Using functional traits to better understand islands

For more than two centuries scientists and naturalists have been fascinated by islands because they are unique environments that differ from the continental mainland. For example, Borneo has very small elephants that reach a maximum height of about 2.5 m. Many Pacific Islands lack any native, terrestrial mammals but have many flightless birds (actually many of these have become extinct). These examples demonstrate the phenomena of dwarfism, taxonomic disharmony and loss of dispersal abilities that have been reported for islands. In the 1960s, Sherwin Carlquist started to highlight the uniqueness of island biota, which is now known as the island syndrome, and brought the field of island biology to the forefront.

The North Island brown kiwi
(Apteryx mantelli), one of New Zealand’s unique flightless bids. Photo: Gunnar Keppel

However, these “island syndromes” have never been comprehensively quantified. Over the last decade there has been a surge of interest in functional traits, which can quantify characteristics of organisms and hold great promise to advance our understanding of island biology. Functional traits are characteristics of organisms that relate to the organism’s role in the ecosystem. They are measured in a standardized manner, allowing comparisons of these characteristics across individuals, populations, species and communities. They hence provide a way for quantifying phenomena such as dwarfism and disharmony on islands.

In a recent paper , we argue that functional traits should be more frequently integrated in studies of island biogeography. The field of island biogeography originated in the late 1960s when mathematician Robert MacArthur and zoologist Edward O. Wilson worked together to develop a theory to explain the diversity of taxa found on islands. Their Theory of Island Biogeography was highly influential and laid the foundations for the continuously evolving field of island biogeography. We argue that the fusion between island biogeography and functional ecology could provide many new insights into how the biota of islands is put together, and propose three focal themes that would advance the field of island biology.

Some of the potential differences between plants on islands and mainland. Diagram: Modified from Ottaviani et al. (2020) Trends in Plant Science 25: 329-339.

Firstly, we could use functional traits to investigate how unique communities on islands are, when compared to similar communities on the mainland (i.e., whether there is an island syndrome). Secondly, one could investigate how the characteristics of such true islands are different from those from island-like environments on continents, such as springs in deserts. Finally, it would be important to know whether the properties of islands (such as their area and isolation from other landmasses) influence functional traits and hence the island syndrome.

Combining the fields of plant functional ecology with island biogeography will therefore provide new insights on how communities on islands are put together and what plant characteristics are conducive to surviving on islands. Such insights could prove very important beyond islands. Due to land clearing, road construction and other development activities, native ecosystems in our terrestrial landscapes are increasingly resembling islands, meaning that many of the lessons learned may have implications for conservation.

Further Reading:Ottaviani, G., Keppel, G., Götzenberger, L., Harrison, S., Opedal, Ø.H., Conti, L., Liancourt, P., Klimešová, J., Silveira, F.A., Jiménez-Alfaro, B. and Negoita, L., 2020. Linking Plant Functional Ecology to Island Biogeography. Trends in Plant Science 25: 329-339 (https://doi.org/10.1016/j.tplants.2019.12.022)

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