Australian family ties: does a lack of relatives help invasive plants escape natural enemies?

Invasive plants may initially be released from natural enemies when introduced to new regions, but once established, natural enemies may accumulate. How closely related invasive species are to species in the native recipient community may drive patterns of herbivore and pathogen damage and therefore, may be important in understanding the success of some invasions. We compared herbivore and pathogen damage across a group of invasive species occurring in natural environments on the east coast of Australia. We examined whether the level of damage experienced by the invasive species was associated with the degree of phylogenetic relatedness between these plants and the native plants within the region. We found that phylogenetic distance to the nearest native relative was a good predictor of herbivore and pathogen damage on the invasive plants, explaining nearly 37 % of the variance in leaf damage. Total leaf damage and the variety of damage types declined with increasing phylogenetic distance to the nearest native relative. In addition, as the phylogenetic distance to the nearest native relative increased, invasive species were colonized by fewer functional guilds and the herbivore assemblage was increasingly dominated by generalist species. These results suggest that invasive species that are only distantly related to those in the native invaded community may be released from specialist natural enemies. Our results indicate that the phylogenetic relatedness of invasive plants to species in native communities is a significant predictor of the rate of colonization by the herbivore and pathogen community, and thus a useful tool to assess invasion potential.