Carnivorous plant 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
Carnivorous plant more or less than this optimum will take up less carbon dioxide than an optimal plant, and hence growing less well. These plants will be at a selective disadvantage. At zero investment the growth is zero, because a non-carnivorous plant cannot survive in a habitat with absolutely no soil-borne nutrients. Such habitats do not exist, so for example, "Sphagnum" absorbs the tiny amounts of nitrates and phosphates in rain very efficiently and also forms symbioses with diazotrophic cyanobacteria. In a habitat with abundant soil nutrients but little light (as shown above), the gross photosynthesis curve will be lower and flatter,