Functional diversity: an overview of its history and applicability

Ecological investigations are increasingly using functional diversity in order to understand different patterns, such as species occurrence, species competitive abilities, and the influence of biological communities on ecosystem functioning. Here we provide an overview of the history and applicability of functional diversity in ecological studies. We found that the idea of functional diversity emerged many times and in distinct fields over the years. Functional diversity was conceived as an alternative classification to measure the ecological importance of species in a community, as well as a way to understand how biodiversity affects specific ecosystem functions. Gradually, new questions regarding functional traits emerged. Some examples include understanding species competitive abilities, patterns of species co-occurrence, community assembly, and the role of different traits on ecosystem functioning. The increasing use of functional-based approaches fueled the search for new metrics aiming at accurately estimating functional diversity and, consequently, categorical-based classifications of functional traits have been gradually replaced by continuous multi-trait approaches. More recently, the role of functional diversity was recognized as a key factor to maintain important functions and services of ecosystems. We present empirical evidence supporting this statement.