Phylogenetic structure of an arthropod consumer community: Specialization, turnover and response to plant diversity manipulation

Background/Question/Methods

Species interactions are influenced to varying degrees by ecological similarity, which is often reflected in phylogenetic relatedness. Studies of primary producer species such as phytoplankton, herbaceous plants, and trees demonstrate that co-occurring species are often more distantly related than expected by chance; however, animal examples of this phenomenon are relatively few. Consumer species, including multiple trophic levels and spanning deep branches in the animal tree of life, are structured, in theory, by evolutionary history shared with their host plants. To test for animal community structure driven by shared evolutionary history, we develop a phylogeny estimate for a grassland arthropod community at Cedar Creek LTER in Minnesota, USA.  This phylogeny, the largest of its kind to date, includes >900 co-occurring taxa sampled from a plant biodiversity experiment.

We use this phylogeny to address three interrelated questions. First, does phylogenetic relatedness play a role in the traits of co-occurring arthropods such as trophic role, body size, or host plant specialization? Second, does higher phylogenetic diversity among plant patches lead to higher phylogenetic diversity among the consumers in those patches? Finally, does manipulation of plant species richness lead to predictable responses in phylogenetic structure of whole arthropod communities, or individual trophic guilds?

Results/Conclusions

Both trophic role and body size in the arthropod community reveal significant phylogenetic signal. Interestingly, consumer specialization as measured by association through time with monocultures of particular host plant species also shows significant phylogenetic signal, though the strength of the influence varies by plant species. Further, the phylogenetic distance among plant species in monocultures does not lead to higher phylogenetic distance among consumers. However, with increased plant species richness, more phylogenetically dissimilar plant patches lead to more phylogenetically dissimilar consumer communities. Finally, experimentally manipulated plant species richness has opposing effects on consumer phylogenetic diversity: phylogenetic diversity of herbivores increases with plant diversity, whereas higher trophic levels (predators and parasitoids) experience reduced phylogenetic diversity. Together these results demonstrate the degree to which evolutionary history of plant-insect associations  structures contemporary arthropod consumer communities, emphasizing the importance of including these phylogenetic relationships into our understanding of animal community ecology.