Final answer:
Natural selection, genetic drift, gene flow, and mutation are all mechanisms of evolution that can act on a single population at the same time, contributing to genetic changes and population dynamics.
Step-by-step explanation:
The mechanisms of evolution that can act on a single population simultaneously include natural selection, genetic drift, gene flow, and mutation. Each of these mechanisms contributes to the changes seen in the genetic makeup of a population. Natural selection operates based on the differential survival and reproduction of individuals with certain traits, while genetic drift refers to the random fluctuations in allele frequencies that can occur in small populations. Gene flow involves the transfer of alleles between populations, which can introduce new genetic variation, and mutation is the random change in DNA that can contribute new alleles to the gene pool. All these mechanisms can occur concurrently within a single population, influencing its evolutionary trajectory in unique ways.