population density

Examples of population density in the following topics:

• Density-Dependent and Density-Independent Population Regulation

  • Population regulation is a density-dependent process, meaning that population growth rates are regulated by the density of a population.
  • In population ecology, density-dependent processes occur when population growth rates are regulated by the density of a population.
  • Its chances of survival are the same whether the population density is high or low.
  • A dense population that is reduced in a density-independent manner by some environmental factor(s) will be able to recover differently than would a sparse population.
  • In this population of roundworms, fecundity (number of eggs) decreases with population density.

• Population Size and Density

  • Population size and density are the two most important statistics scientists use to describe and understand populations.
  • Individuals in a low-density population are thinly dispersed; hence, they may have more difficulty finding a mate compared to individuals in a higher-density population.
  • Many factors influence density, but, as a rule-of-thumb, smaller organisms have higher population densities than do larger organisms .
  • Analyses of sample data enable scientists to infer population size and population density about the entire population.
  • Scientist uses a quadrat to measure plant population size and density

• Overcoming Density-Dependent Regulation

  • Humans have exceeded density-dependent limits on population by enacting various environmental changes to accommodate our needs for hygiene, shelter, and food.
  • This capability is an underlying reason for human population growth as humans are able to overcome density-dependent limits on population growth, in contrast with all other organisms.
  • Migration has also contributed to human population growth.
  • In the fourteenth century, the bubonic plague killed as many as 100 million people: between 30 to 60 percent of Europe's population.
  • Describe ways in which humans overcome density-dependent regulation of population size

• The Study of Population Dynamics

  • 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.
  • A high population density may lead to more reproductive encounters between individuals, as would a clumped distribution pattern.
  • Biological features of the population also affect population changes over time.
  • The demographic characteristics of a population are the basic determinants of how the population changes over time.

• Theories of Life History

  • The regulation of population growth by these factors can be used to introduce a classical concept in population biology: that of K-selected versus r-selected species.
  • By the second half of the twentieth century, the concept of K- and r-selected species was used extensively and successfully to study populations.
  • The first variable is K (the carrying capacity of a population; density dependent), and the second variable is r (the intrinsic rate of natural increase in population size, density independent).
  • Many population biologists have abandoned or modified it.
  • Furthermore, the theory ignored the age-specific mortality of the populations which scientists now know is very important.

• Signaling in Bacteria

  • When the population density of the bacteria reached a certain level, specific gene expression was initiated: the bacteria produced bioluminescent proteins that emitted light.
  • Because the number of cells present in the environment (the cell density) is the determining factor for signaling, bacterial signaling was named quorum sensing.

• The Phosphorus Cycle

  • Worldwide, large dead zones are found in coastal areas of high population density.

• Species Distribution

  • Density and size are useful measures for characterizing populations.
  • Dispersion or distribution patterns show the spatial relationship between members of a population within a habitat.
  • 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.
  • A population may have a uniform, random, or clumped distribution.

• Organismal Ecology and Population Ecology

  • Organisms that are all members of the same species, a population, are called conspecifics.
  • A population is identified, in part, by where it lives; its area of population may have natural or artificial boundaries.
  • The study of population ecology focuses on the number of individuals in an area and how and why population size changes over time.
  • However, the distribution and density of this species is highly influenced by the distribution and abundance of wild lupine.
  • Describe populations as studied in population ecology and organisms as studied in organismal ecology

• Population Genetics

  • Population genetics is the study of the distributions and changes of allele frequency in a population.
  • Population genetics is the study of how selective forces change a population through changes in allele and genotypic frequencies.
  • In population genetics, the term evolution is defined as a change in the frequency of an allele in a population.
  • When a small number of individuals become the basis of a new population, this new population can be very different genetically from the original population if the founders are not representative of the original.
  • Define a population gene pool and explain how the size of the gene pool can affect the evolutionary success of a population