Long-term demographic consequences of eavesdropping for sagebrush

Summary 1. There are now approximately 10 examples of plants that use volatile cues emitted by damaged neighbours to adjust their defences against herbivores. For two of these examples, preliminary evidence suggested that plants may experience net benefits from such eavesdropping, although eavesdropping was uncommon in one case and estimates of plant fitness were ambiguous in the other case. 2. In the current study, we examined the long-term consequences of exposure to cues emitted by experimentally clipped sagebrush neighbours. In this sagebrush system we have repeatedly found that sagebrush plants that have experimentally clipped neighbours experience less herbivore damage over the season than plants with unclipped control neighbours under field conditions. We followed a cohort of young sagebrush plants from emergence in 1999 for 12 years. Neighbours of half of these plants were artificially clipped every spring from 2004–08 and survival and flowering was measured in each autumn from 1999–2011. 3. Survival of marked branches of young plants was not consistently affected by whether its neighbour was clipped. Plants near clipped neighbours produced more branches during this period than those near unclipped neighbours. There were no measurable treatment effects on plant survival over the 12 years. Branches near clipped neighbours produced more inflorescences than branches near unclipped neighbours. 4. Seedlings were more likely to survive to the end of their first dry season in two different years near clipped neighbours compared to unclipped neighbours. 5. Synthesis. The results suggest different effects of clipped neighbours that depend on plant age. Responding to the cues of experimental clipping may provide a slight net benefit, considering these results and other published studies, even though these cues provided little predictive value about actual risk of herbivory. Responding to reliable cues may be even more beneficial and may favour plants that eavesdrop on neighbours.