Chemical Defense Of Boreal Woody Plants Against Vertebrate Herbivores (Snowshoe Hare, Defense, Secondary Metabolite)

Abstract

Snowshoe hares avoid feeding upon winter-dormant woody plant species, growth stages and parts that contain high concentrations of deterrent secondary plant metabolites. Winter browse that is highly palatable to showshoe hares is also high quality food for these hares: snowshoe hares maintain weight in winter when fed highly palatable browse, but do not maintain weight when fed unpalatable browse. A theory is presented that accounts for the allocation of resources to secondary plant metabolites on both evolutionary and physiological time scales. This theory predicts that: (1) Slowly growing woody plants adapted to growth on nutrient-deficient soils or in deep shade will have more effective constitutive antiherbivore defenses than more rapidly growing woody plants adapted to growth in early stages of succession on fertile soils. (2) Juvenile woody plants will be more strongly selected for antiherbivore defenses than adult woody plants. (3) Ontogenetic variation in the effectiveness of antiherbivore defenses will usually be greater in rapidly growing than slowly growing woody plants. (4) A widespread juvenile reversion of rapidly growing woody plants caused by severe winter hare browsing in the peak phase of the hare cycle is a partial cause of the cycle. Evidence for this theory is presented.