Abstract
The cultural keystone species theory predicts plant species that are culturally important, play a role in resource acquisition, fulfil a psycho-socio-cultural function within a given culture, have high use-value, have an associated naming and terminology in a native language, and a high level of species irreplaceability qualify for cultural keystone species designation. This theory was proposed as a framework for understanding relationships between human societies and species that are integral to their culture. A greater understanding of the dynamic roles of cultural keystones in both ecosystem processes and cultural societies is a foundation for facilitating biocultural conservation. Given such important direct conservation implications of the cultural keystone species theory, we reviewed the use of this theoretical framework across the literature to identify new directions for research. Most studies often emphasized the role of cultural keystones species in human societies but failed to provide a robust and reproducible measure of cultural keystone species status or direct test of the predictions of the theory and underemphasized their potential roles in ecosystem processes. To date, no studies that mentioned cultural keystone species tested the predictions of the theory. Only 4.4% provided a measure for cultural keystone status and 47.4% have cited or applied keystone designation to a given species without providing a reproducible measure for cultural keystone species. Studies that provided a measure for cultural keystone species primarily occurred in North America while few of these studies occurred in Australia and Europe with none occurring in Africa. As such, most cultural keystone species have been designated as such qualitatively based on researcher subjectivity while other studies have designated keystone species with quantitative indices of cultural importance, often incorporating researcher biases or measuring a few of the cultural keystone status predictors rather than all of them, indicating a lack of consensus in identifying cultural keystone species. Thus, we pose the need for a paradigm shift toward the development of serious and systematic approaches for keystone designation.