[Rails] running bundle sometimes installs other gems than ones specified in Gemfile

Quick question. Often I add a gem to my Gemfile and then run bundle
install and I notice that it installs a bunch of other stuff (in
addition to what I wanted):

Installing warden (1.2.1)
Installing devise (2.2.3)
Installing fastercsv (1.5.5)
Installing formtastic (2.2.1)
Installing has_scope (0.5.1)
Installing responders (0.9.3)
Installing inherited_resources (1.4.0)

Does this mean that the gem I want to install is dependent on the
aforementioned gems?

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