Text by Guillermo Bueno
Taking as a reference the distribution of herbivores in the Arctic, James Speed with the contribution of 22 researchers of the herbivory network (including Guillermo Bueno from the Botany department of the UT) have tried to answer this question. Similar to large-scale diversity patterns, functional and phylogenetic diversities are commonly assumed to be driven by abiotic factors (i.e. climate), while few efforts have attempted to analyze whether biotic factors (i.e. trophic interactions) can have a role in large (functional and/or phylogenetic) diversity patterns. Here we estimated the functional diversity, considering herbivore traits including diet, digestive system type, group and body size, wintering strategy, mobility, habitat, population dynamics and litter size, and phylogenetic diversity through building an Arctic herbivore phylogeny using nucleotide sequences accessed from GenBank. We tested whether the spatial pattern of both diversities is driven by abiotic: climate severity (f.e. winter temperatures) and landscape heterogeneity, or biotic (trophic; predator diversity or vegetation productivity). In addition, we calculated the functional convergence (which is the functional similarity among species after taking into account their relatedness). Functional convergence will happen if a large functional diversity occurs within a group of closely related species (low phylogenetic diversity) and functional divergence in the opposite situation, when low functional diversity is not much clustered in the phylogeny. Convergence can indicate that the trait evolution has had certain constrains. In fact, our results showed that the assemblages of herbivores were functionally convergent in some parts of the Arctic, like Victoria Island and Subarctic Quebec region (see bottom figure), possibly indicating some weak environmental limitations. Overall, we found a predominant role of biotic interactions, both predators (top-down) and vegetation productivity (bottom-up) to herbivore functional and phylogenetic diversity, which along with winter temperature are driving the spatial patterns of functional and phylogenetic diversity (see figure below). These results highlight the need to consider biotic interactions at larger scales and under current changes in winter climate.
Figure including at the top – Hypothetical pairings of Arctic herbivores demonstrating high and low levels of functional (browsers and grazers) and phylogenetic diversity (Aves and Artiodactyla) and functional divergence to convergence (ratio of functional diversity to phylogenetic diversity); and at the bottom, the standardised effect sizes of phylogenetic and functional diversity and functional convergence (full details can be found in the paper
Citation: Speed, J. D., Skjelbred, I. Å., Barrio, I. C., Martin, M. D., Berteaux, D., Bueno, C. G., … & Grytnes, J. A. (2019). Trophic interactions and abiotic factors drive functional and phylogenetic structure of vertebrate herbivore communities across the Arctic tundra biome. Ecography, https://doi.org/10.1111/ecog.04347 (link to full text)
Communities are assembled from species that evolve or colonise a given geographic region, and persist in the face of abiotic conditions and interactions with other species. The evolutionary and colonisation histories of communities are characterised by phylogenetic diversity, while functional diversity is indicative of abiotic and biotic conditions. The relationship between functional and phylogenetic diversity infers whether species functional traits are divergent (differing between related species) or convergent (similar among distantly related species). Biotic interactions and abiotic conditions are known to influence macroecological patterns in species richness, but how functional and phylogenetic diversity of guilds vary with biotic factors, and the relative importance of biotic drivers in relation to geographic and abiotic drivers is unknown. In this study, we test whether geographic, abiotic or biotic factors drive biome‐scale spatial patterns of functional and phylogenetic diversity and functional convergence in vertebrate herbivores across the Arctic tundra biome. We found that functional and phylogenetic diversity both peaked in the Western North American Arctic, and that spatial patterns in both were best predicted by trophic interactions, namely vegetation productivity and predator diversity, as well as climatic severity. Our results show that both bottom‐up and top‐down trophic interactions, as well as winter temperatures, drive functional and phylogenetic structure of Arctic vertebrate herbivore assemblages.. This has implications for changing Arctic ecosystems; under future warming and northward movement of predators potential increases in phylogenetic and functional diversity in vertebrate herbivores may occur. Our study thus demonstrates that trophic interactions can determine large‐scale functional and phylogenetic diversity just as strongly as abiotic conditions.