726 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [44] 
food than during ordinary years, then the snails, crabs, sea-urchins, and 
star-fish, and all other species living together upon the bank, will also 
produce more young, as repeated observations have shown to be the case. 
But since there is neither room nor food enough in such a place for the 
maturing of all of the excessively large number of germs, the sum of indi- 
viduals in the community soon returns to its former mean. The surplus 
which nature has produced by the augmentation of one of the biocénotie 
forces is thus destroyed by a combination of all the forces, and the bioc6- 
notic equilibrium is by this means soon restored again. Where it is pos- 
sible for one to furnish suitable ground and food for an excessive num- 
ber of young germs, a greater proportion of them can arrive at maturity 
than in an entirely natural biocOnose. The oyster-breeders of Arcachon 
and Auray increase very much the mean number of oysters which arrive 
at maturity upon their beds by placing tiles in the water, upon which 
the young can attach themselves. These young are then provided with 
a suitably prepared ground over which water containing food is allowed 
to flow. If in a community of living beings the number of individuals 
of one species is lessened artificially, then the number of mature indi- 
viduals of other species will increase. Thus, upon the west coast of 
France cockles and edible mussels took the place of the oysters which 
had been caught from the beds; and upon the fertile prairies of North 
America herds of tame horses and cattle are now pastured where im- 
mense throngs of wild buffaloes (bos americanus) once ranged in full 
liberty. 
If the germ-fecundity of a species is lessened by the artificial distinction 
of many mature breeding individuals, while all the other forces of the 
community are working with their accustomed vigor, so surely must » 
there be a decrease in the number of individuals of this species which 
arrive at maturity. A largenumber of the most productive oyster-beds 
upon the west coast of Europe have been devastated by overfishing, 
and many fresh waters have, through the incessant catching of half- 
grown fish, been almost entirely depopulated. It is very natural that 
those years during which a large number of herring, salmon, or sturgeon 
are caught upon a certain stretch of territory should be followed by years 
when fewer fish appear, because in the years when large catches are 
made very many breeding individuals are destroyed. 
If in a case of subtraction the minuend is lessened while the subtra- 
hend remains the same, the remainder will be lessened also. By the 
continued artificial destruction of breeding individuals, the fecundity 
of any one species of a community may sink so low that it is no longer 
able to produce sufficient germs to insure in all cases the maturing of a 
sufficient proportion which shall escape the ordinary natural assaults 
to which they are subject in the community; the species therefore dies 
out. In this manner the dodo (Didus ineptus) became extinct upon the 
island of Mauritius in the seventeenth century, after the Portuguese, 
in 1507, had disturbed the biocGnose of the island by the introduction 
