Habitat type and island identity as drivers of community assembly in an archipelago

By Alessandro Chiarucci, Fabrizio Buldrini, Marco Cervellini, Riccardo Guarino, Marco Caccianiga, Bruno Foggi, Daniele Viciani, Lorenzo Lazzaro, Laura Casella, Pierangela Angelini, Bruno Enrico Leone Cerabolini, Salvatore Pasta, Mirko Enea & Piero Zannini

A Mediterranean mountain heath with Genista desoleana Vals. on top of Monte Capanne, Elba Island (1089 m a.s.l.). Monte Capanne is the highest peak of the Tuscan Archipelago. Photo credit: Bruno Foggi.

Islands represent ideal study models in ecology and biogeography because of their well-delimited nature. Numerous papers have been exploring the mechanisms affecting the number of species found on islands and their composition, trying to relate them with islands’ characteristics. However, these patterns have typically been investigated by using floras, while the growing availability of vegetation data is still far from being exploited in this topic.

Island’s area and degree of isolation are the two most studied factors driving the number of species and composition on islands. However, it is becoming increasingly clear that the type, number and extension of habitats found on islands, also play a primary role in shaping these patterns.

Here we take advantage of a well-known island system, the Tuscan Archipelago (Italy), which is composed by land-bridge islands, namely islands that are geologically part of the continent and have been isolated because of sea-level rise. We test the following hypotheses: 1) vegetation data can be used to investigate island biogeographic patterns; 2) habitat area can be used to predict the number of species within island independently from the island area; 3) the number of species and their composition is mostly driven by the type of habitat rather than the island identity on land-bridge islands.

Pianosa Island coast with Elba Island on the background. Photo credit: Bruno Foggi.

We assembled a dataset of 1561 vegetation plots collected between 1975 and 2010, along with data from recently published floras. We classified the plots in major habitat type, in accordance with the available habitat cartography.

Our results demonstrated that typical biogeographic patterns can be investigated by means of vegetation data, as trends calculated on plots are similar to those calculated on floras, although different values of the parameters. In particular, vegetation data exasperated differences across different islands. Moreover, the number of species per habitat was related to habitat area. Only the third hypothesis was partially rejected. Notably, either habitat type and island identity had an important role in determining species richness and composition. However, the species composition of our plots was mostly driven by habitat type, whereas island identity was the main driver of species richness.

While providing original insights on the role of habitats and islands in shaping species patterns on archipelagos, this paper highlights the potential of vegetation data to investigate biogeographic patterns and test classical – and novel – biogeographic theories.

This is a plain language summary for the paper of Chiarucci et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.12953). The blog post was prepared by Piero Zannini and Alessandro Chiarucci.