Male deer have large antlers that are used to challenge each other in fights for territory and females. The females of this group actively choose the strongest males. Which type of sexual selection is occurring with the deer population?

Both inter and intra sexual selection is taking place in the given case.

Explanation:

Intersexual and intrasexual selection are the two fundamental kinds of sexual selection. Intersexual selection takes place due to the association between the males and females of a similar species. In this form of selection, males develop certain traits to fascinate the opposite sex.  

On the other hand, intrasexual selection takes place between same-sex individuals. In this form of selection, competition takes place between the males, like deer with large antlers fight for supremacy and to mate with the females. Both these forms of selection help in the origination of sexually selected features in various species. Hence, in the mentioned deer population, both intersexual and intrasexual selection is taking place.