Dark diversity of flea (Siphonaptera) assemblages in South American rodents: Latitudinal and altitudinal gradients

Abstract The dark diversity of a locality is represented by species from the regional pool that are absent from this locality, even though ecological conditions of this locality are suitable. We tested for latitudinal and altitudinal gradients in the dark diversity and community completeness of flea assemblages parasitic on rodents in three regions of South America at two scales, namely (a) within a locality across all host species (= compound community) and (b) within a locality within a host species (= component community). We found that the dark diversity of compound flea communities increased from north to south and from lower to higher altitudes, but no effect of the interaction between latitude and altitude was detected. The completeness of compound communities decreased from north to south but was not affected by altitude. Similar relationships between dark diversity and latitude were found for component flea communities, but no significant effect of altitude was detected. The relationship between the completeness of component communities and latitude was similar to that of compound communities. We explained the positive relationship between latitude and flea dark diversity by the fact that the latitudinal pattern of flea species richness in South America is opposite to the classical latitudinal gradient of species richness. The occurrence of the altitudinal effect on dark diversity in compound communities and the lack of this effect in component communities suggest that the factors driving the dark diversity of flea communities depend on the scale of consideration.