Dispersal: Biogeography


Dispersal is one of the fundamental processes in biogeography, crucial to understanding the distribution of organisms. The most basic distinction between different types of dispersal is between organisms that disperse using their own energy and those that use energy from the environment. Dispersal can lead to two main patterns of range expansion. Either a population can slowly expand from the margins of its geographical range or a small number of individuals can disperse to a new location some distance from the current edge of the species range, or a combination of both of these processes can occur. Dispersal is also of importance in applied ecology, for example, humans have assisted the dispersal of many organisms to new parts of the world – sometimes leading to problems when they become pests in their new range. Understanding dispersal is also important in attempting to predict how organisms will respond to climate change.

Key Concepts

  • There are three fundamental processes in biogeography: evolution, extinction and dispersal.
  • The most basic distinction between types of dispersal is between organisms that disperse using their own power (active dispersal) and those that use energy from the environment (passive dispersal).
  • Much of biodiversity is microscopic; organisms of this size can often be easily dispersed by air or water currents – the extent to which geographical barriers are important for such organisms is currently an active area of research.
  • Many larger animals are capable of dispersal under their own power, especially ones that can fly such as birds and bats.
  • Individual organisms can sometimes appear at a location well outside their normal range, and such individuals are referred to as vagrants.
  • There are two main patterns of range expansion ‘diffusion’ and ‘jump dispersal’.
  • Vicariance biogeography has been an alternative to dispersal biogeography, which downplays the importance of dispersal, replacing it with the idea that a taxon's range can be divided by the formation of physical barriers.
  • A key applied question is whether organisms will be able to disperse at a speed that will allow them to track future climate change.
  • Human influence has had a big role in reducing the effects of dispersal barriers by moving organisms around the world.
  • When a species is dispersed to another part of the world by human actions, its main parasites and predators can be left behind; occasionally, this can cause a dramatic increase in its population at the new site, and the introduced organism can become a pest species.

Keywords: dispersal; biogeography; migration; climate change; jump dispersal; vicariance; vagrancy; nomadism

Figure 1. Role of the three fundamental processes in biogeography.
Figure 2. The Stinkhorn Phallus impudicus is a fungus found in both Europe and North America – although there are many closely related tropical forms. In these fungi, the spores are dispersed mainly by flies, which are attracted to the strong smell of rotting flesh and then feed on the sticky spore mass – which can be seen in the photograph partly covering the top of the fruiting body. The flies then transport spores to new locations (Spooner and Roberts, ).
Figure 3. Types of range expansion. (a) Diffusion: range expansion as a steady expanding front. (b) Jump dispersal: founding a new population well outside the species current range. (c) Combination of diffusion and jump dispersal: over time, the new population founded by a jump dispersal event may merge with the main population as both expand by diffusion.
Figure 4. Distribution of seed dispersal distances for many organisms has a very long tail with a few diaspores or individuals dispersing much further than the average distance. The shape of the curve illustrated is typical for plant species as different as the herb Asarum canadense and the tree Picea species. Factors such as wind eddies (for wind‐dispersed trees) can make the tail surprisingly long (Horn, ). Active dispersal, for example, by birds, is often assumed to be very important for the far right‐hand side of the tail of this distribution – even for plants which have wind as their main dispersal mechanism (Wilkinson, ).
Figure 5. Canada goose, Branta canadensis, in St James Park, London, England. This North American species was introduced into the Park by the mid‐seventeenth century and is now found over most of Britain. Indeed, the specimen used by Linnaeus in his original description of this species came, not from North America, but from St James Park (Holloway, ).


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Further Reading

Cox CB, Moore PD and Ladle RJ (2016) Biogeography, 9th edn. Oxford: Blackwell.

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Thornton I (2007) Island Colonization; the Origin and Development of Island Communities. Cambridge: Cambridge University Press.

Whittaker RJ and Fernandez‐Palacios JM (2006) Island Biogeography. Oxford: Oxford University Press.

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Wilkinson, David M(Sep 2017) Dispersal: Biogeography. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003237.pub3]