دانلود رایگان مقاله پیش گویی بازده استتار تراکم جمعیت در لاک پشت چهار چشم

Abstract

Background matching is an important way to camouflage and is widespread among animals. In the field, however, few studies have addressed background matching, and there has been no reported camouflage efficiency in freshwater turtles. Background matching and camouflage efficiency of the four-eyed turtle, Sacalia quadriocellata, among three microhabitat sections of Hezonggou stream were investigated by measuring carapace components of CIE L*a*b* (International Commission on Illumination; lightness, red/green and yellow/blue) color space, and scoring camouflage efficiency through the use of humans as predators. The results showed that the color difference (E), lightness difference (L∗), and chroma difference (a∗b∗) between carapace and the substrate background in midstream were significantly lower than that upstream and downstream, indicating that the four-eyed turtle carapace color most closely matched the substrate of midstream. In line with these findings, the camouflage efficiency was the best for the turtles that inhabit midstream. These results suggest that the four-eyed turtles may enhance camouflage efficiency by selecting microhabitat that best match their carapace color. This finding may explain the high population density of the four-eyed turtle in the midstream section of Hezonggou stream. To the best of our knowledge, this study is among the first to quantify camouflage of freshwater turtles in the wild, laying the groundwork to further study the function and mechanisms of turtle camouflage. ©

4. Discussion

Our results are broadly in line with our expectations above. They illustrated thatthe substrate ofthe midstream section best matches the body color of the turtle, and the camouflage efficiency of the turtle is optimal when inhabiting this section. This study indicated that color, lightness, and chroma differences are lower in midstream than upstream or downstream, and showed that the score of camouflage efficiency is higher in midstream than in upstream or downstream. We discovered that the difference of color matching might be associated with the components of substrate and the background color in different sections of the stream. In the midstream, the substrate is mainly made of a large number of cobbles and pebbles (Fig. 4B) of various colors. However, because sunlight can reach midstream at noon on a sunny day, these cobbles and pebbles basically appear brown-yellow, and this color is very similar to the body color ofthe four-eyed turtle. As for substrate in upstream, however, it consists of some boulders and some sand (Fig. 4A), and the color of these boulders is dark because of very high canopy density (90%) in this section. In contrast, in downstream the substrate consists of a large amount of sand and silt (Fig. 4C) with similar color, and is the brightest due to the lowest canopy density (30%). This could explain why the lightness difference (37.08 ± 1.18) between turtle and substrate was so high in downstream