Both Pentax WG-2 GPS and Nikon W300 have 16.0 MP resolution sensors but Pentax WG-2 GPS's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and Nikon W300's sensor is 1/2.3 (6.17 x 4.55 mm ).
Since Nikon W300'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 Pentax WG-2 GPS.
Below you can see the WG-2 GPS and W300 sensor size comparison.
Pentax WG-2 GPS and Nikon W300 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. On the other hand, since Pentax WG-2 GPS has 15% larger pixel area compared to Nikon W300, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.