Helminth faunas of wild African ruminants: effects of host traits and environmental variables on species richness and diversity

Both host identity and environmental factors are known to influence parasite species richness. Here, we analysed selected host traits and environmental variables associated with 3 aspects of helminth diversity in African ruminants. Based on the helminth faunas of 35 species of antelope and 1 species of giraffe, we studied drivers of species richness as well as taxonomic and functional diversity, combined for all helminths and separately for nematodes, cestodes and trematodes. A larger geographic host range and/or multiple habitats were associated with higher species richness in all helminths and each group individually as well as with functional diversity in all helminths, trematodes and cestodes. A wider host distribution range and larger relative brain size were both linked to higher taxonomic diversity in all helminths, and an increase in host longevity was linked to higher taxonomic diversity in nematodes. A higher level of climate moisture, relative humidity and primary production had a positive effect on trematode species richness and taxonomic diversity in all helminths, while trematode taxonomic diversity decreased in hosts from drier areas but increased in cestodes harboured by hosts from warmer areas. Our results highlight that patterns in parasite species richness and diversity emerge from an interplay of numerous factors, including host biology, environmental conditions and ecological traits of the parasites themselves. This points to the importance of carefully choosing the range of hosts considered for large-scale parasite diversity studies and underscores the need to avoid grouping too many types of parasites when looking for ecological patterns.