[Taxacom] Galapagos biogeography and geology

[John Grehan]

Following paper is available on request. Please email directly, not as a
reply so as not to lose track.

The Galápagos Islands: biogeographic patterns
and geology
Michael Heads1* and John R. Grehan2

ABSTRACT
In the traditional biogeographic model, the Galápagos Islands appeared a
few million years ago in a sea where no other islands existed and were
colonized from areas outside the region. However, recent work has shown
that the Galápagos hotspot is 139 million years old (Early Cretaceous), and
so groups are likely to have survived at the hotspot by dispersal of
populations onto new islands from older ones. This process of
metapopulation dynamics means that species can persist indefinitely in an
oceanic region, as long as new islands are being produced. Metapopulations
can also undergo vicariance into two metapopulations, for example at active
island arcs that are rifted by transform faults. We reviewed the geographic
relationships of Galápagos groups and found 10 biogeographic patterns that
are shared by at least two groups. Each of the patterns coincides spatially
with a major tectonic structure; these structures include: the East Pacific
Rise; west Pacific and American subduction zones; large igneous plateaus in
the Pacific; Alisitos terrane (Baja California), Guerrero terrane (western
Mexico); rifting of North and South America; formation of the Caribbean
Plateau by the Galápagos hotspot, and its eastward movement; accretion of
Galápagos hotspot tracks; Andean uplift; and displacement on the Romeral
fault system. All these geological features were active in the Cretaceous,
suggesting that geological change at that time caused vicariance in
widespread ancestors. The present distributions are explicable if ancestors
survived as metapopulations occupying both the Galápagos hotspot and other
regions before differentiating, more or less in situ.