Do degraded grasslands provide a better habitat for plateau pika? —Testing the nutritional hypothesis

Abstract

Besides overgrazing by livestock, browsing by small native mammals, such as plateau pikas, is considered an important cause of alpine grassland degradation on the Qinghai-Tibetan Plateau (QTP). Preference of pikas for degraded grasslands, resulting in increased population density, has been proposed as the most accepted hypothesis. However, few studies have explored the mechanisms underlying the habitat preferences of pikas. Herein, we analyzed aboveground biomass, community composition, forage quality of lightly and severely degraded alpine grasslands, and the diet and nutritional intake of pikas living there to test whether the plant community structure and associated nutrient composition of severely degraded grasslands are more suitable for pikas in terms of dietary and nutritional requirements. Our results showed that the plant community structure differed between lightly and severely degraded grasslands, with lightly degraded grasslands containing more food plants preferred by pikas. The nutritional composition of plants in severely degraded grasslands was less suitable for pikas than that in lightly degraded grasslands. Our results reject the nutritional hypothesis that severely degraded grasslands meet the dietary and nutritional needs of pikas better. We conclude that food and nutrient selection are not drivers of population increase in pikas in the severely degraded grasslands of the QTP.