A food web basically shows the transfer of energy from the sun all the way up to apex predators. The food web above is the food web of a Long Eared Jerboa, it shows what the Jerboa eats and what eats it.
Producers (red): grass, berries, rotting wood/leaves
Primary Consumers (blue): lizard, grasshopper, beetle
Secondary Consumers (green): Jerboa, spider
Tertiary Consumers (pink): little owl, fennec fox
Apex Predators (orange): eagle owl, Peregrine Falcon
Decomposers: asian water monitor, gray faced buzzard
Producers (red): grass, berries, rotting wood/leaves
Primary Consumers (blue): lizard, grasshopper, beetle
Secondary Consumers (green): Jerboa, spider
Tertiary Consumers (pink): little owl, fennec fox
Apex Predators (orange): eagle owl, Peregrine Falcon
Decomposers: asian water monitor, gray faced buzzard
Biomagnification
It is very unlikely that a toxic chemical will ever be introduced into the environment of the Jerboa but if it were the population of the Jerboa would probably go down significantly. Because of bio-magnification the Apex predators in the environment would die off and the tertiary predators population would go way up; because of that the Jerboas would have more predators so their population would drop.
Note: According to Dr. Jonathan Baillie (Zoological society of London) very little is known about the Jerboa and it's only known predator is the Little Owl (Athene Noctura)