Pool diversity shapes unique island communities

Compiling a new island dataset enables a global perspective on the unique diversity of the smallest communities.

Above: A group of small islands Pianemo, Raja Ampat, Indonesia. Like many before us, we studied island systems to better understand the drivers community composition.  Photo by Sutirta Budiman on Unsplash.

Island biogeography is one of the most iconic, foundational areas of ecological research. With their clear boundaries and convenient spatial arrangements, islands have historically been used to better understand evolution, species richness, the distribution of certain species traits, among others. I’ve always loved reading island biogeography articles for this very reason: islands are natural “test tubes” that provide unique opportunities to elegantly answer questions about how biodiversity is developed and maintained through time, and in different places.

Cover image article: (Free to read online for a year.)
Hébert, K., Millien, V. and Lessard, J.-P. (2021), Source pool diversity and proximity shape the compositional uniqueness of insular mammal assemblages worldwide. J Biogeogr. https://doi.org/10.1111/jbi.14156oi.org/10.1111/jbi.14070 

Our paper is no exception: we use islands to delve into the processes that shape mammal communities, like selection, dispersal, and stochasticity. We also take advantage of the diversity of islands worldwide in an attempt to uncover some global-scale generality in the driving forces shaping ecological communities on islands. This “zoomed out” look at how different regions differed in the processes that shape their local communities is the most exciting part of our paper (to me!). Because of this, we were able to ask whether communities differ according to their “source pool”, which is all the species in a broad region that are able to get to, and live in, a given habitat, at a global scale – a question that has remained challenging to answer empirically because it is so difficult to sample many regions in one study. Thanks to range maps published by the International Union for Conservation of Nature, we were able to construct source pools for each of the nine island systems to see how the regions varied in their diversity. We also took this a step further and built source pools for each of the 206 islands in our dataset, which showcased the exceptionally high mammal diversity in South-East Asia (some islands have more than 500 species in their source pool!) which contributes to the unique communities we observed. Inferring these local and regional source pools allowed us to ask our questions at both scales, which is not usually accessible to many ecological studies.

Using these pools, we found that both the composition and the proximity to the source pool have a strong influence on the composition of mammal communities on islands worldwide. When islands are further from their source pool (such as the other landmasses surrounding them, or the mainland), their mammal communities tend to be more phylogenetically ‘unique’, especially if this source pool is phylogenetically diverse. In other words, island communities tend to include species from more unique evolutionary lineages if they are isolated and in a highly biodiverse region.

The Philippine tarsier (Carlito syrichta) is endemic to the Philippines, contributing to the unique phylogenetic composition of the insular mammal communities we observed in this region. Photo by Deb Dowd on Unsplash.

Although island biodiversity is often studied, it can actually be quite difficult to find occurrence data for entire island communities, even for one of the most beloved groups: mammals! Although we had some data from Virginie’s previous work on mammal body size on islands, we quickly realised we would have to expand on these data to build a multi-region island community dataset if we wanted to answer the questions we wanted to explore. So, I spent months scanning the literature and flipping through atlases and checklists to build a portrait of mammal community composition for several other island systems across the world. The result is a dataset of mammal community composition for about 200 islands in nine archipelagos around the world (which is available at https://doi.org/10.5061/dryad.rfj6q579r). It has incredible potential for ecological research including community ecology, island biogeography, and conservation biology, and we hope the dataset can be used to answer many other questions about the ecological world in the future.

Written by:
Katherine Hébert
PhD candidate, Department of Biology, Université de Sherbrooke, 2500 Bd de l’Université, Sherbrooke, QC J1K 2R1

Additional information:
GitHub: github.com/katherinehebert

Published by Biogeography.news

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