The seeds of the plant, when moistened, secrete a viscous fluid that actively attracts and kills prey. There is also evidence of protease activity and absorption of nutrients. The only carnivory criterion not explored is how much the plant benefits from the carnivorous adaptation. A few plants that could be considered protocarnivorous or paracarnivorous are those that once had carnivorous adaptations but appear to be evolving or have evolved away from a direct prey relationship with arthropods and rely on other sources for obtaining nutrients. One example of such a phenomenon is the pitfall trap of "Nepenthes ampullaria", a tropical pitcher plant. Although it retains its ability to attract, capture, kill, and digest insect prey, this species has acquired adaptations that appear to favor digestion of leaf litter. It could potentially be referred to as a detritivore. Another tropical pitcher plant, "Nepenthes lowii", is known to catch very few prey items compared to other "Nepenthes". Preliminary observations suggest that this particular species may have moved away from a solely (or even primarily) carnivorous nature and be adapted to "catching" the droppings of birds feeding at its nectaries. A 2009 study found that mature "N. lowii" plants derived 57–100% of their foliar nitrogen from treeshrew droppings. "Utricularia purpurea", a bladderwort, comes from another genus of carnivorous plants and may have lost its appetite for carnivory, at least in part. This species can still trap and digest arthropod prey in its specialized bladder traps, but does so sparingly. Instead, it harbors a community of algae, zooplankton, and debris in the bladders, giving rise to the hypothesis that the bladders of "U. purpurea" favor a mutualistic interaction in place of a predator-prey relationship. The disciplines of ecology and evolutionary biology have presented several hypotheses on the evolution of carnivorous plants that may also apply to protocarnivorous plants. The name "protocarnivorous plant" itself suggests that these species are on their way to carnivory, though others may simply be an example of a defense-related adaptation, such as that found in "Plumbago". Still others ("Utricularia purpurea", "Nepenthes ampullaria", and "Nepenthes lowii") may be examples of carnivorous plants moving away from the carnivorous syndrome.