Many examples of associational resistance have been reported, in which a plant’s neighbors reduce the rate of damage by herbivores
that it experiences. Despite 30 years of interest and hundreds of examples of associational resistance, we still know very
little about how plants avoid their herbivores. This lack of mechanistic understanding prevents us from predicting when or
where associational resistance will be important or might affect species’ distributions. I demonstrate here that the plant
neighborhoods that surrounded focal mule’s ears (
Wyethia mollis) individuals affected the damage they received. In particular, distance between a focal mule’s ears individual and its nearest
sagebrush neighbor (
Artemisia tridentata) was a good predictor of how much leaf area the mule’s ears would lose to herbivores over 2 years. Mule’s ears close to sagebrush
suffered less loss than those with more distant nearest sagebrush neighbors. Mule’s ears with near sagebrush neighbors suffered
half the leaf loss as mule’s ears with sagebrush experimentally removed. This associational resistance was probably not caused
by sagebrush attracting or increasing populations of predators of generalist herbivores. Sagebrush is known to emit chemicals
that are feeding deterrents to generalist grasshoppers and these deterrents were probably involved here. Volatile chemicals
emitted by damaged sagebrush have been found to induce resistance in neighboring plants of several species. However, I found
no evidence for such eavesdropping here as mule’s ears gained associational resistance from sagebrush neighbors whether or
not those sagebrush neighbors had been experimentally damaged. Understanding the mechanisms responsible for associational
resistance is critical to predicting where and when it will be important.
Keywords Associational resistance - Eavesdropping - Herbivory - Plant neighborhood - Volatile cue