Some physiological carnivores consume plant matter and some physiological herbivores consume meat. There are many more carnivore species on the reefs than herbivores. They are eaten by rodents, birds and larger herbivores. Poisonous to mammals, it is found in quantities sufficient to discourage herbivores. Other herbivores and their predators mimic the appearance of the leaf. Several marsupial herbivores, notably koalas and some possums, are relatively tolerant of it. Hay is generally one of the safest feeds to provide to domesticated grazing herbivores. In parallel they produce other volatiles to attract parasites which attack these herbivores. Poisonous plants are plants that produce toxins that deter herbivores from consuming them. Pyrrolizidine alkaloids are produced by plants as a defense mechanism against insect herbivores. This is partly because Australian desert vegetation evolved without any major herbivores present. JAs are especially important in the plant response to attack from herbivores and necrotrophic pathogens. It is highly toxic to many insect herbivores. In many cases the plants themselves evolved these toxic substances as protection against herbivores. In return, the ants add protection to the plant against herbivores.