Dark butterflies camouflaged from predation in dark tropical forest understories

Abstract

1. Morphological characteristics, especially coloration, are related to thermoregulation and camouflage, both of which are crucial for species survival and fitness. In cool environments such as the understorey of closed rainforests, darker organisms have thermal advantages and may be able to absorb heat more efficiently. However, such habitats are also suitable for darker organisms with respect to camouflage, making it difficult to elucidate whether the association of dark-coloured organisms with shady environments is a consequence of thermal stress or predation pressure, or both.2. In this study, butterfly communities were surveyed and artificial butterflies (mealworms attached to plastic sheeting to mimic adult butterflies) used to test whether differences in wing luminance are related to predation rates within open and closed habitats in monsoonal tropical forests of southwestern China.3. Using artificial butterflies, significantly lower predation rates were found for dark-coloured artificial butterflies within closed habitats, whereas such relationships were not found within open habitats. It was found that actual butterfly communities were also significantly darker in closed than in open habitats.4. These results demonstrate that darker colours may have the effect of reducing predation rates in shady environments and that different habitat types can have contrasting effects on luminance and therefore predation risk.

Opposite latitudinal patterns for bird and arthropod predation revealed in experiments with differently colored artificial prey

“…By contrast, in the shady understorey of dense tropical forests, white models showing the highest luminance were the most frequently attacked by birds. This finding is in line with the results of Cheng et al (), who found that black butterfly models in tropical forests experienced lower predation rates in shady habitats than in open habitats, whereas white models showed the opposite pattern.…”

“…By contrast, in the shady understorey of dense tropical forests, white models showing the highest luminance were the most frequently attacked by birds. This finding is in line with the results of Cheng et al (2018), who found that black butterfly models in tropical forests experienced lower predation In our tropical sites, models of different colors were generally attacked at similar rates (except for the brightest, most attacked, white models), which may be explained by a decreased ability of birds to discriminate colors in the understory of tropical forest due to low light intensity (Gomez et al, 2014;Olsson, Lind, & Kelber, 2015).…”

“…Taking these results together with the observed lack of correlations between prey attack rates and the chromatic characteristics of models indicates that the luminance of the prey, rather than the color itself, is the most important determinant of predation rates in environments varying in background characteristics and ambient light availability. Similarly, Cheng et al (2018) concluded that tropical habitats that differ in light regime can have contrasting effects on prey luminance and therefore on predation risk. Luminance is especially important in the spatial vision of birds (Stevens & Cuthill, 2006), and birds generally avoid objects with high reflectance.…”

“…Therefore, variation in the illumination regime, both between and within habitats, may cause considerable differences in predation rates on the same kind of prey. For example, predation intensity on the same object can differ between illuminated and shady environments (Cheng et al, 2018;Rojas, Rautiala, & Mappes, 2014), and variations in ultraviolet light may considerably affect the search behavior of insectivorous birds (Church, Bennett, Cuthill, & Partridge, 1998).…”

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

“…Traditionally, Bogert's rule has been applied mainly to ectotherms (Clusella Trullas et al 2007) and Gloger's rule was formulated for endotherms, although the possibility that it also applies to ectotherms was left open (Rensch 1929). Past and recent work indicates that these rules could apply more broadly across animals (Amtmann 1965;Xing et al 2016;Friedman & Reme s 2017;Cheng et al 2018;Delhey 2018;Galv an et al 2018), fungi (Cordero et al 2018) and perhaps even in plants Figure 4 The association between the strength of the climatic (temperature [a, d], annual precipitation [b, e]) and environmental (tree cover [c, f]) effects on female (red) and male (blue) plumage lightness and the correlation between temperature and rainfall for different bird families (a) -(c), 65 families with 10 or more species, but results are similar using only families with 15 or more species, Table S3) or zoogeographic realm (d-f), 11 realms). Each dot depicts a family-or realm-specific effect.…”