Submitted to: Biological Invasions
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/18/2007
Publication Date: 4/1/2008
Citation: Franks, S.D., Pratt, P.D., Dray Jr, F.A., Simms, E. 2008. No evolution of increased competitive ability or decreased allocation to defense in melaleuca quinquenervia since release from natural enemies.. Biological Invasions 10(4): 455-466. (published online: Aug 2007) Interpretive Summary: Melaleuca quinquenervia is a native of eastern Australia and was 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. In an effort to curb the invasion of this weed, scientists have identified natural enemies or biological control agents that help in the suppression of melaleuca. This article provides details on the development of resistance of Melaleuca to introduced biological control agents Oxyops vitiosa and Boreioglycaspis melaleucae.
Technical Abstract: If invasive plants are released from natural enemy pressure in their introduced range, they may evolve decreased allocation to defense and increased growth, as predicted by the evolution of increased competitive ability (EICA) hypothesis. We conducted a field experiment using seedlings of the invasive tree Melaleuca quinquenervia to test this hypothesis. Specifically, we sought to determine 1) if genotypes from the introduced range were more susceptible (contained more insects) and less resistant (suffered greater damage) to herbivory than genotypes from the home range, 2) if in the absence of insects genotypes from the introduced range had greater competitive ability (grew taller) than home range genotypes, and 3) what plant traits relate to herbivory defense. We collected seeds from 120 maternal trees: 60 in Florida (introduced range) and 60 in Australia (home range). Seedlings from these trees were either subjected to herbivory by two specialist biological control insects imported from Australia or protected from herbivores using insecticides. Genotypes from the introduced range were initially more susceptible (a greater proportion of the plants attracted insects) than genotypes from the home range, supporting EICA. However, genotypes from the introduced and home range did not differ in resistance to insects (amount of herbivore damage) or in competitive ability (growth), which does not support EICA. Plants from the introduced range had a lower leaf hair density, lower leaf: stem mass ratio, and a higher ratio of nerolidol: viridifloral chemotypes compared to plants from the native range. Plants with an intermediate density of leaf hairs and with high specific leaf area were more susceptible to herbivory damage, but there were no effects of leaf toughness or chemotype on presence of and damage by insects. While there was an initial preference by the insects for introduced genotypes, the results of the study generally do not support the EICA hypothesis.