When a species, owing to highly favourable circumstances, increases inordinately in numbers in a small tract,
epidemics— epidemics— 1859 1860 1861 1866 1872 | epidemics—at 1869 |
at at 1859 1860 1861 1866 1872 | at 1869 |
least, this seems generally to occur with our game
animals— animals— 1859 1860 1861 1866 1872 | animals—often 1869 |
often often 1859 1860 1861 1866 1872 | often 1869 |
ensue: ensue: 1859 1860 1861 1866 1869 | ensue; 1872 |
and here we have a limiting check independent of the struggle for life. But even some of these so-called epidemics appear to be due to parasitic worms, which have from some cause, possibly in part through facility of diffusion amongst the crowded animals, been
disproportionally disproportionally 1861 1866 1869 1872 | disproportionably 1859 1860 |
favoured: and here comes in a sort of struggle between the parasite and its prey. |
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On the other hand, in many cases, a large stock of individuals of the same species, relatively to the numbers of its enemies, is absolutely necessary for its preservation. Thus we can easily raise plenty of corn and rape-seed, &c., in our fields, because the seeds are in great excess compared with the number of birds which feed on them; nor can the birds, though having a superabundance of food at this one season, increase in number proportionally to the supply of seed, as their numbers are checked during
winter: winter: 1859 1860 1861 1866 1869 | winter; 1872 |
but any one who has tried, knows how troublesome it is to get seed from a few wheat or other such plants in a
garden: garden: 1860 1861 1866 1869 1872 | garden; 1859 |
I have in this case lost every single seed. This view of the necessity of a large stock of the same species for its preservation, explains, I believe, some singular facts in
nature, nature, 1859 1860 1861 1866 1869 | nature 1872 |
such as that of very rare plants being sometimes extremely
abundant abundant 1859 1860 1861 1866 1869 | abundant, 1872 |
in the few spots where they do
occur; occur; 1859 1860 1861 1866 1869 | exist; 1872 |
and that of some social plants being social, that
is, is, 1859 1860 1861 1866 1869 | is 1872 |
abounding in individuals, even on the extreme
confines confines 1859 1860 1861 1866 1869 | verge 1872 |
of their range. For in such cases, we may believe, that a plant could exist only where the conditions of its life were so favourable that many could exist together, and thus save
the species the species 1860 1861 1866 1869 1872 | each other 1859 |
from utter destruction. I should add that the good effects of
frequent frequent 1859 1860 1861 1866 1869 | frequent 1872 |
intercrossing, and
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