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.

研究目标：岛屿物种面积关系（island species-area relationship, ISAR）及其理论依据均假设群岛内各岛屿的面积均一，但实际情况往往并非如此。本研究对比了以生境多样性、岛屿年龄和资源可获得性指标调整或替代岛屿面积的模型性能，以修正该假设不成立带来的偏差。此外，本研究还针对两个分类群对比了不同模型的表现。
研究区域：5个热点群岛（hotspot archipelagos），即亚速尔群岛、加拉帕戈斯群岛、夏威夷群岛、佛得角群岛与加那利群岛。
研究类群：维管植物与鸟类。
研究方法：本研究采用幂律（power law）的数学框架对比相关模型，将仅包含面积项的模型作为零模型（null model），用于与其他模型进行对照。数据源自全球岛屿植物数据库（GIFT database）与已发表文献。模型对比采用群岛内线性回归分析，以及以群岛作为随机效应的混合效应模型（mixed effect models）。
研究结果：相较于仅包含面积项的幂律模型，基于生境多样性与资源可获得性对岛屿面积进行加权的方式，系统性提升了统计显著性与模型拟合度。而纳入岛屿年龄的模型并未展现出相同的拟合度系统性提升。对于维管植物而言，基于资源可获得性（能量与水分）的岛屿面积加权效果优于基于生境多样性的加权方式；但对于鸟类而言，两种加权方式的表现相当。
主要结论：鉴于群岛内各岛屿的气候、地形与地质条件整体较为均一，在岛屿物种面积关系研究中纳入此类因素具有实际价值。本研究结果表明，对于火山热点群岛中的岛屿而言，通过直接测定生境多样性与资源可获得性指标来修正面积项，要优于以岛屿年龄作为替代指标的方式。由于基于生境多样性与资源可获得性的面积加权方法能够获得更优的物种多样性预测模型，该方法在保护科学领域具备较高的应用价值。