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Export to Excel select * from OriginOfSpecies where subject = '03 - Struggle for Existence' order by subject, title, ordinal limit 20, 4 (Page 6: Row)
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03 - Struggle for Existence 03-09 - Complex Relations of all Animals and Plants Throughout Nature 40 In the case of every species, many different checks, acting at different periods of life, and during different seasons or years, probably come into play; some one check or some few being generally the most potent; but all will concur in determining the average number or even the existence of the species.

In some cases it can be shown that widely-different checks act on the same species in different districts.

When we look at the plants and bushes clothing an entangled bank, we are tempted to attribute their proportional numbers and kinds to what we call chance.

But how false a view is this!

Every one has heard that when an American forest is cut down a very different vegetation springs up; but it has been observed that ancient Indian ruins in the southern United States, which must formerly have been cleared of trees, now display the same beautiful diversity and proportion of kinds as in the surrounding virgin forest.

forest
forest


What a struggle must have gone on during long centuries between the several kinds of trees each annually scattering its seeds by the thousand; what war between insect and insect- between insects, snails, and other animals with birds and beasts of prey- all striving to increase, all feeding on each other, or on the trees, their seeds and seedlings, or on the other plants which first clothed the ground and thus checked the growth of the trees!

insect
insect

snail
snail

bird
bird

prey
prey

tree
tree

seeds
seeds

seedling
seedling


Throw up a handful of feathers, and all fall to the ground according to definite laws; but how simple is the problem where each shall fall compared to that of the action and reaction of the innumerable plants and animals which have determined, in the course of centuries, the proportional numbers and kinds of trees now growing on the old Indian ruins!

feather
feather
03 - Struggle for Existence 03-09 - Complex Relations of all Animals and Plants Throughout Nature 50 The dependency of one organic being on another, as of a parasite on its prey, lies generally between beings remote in the scale of nature.

parasite
parasite

prey
prey


This is likewise sometimes the case with those which may be strictly said to struggle with each other for existence, as in the case of locusts and grass-feeding quadrupeds.

locust
locust


But the struggle will almost invariably be most severe between the individuals of the same species, for they frequent the same districts, require the same food, and are exposed to the same dangers.

In the case of varieties of the same species, the struggle will generally be almost equally severe, and we sometimes see the contest soon decided: for instance, if several varieties of wheat be sown together, and the mixed seed be resown, some of the varieties which best suit the soil or climate, or are naturally the most fertile, will beat the others and so yield more seed, and will consequently in a few years supplant the other varieties.

wheat
wheat


To keep up a mixed stock of even such extremely close varieties as the variously-coloured sweet peas, they must be each year harvested separately, and the seed then mixed in due proportion, otherwise the weaker kinds will steadily decrease in number and disappear.

pea
pea


So again with the varieties of sheep; it has been asserted that certain mountain-varieties will starve out other mountain-varieties, so that they cannot be kept together.

sheep
sheep


The same result has followed from keeping together different varieties of the medicinal leech.

leech
leech


It may even be doubted whether the varieties of any of our domestic plants or animals have so exactly the same strength, habits, and constitution, that the original proportions of a mixed stock (crossing being prevented) could be kept up for half-a-dozen generations, if they were allowed to struggle together, in the same manner as beings in a state of nature, and if the seed or young were not annually preserved in due proportion.
03 - Struggle for Existence 03-10 - Struggle for Life most severe between Individuals and Varieties of the same Species 10 As the species of the same genus usually have, though by no means invariably, much similarity in habits and constitution, and always in structure, the struggle will generally be more severe between them, if they come into competition with each other, than between the species of distinct genera.

We see this in the recent extension over parts of the United States of one species of swallow having caused the decrease of another species.

United States
United States

swallow
swallow


The recent increase of the missel-thrush in parts of Scotland has caused the decrease of the song-thrush.

Scotland
Scotland

Missel Thrush
Missel Thrush

Song Thrush
Song Thrush
03 - Struggle for Existence 03-10 - Struggle for Life most severe between Individuals and Varieties of the same Species 20 How frequently we hear of one species of rat taking the place of another species under the most different climates!

In Russia the small Asiatic cockroach has everywhere driven before it its great congener.

rat
rat

Russia
Russia

cockroach
cockroach


In Australia the imported hive-bee is rapidly exterminating the small, stingless native bee. One species of charlock has been known to supplant another species; and so in other cases.

Australia
Australia

Hive Bee
Hive Bee

charlock
charlock


We can dimly see why the competition should be most severe between allied forms, which fill nearly the same place in the economy of nature; but probably in no one case could we precisely say why one species has been victorious over another in the great battle of life.