Here's why:
* Different dietary needs: Guinea pigs are herbivores, while gerbils are omnivores. This means they need different types of food.
* Different social structures: Guinea pigs are social animals who live in groups, while gerbils are more solitary.
* Size and strength differences: Guinea pigs are significantly larger and stronger than gerbils. This could lead to the gerbil being injured or stressed.
* Different housing needs: Guinea pigs need a large cage with plenty of space to run around, while gerbils can be housed in smaller cages.
* Disease risks: Different species can carry different diseases that can be transmitted to each other.
In conclusion, it is highly recommended to keep guinea pigs and gerbils in separate cages. This is the safest and healthiest option for both animals.