The role of birds in shaping arthropod communities

Background/Question/Methods

Birds exert top-down pressure on arthropod prey populations, therefore a change in bird communities should affect the arthropod community. However, this impact is likely to be complicated due to interactions between arthropods, and difficult to study on a relevant spatial scale. Here, we use the functional extirpation of birds following the introduction of the brown tree snake to Guam to ask how bird loss impacts arthropod community composition. We collected arthropods along transects in three islands with intact bird communities (Saipan, Tinian, Rota) and Guam. We used branch beating to sample arthropods on vegetation and a Winkler sifter to collect ground-dwelling arthropods from the leaf litter. We then prepared a DNA library of the collected arthropods targeting the CO1 region, sequenced the library using Illumina sequencing, and generated an OTU table based on the NCBI database. Using the OTU table, we analyzed species diversity and composition across the islands.

Results/Conclusions

Arthropod species diversity and composition differed between Guam and the other islands, suggesting that landscape-level bird extirpation alters arthropod dynamics. Spiders were more abundant on Guam than on nearby islands, consistent with previous work. We find Coleoptera, Hymenoptera (predominantly ants), and Psocoptera to be abundant taxa in our samples, and ants to be more common in the absence of birds. Species turnover, calculated as the Jaccard distance measure, was high transect to transect. As expected, we found distinct arthropod communities from each collection method.