[14]. However, if pollinator trapping increases the fitness of carnivorous plants, it
may be evolutionary favorable to use a strategy that increases the efficiency of
trapping pollinators, for example, by producing the flowers and active trap leaves
simultaneously and having them in close proximity to each other.
The second characteristic that will affect the efficiency of trapping pollinators is
the expression of visual and/or chemical signals in trap leaves through the production of secondary metabolites. If trapping pollinators reduce the fitness of carnivorous plants, it may be advantageous to separate the groups of insects that are
visiting the flowers and trap leaves through the production of attractants or
repellents. Three mechanisms can be used to achieve this: (1) attracting pollinators
specifically to the flowers, (2) making the trap leaves unattractive to pollinators, or
(3) making the trap leaves attractive to non-pollinating insects specifically [12]. On
the other hand, if trapping pollinators increase the fitness of carnivorous plants, it
may be adaptive to use a strategy that exploits the perceptual biases of pollinators
visually and/or chemically to attract them to the trap leaves [15, 16], and pollinators may accordingly evolve to recognize the cues of the trap leaves to avoid being
trapped.
In this chapter, I focus on pollinator trapping by carnivorous plants and the
secondary metabolites that affect their trapping efficiency. In Sect. 2, I provide an
overview of empirical studies that have examined pollinator trapping by various
types of carnivorous plants, and in Sect. 3, I summarize the visual and chemical
signals that promote or suppress pollinator trapping. In Sect. 4, I consider the
relationships between carnivorous plants and co-occurring noncarnivorous plants
and discuss how co-occurring plants affect the efficiency of pollinator trapping by
carnivorous plants. Finally, in Sect. 5, I discuss the counteradaptations of pollinators
to carnivorous plants.
2
Empirical Studies on Pollinator Trapping in Carnivorous
Plants
There are five main types of trap leaves in carnivorous plants: adhesive/flypaper
traps, pitcher/pitfall traps, snap traps, eel traps, and suction/bladder traps [9]. Among
these, adhesive traps, pitcher traps, and snap traps catch terrestrial invertebrates,
including flower-visiting insects, and so will be the focus of this section.
The mechanism of capturing prey varies greatly among these three types of trap
leaves. With adhesive traps, a large area of the trap leaf is exposed to the outside to
allow any insects that are passing by to be trapped [17]. By contrast, pitcher and
snap traps guide insects inside the pitchers and laminar lobes, respectively, meaning that it is more difficult for them to capture passing insects, so these types of trap
leaves may face stronger selection pressures than adhesive traps to develop traits
that attract insects. Consequently, the types of trap leaves may affect the mechanism that is used to promote or suppress pollinator trapping. An overview of
previous studies on pollinator trapping by each type of carnivorous plant is
provided below.
30 Pollinator Trapping in Carnivorous Plants
777
may be evolutionary favorable to use a strategy that increases the efficiency of
trapping pollinators, for example, by producing the flowers and active trap leaves
simultaneously and having them in close proximity to each other.
The second characteristic that will affect the efficiency of trapping pollinators is
the expression of visual and/or chemical signals in trap leaves through the production of secondary metabolites. If trapping pollinators reduce the fitness of carnivorous plants, it may be advantageous to separate the groups of insects that are
visiting the flowers and trap leaves through the production of attractants or
repellents. Three mechanisms can be used to achieve this: (1) attracting pollinators
specifically to the flowers, (2) making the trap leaves unattractive to pollinators, or
(3) making the trap leaves attractive to non-pollinating insects specifically [12]. On
the other hand, if trapping pollinators increase the fitness of carnivorous plants, it
may be adaptive to use a strategy that exploits the perceptual biases of pollinators
visually and/or chemically to attract them to the trap leaves [15, 16], and pollinators may accordingly evolve to recognize the cues of the trap leaves to avoid being
trapped.
In this chapter, I focus on pollinator trapping by carnivorous plants and the
secondary metabolites that affect their trapping efficiency. In Sect. 2, I provide an
overview of empirical studies that have examined pollinator trapping by various
types of carnivorous plants, and in Sect. 3, I summarize the visual and chemical
signals that promote or suppress pollinator trapping. In Sect. 4, I consider the
relationships between carnivorous plants and co-occurring noncarnivorous plants
and discuss how co-occurring plants affect the efficiency of pollinator trapping by
carnivorous plants. Finally, in Sect. 5, I discuss the counteradaptations of pollinators
to carnivorous plants.
2
Empirical Studies on Pollinator Trapping in Carnivorous
Plants
There are five main types of trap leaves in carnivorous plants: adhesive/flypaper
traps, pitcher/pitfall traps, snap traps, eel traps, and suction/bladder traps [9]. Among
these, adhesive traps, pitcher traps, and snap traps catch terrestrial invertebrates,
including flower-visiting insects, and so will be the focus of this section.
The mechanism of capturing prey varies greatly among these three types of trap
leaves. With adhesive traps, a large area of the trap leaf is exposed to the outside to
allow any insects that are passing by to be trapped [17]. By contrast, pitcher and
snap traps guide insects inside the pitchers and laminar lobes, respectively, meaning that it is more difficult for them to capture passing insects, so these types of trap
leaves may face stronger selection pressures than adhesive traps to develop traits
that attract insects. Consequently, the types of trap leaves may affect the mechanism that is used to promote or suppress pollinator trapping. An overview of
previous studies on pollinator trapping by each type of carnivorous plant is
provided below.
30 Pollinator Trapping in Carnivorous Plants
777