Age and area; a study in geographical distribution and origin of species (1922) (14592008249)

Identifier: ageareastudyinge00will_0 (find matches)

Title: Age and area; a study in geographical distribution and origin of species

Year: 1922 (1920s)

Authors: Willis, J. C. (John Christopher), 1868-1958

Subjects: Biogeography Evolution

Publisher: Cambridge (Eng.) The University press

Contributing Library: Wellesley College Library

Digitizing Sponsor: Boston Library Consortium Member Libraries

Text Appearing Before Image:

Cooks Strait having checked the dispersal of some of thespecies (127, p. 455). If, dipping at random into the NewZealand flora, one take the Boraginaceae, and divide the en-demics into five classes, one finds 2/1 (two in class 1), 1/2, 2/3,5/4, 13/5; or if one take Olearia, one finds 2/1, 5/2, 4/3, 6/4, 14/5.Always the same type of curve is formed, with an accumulationof species at one end. But this same phenomenon shows in the case of all otherspecies, whether endemic or not. In Doona in Ceylon, for ex-ample, one finds one species of large area, three of smaller, andseven of areas smaller yet. With the largest endemic genus inthe Hawaiian Islands, Cyanea, one finds (cf. Cyrtandra above)one species on four islands, six on two, and 21 on a single island.Pelea, the next largest genus, shows 1/8 (one species on allislands), 3/4, 3/3, 2/2, 11/1, again a hollow curve, running outvery much at one end. If one add up all the species of thew.a. 11 162 ENDEMISM AND DISTRIBUTION: SPECIES (pt. ii

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Arck occupied Endemic species by area from small to large ch. xv) ENDEMISM AND DISTRIBUTION: SPECIES 163 endemic genera of the Sandwich Islands, and compare them withthe endemic species in the non-endemic genera, one gets: Table showing the numbers and proportions of species of endemicand of non-endemic genera that occur on all the Hawaiian Islands,or on four to six islands, etc. Thus on all islands there occur 3-1 percent, of the species of endemic, 9-5 per cent, of the endemic speciesof non-endemic genera. Species ofendemic genera Endemic species ofnon-endemic genera A Occurring on r species % ( species /o All islands 7 31 34 9-5 4-6 23 10-2 51 14-3 3 25 111 55 15-4 2 41 18-2 72 20-2 1 island 129 57-2 144 40-4 225 99-8 356 99-8 Average dispersal 1-8 islands 2-3 islands Thus the species of the endemic genera are dispersed on theaverage some 25 per cent, less than those of the non-endemicgenera. This proves on examination to be a general rule, and isa powerful argument against local a

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