[New Paper] Birds in paradise: biogeography in the subtropics

Light-vented bulbul (Pycnonotus sinensis), one of the species of interest in the Ryūkyū archipelago.

Biogeography is often more complicated than the species-area relationship as discussed in a recent Journal of Animal Ecology paper testing multiple extensions of island biogeography theory. Sam Ross, lead author of the study, describes how this work fits into the long history of biogeography research.

The species-area relationship is considered one of the only ‘rules’ in ecology. We have observed more species on larger ‘islands’ (whether true islands or simply some habitat patch of interest) in studies of different plants and animals all around the world. When MacArthur and Wilson (1967) proposed this pattern and the pioneering biogeographical principles which underpin it, they acknowledged that a piece of the puzzle was missing: species identity.

Biogeographers have since recognised that species aren’t randomly distributed across the globe. We now believe there to be ecological factors which predict where species occur. For example, predators can only live in habitats where their prey are sufficiently abundant, otherwise they’ll starve. This led Dominique Gravel and colleagues to predict that larger islands should have more complex food webs, since smaller islands support fewer prey species and so can in turn support fewer, if any, predators (Gravel et al. 2011). They then proposed that predators should be more influenced by island size than their prey, producing steeper species-area relationships for higher trophic levels. They called this idea the ‘trophic theory of island biogeography.’

We tested this empirically using checklists of bird sightings across the Ryūkyū archipelago running from southern mainland Japan to Taiwan. We separated birds by their trophic groups and found that contrary to the trophic theory of island biogeography, our predatory birds didn’t really differ in the slope of their species-area relationship from our herbivorous birds. This wasn’t really what we expected to find but the trophic theory hasn’t yet been tested across a range of different study systems, so our test helps us to understand whether communities may be structured by trophic level or not.

Expectation versus reality of our test of the trophic theory of island biogeography with the birds of the Ryūkyūs.

Another way species’ identities might structure communities is based on the idea of environmental filtering. These filters are thought to be strongest on small islands, where there is little opportunity to just scrape by. Small islands are harsh; there are many ways populations can go extinct on small islands, but particularly life on these islands is strongly affected by environmental conditions. This means that only species particularly suited to the environment are likely to survive and thrive on small islands. By expanding on the work of Claire Jacquet and colleagues (Jacquet et al. 2017), we could then predict that small islands would have species which are similar to each other and are all adapted to the local environment, whereas larger islands are more likely to contain random species from the regional pool of all species which could possibly live there.

Another longstanding idea predicts the opposite pattern. Because smaller islands have fewer resources, species must compete for those finite resources to survive. This means that on small islands, we might expect species to be widely different from each other to minimise competition for food and space. If there’s only one small grasshopper population on the island for example, it seems more likely that we’ll find five species of birds that all eat different things than five that are competing for the chance to eat this one grasshopper. So, we might expect that competition results in distinctive species on smaller islands and that as competitive pressure relaxes on larger islands, these islands again are more likely to contain a random assortment of species.

Blue Rock Thrush (Monticola solitarius) pictured at Cape Zanpa, Okinawa—the edge of the island.

We tested whether either of these two processes structured the bird communities of the Ryūkyūs by calculating the functional and phylogenetic diversity of birds on each island using two global databases. We used the global phylogeny of birds and a database of functional traits to measure the observed functional and phylogenetic diversity of birds on each of our study islands. We also tested whether this observed diversity was higher or lower than expected by random chance by shuffling the names of species on the phylogeny and functional trait matrix. Together, this meant we could test whether diversity was lower than expected by random on small islands and increasing to a random sample of the regional pool (trait-based assembly), or whether competitive assembly occurred, where diversity was higher than expected on small islands and closer to random on larger islands.

We found no clear overall pattern of either trait-based or competitive assembly of bird communities in the Ryūkyūs, but we did find some differences among our trophic groups in whether communities were structured randomly or not. The insectivorous intermediate predators showed patterns of trait-based community assembly since their phylogenetic and functional diversity was lower than expected on small islands and increased to random on larger islands.

Community assembly processes across our trophic groups of birds. We found no clear patterns for apex predators or herbivores, but intermediate predators followed the predictions of trait scaling by Jacquet et al. (2017).

Overall, we tested multiple extensions to the theory of island biogeography which have been rarely tested, and certainly not extensively across a range of study locations and focal species. In the subtropical Ryūkyū archipelago, we found that bird communities did not clearly conform to the theories laid out by recent extensions to island biogeography theory, but that some held true. For now, we encourage others to continue testing these hypotheses in a variety of study systems to see whether our subtropical bird communities show the same biogeographic patterns as animal communities around the world.

This post is written by: Sam Ross, a PhD student at Trinity College Dublin studying ecological responses to global change and a visiting research student at the Arilab.

More Info:

Ross, S. R. P-J., Friedman, N. R., Janicki, J., & Economo, E. P. (2019). A test of trophic and functional island biogeography theory with the avifauna of a continental archipelago. Journal of Animal Ecology. DOI: 10.1111/1365-2656.13029

You can read the full paper here.

Nick on Wonderlabs Podcast!

Nick chatted with Chris, OIST’s Science Communication Fellow and the host of Wonderlabs Podcast, on his soundscape research as part of the OKEON project. They dove into how the sound data is collected, processed and interpreted, and also headed into the field to listen to some birds and insects.

Check it out here!

Congrats, Graduates!

Congrats to Patricia Wepfer and Yafei Mao, the two latest PhD graduates from the lab!  Patricia is back in Switzerland working on a project at ETH Zurich, but came back for OIST graduation, and Yafei is about to leave for a postdoc at the U. of Washington.  Both Patricia and Yafei did great PhDs on coral evolution. Corals aren’t very ant-like, but we like them anyway.

Yafei and Evan
Patricia, Evan, and Satoshi Mitarai, her other advisor
Patricia signs the great ant of success (aka Strumigenys nidifex)

We had a signing “ceremony” with Patricia, Yafei, and Cong Liu, the first lab graduate from last year and is about to leave to be the E.O. Wilson postdoc at Harvard. 

Congrats everyone and Gambatte at your new jobs!

Welcome New Lab Members!

We are pleased to welcome three new arrivals to the lab recently.

-Jamie Kass (left) is starting a term as a JSPS postdoctoral fellow coming from the US. He is an expert on species distribution modeling and one of the lead developers of Wallace. He is going to be working on our OKEON community monitoring data and also collaborating on other projects related to global biodiversity.

-Fumika Azuma (center), also coming most recently from the UK where she recently got a bachelors in geography from UCL, is the new technician in the lab. She has actually been here for a while as a research intern, but we liked her so much we convinced her to stay. She will be working on a range of tasks, but especially GIS, insect collection curation, micro-CT, and molecular work.

-Kosmas Deligkaris (right), coming from the UK, has a background in neuroscience and is now a computational specialist who will be working on computational support, data and database management, server admin, workflow design, and other related projects for the lab.

Welcome everyone and Gambatte!

Open Research Technician Positions

Note added Jan 2019: These positions have been filled. Thank you for your interest.

We’re hiring!  Please see the ad below and get in touch if you are interested:

The Economo Lab (http://arilab.unit.oist.jp/) at the Okinawa Institute of Science and Technology Graduate University (http://www.oist.jp/) is seeking qualified applicants for two technician positions.  The lab works at the interface of ecology, evolution, and natural history, with an empirical focus on ant biodiversity.  We use a variety of approaches to understanding biodiversity including field expeditions, collections-based research, x-ray micro-CT, 3D modeling and morphometrics, phylogenomics, biodiversity informatics, and quantitative theory. Although two positions are described below, we are flexible with regards to division of duties among the two hired individuals.


Description:  The hired individual will get involved with a number of research activities in the lab including: curating an entomological research collection, managing lab databases, procuring lab supplies and materials, and performing miscellaneous tasks to support lab research.  In addition, there are exciting opportunities to become an expert in X-ray micro-CT scanning and downstream applications such as segmentation, 3D modeling (e.g. see our gallery online), morphometrics, 3D printing, and interacting with biodiversity data in virtual and augmented reality.

Qualifications: An undergraduate degree or higher in a scientific or technical field and experience with scientific research are required.  Although there is no requirement for proficiency in a specific computational program/language, it is important that the person has strong computational skills and a high ability to learn different software and methods independently. Although not required by any means, experience with any of the following would be highly desirable: biodiversity collections management, 3D modeling, 3D animation, data management, computational phylogenetics, geometric morphometrics, GIS, HPC, VR/AR applications.


Description:  The hired individual will be responsible for computational support of lab research including; designing and maintaining research databases, maintaining lab websites, assist with design and maintenance of bioinformatic data analysis pipelines, application support for utilizing HPC resources, and desktop support to lab members.  In addition, there are opportunities to lead or participate in development of new technologies that facilitate and accelerate biodiversity research.

Qualifications:  An undergraduate degree or higher in a scientific or technical field and experience with scientific research computing are required. As this position is not tied to a single application or task, the ideal candidate would have a good baseline of programming skills, including familiarity with both compiled and interpreted languages, and ability to learn independently. Proficiency with Linux, SQL-based database design and administration, and at least basic familiarity with server administration are required.  Experiences with one or more of the following would be highly desirable but are not required; GIS, bioinformatics, phylogenetics, ecoinformatics, parallel computing, and statistical computing

Job Data:  OIST is a newly established international graduate university located in the resort area of Onna-son, Okinawa, Japan, and offers a high quality of life and good working conditions in an international environment.  Logistical and financial assistance with relocation will be provided, along with a competitive salary and benefits package.  OIST is an English-language working environment, so knowledge of Japanese is not necessary.

To apply, please send a cover letter, CV, and list of three references with contact information to <economo@oist.jp> in an email with subject “Research Technician Application” or “Research Computing Technician Application”, as appropriate.  Informal inquiries are also welcome at the same address. Application review will begin immediately and will remain open until the positions are filled.