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Data from: Elevation is a stronger predictor of morphological trait divergence than competition in a radiation of tropical lizards

Citation

Slavenko, Alex; Allison, Allen; Meiri, Shai (2020), Data from: Elevation is a stronger predictor of morphological trait divergence than competition in a radiation of tropical lizards, Dryad, Dataset, https://doi.org/10.5061/dryad.hdr7sqvgs

Abstract

1. Adaptations for efficient performance are expected to shape animal morphology based on selection for microhabitat use and ecological forces. The presence of competitor species is predicted to cause niches to contract and enhance trait divergence. Therefore, increased species richness is expected to lead to greater trait divergence, and to result in reduced overlap and similarity between morphologies of sympatric species.

2. We examined patterns of morphospace occupancy and partitioning in the skink fauna of New Guinea, the world’s largest tropical island. Because skink species richness is largely decoupled from elevation in New Guinea, we could examine the effects of both factors (as proxies for competition and abiotic conditions), on morphospace occupancy and partitioning.

3. We measured 1860 specimens from 79 species of skinks throughout Papua New Guinea, and examined their morphospace occupancy in a spatial context. We calculated for each assemblage within equal-area cells, the volume of morphospace occupied by all skinks, the mean volume occupied per species, and the mean distance and overlap between all species pairs. We then examined if these metrics are related to species richness and elevation.

4. Elevation is a stronger predictor of morphospace occupancy than species richness. As elevation increases intraspecific variation decreases and morphologies become more similar to each other, such that overall morphospace occupancy decreases. Highland skinks are, on average, smaller, thinner, and shorter limbed than lowland species.

5. We hypothesize that harsh climates in the New Guinea highland habitats impose strong selection on skinks to occupy specific areas of morphospace that facilitate efficient thermoregulation in sub-optimal thermal conditions. We conclude that the effect of competition on trait divergence on a community and assemblage scale is eclipsed by abiotic selection pressures in these harsh environments.

Methods

The dataset is saved as an R project, which includes all the associated data and code necessary to run the analyses. The "data" folder in the project contains two .csv files:

1. data_pca.csv contains all morphometric measurements used in the analyses.

2. all_skinks.csv contains species-specific information used for sensitivity analyses.

Furthermore, the folder contains shapefiles for all species used in the study (PNG_Scincidae), species for sensitivity analyses (PNG_skinks_notMeasured), a quarter-degree grid of PNG (PNG_25), and a raster file with a digitat elevation model of PNG (PNG_DEM).

Descriptions of how the data were collected are written in full in the Methods section of the manuscript.

Usage Notes

The R project is fully standalone, and all analyses can be run by running the .rmd file. The code will export results as .csv files into the "Results" folder, and plots as .pdf files into the "Plots" folder.

The code was designed to function on R v4, and may not run well on earlier versions of R. The code may take several days to fully run, depending on your machine.