Abiotic and biotic predictors of macroecological patterns in bird and butterfly coloration

Abstract

Animal color phenotypes are invariably influenced by both their biotic community and the abiotic environments. A host of hypotheses have been proposed for how variables such as solar radiation, habitat shadiness, primary productivity, temperature, rainfall, and community diversity might affect animal color traits. However, while individual factors have been linked to coloration in specific contexts, little is known about which factors are most important across broad taxonomic and geographic scales. Using data collected from 570 species of birds and 424 species of butterflies from Australia, which inhabit an area spanning a latitudinal range of 35° and covering deserts, tropical and temperate forests, savannas, and heathlands, we test multiple hypotheses from the coloration literature and assess their relative importance. We show that bird and butterfly species exhibit more reflective and less saturated colors in better‐lit environments, a pattern that is robust across an array of variables expected to influence the intensity or quality of ambient light in an environment. Both taxa display more diverse colors in regions with greater net primary production and longer growing seasons. Models that included variables related to energy inputs and resources in ecosystems have better explanatory power for bird and butterfly coloration overall than do models that included community diversity metrics. However, the diversity of the bird community in an environment was the single most powerful predictor of color pattern variation in both birds and butterflies. We observed strong similarities across taxa in the covariance between color and environmental factors, suggesting the presence of fundamental macroecological drivers of visual appearance across disparate taxa.

Reconciling ecogeographical rules: rainfall and temperature predict global colour variation in the largest bird radiation

“…These global patterns are in general agreement with recent work on Australian birds both at the species and assemblage levels, which showed similar negative precipitation effects and positive temperature effects (Friedman & Remeš ; Dalrymple et al . ; Delhey ). However, some of these effects vary in strength depending on the specific region (Dalrymple et al .…”

“…However, some of these effects vary in strength depending on the specific region (Dalrymple et al . ; Delhey ) or taxonomic group assessed (Friedman & Remeš ). Similarly, work on Spanish birds also reported a positive correlation between plumage lightness and temperature, but not with rainfall (Galván et al .…”

“…However, other climatic (and non‐climatic) variables may be playing additional roles (Dalrymple et al . ) and correlations with temperature and precipitation may be driven by other causes. For example, it has been suggested that Gloger's rule should be reformulated in terms of vegetation rather than precipitation because the former is presumably more closely linked to the putative mechanism (darker animals more camouflaged in darker environments)(Zink & Remsen ).…”

“…Here, we deliberately focused on the two climatic variables that are most closely linked to the original ecogeographical rules. However, other climatic (and non-climatic) variables may be playing additional roles (Dalrymple et al 2018) and correlations with temperature and precipitation may be driven by other causes. For Figure 5 Proposed framework integrating the effects of precipitation (Gloger's rule) and temperature (Bogert's rule) on animal light-to-dark variation.…”

Reconciling Ecogeographical Rules: Rainfall and Temperature Predict Global Colour Variation in the Largest Bird Radiation

“…Here we have deliberately focused on the 389 two climatic variables that are most closely linked to the original ecogeographical rules. However, 390 other climatic (and non-climatic) variables may be playing additional roles (Dalrymple et al 2018) 391 and correlations with temperature and precipitation may be driven by other causes. For example, it 392 has been suggested that Gloger's rule should be reformulated in terms of vegetation rather than 393 precipitation because the former is presumably more closely linked to the putative mechanism 394 (darker animals more camouflaged in darker environments) (Zink & Remsen 1986).…”