Food Chains
Let’s clarify terminology:
A food chain is a series of steps in which organisms transfer energy by eating and being eaten.
Miller and Levine, Biology, ed. 2010, page 73
A vegan foodchain has the same starting point as any non-vegan food chains (non sentient primary producers) and the same target point as any non-vegan food chains (humans) – which means that vegans are at the top of their food chain precisely as well as non vegans. Rather than being an argument against veganism, food chains are an argument in favour of veganism: Vegan foodchains are inherently more efficient, because of better http://feed conversion ratios, due to a smaller number of links. This also logically implies that veganism is inherently less resource-intensive than any alternatives (as shown clearly by research).
Circle of life
The concept of “Circle of Life” is often used in arguments against veganism, but it has no biological definition, and has no scientific relevance.
If we define it as some sort of supernatural “energy” flowing through living things, a “symbolic representation of birth, survival and death“, “Nature’s way of taking and giving back life to earth. It symbolizes the universe being sacred and divine. It represents the infinite nature of energy, meaning if something dies it gives new life to another“… : this is just pseudoscience.
If we define it as a concept related to food chains… see section above about food chains.
If we define it as biological life cycle, what is the argument against veganism exactly? What biological cycles would vegan affect, which non-vegan do not affect?
“Circle of Life” arguments against veganism are bullshit, however you define the meaning of the expression.