The anagenetic world of spore-producing land plants
Date
2013Abstract
A fundamental challenge to our understanding of biodiversity is to explain why some
groups of species diversify, whereas others do not. On islands, the gradual evolution of a new
species from a founder event has been called ‘anagenetic speciation’. This process does not
lead to rapid and extensive speciation within lineages and has received little attention.
Based on a survey of the endemic bryophyte, pteridophyte and spermatophyte floras of
nine oceanic archipelagos, we show that anagenesis, as measured by the proportion of genera
with single endemic species within a genus, is much higher in bryophytes (73%) and pteridophytes
(65%) than in spermatophytes (55%).
Anagenesis contributed 49% of bryophyte and 40% of endemic pteridophyte species, but
only 17% of spermatophytes. The vast majority of endemic bryophytes and pteridophytes are
restricted to subtropical evergreen laurel forests and failed to diversify in more open environments,
in contrast with the pattern exhibited by spermatophytes.
We propose that the dominance of anagenesis in island bryophytes and pteridophytes is a
result of a mixture of intrinsic factors, notably their strong preference for (sub)tropical forest
environments, and extrinsic factors, including the long-term macro-ecological stability of
these habitats and the associated strong phylogenetic niche conservatism of their floras.