How does pepper enhance/increase the saltiness of a dish? I have found that after adding ground pepper (any type, color, or heat level), some dishes seem to be saltier. This sometimes occurs with other spices, as well. Note that I am not using anything else that contains salt.

I always taste as I go and something will seem to have the perfect amount of salt. But almost immediately after adding pepper or other spices the dish will seem to be too salty.

Also, I have cooked something that seemed to be perfectly seasoned, but if one adds ground pepper at the table, it seems to be saltier.

Another example is that when I cook certain types of curries and use a wide range of other spices, a minimal amount of salt is needed, and the dishes do not lack any salt flavor.

I have learned over time that when other spices are to be added to decrease the amount of salt, so it's not an issue. (I can always add more, if needed.) However I am curious as to why/how this happens.
It's not just saltiness, but various taste sensitivities that are impacted by pepper.  Basically, piperine (the component in black pepper which causes its pungency) and capsaicin (the "hot" chemical in hot peppers) cause mild irritation and inflammation in the mouth when consumed.  That inflammation leads to additional sensitivity of taste receptors.  Saltiness, acidity (i.e., sourness), and feelings of hot and cold are generally the most impacted by this inflammation; all of these sensations are enhanced.  (For a brief summary of some of the various impacts of pungent pepper compounds, see here.)

However, in excessive amounts, piperine and capsaicin can inhibit the normal taste receptors for the major flavors.  But a small amount of inflammation, as produced by the relatively mild form of black pepper's piperine, will make parts of the mouth more sensitive and thereby enhance certain flavors, including saltiness.

(I don't know the details for which other spices you mention, but many spices have effects beyond the basic taste buds.  In fact, many substances are chosen as spices for the wide variety of bodily sensations they can cause, often resulting in pain or irritation, which is why they tend to be used in very small quantities.  Particularly other "pungent" spices -- ginger and cinnamon, for example -- also have mild irritating effects on the body, which might induce alterations in sensation and taste.)