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

Authors: Pratt, Paul; Rayamajhi, Min; Van, Thai; Center, Ted; Tipping, Philip

Submitted to: Ecological Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2005
Publication Date: 6/1/2005
Citation: Pratt, P.D., Rayamajhi, M.B., Van, T.K., Center, T.D., Tipping, P.W. Herbivory alters resource allocation and compensation in the invasive tree Melaleuca quinquenervia. Ecological Entomology. 30(3):316-326. 2005b.

Interpretive Summary: Melaleuca quinquenervia (melaleuca) is a native to eastern Australia and has been introduced to various locations around the world. One hundred years after its introduction into Florida, melaleuca grows spontaneously and displaces native plants as well as animals in the wetlands that comprise the Florida Everglades. The melaleuca snout weevil, a biological control agent, feeds exclusively on the seasonal flushes of developing foliage at branch apices, which represents ~15% of the total foliar biomass. In this study we conducted a series of field-based experiments to test the hypothesis that M. quinquenervia compensates for feeding damage by the melaleuca weevil. Our results showed that trees experiencing feeding damage over four consecutive years maintained similar levels of foliage 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. In a separate study, a single bout of feeding by the weevil caused an 80% reduction in reproductive structures the following season. Weevil-damaged trees also possessed 54% fewer fruits than undamaged trees. We conclude that M. quinquenervia partially compensates for herbivory by producing new stems and replacing foliage, but this compensation results in a substantial reduction in reproduction.

Technical Abstract: Plants may compensate for the effects of herbivory, especially under favorable growing conditions, limited competition, and minimal top-down regulation. These conditions characterize many disturbed wetlands dominated by introduced plants, implying that exotic, invasive weeds in these systems should exhibit strong compensatory responses. The Australian native Melaleuca quinquenervia is highly invasive in the Florida Everglades, USA, where it experiences little herbivory or competition from natives, making it a likely candidate for compensation. The introduced herbivore Oxyops vitiosa feeds exclusively on the seasonal flushes of developing foliage at branch apices, which represents ~15% of the total foliar biomass. In a series of field-based experiments, we tested the hypothesis that M. quinquenervia compensates for folivory by O. vitiosa. 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. 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 (2 bouts per year) or magnitude (100% simulated herbivory) did not result in a further reduction in fitness. We conclude the M. quinquenervia partially compensates for herbivory by producing new stems and replacing foliage, but this compensation results in a substantial reduction in reproduction.