SB 1.13.47

ahastāni sahastānām
 apadāni catuṣ-padām
phalgūni tatra mahatāṁ
 jīvo jīvasya jīvanam
Word for word: 
ahastāni — those who are devoid of hands; sa-hastānām — of those who are endowed with hands; apadāni — those who are devoid of legs; catuḥ-padām — of those who have four legs; phalgūni — those who are weak; tatra — there; mahatām — of the powerful; jīvaḥ — the living being; jīvasya — of the living being; jīvanam — subsistence.
Translation: 
Those who are devoid of hands are prey for those who have hands; those devoid of legs are prey for the four-legged. The weak are the subsistence of the strong, and the general rule holds that one living being is food for another.
Purport: 

A systematic law of subsistence in the struggle for existence is there by the supreme will, and there is no escape for anyone by any amount of planning. The living beings who have come to the material world against the will of the Supreme Being are under the control of a supreme power called māyā-śakti, the deputed agent of the Lord, and this daivī māyā is meant to pinch the conditioned souls by threefold miseries, one of which is explained here in this verse: the weak are the subsistence of the strong. No one is strong enough to protect himself from the onslaught of a stronger, and by the will of the Lord there are systematic categories of the weak, the stronger and the strongest. There is nothing to be lamented if a tiger eats a weaker animal, including a man, because that is the law of the Supreme Lord. But although the law states that a human being must subsist on another living being, there is the law of good sense also, for the human being is meant to obey the laws of the scriptures. This is impossible for other animals. The human being is meant for self-realization, and for that purpose he is not to eat anything which is not first offered to the Lord. The Lord accepts from His devotee all kinds of food preparations made of vegetables, fruits, leaves and grains. Fruits, leaves and milk in different varieties can be offered to the Lord, and after the Lord accepts the foodstuff, the devotee can partake of the prasāda, by which all suffering in the struggle for existence will be gradually mitigated. This is confirmed in the Bhagavad-gītā (9.26). Even those who are accustomed to eat animals can offer foodstuff, not to the Lord directly, but to an agent of the Lord, under certain conditions of religious rites. Injunctions of the scriptures are meant not to encourage the eaters of animals, but to restrict them by regulative principles.

The living being is the source of subsistence for other, stronger living beings. No one should be very anxious for his subsistence in any circumstances because there are living beings everywhere, and no living being starves for want of food at any place. Mahārāja Yudhiṣṭhira is advised by Nārada not to worry about his uncles’ suffering for want of food, for they could live on vegetables available in the jungles as prasāda of the Supreme Lord and thus realize the path of salvation.

Exploitation of the weaker living being by the stronger is the natural law of existence; there is always an attempt to devour the weak in different kingdoms of living beings. There is no possibility of checking this tendency by any artificial means under material conditions; it can be checked only by awakening the spiritual sense of the human being by practice of spiritual regulations. The spiritual regulative principles, however, do not allow a man to slaughter weaker animals on one side and teach others peaceful coexistence. If man does not allow the animals peaceful coexistence, how can he expect peaceful existence in human society? The blind leaders must therefore understand the Supreme Being and then try to implement the kingdom of God. The kingdom of God, or Rāma-rājya, is impossible without the awakening of God consciousness in the mass mind of the people of the world.