Handling immunocompetence' in ecological studies: do we operate with confused terms?

Immunocompetence is a term used in avian immunological ecology to refer to the ability of an individual to overcome potential parasite infections. However, there are multiple ecological definitions of this term currently used and all of them are rather liberal in immunological terms. This prevents much of the potential intellectual interchange between avian ecologists and immunologists, which decelerates the development of immunological ecology as a scientific discipline. We therefore highlight that the term should be handled with care. In any individual host-parasite interrelationship the demands on host immunity are distinct and thus also the measurements of immunity in any particular case should be aimed differently. Although ornithologists often aspire to obtain a single variable for immunity in their research, due to the enormous diversity of parasites possessing the ability to infect the host, there is no single value for anti-parasite resistance, i.e. no overall immunocompetence per se exists. We propose to use more rigorous terminology, consistent with the one used in classical immunology. The term immunocompetence (defined as the ability to produce anti-parasite or anti-antigen immune response) should be used as 0/1 character. The magnitude of a particular immune response (i.e. a continuous quantitative trait) should be referred to as immune responsiveness. Most importantly, both terms should always be used only with respect to a certain parasite taxon or antigen studied as otherwise they lose their explanatory value.