ECr Feature: Leo Ohyama on species-area diversity relationships in ants

Leo Ohyama is currently working toward his PhD at the University of Florida. He is an ecologist broadly interested in processes that shape the distribution of biodiversity. Leo shares his recent work on how species divesity scales across space in ant species across the globe.

Leo digging for ants in the flatwoods of Florida, USA before his interest in programming got him into an air conditioned room.

Personal links. Twitter | ResearchGate

Institute. University of Florida, Biodiversity Institute

Academic life stage. PhD

Major research themes. Broadly I am interested in how and why global biodiversity patterns are assembled and whether we can apply predictive frameworks to better understand the future of the biosphere. I am also interested in scaling up natural history to global scales through the collection and curation of traits-based data in ants (sociometric data). My themes of research lie along macroecology, island biogeography, and community ecology.

Current study system. Ants! Ants are one of the most widespread and globally distributed groups of invertebrates on the planet and make up anywhere from 15 to 20% of terrestrial biomass. They are also one of the most well-sampled invertebrates in island systems and have thrived and found success in colonizing islands around the world. Given their success they are a key insect group to include in studies that attempt to understand the spatial scaling of biodiversity.

Recent paper in JBI. Ohyama L, Holt RD, Matthews TJ, Lucky A. The species-area relationship in ant ecology. Journal of Biogeography. 2021;00:1-18

Motivation behind this paper. The motivation was really two-fold. The first one being that while patterns of ant diversity have been well documented across the planet, no one has really looked at the scaling properties of all these studies at a global scale. To me, understanding these scaling properties are just as important as understanding the general patterns of diversity as they can link local-scale processes to global-scale processes. Islands in both mainland and insular areas are an excellent system to leverage to understand these scaling properties given that ants have been well sampled across many islands around the globe.

The second motivation was that this paper was conceptualized during the beginning of the pandemic when my fieldwork was cancelled. Without any fieldwork and extra time, working on a more computational, data-synthesis project was ideal as I could work on it remotely, although it involved many weeks of reading and reviewing the literature. This was happening before finalizing and proposing my dissertation research topic. Being able to survey the literature, run analyses, and write up this paper really helped me flesh out my plans for what I wanted to do with the rest of my dissertation.   

Heavily armored ‘tank ants’ (Nomamyrmex esenbeckii) are a species of army ants that roam the forest floors of Ecuador and were recorded in several mainland fragments from the studies leveraged for the paper. They are top-predators in tropical rainforests, and specialize in raiding the nests of leaf-cutter ants. Their long raiding parties are often protected by fierce guards, fending off anything that comes too close. Picture by Philipp Hönle

Key methodologies. A novel methodology that we utilized in this study was the application of piecewise models to identify specific breakpoints which estimate the spatial scales where the slope of species-area relationships significantly shifted. These models were made available from a new function in the ‘sars’ package (Matthews & Rigal, 2021), of which one of my co-authors, Tom Matthews, was a developer. These breakpoints can be compared between different systems, such as mainland and insular systems, which helps us better see how species-area relationships change at different spatial scales among different systems.

Unexpected results and challenges. We surprisingly found that the rate at which species richness increases across area was higher in mainland relative to insular systems. This is opposite to what is often observed in the literature across a variety of taxa. Additionally, we found that precipitation was a key driver in the scaling of ant biodiversity, which contrasted other works that suggested precipitation was less influential on ant biodiversity. In terms of challenges, this was my first time writing a paper where all the co-authors were only reachable over zoom and email. In fact, two of the authors were in different countries and time zones. However, my co-authors were amazingly supportive, and I was able to proactively seek out zoom meetings with other colleagues to discuss the paper and get insight when needed.

Major results. The major result of this paper is a more comprehensive understanding of how different factors affect spatial scaling in ant biodiversity. We not only find that ant biodiversity scales at higher rates across mainland areas relative to insular ones, but we also find strong differences in these scaling properties across different biogeographical realms while also being heavily influenced by precipitation. Although ant diversity patterns are well studied across the world, the scaling properties of this diversity are less well understood, so our analyses provide much needed insight into these lesser-known areas. Additionally, our thorough review of the many studies allowed us to identify key areas for further research, including the assessment of island age and the interactions between non-native and native ants in insular systems. Finally, we accumulated a decent-sized dataset of ant diversity across a variety of islands and archipelagos around the world that can be used by other scientists to conduct their own studies on spatial scaling.

Next steps. One of my more exciting ideas is actually written in the paper! We discuss how the age of mainland islands (oftentimes habitat fragments) influence the species-area relationship. As such we propose a continental analog to the general dynamic model of island equilibrium. The inclusion of a temporal dimension to the species-area relationship has been explored but the comparison of this between insular systems and mainland systems is less well understood. This idea excites me as it involves two important dimensions, space and time, which are both crucial to the scaling of biodiversity. Temporal scale data is often rare but for ants this is not always the case.

If you could study any organism on Earth, what would it be? That’s a tough question! My initial answer would be ants because I’ve worked with them for a while now and have developed a particular fondness for them. But if I had the opportunity, I would like to study freshwater fish. This is mostly driven by the completely different system that these organisms live in. For example, in river systems, you have water currents and a network of streams and water sheds to consider when thinking about dispersal or other assembly mechanisms in a community. As a person who has mostly stuck to working with ants, these new challenges are mind-bending but also excite me because they prompt new ways of thinking. I guess I am usually more drawn to the questions and would love to keep challenging myself with different organisms, but ants will always be a staple for me (there’s plenty of them around!).

Leo observing harvester ants in the sagebrush landscape of Idaho, USA.

Anything else to add? Two things! First, my inspiration to tackle scaling topics originates from a biogeography class I took when I was a master’s student. One day in this class we spent two hours debating the concept of scale and never came to a conclusion other than “it all depends on scale”. This was a powerful moment for me and really inspired me to keep thinking about scale and the synthesis between different scales which has ultimately led to this paper. The other thing I would like to add is that I was privileged to spend an extensive amount of time doing fieldwork and studying the natural history of ants at the local community scale during my master’s degree. While I enjoy programming and working on the computer, I believe that having a grounded understanding of the study organism, including its natural history is important. It’s also important to tie the inference we make at global scales to these local scale mechanisms or local-scale studies.

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