Download Lecture 11 – Problems with the Enemy Release Hypothesis •

Lecture 11 – Problems with the Enemy Release Hypothesis
• Weaknesses in the original ERH
• Somewhere around 50% of studies don’t support it.
• Natural enemies already present at introduction
• Acquire new natural enemies as native species adopt invaders
as hosts or prey
• Plants may not be able to take advantage of the lack of enemies
because of other constraints.
• Successful biological control does not necessarily provide
support for the ERH. Some biological control agents have
negligible impact on species where they are native but become
important in a species ecology after it is introduced elsewhere.
• Recent focus has been on developing a better synthetic ERH incorporating
ecology and evolution
• Combines the ERH with two other related models
• ERH is an ecological time scale explanation. An expanded ERH
incorporates evolutionary processes as well.
•
EICA = Evolution of increased competitive ability - idea is that
plants free of their natural enemies can evolve strategies to divert
resources away from defense and toward life-history attributes that
enhance their ability to compete.
•
DNWH = Darwin’s Novel Weapon hypothesis - idea is that
‘weapons’ (e.g., allelochemicals or toxins) are more potent against unadapted naïve species.
• With respect to the ERH, in the absence of natural enemies, more
resources could be devoted to pathways or end products that would
enhance these novel weapons.
Ecological
Bossdorf 2013
Evolutionary