Why do Venus flytraps and pitcher plants trap and digest insects if they are fully capable of photosynthesis? If this is an adaptation to ensure there is always food, then why don鈥檛听other plants do the same? (continued)
David Muir
Edinburgh, UK
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Plants require 17 essential nutrients. Through photosynthesis, carbon and oxygen are derived from carbon dioxide in the air, and hydrogen comes from water. The other 14 elements: nitrogen, phosphorus, potassium, calcium, magnesium, sulphur, iron, zinc, copper, boron, nickel, molybdenum, manganese and chlorine, would normally come from the soil for land plants. Aquatic plants get their nutrients directly from the water they live in, or from the substrate in which they are fixed. For these land and aquatic plants, the benefits of听evolving insect-trapping mechanisms isn鈥檛 worth the cost.
Evolution can bring about adaptations that听are beneficial, but听only if the advantages outweigh the disadvantages
Carnivorous plants generally grow in boggy places, often sunny, where they can photosynthesise. But such environments are nutrient-poor. To catch animal sources of essential elements, such听plants have evolved adaptations: snap traps (Venus flytrap), bladder traps that use听a听vacuum to suck in prey (bladderworts), flypaper traps that听use a glue (sundew), lobster-pot traps that use angled hairs to听direct prey one-way to their demise听(corkscrew plants) and pitfall traps that send prey down听into a swimming pool听of digestive enzymes (pitcher听plants). For these plants, the benefits of evolving insect-trapping features is听well worth the听cost.
Under Mother Nature鈥檚听 cost-benefit analysis of natural听selection, evolution can听bring about adaptations that听are beneficial, but only if听the听advantages outweigh the听disadvantages.
听
Rob Leah
London, UK
Most carnivorous plants live in听acidic, boggy soils, which are听notoriously poor in various nutrients 鈥� particularly nitrogen needed to make proteins. They听therefore evolved to trap and听digest insects, to provide the听nutrients that weren鈥檛 available听from the soil.
A surprising number of plants are weakly carnivorous (such as tomatoes, which have stems covered in sticky hairs that can capture small insects and absorb the nutrients from their decomposition), but presumably, the evolutionary cost of being actively carnivorous only makes sense in very specific environments.
听
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