seed were never destroyed, and could be ensured to germinate in a
fitting place. So that in all cases, the average number of any animal
or plant depends only indirectly on the number of its eggs or seeds.
In looking at Nature, it is most necessary to keep the foregoing
considerations always in mind never to forget that every single organic
being around us may be said to be striving to the utmost to increase in
numbers; that each lives by a struggle at some period of its life; that
heavy destruction inevitably falls either on the young or old, during
each generation or at recurrent intervals. Lighten any check, mitigate
the
destruction ever so little, and the number of the species will almost
instantaneously increase to any amount. The face of Nature may be
compared to a yielding surface, with ten thousand sharp wedges packed
close together and driven inwards by incessant blows, sometimes one
wedge being struck, and then another with greater force.
What checks the natural tendency of each species to increase in number
is most obscure. Look at the most vigorous species; by as much as it
swarms in numbers, by so much will its tendency to increase be still
further increased. We know not exactly what the checks are in even one
single instance. Nor will this surprise any one who reflects how
ignorant we are on this head, even in regard to mankind, so
incomparably better known than any other animal. This subject has been
ably treated by several authors, and I shall, in my future work,
discuss some of the checks at considerable length, more especially in
regard to the feral animals of South America. Here I will make only a
few remarks, just to recall to the reader s mind some of the chief
points. Eggs or very young animals seem generally to suffer most, but
this is not invariably the case. With plants there is a vast
destruction of seeds, but, from some observations which I have made, I
believe that it is the seedlings which suffer most from germinating in
ground already thickly stocked with other plants. Seedlings, also, are
destroyed in vast numbers by various enemies; for instance, on a piece
of ground three feet long and two wide, dug and cleared, and where
there could be no choking from other plants, I marked all the seedlings
of our native weeds as they came up, and out of the 357 no less than
295 were destroyed, chiefly by slugs and insects. If turf which has
long been mown, and the case would be the same with turf closely
browsed by quadrupeds, be let to grow,
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