Primary consumer

In grass → rabbit → fox, the rabbit is the primary consumer and the fox is the secondary consumer. In a longer chain such as alga → water flea → small fish → heron, the water flea is the primary consumer, the small fish is the secondary consumer and the heron is the tertiary consumer.

A primary consumer is often a herbivore because it feeds on a producer. Secondary and tertiary consumers feed on other consumers. Notice that the primary consumer is trophic level 2: trophic level 1 is occupied by the producer.

A primary consumer eats a producer, so it is at the second trophic level. A secondary consumer eats a primary consumer and is at the third level. A tertiary consumer eats a secondary consumer and is at the fourth level.