Abstract:
Humanity strongly depends on biodiversity and services it provides. To prevent the biodiversity loss and to
establish sustainable relations with nature humanity has to efficently manage and protect natural resources. The
problem of “what to protect” is not new but became more important than ever and could be resolved by an
appropriate use of biodiversity measures. Many indices of biodiversity have been developed in the last four
decades, with species being one of the central units. However, evolutionary and ecological studies need a precise
description of species’ characteristics to best quantify inter-species diversity, as species are not equivalent and
exchangeable. First measures taking into account species biological differences were based on species phylogenetic
relations and trait values. However, many of them measure a diversity of a set of species, and does not indicate
the respective contribution of each species to the diversity of the set. To find a remedy to this issue, other type of
measures appeared in early 90’s, comparing species through the shared amount of characteristics, but were put
aside, erroneously classified as diversity measures too. In this thesis we refer to these measures as species originality
indices. A species is original if it possesses unusual trait values compared to all others in a community or if it is
distantly related with other species in a community. Thus, the most original species have the greatest contribution
to the diversity of that community. In this thesis we sought to demonstrate the benefits of originality metrics,
particularly in conservation biology and community ecology. First we review the relation of species originality with
concepts of species’ diversity and rarity and we compare their related measures. Following theoretical links
between originality and diversity measures we propose a practical application of a two-step (and two-scale)
originality framework to a real plant species data along an urbanization gradient. Finally, we discuss main pitfalls and advantages related to species
data, to the spatial scale of a study and to the choice of an originality measure. Future studies could use originality measures
with other entities than species, such as genes or habitats, and therefore broad the extent of biodiversity assessment
and conservation.
