Basic Concepts - Evolutionary Biogeography - page 22

en areas, representing biogeographic units, from a synchronic or proximal
perspective. Cenocrons are sets of taxa that share the same biogeograph-
ic history, constituting identifiable subsets within a biotic component by their
common biotic origin and evolutionary history, from a diachronic perspect-
ive.
Figure 2.6 Stages of the dispersal-vicariance model: (a-c) dispersal; (d, e) vicari-
ance.
Biotic components are basically like other perduring biological entities
(Boniolo and Carrara 2004). They may remain the same despite the pos-
sible transformations they could incur (e.g., extinction of particular clades,
dispersalofspeciesfromotherbioticcomponents), theymaysplitintotwoor
more independent biotic components as a result of vicariance, they may mix
into a new biotic component as a result of biogeographic convergence, and
eventually they may become extinct. From a diachronic perspective, ceno-
crons allow one to represent how the convergence of biotic components oc-
curs during biotic evolution ( fig. 2.7 ). If a biotic component evolves in isol-
ation ( fig. 2.7a ) , taxa integrated within it will represent a biotic unit, within
which it could be possible to track the cenocrons that have contributed to
it. When there is biotic convergence ( fig. 2.7b ) as a result of geodispersal,
two or more cenocrons are combined into a single component. Vicariance
( fig. 2.7c ) splits a biotic component into two or more descendant compon-
ents. Information about fossils, intraspecific phylogeography, and molecular
clocks helps identify cenocrons.
The concepts similar to biotic components (Morrone 2004a; Real et al.
1992) are the lineages (Jeannel 1942), generalized tracks (Croizat 1958b,
1964), horofaunas (Reig 1962, 1981), and areas of endemism (Nelson and