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PACIFIC SCIENCE, Vol. XXII, April 1968 
another method, in plants at least, by which the 
replacement rate may be held in check. Ratten- 
bury (1962:354) has said of New Zealand 
forms: 
"Furthermore, the germination of seeds of 
many native species is a matter of extreme dif- 
ficulty, as is evidenced by the sporadic ap- 
pearance of seedlings which often seem to 
require special conditions for their develop- 
ment. Competent nurserymen have experienced 
great difficulty in germinating native seeds, 
often resorting to powerful treatments for 
breaking the dormancy. In many cases the via- 
ble period is very short.” 
Under conditions of severe interspecific com- 
petition, a reduction in the reproduction rate, 
however accomplished, would seem to be feasi- 
ble only to the extent that it enables the species 
to raise a greater number of offspring (Lack, 
1954). To drop below that rate would invite 
replacement by competitors (including possi- 
ble subsequent immigrants of the same spe- 
cies). If, however, there is very slight 
interspecific competition, the reproductive rate 
might theoretically fall to and somewhat below 
the maximum possible replacement rate with- 
out immediate harm. In my opinion, this is 
what seems to have occurred in many forms 
among the native terrestrial Hawaiian biota. 
If this is true, a species that experienced essen- 
tially no natural selection from infra- and inter- 
specific competition during the initial increase 
might again avoid natural selection after an 
equilibrium had been reached. In the process, 
however, the species would of course lose its 
aggressiveness, especially as compared with 
subsequently introduced rapidly breeding 
forms. 
Possible examples of a loss in fertility, ap- 
parently before any overpopulation has taken 
place, are provided by the Hawaiian hawk ( Bu - 
teo solitarius ) and the Hawaiian crow ( Corvus 
tropicus ), both of which are, and so far as 
known always have been, confined to relatively 
small areas of the single island of Hawaii. In 
view of the general adaptability of related 
mainland forms this geographic restriction is 
most difficult to explain. Possibly here we have 
a "depauperization of biotype” (Hulten, 1937) 
arising from small population effects. Such a 
"depauperization” of course could and prob- 
ably often does result in a lowering of repro- 
ductive capacity. 
Returning finally to the achatinellid snails 
of Oahu, it seems obvious from the isolation 
of many of the colonies of Achatinella (even 
before their extensive extermination by the 
introduced carnivorous snails Euglandina and 
Gonaxis; see Krauss, 1964) that they were not 
spreading. Presumably they can only have been 
developed from some more "aggressive” an- 
cestral form (and/or a less dissected topogra- 
phy than exists today). But given the more 
recent isolation in separate colonies there seems 
to be no reason why, in the absence of further 
gene flow, each colony should not evolve in its 
own way as do so many other small popula- 
tions, particularly land snails. A basically sim- 
ilar provisional hypothesis has been advanced 
by Carson (1966:405) to explain the forma- 
tion of Hawaiian species of Drosophilidae. 
ACKNOWJLEDMENTS 
My acquaintance with this subject has been 
gained over the years through the kind help 
of colleagues too numerous to mention. For 
specific suggestions and comments on the manu- 
script I wish sincerely to thank Dr. A. H. Ban- 
ner, Dr. E. A. Kay, and Dr. C. H. Lamoureux 
of the University of Hawaii, and Dr. Y. Kondo 
of the Bishop Museum, all of whom have been 
residents of Hawaii and interested in the 
Flawaiian biota for much or most of their lives. 
REFERENCES 
Baldwin, P. H. 1953. Annual cycle, environ- 
ment and evolution in the Hawaiian honey- 
creepers (Aves: Drepaniidae) . Univ. Calif. 
Publ. Zool. 52:285-398, pis. 8-11, 12 figs. 
Brock, V. E. 1948. An addition to the fish 
fauna of the Hawaiian Islands. Pacific Sci. 
2:298. 
Bryan, E. H., Jr. 1942. American Polynesia 
and the Hawaiian Chain. Tongg Publishing 
Co., Honolulu. 253 pp., illus. 
Carlquist, S. 1965. Island Life. The Natural 
History Press, Garden City, New York, 
viii -}- 451 pp., 7 col. pis., text figs. 
1966. The biota of long-distance dis- 
