A separate dedicated antenna is required for AIS transmit/receive systems.
However, for receive only, you can share your VHF antenna by using a splitter. The splitter disconnects the antenna from the AIS to protect it when the VHF is transmitting.
Advantages of a splitter:
No second antenna is needed, wiring is greatly simplified and antenna location issues are avoided.
Some splitters include an amp to increase signal reception range.
Some splitters include a USB output for a laptop to receive AIS signals for input to a navigation SW.
Some splitters include an AM/FM output saving installation of another antenna.
Disadvantages of a splitter:
Momentary loss of AIS update signals while transmitting on the VHF.
Possible minor loss of VHF reception distance (which can be offset by number 3 above).
Make sure the splitter is designed to fail in the VHF transmit mode. Also, make sure the splitter is always on when the VHF is on by connecting it's power to the same breaker as the VHF.
I selected the Comar ASR 100 VHF/AIS Antenna Splitter which has all the features above and cost much less than a second antenna.
Here you can see the Raymarine 350 and Comar ASR 110 mounted in the ceiling above the navigation console. The back of the ICOM is on the right. The antenna cable input is moved to the splitter and the splitter output cable goes to the ICOM.