Replacing qualitative life‐history traits by quantitative indices in parasitoid evolutionary ecology

Life‐history traits, which describe the various aspects of the life cycle of a species, can be either quantitative or qualitative. Quantitative traits are likely to adapt to gradual changes in the environment of a species, whereas qualitative traits, which refer to traits that are discontinuous in their variation, pose constraints on the evolution of a species. Traits that are described as qualitative may indeed represent discontinuous characteristics or they can be the result of an oversimplification in the description of the life history of a species. The ovigeny index, which describes the temporal distribution of egg production for a species, has replaced a qualitative life‐history trait and has been an important contribution in our understanding of the reproductive ecology of insect parasitoids. We propose here that several other qualitative life‐history traits, currently used to describe the evolutionary ecology of insect parasitoids, could advantageously be replaced by quantitative life‐history traits. Although replacing these qualitative life‐history traits will require devising indices that are biologically and ecologically meaningful, the potential gain in our understanding of the evolutionary forces that have shaped the diversity of life‐history strategies of insect parasitoids is important and would fully warrant this effort.