Big Cats as Nature’s Check Against Disease

A summary of theoretical, empirical, and experimental evidence supporting predator cleansing of CWD in deer and elk herds by mountain lions and wolves.

Predator cleansing is the idea or hypothesis that predators, especially apex carnivores sitting atop their ecosystem’s food chain, can prevent or control the spread of infectious diseases in prey populations by hunting and killing the sickest and most infectious animals. In theory and perhaps in practice, this reduces the transmission, incidence, and prevalence of wildlife infections and improves the overall health, survival, and fitness of the prey population.

The predator cleansing concept, also sometimes referred to as disease sanitizing, is derived from the intuitive wildlife ecology notion that predators selectively target, pursue, kill, and consume sick, injured, weak, very young, very old, and otherwise vulnerable individuals—“the newly born and the nearly dead” — among the prey population. By carnivore calculus, these “less fit” individual prey might be easier to hunt (less energy expenditure by the predator) and be less likely to cause serious injury to the predator during the pursuit, takedown, and kill.

A prevailing idea in wildlife ecology is that coursing predators (such as wolves and coyotes) who approach their prey openly or pursue them for long distances will capture young, old, sick, weak, injured, or inexperienced individuals from prey populations in higher-than-expected (i.e., non-random) proportions. Whether stalking opportunistic predators (such as mountain lions and bobcats) also preferentially select ill prey remains to be tested. Even for coursing predators, despite its wide acceptance, this idea rarely has been tested and to our knowledge not for wolves.

Separate from whether predators preferentially select (deliberately target) diseased individuals, apex- and meso-carnivores, both predators and scavengers, are hypothesized to function as potential disease-sanitizing agents (“predator cleansers”) by removing infected and infectious prey (or their dead but infectious remains). This reduces the infection or disease incidence across a prey population. The effectiveness of predators as sanitizers needs scientific evaluation with a long-term study of prey disease loads.