Yes, you can get "big sized" guinea pigs.They will be bigger because they have eaten a lot of food,(maybe filling food) or because they're older, or both!

Bite-sized.

A food that is a size of a halfed sized of square

a shark is one if u want a food chain of the ocean-

plankton -> tiny water animals -> small sized fish -> middle sized fish -> large fish.

Small sized animals need less food as compared to large sized animals. A field of plants can support more numbers of small animals as compared to large sized animals which need more food, it is why smaller animals are numerous .