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Galápagos Island Species Data

Keywords: binomial regression, transformation

Description

The Galápagos Islands about 600 miles off the coast of Ecuador provide an excellent laboratory for studying the factors that influence the development and survival of different life species. They were the site of much of Charles Darwin’s original research leading later to publication of his “Origin of Species”. Descending from a few stranded ancestors and cut off from the rest of the world, the Galápagos animals offer much more obvious proofs of the fact of evolution than can be seen in the more intricate complexities of life in most environments. Darwin wrote

The natural history of these islands is eminently curious, and well deserves attention. Most of the organic productions are aboriginal creations, found nowhere else; there is even a difference between the inhabitants of the different islands; yet all show a marked relationship with those of America, though separated from that continent by an open space of ocean, between 500 and 600 miles in width. The archipelago is a little world in itself, or rather a satellite attached to America, whence it has derived a few stray colonists and has received the general character of its indigenous productions. Considering the small size of the islands, we feel the more astonished at the number of their aboriginal beings, and at their confined range. Seeing every height crowned with its crater, and the boundaries of most of the lava-streams still distinct, we are led to believe that within a period geologically recent the unbroken ocean was here spread out. Hence, both in space and time, we seem to be brought somewhere near to that great fact---that mystery of mysteries---the first appearance of new beings on earth.

And from elsewhere in Darwin's diary:

I never dreamed that islands 50 or 60 miles apart, and most of them in sight of each other, formed of precisely the same rocks, placed under a quite similar climate, rising to a nearly equal height, would have been differently tenanted … It is the circumstance that several of the islands possess their own species of the tortoise, mocking-thrush, finches and numerous plants, these species having the same general habits, occupying analogous situations, and obviously filling the same place in the natural economy of the archipelago, that strikes me with wonder.

Johnson and Raven (1973) presented data giving the number of plant species and related variables for 29 different islands. Counts are given for both the total number of species and the number of species that occur only in the Galápagos (i.e., are endemic to the Galápagos).

Download

Data File (tab-delimited text)

Source

M.P. Johnson and P.H. Raven (1973). Species number and endemism: The Galápagos Archipelago revisited. Science 179, 893-895.

The elevations for Baltra and Seymour were obtained from web searches. The elevations for four other small islands were obtained from inspection of large-scale maps.

Analysis

Find factors that affect (a) the number of species and (b) the proportion of endemic species.