[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.

OIST minisymposium on using advanced imaging techniques to study evolution of ant phenotypes

Last week our lab hosted an OIST Mini Symposium titled “Advances in imaging, quantifying, and understanding the evolution of ant phenotypes” organized by Evan Economo and Francisco Hita Garcia. The aim of the symposium was to gather a small but selected group of leading researchers interested in the evolution of ant phenotypes with a strong focus on the use of x-ray microtomography (micro-CT). Our list of speakers covered experts in the fields of molecular and morphological systematics, anatomy, functional morphology, comparative morphology, adaptive trait evolution, reproductive biology, linear and geometric morphometrics, and paleontology. All invitees gave outstanding talks and presented published or ongoing research in great detail and with beautiful 2D or 3D illustrations and/or videos.

Some talks provided conceptual and technical backgrounds and perspectives of how to use micro-CT for ant morphology, how to better integrate next-generation phenomics into systematics, palaeontology, and evolutionary biology, and how to use micro-CT data and downstream 3D applications for education and public outreach.

A strong focus of the symposium was the use of micro-CT for ant functional morphology, biomechanics, and the evolution of complex phenotypes. Some guests also showed recent advances in histology-based anatomy and reproductive biology, and shared ideas of how to combine traditional histology with modern 3D imaging technologies, such as micro-CT.

We also had a session focusing on the use of 2D linear and 3D geometric morphometrics and their application for ant phylogenetics, taxonomy, trait evolution, and more generally how to use large 3D phenotypical datasets to answer questions in evolutionary biology.

One afternoon was completely devoted to practical demonstrations of how to use 3D data. Our lab shared how we scan data post-processing, 3D virtual reconstructions, 3D animations, virtual/augmented reality, 3D printing. It was useful for sharing knowledge of methodology, and stimulating ideas for future directions and applications.

The three-day symposium provided ample opportunities for socializing and chatting about on-going and potential collaborations, discussions about methods and research results, as well as brainstorming about future directions for the field. At the same time our invitees got the chance to enjoy Japanese and Okinawan culture and cuisine and show off their Karaoke skills.

Invited speakers:
Phil Barden (New Jersey Institute of Technology)
Johan Billen (KU Leuven)
Benjamin Blanchard (U. Chicago and Field Museum)
Ayako Gotoh (Konan U.)
Yoshiaki Hashimoto (U. Hyogo, Museum of Nature and Human Activities, Hyogo)
Fuminori Ito (Kagawa U.)
Roberto Keller (Museu Nacional de História Natural e da Ciência)
Andrea Lucky (U. Florida)
Christian Peeters (U. Pierre et Marie Curie)
Shauna Price (Field Museum)
Andrew Suarez (U. Illinois)

Internal speakers:
Evan P. Economo
Georg Fischer
Nick Friedman
Francisco Hita Garcia
Adam Khalife (U. Pierre et Marie Curie and OIST)

ESJ 2018 in Sapporo

Several Arilab members attended the 65th Annual Meeting of the Ecological Society of Japan in Sapporo, Hokkeido, from March 14th to march 18th. It was a great opportunity for students, postdocs, and staff scientists to present Arilab research to a broader Japanese audience. At the same time, it was a good occasion for networking, chatting about potential future collaborations, and learn more about the research done in other labs throughout Japan.

Spearheaded by Nick Friedman and supported by Nao Takashina and Francisco Hita Garcia our lab organized a successful English-speaking symposium with the title “Biodiversity: linking biogeographic pattern and process”.

Masashi Yoshimura also gave an interesting about the OKEON Churamori Project and Yuka Suzuki successfully presented her poster showing her PhD project.

We also enjoyed the local Hokkeido cuisine, especially a visit to the Sapporo Bier Garten!

Listening to ecosystems: New study published using acoustic monitoring to study Okinawa’s “Soundscape”

At every OKEON site there is a small green box attached to a tree. These boxes are acoustic monitors, and they are recording natural sounds almost constantly. As part of the OKEON project, we use these natural sound recordings, or “soundscapes”, as a way of monitoring biodiversity.

Sam Ross sets up an acoustic monitoring device at the OIST field site.

We collect more than 1 terabyte of audio data every week. If you wanted to listen to all of the recordings we’ve made so far, it would take you about 8 years… if you listened all day and never went to sleep. To sort through all this audio data, we use two approaches. First, we break the sounds up into sounds at different frequencies (i.e., pitch). This lets us get a big picture view of when and where animals are active on Okinawa. Second, we use machine learning to train our computers to detect species in which we are interested. This helps us understand more about which particular species are in each area of the island, and how their behavior varies across the year.

In many parts of Okinawa, humans and nature live close together. Managing this interaction is important for preserving wild populations of plants and animals.

Ultimately, our project aims to understand the ways that human activity affects Okinawa’s wildlife, and how we can better protect these species in the future. For more information (including videos), please see the OIST press release. A link to the study can be found here.

OKEON Churamori Project Symposium 2017

On Saturday, July 29th, many collaborators of the OKEON Churamori Project along with the general public gathered at OIST to attend the OKEON Churamori Project Symposium 2017. This event was the project’s first symposium and it was a great success, with over 170 attendees, interesting and informative talks, a panel discussion, and a post-symposium gathering that included hands-on exhibitions and a poster session where participants were able to exchange ideas.