Lastly, it is important to note that a spatial correlation in FIV prevalence between connected populations can be observed only if external infections have a substantial impact on FIV prevalence within the population. An analysis of the confidence region of the male transmission parameters shows that the impact of external infections on FIV prevalence within populations is very limited for the smallest values of the external transmission rate (see Fig. 4c ). In this case, the connectivity between populations cannot be revealed by a corresponding correlation in FIV prevalence. In contrast, for the highest values of external transmission rate in the confidence region, we can expect a correlation in FIV prevalence between connected populations. To sum up, the fact that no spatial correlation in FIV prevalence is observed may simply be due to the fact that external infections are relatively rare and thus play almost no role for disease prevalence in already infected populations.