Abstract
The American pika (Ochotona princeps) is considered a sentinel species for detecting ecological effects of climate change. Pikas are declining within a large portion of their range, but previous studies have focused only on local pika extinction as a metric of change. We designed a procedure which can provide an earlier warning signal, based on non-invasive sampling and analysis of physiological stress in living pikas. Pikas were sampled at several locations in the Rocky Mountains for the measurement of glucocorticoid metabolites (GCMs) in faeces. Using a time series of faecal pellets from 12 individuals, we detected a significant increase in faecal GCM level in response to capture, thus biologically validating the use of a corticosterone enzyme immunoassay. We also established baseline, peak, and post-peak GCM concentrations for pikas in the Rocky Mountains, which varied according to gender and individual. This is the first study to measure stress hormone metabolites in any species of pika. The methods developed and validated in this study can be used to add non-invasive measurements of physiological stress to pika monitoring programmes and other research designed to assess pika vulnerability to predicted changes in climate. Pika monitoring programmes currently in place use a protocol that relates current site use by pikas with data on local habitat characteristics, such as elevation, to infer potential effects of climate change. Data generated by these monitoring studies can be used to identify the trends in site use by pikas in relationship to habitat covariates. However, this approach does not take into account the role of behavioural thermoregulation and the pika's use of microhabitats to ameliorate variations in climate. Incorporating a stress metric, such as GCM concentration, will provide relatively direct evidence for or against the hypothesis that pikas can be stressed by climate regardless of behavioural adaptations.
Highlights
Due to the severity of change in alpine climates, alpine mammals are predicted to be among the species most threatened by climate change (Hughes, 2000; Parmesan, 2006; Moritz et al., 2008)
We focused on pika populations occurring in the Rocky Mountains, where this species has not experienced the magnitude of decline observed in the Great Basin (Erb et al, 2011), and may better represent baseline physiology for the species
Pikas were non-lethally sampled in the Rocky Mountains in July-August 2011–2012 at Niwot Ridge long-term ecological research site (LTER) and Brainard Lake Recreation Area, both located in Boulder County, (CO, USA), and Emerald Lake, located in Gallatin County (MT, USA)
Summary
Due to the severity of change in alpine climates, alpine mammals are predicted to be among the species most threatened by climate change (Hughes, 2000; Parmesan, 2006; Moritz et al., 2008). The lowest recorded occurrence of pikas in the Great Basin has risen 150 m during the past century (Grayson, 2005), and climate has been implicated as a driver of recent pika losses in the Great Basin (Beever et al, 2010, 2011; Wilkening et al, 2011). The pika’s recent, apparently climate-driven range retraction has been highly publicized, and there has been a growing interest in documenting changes in pika distribution. Research efforts have intensified over the past decade, and government agencies and citizen science organizations throughout the western USA have initiated programmes to monitor pika distribution and assess vulnerability to predicted climate change (Garrett et al, 2011)
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