Negative Interactions — Predation, Parasitism, Competition, Amensalism

In a negative interaction, one of the participating species benefits while the other is harmed (or, in one special case, both are harmed). Four such interactions are covered: predation, parasitism, competition and amensalism. In predation, one species (the predator) captures, kills and consumes the other (the prey); several plants have turned this around and become predators of small animals themselves, including the sundew Drosera, the pitcher plant Nepenthes, the Venus flytrap Dionaea, the bladderwort Utricularia and Sarracenia — all grouped together as insectivorous plants that trap and digest insects mainly as a nitrogen source. Herbivores such as cattle, camels and goats are themselves a form of predator on plants, browsing tender shoots (annual plants generally suffer more from this than perennials do), and roughly 25% of all insect species are phytophagous (feeding on plant sap or tissue). In response, plants have evolved a wide array of chemical and physical defences against predation: Calotropis produces poisonous cardiac glycosides, tobacco produces nicotine, coffee produces caffeine, and Cinchona produces quinine, while thorns (Bougainvillea), spines (Opuntia) and latex (cacti) provide physical deterrence. Parasitism is an interaction in which a smaller partner (the parasite) draws food from a larger partner (the host), benefiting the parasite while harming the host; based on how completely the parasite depends on its host, parasites are split into holoparasites (totally dependent on the host for all their nutrition, e.g. the leafless stem parasite Cuscuta and root parasites like Balanophora, Orobanche and Rafflesia) and hemiparasites or partial parasites (which draw only water and minerals from the host while still photosynthesising their own food, e.g. the partial stem parasites Viscum and Loranthus, and the partial root parasite Santalum/sandalwood); all parasitic plants produce specialised haustoria — root-like structures that penetrate the host's vascular tissue to draw out nutrients. Competition is an interaction that harms both participating organisms or species, and is most severe in populations with an irregular (clumped) distribution; it is classified as intraspecific (between individuals of the same species, which is especially fierce since all individuals share identical resource needs and adaptations) or interspecific (between individuals of different species — for instance, different grassland grass species competing hardest for water during a drought, or the bladderwort Utricularia competing with small fish for the same crustacean and insect prey). Finally, amensalism (also called antibiosis) is an interspecific interaction in which one species i …