Summary

Classical ecological theory posits that species partition resources such that eachspecies occupies a unique resource niche. In general, the availability of more resources allowsmore species to co-occur. Thus, a strong relationship between communities of consumers andtheir resources is expected. However, correlations may be influenced by other layers in the foodweb, or by the environment. Here we show, by studying the relationship between communitiesof consumers (land snails) and individual diets (from seed plants), that there is in fact nodirect, or at most a weak but negative, relationship. However, we found that the diversity of theindividual microbiome positively correlates with both consumer community diversity and indi-vidual diet diversity in three target species. Moreover, these correlations were affected by vari-ous environmental variables, such as anthropogenic activity, habitat island size, and a possiblyimportant nutrient source, guano runoff from nearby caves. Our results suggest that the micro-biome and the environment explain the absence of correlations between diet and consumercommunity diversity. Hence, we advocate that microbiome inventories are routinely added toany community dietary analysis, which our study shows can be done with relatively little extraeffort. Our approach presents the tools to quickly obtain an overview of the relationshipsbetween consumers and their resources. We anticipate our approach to be useful for ecologistsand environmentalists studying different communities in a local food web.