BIOSCI 109: Lecture 4 - Population II: Dispersion, Dispersal & Distribution

Dispersion

The pattern of spacing among individuals within the boundaries of the population.

It is closely linked to local densities and different abiotic & biotic factors influence why and how populations disperse.

Things as what's happening around them, the timing, resources, and so on are factors. This means that dispersion patterns are not static and changes according to the situation and available space.

Clumped Dispersion

When individuals are aggregated in patches. Typically, this is seen when communities gather around some sort of resource whether that be water, food, or mates.

Uniform Dispersion

When individuals are evenly spread out within a space. This is typically seen with territoriality where each individual controls a specific amount of area.

Random Dispersion

When the position of each individual is independent from one another. This is typically seen when animals are just resting and nothing is happening or the dispersion patterns of weeds and other similar plants.

Dispersal

The process of individual/s moving away from their original population to settle and reproduce in another area. The process of immigration and emigration.

Typically occurs due to resource availabilities. To persist, individual/s may have to move and settle elsewhere. The change in populations has implications on competition, predation, genetic diversity, diseases and so on. Challenges arise when emigration is higher than immigration.

Active Dispersal

Organisms moving using energy to move themselves such as flying, swimming, walking, running, and so on.

Passive Dispersal

Organisms that disperse using the forces of others or nature such as floating, rafting, or being transported by another organism

When do Organisms Disperse?

It can be opportunistic, taking advantage of natural events such as currents & winds to carry them.

It can be innate, meaning it's in their genetic cues or learned by observing others.

It can also be based on environmental cues, typically based on specific conditions like temperature, resource availability, seasonality, etc.

Barriers to Dispersal

There are many barriers that may prevent an individual from moving.

It can morphological related such as their own physical ability. Or they may rely on another species for dispersal.

There can be physical barriers such as a rushing river or large-scale barriers like mountain ranges, winds, currents, and so on.

There are also anthropogenic barriers such as cities, roads, dams, and so on.

Spatial Distributions & Relationships to Others

How a species is distributed can affect the distribution of other organisms as well.

Populations may apply pressure to other populations, leading to selective pressures that leads to evolutionary change. They may develop new defence mechanisms, new behaviours, and new niches in response.

It may shift ecological relationships and this tends to affect species with narrow ranges & niches more. In some cases, organisms may rely on each other to successfully survive and breed.

Shifting Ranges

The ranges of organisms have been shifting, some expanding and others shrinking. This change in ranges is typically due to climate change.

Some natural reasons may shift include evolutionary forces opening up new adaptations and niches. Or they may adopt new behaviours. They may also experience natural pushes that move them.

Some anthropgenic reasons include translocation of species to new areas (reintroduction, accidental, etc). Humans tend to also impose biocontrol efforts to restrict the ranges of invasive species.