The effect of small-scale topography on patterns of endemism within islands

The Importance of Including Spatial Autocorrelation When Modelling Species Richness in Archipelagos: A Bayesian Approach

One of the aims of island biogeography theory is to explain the number of species in an archipelago. Traditionally, the variables used to explain the species richness on an island are its area and distance to the mainland. However, increasing evidence suggests that accounting for other variables is essential for better estimates. In particular, the distance between islands should play a role in determining species richness. This work uses a Bayesian framework using Gaussian processes to assess whether distance to neighbouring islands (spatial autocorrelation) can better explain arthropod species richness patterns in the Azores Archipelago and in the Canary Islands. This method is flexible and allows the inclusion of other variables, such as maximum altitude above sea level (elevation). The results show that accounting for spatial autocorrelation provides the best results for both archipelagos, but overall, spatial autocorrelation seems to be more important in the Canary archipelago. Similarly, elevation plays a more important role in determining species richness in the Canary Islands. We recommend that spatial autocorrelation should always be considered when modelling an archipelago’s species richness.

Habitat Islands on the Aegean Islands (Greece): Elevational Gradient of Chasmophytic Diversity, Endemism, Phytogeographical Patterns and need for Monitoring and Conservation

The Aegean archipelago, characterized as a natural laboratory for research concerning plant species diversity and phytogeography has a complex geological and paleogeographical history that varies among its phytogeographical areas. A different combination of factors of variable intensity and duration time drives patterns of its impressive plant species richness and endemism. Cliffs, a conspicuous feature of the Aegean landscape, consist of biologically closed communities that serve as refugia for obligate chasmophytes, the majority of which are Greek or Aegean endemics, and for this reason, they are also considered as habitat islands on the Aegean islands. A synoptic analysis is presented concerning chasmophytic plant diversity focusing on endemic obligate chasmophytes. Phytogeographical patterns of obligate chasmophytes, and especially the endemic ones as well as their elevational range and distribution and zeta diversity, are analyzed and discussed in the frame of climatic change, mentioning that the most threatened endemic obligate chasmophytes are those specialized in high elevation areas, and focusing on the need for monitoring and conservation.