Grazing-Induced Proteinase Inhibitors: A Possible Cause for Lemming Population Cycles

Abstract

Neutral extracts of experimentally wounded Carex bigelowii and Eriophorum angustifolium inhibit the proteolytic activity of trypsin. Increasing trypsin inhibitor activity was associated with a concomitant decrease in the concentration of soluble plant proteins (TI/SPP-ratio). At different phases of a three year lemming cycle, the TI/SPP-ratio was highest at peaking and declining densities and lowest when lemming density increased. Moreover, lemmings from a declining population showed pancreatic hypertrophy, which is a well documented pathology caused by a prolonged dietary intake of trypsin inhibitors