Final answer:
The small vertebrate that is unlikely to be part of a soil food web is the small bird.
Step-by-step explanation:
Based on the options provided, the small vertebrate that is unlikely to be part of a soil food web is the small bird. Soil food webs primarily consist of organisms that live in or interact with the soil, such as earthworms, bacteria, fungi, and small animals like rats and squirrels. While foxes and small birds may be predators or prey in other ecosystems, they typically do not have a direct role in soil food webs.
Learn more about Soil food web