Understanding indirect interactions when livestock occupy protected areas

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Human-livestock settlements are permanent features in natural areas. A Maldhari settlement in Gir Sanctuary, western India

New research suggests that wise management of mixed predator-prey communities can often create desirable indirect effects for the conservation of native biodiversity. Field studies document reduced vigilance behaviour in areas of high livestock density where predators kill proportionately more livestock.

Domestic Prey in Natural Areas

Domestic ungulate herbivores form an integral part of many natural areas and often their abundance exceeds that of native prey. The wide spectrum of negative effects associated with domesticated livestock living in protected areas ignites controversy and debate among wildlife biologists, park managers, stakeholders and policy makers. Much of the controversy arises when managers attempt to mitigate resource competition with native ungulates, habitat destruction, and persecution of large and charismatic carnivores by livestock owners.

Needless to say, these issues have received considerable interest and concern from the scientific community that aims to understand, contain or reduce negative interactions in a human- and livestock-dominated landscape. But do we know enough about all the possible interactions involving domestic and native herbivores and their predators?

Indirect Interactions via a Common Predator

Shared predation is a common phenomenon in nature, but all possible outcomes of sharing a predator have rarely been studied for native prey species coexisting with livestock populations.

In some natural areas livestock may dominate prey abundance and biomass, with acute consequences for the native prey. Interactions between native prey and livestock can be asymmetrical (one organism benefits and the other loses) and can result in negative (apparent competition) or positive effects (apparent mutualism or commensalism) for the prey species involved.

The outcome of shared predation is shaped by the functional response (number of prey that an individual predator kills with changes in prey density) of a common predator, which in turn is influenced by prey attributes such as body size and vulnerability (anti-predator behaviour), as well as predator handling times involved in pursuing, subduing, and consuming prey.

Wise management of mixed predator-prey communities can often create desirable indirect effects for the conservation of native biodiversity

High livestock densities are likely to result in higher predator encounter rates, especially when livestock are preferred over native prey species. Thus, any differential consumption rate among prey, either by killing or scavenging, is likely to affect the consumption of a native prey in a livestock-dominated system.

Evidence for Positive Interaction

We looked for the effects of shared predation in Gir lion sanctuary, western India, where an abundant native prey, Chital deer, coexists with large domestic livestock (cattle and buffalo). The western and eastern areas of the sanctuary are home to several human-livestock settlements that harbour low and high densities of livestock respectively.

Asiatic lions forage on both prey species, which constitute a major portion of their diet in the system. Other large native prey types such as Sambar deer and Nilgai antelope are rare in, or absent from, many parts of the sanctuary. The government compensation to Maldari pastoralists for livestock kills, coupled with the benefits they receive for allowing livestock to graze within a protected area, as well as cultural acceptance of lions by the Maldharis, plays an important role in reducing the human-wildlife conflicts in the Gir forest.

interaction schematic

Schematic representation of interactions via shared predation in livestock dominated natural systems

We compared the Chital’s vigilance, a reliable behavioural indicator that reveals an animal’s perceived predation risk, in areas with low and high livestock density. Vigilance behaviour was less in areas where Chitals occurred with higher densities of livestock. The lower vigilance of native deer emerges through reduced predation in areas of high livestock density where lions kill proportionately more livestock (a positive effect — increased predation on livestock benefits Chitals).

Complexity of Indirect Interactions

Livestock interactions with coexisting native herbivores may be more complex than generally thought. Our research in Gir suggests that native prey will often face a trade-off between the benefits of lower predation risk in the company of the livestock and the costs of quickly depleting food resources associated with resource competition. The trade-off is likely to have significant consequences for how prey species manage their use of space and time, and for downstream effects on population dynamics and persistence.

Although we report an indirect positive effect in Gir, we would caution that livestock-induced indirect interactions may, in other protected areas, take different paths and effects, including predator-driven top-down or resource-driven bottom-up effects.

Other studies

In Kenya, the net effect of livestock grazing in areas with wild herbivores is positive even though the potential exists for resource competition. Somewhat more complicated dynamics likely occur in Yellowstone National Park where indirect effects are mediated through a large-bodied native herbivore rather than through livestock.

Wolves were reintroduced as both an active conservation measure to protect these large carnivores and as a foil to the concept of ‘natural regulation’ of native prey. The reintroduction, that appears to reduce elk density may eventually contribute to increased bison and pronghorn abundance by at least two mechanisms: 1. Fewer elk relax resource competition with other herbivores (yielding a strong positive effect on bison); 2. Intra-guild predation by wolves on coyotes reduces their ability to limit pronghorn populations.

The palpable lesson is that wise management of mixed predator-prey communities can often create desirable indirect effects for the conservation of native biodiversity. We urge other scientists to evaluate the net consequences of wildlife interactions in protected areas. Such studies are necessary in order to gain a better understanding of the characteristics that lead to positive versus negative impacts of livestock on wild prey species.

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