From Access Science and http://www.nature.com/scitable/knowledge/library/densityand-dispersion-19688035
Population dispersion is the spatial distribution at any particular moment of the individuals of a species of organism. Under natural conditions organisms are distributed either by active movements, or migrations, or by passive transport by wind, water, or other organisms. The act or process of dissemination is usually termed dispersal, while the resulting pattern of distribution is best referred to as dispersion.
Dispersion is a basic characteristic of populations, controlling various features of their structure and organization. It determines population density, that is, the number of individuals per unit of area, or volume, and its reciprocal relationship, mean area, or the average area per individual. So, dispersion determines how many organisms are found per unit space and the average amount of space each organism has.
It also determines the frequency, or chance of encountering one or more individuals of the population in a particular sample unit of area, or volume. Ecologists, therefore, study not only the fluctuations in numbers of individuals in a population, but also the changes in their distribution in space.
The following diagrams show the population dispersion for several different populations.
Describe the population dispersion patterns you see, and explain why populations may distribute themselves in that manner. Lastly, classify the population distribution as
clumped, uniform or random.
For clumped dispersion patterns: What factors would make a population clump together?
What kinds of populations would display such a dispersion pattern? (Consider organisms other than animals!)
For uniform dispersion patterns: What factors would make a population separate evenly?
What kinds of populations would display such a dispersion pattern? (Consider organisms other than animals!)
For random dispersion patterns: What factors would make a population not show a consistent dispersion patterns? What kinds of populations would display such a dispersion pattern? (Consider organisms other than animals!)

A Case Study: Dispersion Patterns in Spiders
Agelenopsis aperta is a sheet-web weaving spider found in the grasslands of the desert southwest (Riechert & Gillespie 1986). These spiders build sheet webs that resemble funnels and are in the family Agelenidae. At a small scale (1–3 m) spiders are uniformly distributed. However, at a larger scale the spiders are clumped. Why?
Explaining these patterns requires investigation of the availability of suitable habitat as well as the interactions among individuals. At a larger spatial scale a very small amount of the habitat is suitable for websites and, of course, that is where the spiders are (Riechert
1981). (Note: Websites in this context refers to places where spiders make and inhabit webs.) These spiders prefer large depressions in grassland habitats with characteristics attractive to insect prey (e.g., flowering shrubs, the presence of litter, and animal feces) and have favorable thermal properties (Reichert & Gillespie 1986).
The spatial distribution of these suitable habitats is what generates the clumped pattern at a larger scale. Since high quality websites are limited in the habitat, and the presence of other spiders in close proximity reduces the fitness of the resident spider, residents will actively patrol their website and engage in aggressive behavior towards other spiders enter into their territory (Riechert 1981). These interactions generate a minimum spacing among individuals within suitable habitat patches, and the occasional displacement of individuals from their website (Riechert 1981, Riechert & Gillespie 1986). Aggressive interactions like these are typical of the types of behavioral interactions that generate uniform spacing patterns.
1.
Diagram the spiders’ dispersion pattern at a large-scale and small-scale level.
2.
What other populations might display similar dispersion patterns to those described above?
3.
Do humans display population dispersion patterns similar to those described for these spiders? Why or why not?