Aim: The General Dynamic Model (GDM) links island biogeographical processes to island geological history. A key premise of the GDM implies that environmental factors shaping the ecology and evolution of insular biota follow a hump-shaped trend over the island’s life span and drive dynamics in carrying capacity, species diversity and endemism. An important component of the GDM is environmental heterogeneity (EH), but its effects on insular diversity remain poorly understood. Here, we first quantified EH, tested whether EH follows the expected hump-shaped trend along island ontogeny and evaluated how EH relates to plant diversity.

Location: 135 oceanic islands of volcanic origin.

Taxon: Vascular plants.

Methods: We calculated 20 alternative EH metrics for focusing on topographic and climatic components of EH, and comparing whole-island metrics (e.g., range) and moving-window metrics (e.g., roughness). Using linear mixed-effects models, we evaluated the trends of EH with island age and the EH-plant diversity relationship expected based on the GDM.

Results: Our analysis revealed some EH components to be collinear, e.g., elevation and temperature heterogeneity, but also underlined that EH metrics capture different aspects of EH, e.g., climatic gradients vs. climatic complexity. EH generally followed a hump-shaped trend with island age with an early peak in island ontogeny. Among the EH components, climatic heterogeneity had the strongest effect on plant species richness and elevation heterogeneity on endemism. Including EH into previous analytical models to test the GDM improved their predictive power.

Main conclusions: The EH metrics compared here captured various attributes of the environment that influence insular plant diversity. In line with the GDM, our results strongly support the hump-shaped relationship between EH and island age, suggesting that islands become highly heterogeneous early in their ontogeny. Finally, the contribution of EH to GDM-based models of species richness and endemism suggests that EH is a main driver of the diversity of oceanic island biotas.

Data analysed and produced in this study

1. Number of native and single-island endemic species, age, area and archipelago information per island were obtained from the Global Inventory of Floras and Traits (GIFT). The GIFT database provides information of distributions and floristic status (native, endemic, alien) of plant species based on a wide range of regional floristic databases, floras and checklists (Weigelt et al., 2020)

2. Information of environmental components:

1.1. Elevation was downloaded from URL: https://cgiarcsi.community/data/srtm-90m-digital-elevation-database-v4-1/. Heat load index, was derived from elevation data using the Spatial Analyst extension and the Geomorphometry & Gradient Metrics toolbox (Evans et al., 2014) in ESRI ArcGIS version 10.4. URL: https://github.com/jeffreyevans/GradientMetrics.

1.2 Precipitation and temperature were downloaded from URL: http://chelsa-climate.org/

1.3. Heterogeneity rasters were produced using the Spatial Analyst extension and the Geomorphometry & Gradient Metrics toolbox (Evans et al., 2014) in ESRI ArcGIS version 10.4.

3. The code created in R software is also available. With the code EH metrics can be calculated and statistical anylsis can be reproduced.