a widely cited minimum threshold of 2,000 mg/kg, below which most vertebrates begin suffering growth and reproductive issues. Large animals were more likely to be under this threshold. Prolonged continuation of off-site wildlife removal may result in nutrient losses that can lead to long-term ecological degradation. Natural predation levels were, however, found sufficient to mitigate the need for wildlife removal and present a management strategy whereby herbivore populations can be regulated without a loss of nutrients. Synthesis and applications. We find that the capture and permanent removal of large-bodied animals from wildlife reserves can be a significant cause of nutrient loss. Over time, in sites where nutrient input and/or retention is low, this may contribute to nutritional stress for remaining resident animals. Where possible, holistic management strategies that promote the retention of animals and carcasses within the reserve-such as the reintroduction of large carnivores-should be preferred.

Key words

• animal ecology
• calcium
• dry season
• ecosystems
• faeces
• faeces composition
• herbivores
• Kalahari Desert
• losses
• minerals
• nature reserves
• nutrients
• phosphorus
• predation
• predator prey relationships
• predators
• reintroduction
• removal
• retention
• synthesis
• wild animals
• wildlife conservation
• wildlife management
• arid lands
• natural enemies
• deserts