CHAPTER III. STRUGGLE FOR EXISTENCE.
6. STRUGGLE FOR LIFE MOST SEVERE BETWEEN INDIVIDUALS AND VARIETIES OF THE SAME SPECIES. (continued)
The store of nutriment laid up within the seeds of many plants seems at
first sight to have no sort of relation to other plants. But from the
strong growth of young plants produced from such seeds, as peas and beans,
when sown in the midst of long grass, it may be suspected that the chief
use of the nutriment in the seed is to favour the growth of the seedlings,
whilst struggling with other plants growing vigorously all around.
Look at a plant in the midst of its range! Why does it not double or
quadruple its numbers? We know that it can perfectly well withstand a
little more heat or cold, dampness or dryness, for elsewhere it ranges into
slightly hotter or colder, damper or drier districts. In this case we can
clearly see that if we wish in imagination to give the plant the power of
increasing in numbers, we should have to give it some advantage over its
competitors, or over the animals which prey on it. On the confines of its
geographical range, a change of constitution with respect to climate would
clearly be an advantage to our plant; but we have reason to believe that
only a few plants or animals range so far, that they are destroyed
exclusively by the rigour of the climate. Not until we reach the extreme
confines of life, in the Arctic regions or on the borders of an utter
desert, will competition cease. The land may be extremely cold or dry, yet
there will be competition between some few species, or between the
individuals of the same species, for the warmest or dampest spots.
Hence we can see that when a plant or animal is placed in a new country,
among new competitors, the conditions of its life will generally be changed
in an essential manner, although the climate may be exactly the same as in
its former home. If its average numbers are to increase in its new home,
we should have to modify it in a different way to what we should have had
to do in its native country; for we should have to give it some advantage
over a different set of competitors or enemies.