Two types of libraries
The DAM apps (i.e. iPhoto, Aperture, Lightroom,..etc.) handle photos using either a managed library/catalog or a referenced library/catalog.
The managed library/catalog is where the app copies the original image file and puts it inside its own database files/packages. The intent is that the user would not be directly accessing (and losing) the file. This approach is OK if your library/catalog is small enough to fit on a single drive.
The referenced library/catalog is where the app may, or may not, help you move the files from the camera or card to the OS file system folders. Aperture and LR do that. Once the images are in the file system folder, the app knows where they are and references them to do any editing work. Two advantages of this approach: the images can be on a different and larger drive than the your /boot/apps drive, the library's images can be referenced by more than one app (i.e. Aperture and LR).
LR only does the referenced library approach. Aperture can do either the managed (default) library or the referenced library. I believe iPhoto can do both the referenced or managed; however, iPhoto will not help with moving the images form the camera's cards to the file system.
My recommendation: Move to Aperture ($79 at the App Store) and use the referenced library approach. With luck, we will hear Apple announce a new Aperture release at WWDC next week on June 2nd.