Do exotic plants escape their enemies? Tests using congeneric pairs.
Kotanen, Peter*,1, 1 University of Toronto, Mississauga, ON, Canada
ABSTRACT- In order to test whether exotic plants experience reduced levels of damage by natural enemies, a series of field and laboratory experiments was conducted using more than 30 herbaceous species of Ontario old fields. For each experiment, natives were paired with exotic congeners to investigate whether exotics suffer less damage than similar natives, while controlling for phylogenetic variation. In all experiments, there was considerable interspecific variation in rates of attack. Comparisons of congenerics detected no evidence that seeds of exotic species were less likely to be attacked by pathogens than seeds of natives. Foliar herbivores attacked exotics more severely than natives in the first year, but this pattern was reversed in the following year: exotics were less attacked than natives, despite apparently higher palatability. Finally, exotic plants suffered less negative feedback from soil organisms than did natives. Together, these results suggest that exotics often do escape enemies, even when compared with otherwise similar natives. However, attack by different enemies (seed pathogens vs. foliar herbivores vs. root pathogens) is not necessarily correlated. Enemy release may be important to many invaders, but may function differently for different groups of enemies, and may contribute to the stochastic nature of the invasion process.
Key words: enemy escape, invasions, herbivores, pathogens
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