Both Nikon L31 and Olympus VR-340 have 16.0 MP resolution sensors but Nikon L31's sensor is 1/2.3' (6.17 x 4.55 mm ) and Olympus VR-340's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Olympus VR-340's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Nikon L31.
Below you can see the L31 and VR-340 sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon L31 and Olympus VR-340 Cameras
Nikon L31 and Olympus VR-340 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.