Data for: Habitat diversity, resource availability, and island age in the species-area relationship

Aim: The island species-area relationship (ISAR) and its theoretical
justifications assume the area of islands to be homogeneous across an
archipelago, which is generally not the case. We compare the performance
of models that adjust or substitute for island area with measures of
habitat diversity, island age, and resource availability to account for
the violation of this assumption. We further compare the performance of
models for two taxonomic groups. Location: Five hotspot archipelagos
(Azores, Galapagos, Hawaii, Cape Verde, Canary Islands). Taxa: Vascular
plants and birds. Methods: We used the mathematical framework of the power
law to compare relevant models, treating the one containing only area as a
null model against which others were compared. Data was collated from the
GIFT database and from the literature. Models were compared using linear
regression within archipelagos and via mixed effect models with
archipelago as a random effect. Results: Weighting of island area by
habitat diversity and resource availability systematically improved
statistical significance and model fits versus the area only power law.
Models including island age did not show the same systematic improvement
in model fits. For vascular plants, weighting islands by resource
availability (energy and water) performed better than weighting by habitat
diversity, although for birds these weightings performed equally well.
Main Conclusions: Given that islands within archipelagos are fairly
uniform in climate, topography, and geology, it is worth accounting for
this in ISARs. Our results suggest that, for islands in volcanic hotspot
archipelagos this is best done by using direct measures of habitat
diversity and resource availability rather than using island age as a
proxy. Because weighting area by habitat diversity and resource
availability produced better predictors of species diversity, the proposed
approach may be particularly valuable in conservation science.