Carnivorous Plants and Their Prey

Digestion of prey provides carnivorous plants with several distinct advantages in their
growth, maintenance, and reproduction (28). Carnivorous plants with insect prey show greater
rates of photosynthesis (25). Improved photosynthesis, however, may be a secondary result of
carnivory. In studies of carnivorous plants in which supplemental prey was provided, nitrogen
acquisition from insects, although relatively small, resulted in a much larger uptake of soil
nitrogen (13). Prey capture may, therefore, indirectly increase carbon fixation (13, 15). More
nitrogen equates to either more shoot production or an improved photosynthetic rate (15).
Carnivory may not necessarily result in a total gain with respect to photosynthesis. The need to
produce traps may lead to production of fewer photosynthetic leaves or leaves that have lower
rates of photosynthesis (13). A tradeoff accordingly exists between maintaining photosynthetic
leaves versus carnivorous traps (13, 15, 39, 40). When soil nitrogen is readily available, for
example, plants may opt for production of more photosynthetic leaves and fewer traps (39). To
illustrate, Sarracenia purpurea invests more into construction of photosynthetic leaves than traps
when nitrogen is non-limiting. In some cases, these pitcher plants may entirely neglect the
production of traps. Greater investment in leaf tissue when nutrients are not limiting is especially
important to carnivorous plants because their photosynthetic rate may be as much as half of that
of non-carnivorous neighbors (13). The transition from predominately leaf to trap or trap to leaf
production can occur relatively quickly (39). Selective investment into traps or leaves becomes
especially important for plants that occur in ecosystems that diverge from the carnivorous norm
of high light, high moisture, and low nutrients (13).
As shade increases or moisture decreases, carnivory becomes less beneficial. Shaded
plants are typically more limited by light than soil nutrients; therefore, carnivory becomes an
expensive burden that could take resources away from construction of more photosynthetic tissue
(28, 30, 39). Trap production and its associated features such as digestive enzymes and nectar or
other lures become too costly to produce because of the lowered rates of photosynthesis (13, 15,
40). Low light environments, too, may necessitate initiation of more photosynthetic surface at the
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