The above movie is a model simulation.  The numbered axis represents the number of host individuals: higher on the axis represents more individuals.  The other two axis make up a metapopulation grid, providing a spatially structured population.  Individuals within each square are assumed to move and mate randomly.  However, movement between squares is limited.  The three-digit number in the bottom corner shows model iterations (representative of time).  Green indicates uninfected individuals.  Red indicates infected individuals.

At the start (time=000), the island is uniformly inhabited with an uninfected population (green) at a density of 175 individuals/square.

At the next time point, Wolbachia-infected individuals (red) are introduced into the center of the island.  No additional introductions are made.

Subsequently, unidirectional cytoplasmic incompatibility results in the spread of Wolbachia, resulting in an island that is uniformly infected with Wolbachia.  Note the change in the total population size that occurs following replacement.  Specifically, the number of individuals/square drops from 175 to 150.

What if fewer Wolbachia were introduced onto the island? ...

Click HERE, to see a simulation of multiple population replacement events that can result from Wolbachia superinfections and additive unidirectional incompatibility.

Population Replacement