Lord of the Flies
(or how tarweeds lure fruit flies to their doom and use the poor unsuspecting victims to bribe predator defenders)
Smell is the sense of memory, and anyone who has walked through a Californian grassland in the heat of summer will never forget the scent of tarweeds. That scent oozes from thousands of glandular trichomes that produce the characteristic sticky stink, and a big question is WHY? Why do tarweeds produce this sticky, nauseating elixir? A recent paper by Krimmel and Pearse (Ecology Letters 2013) sheds some light on this natural history mystery while introducing a new form of plant indirect defense and complexities to grassland food webs rarely considered.
Trichomes (small hairs or spines on the leaf surface) are a confusing plant defense. On one hand, they may inhibit feeding by herbivores. On the other hand, they also pose challenges to the predators and parasitoids that protect plants from herbivores. Here Krimmel and Pearse hypothesize that the glandular trichomes found on tarweed and other plants act as sticky traps for unsuspecting prey–prey that in turn serve as bait to attract predators that help protect plants from herbivores. Like the vendors at ESA who lure grad students to their booths with t-shirts and beer in hope that the unsuspecting students will leave with dreams of a Licor or increased journal loyalty, the plant offers up trapped carrion snacks to predators with the hope that the predators also will annihilate a few herbivores while there. Krimmel and Pearse use experimental carrion additions to support their hypothesis and show that plants with more carrion attract more predators, experience less herbivory, and have higher fitness. This paper convincingly illustrates a new plant defense while highlighting the complexity of grassland communities, showing that even common predators can be wooed by a little carrion.
Why this paper is BIG…
- They had me at “carrion addition”…rarely heard words in the plant-insect realm.
- Novel but potentially important form of indirect defense.
- The importance of carrion to predator behavior is almost reminiscent of Gary Polis’ seminal works showing how omnivores influence and complicate food web dynamics. How much do we know about the importance of carrion to taxa typically thought of as predators and plant defenders?