"I suspect that the German term, Kampf etc., does not give quite the same idea. The words 'struggle for existence' express, I think, exactly what 'concurrency' does. It is correct to say in English that two men struggle for existence, who may be hunting for the same food during a famine, and likewise when a single man is hunting for food; or again it may be said that a man struggles for existence against the waves of the sea when shipwrecked."
Kutschera then goes on to claim that the definition of "concurrency" includes cooperation and competition. I am not sure I agree with this interpretation. Instead, I think it is worth pointing out the value of Darwin's central insight, that the struggle for existence includes not just the struggle between, say, the lion and the zebra, but should be used more widely in a broad metaphorical sense and is in fact most intense between organisms within the same species:
I should premise that I use the term Struggle for Existence in a large and metaphorical sense, including dependence of one being on another, and including (which is more important) not only the life of the individual, but success in leaving progeny. Two canine animals in a time of dearth, may be truly said to struggle with each other which shall get food and live. But a plant on the edge of a desert is said to struggle for life against the drought, though more properly it should be said to be dependent on the moisture. A plant which annually produces a thousand seeds, of which on an average only one comes to maturity, may be more truly said to struggle with the plants of the same and other kinds which already clothe the ground. The missletoe is dependent on the apple and a few other trees, but can only in a far-fetched sense be said to struggle with these trees, for if too many of these parasites grow on the same tree, it will languish and die. But several seedling missletoes, growing close together on the same branch, may more truly be said to struggle with each other. As the missletoe is disseminated by birds, its existence depends on birds; and it may metaphorically be said to struggle with other fruit-bearing plants, in order to tempt birds to devour and thus disseminate its seeds rather than those of other plants. In these several senses, which pass into each other, I use for convenience sake the general term of struggle for existence. On the Origin of Species (1859), Chapter III
This point is nicely illustrated by a joke about two zoo-keepers. On doing their rounds after the zoo has closed, they notice that one of the lions has escaped from its enclosure and is advancing towards them. One says to the other: "Oh dear, what are we going to do now?". The other replies "I don't know about you, but I am going to run!", to which the first zookeeper replies: "But don't be silly, you can't outrun a lion!", which elicits the reply: "I don't need to outrun the lion. I just need to outrun you!"