The merits of studying oceanic island floras in a team of early career researchers

The post is provided by Dagmar Martina Hanz

This post refers to the article “High species turnover and low intraspecific trait variation in endemic and non-endemic plant species assemblages on an oceanic island” by Hanz et al., published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.13120).

Learning from oceanic islands

As an ecology student, you learn plenty of ecological theory is based on scientific work that has been carried out on oceanic islands. However, if you have never been to an oceanic island, the scope of the knowledge that has been gained and still can be gained from such an isolated and heterogeneous study system is beyond your imagination, no matter how many lectures you visit or how many books you read. Hence, when I got the chance to travel to la isla bonita, La Palma (Canary Islands), to conduct a research study within a Science School organized by the Department of Biogeography at the University Bayreuth, I was clearly excited. Not only was I about to study the flora of the Canary Islands, but I was also about to work in a wonderful team of early career researchers.

My particular interest is in analysing functional differences and similarities of endemic and non-endemic plants. Hence, it was clear that I would want to study patterns in traits of plants from different evolutionary origins along La Palma’s pronounced environmental gradients. Luckily, two other students showed interest in studying plant traits as well: Mirela Beloiu, a driven and ambitious PhD researcher focused on forest ecology, and Raja Wipfler, a vivacious and highly motivated Bachelor’s student focused on conservation ecology. As a committed research team, we now happily tackled the task of designing and conducting a research study from ‘A’ to ‘Z’.

Oceanic islands are the ideal study system to analyse spatio-temporal drivers of biodiversity. However, so far, most studies on islands have focused on species richness, and only some on species traits, let alone on intraspecific variation in traits. This research gap exists even though traits can offer novel insights into how species assemble and how they can persist, evolve, and interact with other species on islands (Ottaviani et al., 2020; Schrader et al., 2021). Moreover, intraspecific variation in traits of species assemblages can inform us about the demographic resilience and evolutionary potential of floras (Des Roches et al., 2018). Yet, it is not clear whether intraspecific variation differs between plant species of different evolutionary origins (such as species that are endemic and species that are non-endemic to an island or archipelago) and whether it might impose an evolutionary advantage on such. Hence, it was clear to us that we wanted to address this research gap by analysing intraspecific variation in traits of endemic and non-endemic plant assemblages on La Palma.

Simple measurements to answer complex study questions

After determining our hypotheses, we had to come up with an adequate research design to sample the data we needed to test our hypotheses. The obstacle of our research project was that within two weeks we had to sample enough data while using low-tech methods for trait measurements which can be directly conducted in the field. To do so, we selected a minimum and a maximum number of plots and individuals that we wanted to sample. Further, we decided to measure plant height, (approximate) leaf area, and leaf thickness as those traits have important links to ecological and physiological processes and are easy to measure in the field, i.e., we had to use the ruler a lot.

Once we arrived in La Palma, we realised that the greatest obstacle might not be to frantically measure traits but to first arrive at the designated plots. Beforehand, we decided to sample species assemblages in the Tabaibal-Cardonal, an arid-dry vegetation zone along the islands’ coast. In theory, this meant to drive to the plot as close as possible, measure traits, drive to the next plot, and repeat along the entire coast of the island. However, the steep roads through the ravines and the rough terrain made it much more difficult, and sometimes almost impossible, to locomote along the coast. Even though we spent a great amount of time on the way to our plots, we were able to sample 44 plots and 1,223 individual plants. Plus, with every single plot, we were rewarded with an invaluable view of rugged cliffs dotted with the myriad green shades of the islands’ vegetation against the dark blue of the Atlantic Ocean.

Linking traits to conservation

With our study, we could show that endemic and non-endemic assemblages have similar levels of intraspecific variation despite their distinct evolutionary history. This challenges the theory that non-endemic native plants need to have a high intraspecific trait variation to proliferate in a novel environment. Moreover, we could show for the first time that intraspecific variation is more important in ‘harsh’ environments with seasonal resource availability. This underlines the demand for a higher potential in morphological flexibility across seasonal environments. Interestingly, our conclusions were derived from the collection of easy-to-measure plant traits. Hence, I am confident that the study can be reproduced on many other islands around the world to find more general patterns and processes in intraspecific variation.

At first glance, analysing intraspecific variation in plant assemblages of different evolutionary origins does not have an obvious link to conservation. However, intraspecific variation can structure assemblages and influence species’ responses to invasion, and climate change, which ultimately reflects on the ecosystem services plants provide (Des Roches et al., 2018). In the face of trait homogenization through rapid extinction of plant populations worldwide, changes in intraspecific variation might consequently cause extensive alterations to many environments in the future. Ultimately, this conclusion can be seen as a reminder of the importance to continue with our fascination to study processes and patterns in shaping biodiversity.

References:

• Des Roches, S., Post, D.M., Turley, N.E., Bailey, J.K., Hendry, A.P., & Kinnison, M.T. et al. (2018) The ecological importance of intraspecific variation. Nature Ecology & Evolution, 2, 57–64.
• Ottaviani, G., Keppel, G., Götzenberger, L., Harrison, S., Opedal, Ø.H., Conti, L. et al. (2020) Linking plant functional ecology to island biogeography. Trends in Plant Science, 25, 329–339.
• Schrader, J., Wright, I. J., Kreft, H., & Westoby, M. (2021). A roadmap to plant functional island biogeography. Biological Reviews, 96, 2851-2870.

Brief personal summary: Dagmar M. Hanz is a PhD researcher in the Biogeography and Biodiversity Lab at the Goethe-University Frankfurt. She is investigating functional diversity patterns with a particular focus on endemic and non-endemic native plant species in isolated island systems. Find more about her work here and on Twitter (@HanzDagmar).