The plus sign is shorthand for the Latin word "and" or "et" and came about in the late 15th century, making it a simple design for mathematicians to use as visual practice. (We know a little thing or two). For us, the design is shorthand for "and" and is a symbol of simplification between the complexities of the diets, but also the connection between the plants and the animals, the farmers and the consumers, you + V+B.
Plus, ampersand was taken. (Joke).