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, 110 (18), 7360-5

Camouflage Mismatch in Seasonal Coat Color Due to Decreased Snow Duration

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Camouflage Mismatch in Seasonal Coat Color Due to Decreased Snow Duration

L Scott Mills et al. Proc Natl Acad Sci U S A.

Erratum in

  • Proc Natl Acad Sci U S A. 2013 Jul 9;110(28):1660

Abstract

Most examples of seasonal mismatches in phenology span multiple trophic levels, with timing of animal reproduction, hibernation, or migration becoming detached from peak food supply. The consequences of such mismatches are difficult to link to specific future climate change scenarios because the responses across trophic levels have complex underlying climate drivers often confounded by other stressors. In contrast, seasonal coat color polyphenism creating camouflage against snow is a direct and potentially severe type of seasonal mismatch if crypsis becomes compromised by the animal being white when snow is absent. It is unknown whether plasticity in the initiation or rate of coat color change will be able to reduce mismatch between the seasonal coat color and an increasingly snow-free background. We find that natural populations of snowshoe hares exposed to 3 y of widely varying snowpack have plasticity in the rate of the spring white-to-brown molt, but not in either the initiation dates of color change or the rate of the fall brown-to-white molt. Using an ensemble of locally downscaled climate projections, we also show that annual average duration of snowpack is forecast to decrease by 29-35 d by midcentury and 40-69 d by the end of the century. Without evolution in coat color phenology, the reduced snow duration will increase the number of days that white hares will be mismatched on a snowless background by four- to eightfold by the end of the century. This novel and visually compelling climate change-induced stressor likely applies to >9 widely distributed mammals with seasonal coat color.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
Seasonally color changing species around the world. Geographical distributions of nine mammal species with seasonal coat color changes from brown to white in at least some populations. Species include Arctic fox (Alopex lagopus), collared lemming (Dicrostonyx groenlandicus), long-tailed weasel (Mustela frenata), stoat (Mustela erminea), snowshoe hare (Lepus americanus), mountain hare (Lepus timidus), Arctic hare (Lepus arcticus), white-tailed jackrabbit (Lepus townsendii), and Siberian hamster (Phodopus sungorus). Additional species with seasonal coat color change (e.g., least weasel; Mustela nivalis) are not shown. Maps derived from International Union for Conservation of Nature redlist metadata (www.iucnredlist.org/technical-documents/spatial-data#mammals).
Fig. 2.
Fig. 2.
Types of contrast between seasonal coat color and snow background. Radiocollared snowshoe hares from this study showing (A) 100% contrast (mismatch), (B) 60% contrast (mismatch), (C) 0% contrast (no mismatch), and (D) 0% contrast (no mismatch).
Fig. 3.
Fig. 3.
Modeled baseline and future snow conditions. (A) Length of the main snow season for the three observation years (black horizontal lines) and boxplots of snow season length for the recent past (1970–1999) baseline (blue shading) and future time periods (mid-century, 2030–2059; late-century, 2070–2099) and emissions scenarios (orange shading, RCP4.5; red shading, RCP8.5). Future boxplots represent entire population of results from 19-member climate model ensemble. Bold horizontal lines are the median, and diamonds are the mean. B is the same as A except for annual maximum snow water equivalent.
Fig. 4.
Fig. 4.
Coat color phenology, snow cover and degree days. (A) Weekly average of observed coat color for a population of wild snowshoe hares in each of 3 y [2009 (blue), 2010 (red), 2011 (black), and 2012 (green)], with fall seasons on the Left and springs on the Right. Dotted lines show the results of Bayesian change point analyses, giving the 95% credible intervals for the mean dates of initiation and completion of the color molt for each season each year. (B) Weekly average of observed snow cover in a 10-m radius around each wild hare for each of the 3 y (fall on Left and spring on Right). (C) Degree days as a measure of cooling trend in the fall and warming trend in the spring at our study site for each of the 3 y.
Fig. 5.
Fig. 5.
Projections of increasing seasonal color mismatch in the future. The black line for all panels shows average phenology of hare seasonal color molt across the 3 y of the field study. The blue line shows mean modeled snow duration for the recent past (1970–1999). The orange and red lines show the future (mid-century and late-century) mean modeled snow duration for different emissions scenarios. The gray highlighted regions represent coat color mismatch, where white hares (≥60%) would be expected on a snowless background. As the duration with snow on the ground decreases in the future, mismatch will increase by as much as fourfold in the mid-century and eightfold in the late-century.

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