Population distribution denotes the spatial pattern due to dispersal of population, formation of agglomeration, linear spread etc. As an example, the population density of Canada is 4 people per square km in while Population density is the number of individuals in a unit area of land under a defined time period.
As an example, the population density of China is people per square km in The density of the population of a particular area is determined by the geographical features such as the shape and the height of the land, available resources, climate, etc.
Begin typing your search term above and press enter to search. Territorial birds, such as penguins, tend to have uniform distribution. Plants with wind-dispersed seeds, such as dandelions, are usually distributed randomly. Animals, such as elephants, that travel in groups exhibit clumped distribution.
Uniform dispersion is observed in plant species that inhibit the growth of nearby individuals. For example, the sage plant, Salvia leucophylla , secretes toxins, a phenomenon called negative allelopathy.
The chemicals kill off surrounding plants in a circle around the individual sage plants, leading to a uniform distance between each plant. Animals that maintain defined territories, such as nesting penguins, also exhibit uniform dispersion. Random dispersion occurs with dandelion and other plants that have wind-dispersed seeds that germinate wherever they happen to fall in a favorable environment.
Clumped dispersion is seen in plants that drop their seeds straight to the ground, such as oak trees, or animals that live in groups, such as schools of fish or herds of elephants. Clumped dispersions may also result from habitat heterogeneity. If favorable conditions are localized, organisms will tend to clump around those, such as lions around a watering hole.
In this way, the dispersion pattern of the individuals within a population provides more information about how they interact with each other and their environment than does a simple density measurement. Just as lower density species might have more difficulty finding a mate, solitary species with a random distribution might have a similar difficulty when compared to social species clumped together in groups. Demography, or the study of population dynamics, is studied using tools such as life tables and survivorship curves.
Population size, density, and distribution patterns describe a population at a fixed point in time. To study how a population changes over time, scientists must use the tools of demography: the statistical study of population changes over time.
The key statistics demographers use are birth rates, death rates, and life expectancies; although, in practice, scientists also study immigration and emigration rates, which also affect populations.
These measures, especially birth rates, may be related to the population characteristics described in prior sections. For example, a large population would have a relatively-high birth rate if it has more reproductive individuals. Alternatively, a large population may also have a high death rate because of competition, disease, or waste accumulation.
A high population density may lead to more reproductive encounters between individuals, as would a clumped distribution pattern. Such conditions would increase the birth rate. Biological features of the population also affect population changes over time.
Birth rates will be higher in a population with the ratio of males to females biased towards females, or in a population composed of relatively more individuals of reproductive age. The demographic characteristics of a population are the basic determinants of how the population changes over time. If birth and death rates are equal, the population remains stable. The population will increase if birth rates exceed death rates, but will decrease if birth rates are lower than death rates. Life expectancy, another important factor, is the length of time individuals remain in the population.
It is impacted by local resources, reproduction, and the overall health of the population. These demographic characteristics are often displayed in the form of a life table. Life tables, which provide important information about the life history of an organism, divide the population into age groups and often sexes; they show how long a member of that group will probably live. The tables are modeled after actuarial tables used by the insurance industry for estimating human life expectancy. Life tables may include:.
The life table shown is from a study of Dall mountain sheep, a species native to northwestern North America. The population is divided into age intervals, as seen in the leftmost column. The mortality rate per 1, individuals is calculated by dividing the number of individuals dying during an age interval by the number of individuals surviving at the beginning of the interval, multiplied by 1, 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. The average number of individuals per square is 10, and the variance is 4. Figure 3: Random dispersion of individuals. The mean number of individuals per square is 5. Which Dispersion Pattern is it? References and Recommended Reading Blackburn, T.
Krebs, C. Ecological Methodology , 2nd ed. Menlo Park, CA: Longman, White, E. Relationships between body size and abundance in ecology. Trends in Ecology and Evolution 22, — Share Cancel. Revoke Cancel.
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Topic rooms within Population Ecology Close. No topic rooms are there. Lead Editor: Population Ecology. Or Browse Visually. Other Topic Rooms Ecology. Student Voices. Creature Cast. The pattern may reflect characteristics of the species or its environment. Population distribution describes how the individuals are distributed, or spread throughout their habitat.
Patterns of Population Distribution. What factors influence the pattern of a population over space? Is this any way to live? Population Size, Density, and Distribution Communities are made up of populations of different species.
Population Size Population size is the number of individuals in a population. Population Density Population density is the average number of individuals in a population per unit of area or volume. Population Distribution Population density just represents the average number of individuals per unit of area or volume. Summary Population size is the number of individuals in a population.
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