IS POPULATION-DENSITY A SPECIES CHARACTER - COMPARATIVE ANALYSES OF THE NEMATODE PARASITES OF MAMMALS

An increasingly popular approach to the question of what determines po pulation density is to compare the characteristics of common and rare species. However, if densities vary wildly between populations or thro ugh time, or are poorly sampled, the search for species level traits m ay be fruitless, and perhaps not even justified. For example, parasite densities have been considered too variable for comparative analyses. Here, we use repeatability analysis on data of 62 species of mammalia n nematodes where population density of each species was measured in a t least two different host populations, and analysed three measures of parasite density: intensity, abundance and prevalence (abundance = pr evalence x intensity). About half of the variation in population inten sity was found between parasite species rather than between population s within species. For abundance there were significant, but less prono unced differences between parasite species. Population intensify and a bundance also differed significantly across the 25 host species sample d. For prevalence, interpopulation variation within both parasite and host species may be too dominating for cross-species analyses to be fr uitful. In line with this, prevalence and intensity were only weakly c orrelated, and had different frequency distributions. Intensity follow ed a log-normal distribution across both population estimates and spec ies means; population prevalence estimates were bimodally distributed, but species means were normally distributed. Thus, despite striking v ariation within species, differences in population intensity between m ammalian nematode species are identifiable from literature surveys, su ggesting that comparative studies may be important for understanding i ntensity variation. More generally, repeatability analyses may also gu ide meaningful comparisons of cross-species analyses made in different species assemblages.