page_title: Carnivorous plant
section_title: Ecology and modeling of carnivory
hierarchical_section_title: Carnivorous plant / Ecology and modeling of carnivory
context_page_description: Carnivorous plants are plants that derive some or most of their nutrients from trapping and consuming animals or protozoans, typically insects and other arthropods. Carnivorous plants have adapted to grow in places where the soil is thin or poor in nutrients, especially nitrogen, such as acidic bogs. Charles Darwin wrote Insectivorous Plants, the first well-known treatise on carnivorous plants, in 1875. Carnivorous plants can be found on all continents except Antarctica, as well as many Pacific islands.
  True carnivory is thought to have evolved independently nine times in five different orders of flowering plants, and is represented by more than a dozen genera. This classification includes at least 583 species that attract, trap, and kill prey, absorbing the resulting available nutrients. This number has increased by approximately 3 species per year since the year 2000. Additionally, over 300 protocarnivorous plant species in several genera show some but not all of these characteristics.
context_section_description: Carnivorous plants are widespread but rather rare. They are almost entirely restricted to habitats such as bogs, where soil nutrients are extremely limiting, but where sunlight and water are readily available. Only under such extreme conditions is carnivory favored to an extent that makes the adaptations advantageous.
  The archetypal carnivore, the Venus flytrap, grows in soils with almost immeasurable nitrate and calcium levels. Plants need nitrogen for protein synthesis, calcium for cell wall stiffening, phosphate for nucleic acid synthesis, and iron and magnesium for chlorophyll synthesis. The soil is often waterlogged, which favours the production of toxic ions such as ammonium, and its pH is an acidic 4 to 5. Ammonium can be used as a source of nitrogen by plants, but its high toxicity means that concentrations high enough to fertilise are also high enough to cause damage.
  However, the habitat is warm, sunny, constantly moist, and the plant experiences relatively little competition from low growing Sphagnum moss. Still, carnivores are also found in very atypical habitats. Drosophyllum lusitanicum is found around desert edges and Pinguicula valisneriifolia on limestone (calcium-rich) cliffs.
  In all the studied cases, carnivory allows plants to grow and reproduce using animals as a source of nitrogen, phosphorus and possibly potassium. However, there is a spectrum of dependency on animal prey. Pygmy sundews are unable to use nitrate from soil because they lack the necessary enzymes (nitrate reductase in particular). Common butterworts (Pinguicula vulgaris) can use inorganic sources of nitrogen better than organic sources, but a mixture of both is preferred. European bladderworts seem to use both sources equally well. Animal prey makes up for differing deficiencies in soil nutrients.
  Plants use their leaves to intercept sunlight. The energy is used to reduce carbon dioxide from the air with electrons from water to make sugars (and other biomass) and a waste product, oxygen, in the process of photosynthesis. Leaves also respire, in a similar way to animals, by burning their biomass to generate chemical energy. This energy is temporarily stored in the form of ATP (adenosine triphosphate), which acts as an energy currency for metabolism in all living things. As a waste product, respiration produces carbon dioxide.
  For a plant to grow, it must photosynthesise more than it respires. Otherwise, it will eventually exhaust its biomass and die. The potential for plant growth is net photosynthesis, the total gross gain of biomass by photosynthesis, minus the biomass lost by respiration. Understanding carnivory requires a cost-benefit analysis of these factors.
  In carnivorous plants, the leaf is not just used to photosynthesise, but also as a trap. Changing the leaf shape to make it a better trap generally makes it less efficient at photosynthesis. For example, pitchers have to be held upright, so that only their opercula directly intercept light. The plant also has to expend extra energy on non-photosynthetic structures like glands, hairs, glue and digestive enzymes. To produce such structures, the plant requires ATP and respires more of its biomass. Hence, a carnivorous plant will have both decreased photosynthesis and increased respiration, making the potential for growth small and the cost of carnivory high.
  Being carnivorous allows the plant to grow better when the soil contains little nitrate or phosphate. In particular, an increased supply of nitrogen and phosphorus makes photosynthesis more efficient, because photosynthesis depends on the plant being able to synthesise very large amounts of the nitrogen-rich enzyme RuBisCO (ribulose-1,5-bis-phosphate carboxylase/oxygenase), the most abundant protein on Earth.
  It is intuitively clear that the Venus flytrap is more carnivorous than Triphyophyllum peltatum. The former is a full-time moving snap-trap; the latter is a part-time, non-moving flypaper. The energy "wasted" by the plant in building and fuelling its trap is a suitable measure of the carnivory of the trap.
  Using this 
caption: Modelling carnivory in plants: gross photosynthesis, respiration and net photosynthesis as a function of the plant's investment in carnivorous adaptations. Non-zero optimum carnivory occurs in brightly lit habitats with very limiting soil nutrients.
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