Outstanding issues in the study of antipredator defences

Protective defence mechanisms are well documented across the animal kingdom, but there are still examples of antipredator defence that do not easily fit into the current conceptualisation. They either fall within the intersection of multiple mechanisms or fail to fit neatly into pre-existing categories. Here, using Endler’s predatory sequence as the basis of protective defence mechanism categories, we explore areas of confusion and other issues in antipredator mechanisms. We identify several problematic examples of antipredator defences and categorise them as protective mechanisms that may be difficult to classify or act sequentially depending on context. We then discuss four sections of improvement needed to resolve underlying terminological and definitional issues: (1) issues with English and polysemy, (2) expansion of definitions, (3) overlapping aspects of similar mechanisms, and (4) unclear definitions. By synthesising the literature, we disentangle several opaque areas in the study of protective defence mechanisms and highlight areas that require further research. An unclear conceptual framework in protective defence mechanisms can lead to misconceptions in understanding the function of defences displayed by animals, and the interchangeable terminologies and ambiguous definitions can hinder communication in antipredator studies.