How does dispersal affect distribution

Contributors include more than 10, highly qualified scientists and 46 Nobel Prize winners. Environmental Science Ecology - general Population dispersal. You may already have access to this content. Sign In. The pattern of Disjunctions: distantly separated populations [ Larrea ] Dispersalist : C. Darwin, A. Wallace, A. Gray Extensionist : C. Individuals can disperse either actively or passively. Active dispersal involves movement of the entire organism through its own ability and is common in both adult and juvenile animals.

For example, social systems that rely on a single adult male for reproduction e. Active dispersal, in general, is thought to be a density-dependent process in that its magnitude depends on local population size, resource competition, and habitat quality and size. However, evidence supporting the connection between density-dependence and active dispersal is equivocal reviewed by Matthysen Nevertheless, local population conditions may affect juveniles and adults differently, resulting in varying degrees of dispersal between different age groups.

Animals that are highly vagile are considered to be the most efficient at active dispersal. Highly vagile animals include many species of birds, bats, and large insects. The Monarch butterfly Danaus plexippus is a notable example of a highly vagile insect capable of flying hundreds to thousands of kilometers. Other animals, which cannot fly, are also considered highly vagile. Large aquatic animals are effective dispersers, and some terrestrial animals can disperse large distances on foot.

As a result, highly vagile organisms have the greatest capacity for long-distance dispersal. Despite the intrinsic vagility of a species, the extent of dispersal is linked to restrictions imposed by the habitat. Flying animals are less affected by habitat changes because they can bypass barriers by flying over or around them. Additionally, there are fewer barriers in the ocean than on land, so large aquatic species can disperse large distances unimpeded Figure 1.

Dispersal by terrestrial animals is generally considered less effective or energy-efficient because individuals are forced to travel through unfavorable habitats, and contend with potential geographic barriers.

Both individuals were radiotagged in the Bay of Fundy with the purpose to investigate habitat use patterns see Mate et al. Bidens bipinnata , a burr; 2. Desmodium canadense , a burr; 3. Arctium lappa , a burr; 4. Medicago agrestis , a burr; 5. Torilis anthriscus , a burr; 6. Geum urbanum , a burr; 7. Pisonia aculeata , a viscid fruit; 8.

Xanthium spinosum , a burr; 9. Cynoglossum pictum , a burr. See Sorensen for a review of seed dispersal by adhesion. Many disseminules are adapted for movement by specific dispersal agents available in the environment, like wind, water, or another animal capable of active dispersal, or species may have a motile larval stage. Sessile adult animals that utilize passive dispersal include marine invertebrates like sponges and corals. Their disseminules are typically specialized buds or cells used in reproduction.

For example, most corals sexually reproduce by releasing gametes directly into the water. The male gametes are generally motile, and eggs are moved passively via ocean currents.

Other sessile animals exemplify natal dispersal in that they have a free-living, aquatic juvenile stage, wherein larvae drift near the surface and are passively carried by water currents to other locations. In plants, disseminules include seeds, spores, and fruits, all of which have modifications for movement away from the parent plant via available environmental kinetic energy.

Distance traveled by a disseminule is a result of the velocity and direction of movement by the dispersal agent. Winds, flying animals, or water currents are some of the most successful agents of long-distance passive dispersal. Seeds and fruits that have wings, hairs, or inflated processes are carried efficiently by wind.

For example, modifications in Hypochaeris radicata Asteraceae seeds have allowed it to successfully disperse in a fragmented landscape in the Netherlands and counteract the negative effects of population isolation with substantial levels of gene flow Mix et al. Furthermore, some plants have sticky or barbed seeds, or fruits, that adhere to the feathers or fur of mobile animals Figure 2.

Some disseminules are explosively released over short distances whereas others fall to the ground at the base of the parent plant. On the ground, invertebrates, mammals, and birds compete for fallen seeds and fruits.

Seeds and fruits are scattered during feeding and after ingestion are distributed in feces. These seeds are adapted to resist digestive juices and, consequently, can pass through the digestive tract while remaining viable. The distance a disseminule travels by animal transportation, either via ingestion or attachment, is indefinite and depends on the dispersal behavior of their host. For example, some animals may follow a nomadic or brief dispersal trajectory, resulting in variance in the distances traveled.

Multiple processes influence juvenile and adult dispersal. Proximate causes vary but include local population conditions such as crowding and food availability. Environmental stochasticity e. Individuals that emigrate as a result of environmental conditions may experience more favorable conditions in the new location. Additionally, climate change will impact dispersal. Since climate typically influences the distributions of species, the general warming trend that will occur as a result of global climate change will cause species' ranges to shift.

As a result, many areas outside of current distributions may become climatically suitable. However, these areas may be beyond the dispersal capacity of many species. Ultimate causes of dispersal can be explained by avoidance of inbreeding and inbreeding depression.

Small, isolated populations can become inbred and result in decreased fitness, but dispersal can counteract these negative effects. Additionally, dispersal can reduce competition for resources and mates, thereby increasing individual fitness.

Journal of Animal Ecology 75, — Lewis, H. Abundance-body size relationships: the roles of metabolism and population dynamics. Journal of Animal Ecology 77, — Mahall, B.

Root communication: Mechanisms and intracommunity distributions of two Mojave desert shrubs. Ecology 73, — Riechert, S.

The consequences of being territorial: Spiders, a case study. American Naturalist , — Rossberg, A. The top-down mechanism for body-mass-abundance scaling. Ecology 89, — Schenk, H. Spatial root segregation: Are plants territorial?

Advances in Ecological Research 28, — Aging and Its Demographic Measurement. Allee Effects. An Introduction to Population Growth.

Density and Dispersion. Introduction to Population Demographics. Population Dynamics of Mutualism. Population Ecology Introduction. Population Limiting Factors. The Breeder's Equation. Global Atmospheric Change and Animal Populations. Semelparity and Iteroparity. Causes and Consequences of Dispersal in Plants and Animals.

Disease Ecology. Survivorship Curves. The Population Dynamics of Vector-borne Diseases. Density and Dispersion By: Sean E. Walker Dept. Citation: Walker, S. Nature Education Knowledge 3 10 Density and dispersion are two descriptors of populations that can provide insight into processes such as competition and territoriality. Their measurement is therefore fundamental to our understanding of biogeography.

Aa Aa Aa. Patterns of Dispersion. Figure 1: Clumped dispersion of individuals. The average number of individuals per square is 6. Figure 2: Uniform dispersion of individuals.