Final answer:
Annual bluegrass in the southern US exists as a common grass species adaptable to various conditions, precipitating its quick reproduction and survival.
Step-by-step explanation:
The question you've asked pertains to annual bluegrass, which in the southern United States exists as a common type of grass. This grass species, known scientifically as Poa annua, can be found in many environments because of its adaptive nature. It's not exactly clear what specific function of annual bluegrass you are referring to, but it's notable for its ability to reproduce quickly and survive in a variety of conditions, which is possibly an indication of its resilience and proliferation.