Associational resistance in a multiple herbivore system: differential effects of mammal versus insect herbivores

Abstract Recent studies have suggested that associational resistance (AR) should be more effective in protecting plants from grazing by mammals than by herbivorous insects. We tested this hypothesis in a multiple‐herbivore system by comparing herbivory on, and reproductive success of, fireweed plants growing within meadowsweet stands with fireweeds growing outside meadowsweet stands in abandoned fields in Northern Sweden. We showed that meadowsweet mediates AR against shared mammal grazers, but not against shared insect herbivores. The risk of fireweed plants being browsed by mammals when growing in the absence of meadowsweet was at least double (41 % affected) that of plants growing within meadowsweet patches (17.5 % affected). We also showed that whereas mammal browsing had a negative effect on fireweed performance, the effect of insect herbivory was negligible. Our results support the hypothesis that AR is more effective against grazing mammals than against herbivorous insects.