Using taxonomic and phylogenetic evenness to compare diversification in two Island Floras
Date
2010Abstract
This study compares the phylogenetic structure in the Canary Islands and Hawaii by means of the
distributions of the species number for plant families (Taxonomic evenness) and lineages (Phylogenetic
evenness) across archipelagos and across habitats in both archipelagos using the Gini coefficient. We
then investigate phylogenies to identify particular habitats contributing to such differences using
Taxonomic distinctness (AvTD) and its variation (VarTD).
Our results show that the distribution of species number among Hawaiian lineages is much more
uneven than the Canary Islands. In contrast, Hawaii produces a more even distribution of species
number by family than the Canary Islands. This may be due to the Hawaiian Flora being derived from
considerably fewer colonists than the Canarian Flora as a result of its much greater degree of isolation.
At the same time, Hawaii is represented by the same number of families as the Canary Islands. This may
stem from Hawaii’s flora being derived from a greater range of source areas despite its isolation. Finally,
there is much more diversification spread across a larger number of lineages in Hawaii. The higher
degree of Hawaiian diversification may be due to a greater range of habitats, more diverse and
phylogenetically distinct floristic sources, and low initial species diversity resulting from extreme
isolation.
Two Canarian habitats (Rock communities and Thermophilous habitats) and one Hawaiian habitat
(Wet communities) contribute to the differences in phylogenetic structure between the two
archipelagos. These habitats exhibit disproportionate levels of unevenness and may represent centres
of diversification. We propose a combination of two habitat properties, high receptivity and low
stability, to explain these results.