southwards or in descending a mountain. When we reach the Arctic regions, or snow-capped summits, or absolute deserts, the struggle for life is almost exclusively with the elements. |
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That climate acts in main part indirectly by favouring other species, we
may may 1859 1860 1861 1866 1869 | may 1872 |
clearly see in the prodigious number of plants
in our gardens which in our gardens which 1859 1860 1861 1866 1869 |
which in our gardens 1872 |
can perfectly well endure our climate, but which never
become become 1859 1860 1861 1866 1869 | became 1872 |
naturalised, for they cannot compete with our native
plants plants 1860 1861 1866 1869 1872 | plants, 1859 |
nor resist destruction by our native animals. |
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When a species, owing to highly favourable circumstances, increases inordinately in numbers in a small tract,
epidemics—at epidemics—at 1869 | epidemics— 1859 1860 1861 1866 1872 |
....... 1869 | at 1859 1860 1861 1866 1872 |
least, this seems generally to occur with our game
animals—often animals—often 1869 | animals— 1859 1860 1861 1866 1872 |
....... 1869 | often 1859 1860 1861 1866 1872 |
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
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