|
→The causes which
the natural tendency of each species to increase
→are
most obscure. Look at the most vigorous species; by as much as it swarms in numbers, by so much will
to increase
still
We know not exactly what the checks are
even
single instance. Nor will this surprise any one who reflects how ignorant we are on this head, even in regard to mankind,
incomparably better known than any other animal. This subject
→of the checks to increase has
been ably treated by several authors, and I
in
future
→to discuss it
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
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
→it appears that
the seedlings
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
357 no less than
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, the more vigorous plants gradually kill the less vigorous, though fully
thus out of twenty species growing on a little plot of
(three feet by four) nine species
from the other species being allowed to grow up freely. |
| The amount of food for each species of course
the extreme limit to which each can increase; but very frequently it is not the obtaining food, but the serving as prey to other animals, which determines the average numbers of a species. Thus, there seems to be little doubt that the stock of partridges, grouse, and hares on any large estate depends chiefly on the destruction of vermin. If not one head of game were shot during the next twenty years in England, and, at the same time, if no vermin were destroyed, there would, in all probability, be less game than at present, although hundreds of thousands of game animals are now annually
On the other hand, in some cases, as with the
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