Mapping the puzzle of herbivore diversity across the Arctic: Functions and relationships matter

Figure 1 – A phylogenetically diverse Arctic herbivore community including rock ptarmigan and reindeer. Photo: Nicolas Lecomte​

By James D. M. Speed and coauthors

Understanding which species we find where, and why, is a core pillar of ecology. We teach our students that communities are filtered down to those that can arrive at a location (or have evolved there), and those that can survive in the face of abiotic and biotic conditions. When assessing diversity, we often just look at the number of species present within a location, yet not all species are equal.  We can quantify the evolutionary history of species within a community by mapping their phylogenetic diversity and we can quantify the ecological role of species within the same community by mapping their functional diversity. Since phylogenetic and functional diversity relate to the ecological filters of arrival and survival, this can give us a deeper ecological insight into community assembly than considering only species identities.

In our paper, we simultaneously assess the functional and phylogenetic diversity within vertebrate herbivores of the Arctic. Arctic herbivore communities comprise phylogenetically distant birds and mammals, and ecologically different species such migratory grazers and resident browsers (Figure 1; also on the issue cover). So, to understand how Arctic herbivore communities are regulated we need to broaden our scope beyond a single taxon, to cover both birds and mammals.

Figure 2 - Spatial patterns in diversity in terms of species richness, phylogenetic diversity, functional diversity and functional convergence. From Speed et al. (2019).​

To do this we needed to create both a species level phylogeny and a functional classification of 70 vertebrate herbivore species found in the Arctic tundra biome. This required close collaboration between phylogeneticists, ecologists and biogeographers across several countries.  Combining these with species distribution data lets us map the phylogenetic and functional diversity of a whole trophic level, across a whole biome (Figure 2), and address exciting ecological questions like: Where is herbivore diversity greatest? (the Western Nearctic) What factors are associated with high herbivore evolutionary history? (mild regions with productive vegetation and lots of predators) and what factors are associated with high ecological diversity? (regions with many habitats and predators).

Understanding how Arctic herbivore communities are regulated is important and timely. Increasing temperatures, vegetation changes, and northward movement of species are key concerns in the Arctic – and our study suggests that these changes will lead to herbivore communities in the Arctic becoming more phylogenetically and functionally diverse.

Full reference: Speed, J. D. M., Skjelbred, I. Å., Barrio, I. C., Martin, M. D., Berteaux, D. , Bueno, C. G., Christie, K. S., Forbes, B. C., Forbey, J. , Fortin, D. , Grytnes, J. , Hoset, K. S., Lecomte, N. , Marteinsdóttir, B. , Mosbacher, J. B., Pedersen, Å. Ø., Ravolainen, V. , Rees, E. C., Skarin, A. , Sokolova, N. , Thornhill, A. H., Tombre, I. and Soininen, E. M. (2019) Trophic interactions and abiotic factors drive functional and phylogenetic structure of vertebrate herbivore communities across the Arctic tundra biome. Ecography 42(6): 1152-1163 doi:10.1111/ecog.04347

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