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Abstract BIOGEOGRAPHIC SUBDIVISIONING OF THE TROPICAL EASTERN PACIFIC: A SHORE-FISH PERSPECTIVE D. Ross Robertson1 and Katie L Cramer2 The Tropical Eastern Pacific (TEP) stretches from the Gulf of California
to northern Peru. Thanks to its great isolation from both the remainder
of the Pacific and the tropical Atlantic the TEP has perhaps the
highest rate of regional shore-fish endemism in the world: ~80%.
Previous analyses of provincial subdivisions of the TEP, based on
patterns of local endemism among small subsets of the regional shore-fish
fauna, variously identified two or three mainland provinces with
boundaries at different points on the shoreline, indicated that
the Galapagos might represent an additional province, but did not
consider the other 4 oceanic islands/archipelagos (the Revillagigedos
group, Clipperton, Cocos and Malpelo). We examined subdivisioning
of the entire TEP based on the geographic distributions of 1,135
resident shore-fishes, and various subsets of that fauna (reef,
soft-bottom and species), using cluster-analyses refined by Analysis
of Similarity (ANOSIM)). We also examined the distribution of local
endemics throughout the TEP and how differences in faunal size versus
faunal composition contribute to levels of dissimilarity between
different areas and, hence, the definition of provinces within the
TEP. The results of our analyses support the division of the mainland
of the TEP into two provinces: the Cortez (all of the Gulf of California
plus lower Baja) and the Panamic (the remainder), each of which
has a peak in abundance of local endemics. Those analyses support
previous ideas that the northern and southern boundaries of the
TEP are located at Magdalena Bay on Baja California (~25N) and the
southern shore of the Gulf of Guayaquil (~4S), respectively. The
faunas of the five oceanic islands/archipelagos differ from those
of the two mainland provinces in being smaller, including many insular
species and having disproportionately large numbers of local endemics.
Our analyses indicate that those islands collectively represent
a third, Ocean-Island Province.
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