Approaches to measuring predation pressure

Predation pressure is a selective force that leads to the evolution of defensive mechanisms in prey. Efforts are being made to measure and evaluate predation pressure qualitatively and quantitively, using various methods. As a guide for researchers, I review and discuss the advantages and disadvantages of several commonly used methods, including direct field observations, camera traps, animal-borne instruments, prey remains identification, biochemical methods, enclosure/exclusion experiments, prey damage identification, predator survey and spoor tracking. Among these methods, molecular tools to identify prey in the predator's gut, regurgitate or scat provide reliable estimates of the type and even quantity of prey in a predator's diet. Camera traps or direct observations also provide reliable information but are limited by the often-rare predation events. There is considerable potential in combining several methods to balance out the advantages and disadvantages of individual methods. For example, attack bites on artificial prey models can be combined with molecular analyses of the eDNA left behind by the predator. However, most methods still lack experimental validation to demonstrate that they actually quantify aspects of predator–prey interactions.