Here's how it works:
* Marmots are large, burrowing rodents that create extensive tunnel systems in the alpine environment.
* Ground squirrels, smaller rodents, often take advantage of these pre-existing burrows for shelter and nesting.
* The marmots benefit nothing from the ground squirrels sharing their burrows.
* The ground squirrels benefit by having ready-made, safe shelter, saving them the energy and time of digging their own.
This is commensalism because the ground squirrels benefit from the relationship while the marmots are neither helped nor harmed.
