A scale-dependent 'functional' assessment of the concept of endemism

Whether a species can be defined as 'endemic' or not is very controversial in theoretical terms, because the concepts of 'endemism' and 'area of endemism' remain much debated among scientists. We propose that it is necessary to consider the body size scale of an organism and the breadth of its distributional range if we want to define a given species as 'endemic' or not. Thus, for instance, Madagascar can be an appropriate area of endemism for animals as large and vagile as the fossa (Cryptoprocta ferox), but it is much too large to be considered an ecologically appropriate 'area of endemism' for small-sized frogs with limited dispersal abilities. Instead, for these small species it is ecologically more appropriate to consider given forest regions within Madagascar as 'areas of endemism'. Therefore, we propose a fivestep approach in order to define whether a given species can be considered endemic or not within a set of potential candidate species, and we offer a suite of practical examples (African squirrels, African Artiodactyla and a family of freshwater turtles from the Americas) to elucidate the designated concept. We define the new concept presented herein as 'scale-dependent functional endemism'. The new concept has the benefits of including the 'ecological characteristics' of the target species in the concept of 'endemism' and being easily repeated, because it is based on rather objective criteria.