species transported externally by animals can have a variety of adaptations for dispersal, including adhesive mucus, and a variety of hooks, spines and barbs. A typical example of an epizoochorous plant is Trifolium angustifolium, a species of Old World clover which adheres to animal fur by means of stiff hairs covering the seed. Epizoochorous plants tend to be herbaceous plants, with many representative species in the families Apiaceae and Asteraceae. However, epizoochory is a relatively rare dispersal syndrome for plants as a whole; the percentage of plant species with seeds adapted for transport on the outside of animals is estimated to be below 5%. Nevertheless, epizoochorous transport can be highly effective if seeds attach to wide-ranging animals. This form of seed dispersal has been implicated in rapid plant migration and the spread of invasive species. Seed dispersal via ingestion and defecation by vertebrate animals (mostly birds and mammals), or endozoochory, is the dispersal mechanism for most tree species. Endozoochory is generally a coevolved mutualistic relationship in which a plant surrounds seeds with an edible, nutritious fruit as a good food resource for animals that consume it. Such plants may advertise the presence of food resource by using colour. Birds and mammals are the most important seed dispersers, but a wide variety of other animals, including turtles, fish, and insects (e.g. tree wētā and scree wētā), can transport viable seeds. The exact percentage of tree species dispersed by endozoochory varies between habitats, but can range to over 90% in some tropical rainforests. Seed dispersal by animals in tropical rainforests has received much attention, and this interaction is considered an important force shaping the ecology and evolution of vertebrate and tree populations. In the tropics, large animal seed dispersers (such as tapirs, chimpanzees, black-and-white colobus, toucans and hornbills) may disperse large seeds with few other seed dispersal agents. The extinction of these large frugivores from poaching and habitat loss may have negative effects on the tree populations that depend on them for seed dispersal and reduce genetic diversity. Seed dispersal through endozoochory can lead to quick spread of invasive species, such as in the case of prickly acacia in Austalia. A variation of endozoochory is regurgitation of seeds rather than their passage in faeces after passing through the entire digestive tract. The seed dispersal by birds and other mammals are able to attach themselves to the feathers and hairs of these vertebrates,