Herbivory alters resource allocation and compensation in the invasive tree Melaleuca quinquenervia

Abstract. 1. Plants may compensate for the effects of herbivory, especially under favourable growing conditions, limited competition, and minimal top‐down regulation. These conditions characterise many disturbed wetlands dominated by introduced plants, implying that exotic, invasive weeds in these systems should exhibit strong compensatory responses. 2. The Australian native Melaleuca quinquenervia is highly invasive in the Florida Everglades, U.S.A., where it experiences limited competition or herbivory from native species, making it a likely candidate for compensation. The introduced biological control agent Oxyops vitiosa feeds exclusively on the seasonal flushes of developing foliage at branch apices, which represents ≈15% of the total foliar biomass. 3. The hypothesis that M. quinquenervia compensates for folivory by O. vitiosa was tested in a series of field‐based experiments. Trees experiencing folivory over four consecutive years maintained similar levels of foliar biomass after attack yet possessed twice the number of leaf‐bearing terminal stems as undamaged trees. The biomass of these stems was similar among attacked and unattacked trees, indicating that herbivore‐damaged trees produce greater quantities of smaller terminal branches. However, undamaged trees were 36 times more likely to reproduce than herbivore‐damaged trees. 4. In a separate herbivore exclusion study, a single bout of herbivory on previously undamaged M. quinquenervia trees caused an 80% reduction in reproductive structures the following season. Herbivore‐damaged trees also possessed 54% fewer fruits than undamaged trees. An increase in the herbivory frequency (two bouts per year) or magnitude (100% simulated herbivory) did not result in a further reduction in fitness. 5. It has been concluded that M. quinquenervia partially compensates for herbivory by producing new stems and replacing foliage, but this compensation results in a substantial reduction in reproduction.