Secondary defences

Abstract In this chapter we consider defences that are usually deployed during, or just before, contact between a prey and its predator: so-called ‘secondary’ defences. Secondary defences are found right across the tree of life and therefore come in very many forms, including: 1.) chemical defences; 2.) mechanical defences; and 3.) behavioural defences. Here we review selected examples that provide useful illustrations of the ecological and evolutionary characteristics associated with secondary defences. We discuss costs of secondary defences, placing emphasis on the consequences of such costs, especially as they relate to forms of social interaction. We show also that the acquisition of secondary defences may modify niche, life history, and habitat range of prey animals and review a well-known and significant study of predator–prey co-evolution of defensive toxins of prey and resistance to those toxins in predators. We include a small selection of examples and ideas from the plant and microbe defence literature where we think a broader perspective is helpful. We begin the chapter by considering the evolutionary mechanisms that favour secondary defence evolution.