A food chain is a straight line sequence of links in a food web (which animal eats which animal in an ecological community) starting from a group of species that have the same feeding habits and which eat no other species in the web, and ending at a another group of species of animal or animal that is eaten by no other species in the food web. However, food chains always start with plant life and end with an animal.
Plants are at the bottom on the food chain. They produce food for the animals next up the food chain by creating sugars from light, carbon dioxide and water through a chemical process called photosynthesis. Animals cannot make food; they consume food.
The jaguar is a top predator in Mexico, Central and South America. It is at the top of the food chain. It is a big cat and a roaring cat. It is the third largest feline in the world after the lion and tiger. The jaguar is an obligate carnivore like all cats. It prefers large prey that includes deer. Deer are ruminant mammals of the family Cervidae. Ruminants eat and digest plant-based food.
Here then is a schematic of the jaguar food chain in relation to the deer as prey in Mexico.
The jaguar also preys on animals such as the caiman. These are small crocodilians. The caiman is a consumer and eats mollusks, for example. Mollusks are herbivorous, grazing on algae. That puts another layer into the jaguar food chain. Algae are producers and are also capable of photosynthesis. Humans also eat alga such as seaweed.
Notes: the species depicted in these schematics are representational and not necessarily the actual species in this food chain. The photos of the algae and caiman are Wikimedia Commons files. The mollusk is by Orin Zebest (Flickr), the jaguar photo and the deer photo are credited on the photo and the vegetation photo is by icelight (Flickr). Thanks to all for the license to use.