Climate change and foraging efficiency in a territorial herbivore: changes in food cache quality parallel a change in microclimate

Printer-friendly version

Many territorial herbivores expend a large proportion of their annual energy budget accessing and defending food resources.  Climate change might impact such species by altering the amount of energy that must be expended during foraging or territorial defense, as well as by altering the quality of available forage.  Alpine herbivores might be among the most sensitive to these changes, because of the extra metabolic demands associated with concentrated foraging during a short growing season.  For example, the American pika (Ochotona princeps) is a cold-adapted, territorial herbivore that caches food during the growing season.  This species has experienced well-documented local extinctions statistically associated with warmer, drier climates and colder winters (lower snow cover), but the mechanisms responsible for pika losses have not been identified.  We hypothesize that climate change might impact the pika by 1) reducing the quality of available forage, and 2) limiting surface activities like food-cache construction.  To test these hypotheses, pika food caches and available forage were sampled in two locations in the south-central Rocky Mountains for a comparative study spanning two decades and two latitudes: a lower latitude site in Colorado (Niwot LTER) and a higher latitude site in Montana.  To facilitate temporal comparisons, our contemporary quantification of forage characteristics followed methods used previously at each site.  Contemporary pikas at each site were found to prefer plant species high in moisture and nitrogen, and low in fiber and secondary metabolites.  However, plant species low in moisture and nitrogen, and high in fiber, have become more abundant in the environment and in pika food caches at the lower latitude study site.  The lower latitude site has also experienced a decline in the duration of annual snow cover and in the availability of moist meadow species high in nutrients (e.g., Geum rossii), along with an increase in the abundance of lower-nutrient forage species (e.g., graminoids and Minuartia obtusiloba).  At the higher latitude site, changes in available forage, foraging behavior, and  the duration of snow cover were not significant.  Pikas at the lower latitude site may face nutritional deficiencies, especially if the observed changes in climate and available forage continue.