You are studying two species of dung beetles, one of which rolls its dung balls during the day and rests at night. The other rolls its dung balls at night and rests during the day. These species will not breed because of

behavioral isolation.

gametic isolation.

mechanical isolation.

temporal isolation.

sexual selection.

The correct answer is temporal isolation.

Explanation:

The phenomenon of temporal isolation takes place when the two species get separated on the basis of the time of their functioning. This separation could be on the basis of the time of the day when they are active or on the basis of the difference in their mating seasons. This form of isolation creates fewer probabilities of the two species to interbreed, and can eventually result in speciation.  

Like in the given question, two species of beetles are active at a different time of the day and thus they do not interbreed and therefore it can be considered that these species are demonstrating a temporal form of isolation.