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Comparative Study
. 2008 Jul 12;363(1501):2369-75.
doi: 10.1098/rstb.2007.2207.

Climate Change Reduces Reproductive Success of an Arctic Herbivore Through Trophic Mismatch

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Free PMC article
Comparative Study

Climate Change Reduces Reproductive Success of an Arctic Herbivore Through Trophic Mismatch

Eric Post et al. Philos Trans R Soc Lond B Biol Sci. .
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Abstract

In highly seasonal environments, offspring production by vertebrates is timed to coincide with the annual peak of resource availability. For herbivores, this resource peak is represented by the annual onset and progression of the plant growth season. As plant phenology advances in response to climatic warming, there is potential for development of a mismatch between the peak of resource demands by reproducing herbivores and the peak of resource availability. For migratory herbivores, such as caribou, development of a trophic mismatch is particularly likely because the timing of their seasonal migration to summer ranges, where calves are born, is cued by changes in day length, while onset of the plant-growing season on the same ranges is cued by local temperatures. Using data collected since 1993 on timing of calving by caribou and timing of plant growth in West Greenland, we document the consequences for reproductive success of a developing trophic mismatch between caribou and their forage plants. As mean spring temperatures at our study site have risen by more than 4 degrees C, caribou have not kept pace with advancement of the plant-growing season on their calving range. As a consequence, offspring mortality has risen and offspring production has dropped fourfold.

Figures

Figure 1
Figure 1
Onset and progression of the annual seasons of (a) plant growth and (b) calving by caribou in the Kangerlussuaq population, West Greenland, 1993 and 2002–2006. In (a), the data are expressed as the mean daily proportion of the final number of species observed on each plot versus day of observation. In (b), the data are expressed as the proportion of calves (calves/(adult females+calves)) observed each day. See §2 for further details. In each panel, the filled diamond represents the mean (±1 s.d.) among years. In both panels, symbols are unique to each year of observation. Between panels, identical symbols represent observations of plant phenology (a) or calving (b) in the same year.
Figure 2
Figure 2
Dates (in day of year) of emergence of 5% of forage species (open circles, dashed line) and of 5% of caribou births (filled circles, solid line) at the study site in Kangerlussuaq, West Greenland, during the period of continuous annual data collection from 2002 to 2006. Fitted lines are linear regressions.
Figure 3
Figure 3
(a) Relation between the midpoint of the plant-growing season and the index of trophic mismatch between caribou calving and plant phenology each year; an earlier occurrence of the midpoint of the plant-growing season leads to greater trophic mismatch. (b) Relation between the magnitude of trophic mismatch between caribou calving and plant phenology and early calf mortality. Calf mortality is calculated according to equation (2.3) in §2. (c) Relation between the magnitude of trophic mismatch between caribou calving and plant phenology and calf production. Calf production is estimated as the final proportion of calves observed each year according to the approach described in §2.

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