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

Citation

Carey, Mark (2022), Habitat diversity, resource availability, and island age in the species-area relationship, Dryad, Dataset, https://doi.org/10.5061/dryad.ksn02v763

Abstract

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, 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.

Methods

Data was collected from published sources and the current upload is collected analysis relating to the paper JBI-21-0522.