Translated "without which not". The sense is something like: This is the thing without which you will not succeed. It is an absolutely indispensible thing or condition.
.....or "most essential requirement". When one or more of those things disappear in nature, the chain is affected. Take for example the relationship between Desert Mistletoe and the Phainopepla. The Mistletoe spreads by seed with the help of this bird and the bird benefits from the berries in the wild.
You can't have one without the other.