Dispersal vector
Active dispersal involves pollen, seeds and fungal spores that are capable of movement under their own energy.
Other types of dispersal are due to external agents, which can be other organisms, such as animals (zoochory), or non-living vectors, such as the wind (anemochory) or water (hydrochory).
[5] There are five main types of autochory that act on such seeds or spores: ballochory, or violent ejection by the parent organism; blastochory, or crawling with horizontal runners; barochory, or relying on gravity for dispersal; herpochory, or crawling with fine hair-like structures called trichomes;[6] or being pushed or twisted into the ground by hygromorphic awns in response to humidity changes, e.g. Erodium cicutarium.
Long-distance dispersal operates over areas that span thousands of kilometres, allowing it to promote rapid range shifts and determine species distributions.
[10] When a bird is eaten by a cat or another carnivore, that animal will inadvertently consume the seeds that the prey species ate.
Hummingbirds spread pollen on their beaks,[11] and fungal spores may stick to the bottom of birds' feet.
[12] Water birds may also help to disperse aquatic invertebrates, specifically branchiopods, ostracods, and bryozoans.
Just as in ornithocory, ingestion by herbivores helps to disperse seeds, and gut passage increases the rate of germination.
[7][16] Non-flying mammals have been discovered to act as pollinators in Australia, Africa, South and Central America.
Some plants may have traits that evolved with mammals to use them as dispersal vectors, such as having an extremely bad-smelling odour, producing nectar at night, and developing flowers that can handle rough feeders.
[17] Dik-dik, (Madoqua kirkii), Grant's gazelle (Gazella granti), and impala (Aepyceros melampus) all become infected by nematode parasites in their guts that lay on vegetation the antelope consume.
[18] Frogs and lizards have been found to be dispersal vectors for crustaceans and ring worms, specifically bromeliad ostracods (Elpidium bromeliarum) and annelids (Dero superterrenus).
[19] One of the most important examples of dispersal via invertebrates are pollinators such as bees, flies, wasps, beetles, and butterflies.
[7] Invertebrates may also act as dispersal vectors for the spores of ferns and bryophytes via endozoochory, or the ingestion of the plant.
Wind is a major agent of long distance dispersal that helps to spread species to new habitats.
[23] Humans can affect anemochory in three major ways: habitat fragmentation, chemical runoff, and climate change.
[27] Barriers such as mountain ranges, farm land, and urban centers prevent the relatively free movement of dispersal units seen in open bodies of water.
[30] A number of marine invertebrates require ocean currents to connect their gametes once broadcast spawning has occurred.
[31] Kelp, an important group of sea plants, primarily use ocean currents to distribute their spores offspring.
[33] Some non-submerged aquatic plant species, like palm trees and mangroves, have developed fruits that float on sea water in order to use ocean currents to disperse them.
[26] Many plants have evolved with specific adaptations to maximize the distance that seeds, fruits, or propagules are dispersed in the ocean.
[35][36] Some smaller marine organisms maximize their own dispersal by attaching to a raft - a biotic or abiotic object that is being moved by the ocean's currents.
It has been shown that intertidal invertebrates at the deepest part of their habitats will travel up to multiple kilometers using sea ice.
[38] In lakes that lack connecting rivers, some organisms have developed adaptations that use the wind, while in a water body, to disperse reproductive units.
[42] Like in marine ecosystems, organisms take advantage of flowing water via passive transport of drifting along on a raft.
[45][46] Extreme weather events (tropical cyclones, floods and heavy rains, hurricanes, and thunderstorms) are the most intense examples of water functioning as a vector.
[38] A study done by James Carlton of Williams College reports that more than 3000 species are moving across the ocean in ballast tanks on any given day.
[29] The introduction of human-generated waste, like wood planks and plastic bags, into water sources has increased the number of usable rafts for dispersal.
[50] We have been acting as dispersal vectors since we began moving around the planet, introducing non-native plants and animals with us.
As trends in urbanisation have increased, urban environments help to disperse seeds and bring invasive species with us.
