BIO330: Population vs Community and Population Dynamics

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What is a population defined as?

Members of one species living in a particular geographic area

What is population dynamics?

The analysis of factors affecting population increase or decrease over time

What affects population dynamics directly?

Number of additions to the population and number of reductions in the population

What is population size defined as?

The number of individuals present in a subjectively designated geographic range

How do ecologists usually estimate population size?

By counting individuals within a small sample area and extrapolating that sample to the larger population

What is a characteristic of small populations?

They face a greater risk of inbreeding, susceptible to random deaths and extinction

What does survivorship refer to?

The percentage of an original population that survives to a given age

What is characteristic of Type I survivorship curves?

Low mortality rates during early and middle life, followed by high mortality rates among the old

Which of the following organisms is likely to exhibit a Type II survivorship curve?

Lizard

What is characteristic of Type III survivorship curves?

High mortality rates among the young, followed by low mortality rates among the old

Which of the following is NOT a type of survivorship curve?

Type IV

What is the purpose of plotting survivorship curves?

To visualize the number of individuals in a cohort still alive at each age

What is the primary factor that determines the type of life history adaptations favored in a population?

Population density

Which type of population is likely to be found in environments with fluctuating population densities?

r-selected population

What is the term for the maximum population size that can be supported by a given environment?

Carrying capacity

What type of adaptations are favored in populations with high densities?

Adaptations for survival and reproduction with few resources

Which type of factors regulate population growth based on population density?

Density-dependent factors

What is the characteristic of K-selected species or populations?

They are adapted to survive and reproduce with few resources

What is the consequence of large populations approaching carrying capacity?

Lowered fecundity and habitat degradation

What is the definition of population density?

The number of individuals per unit area or volume

What is the primary mechanism of interference competition?

aggression display to exclude others from habitats

What is the purpose of counting indirect indicators in measuring population density?

To estimate the size of population indirectly

What is the capture-mark-recapture method used for?

To estimate population density

Which type of competition involves the use of the same limiting resources?

Exploitative competition

What is the result of high population density in terms of disease transmission?

Disease transmission increases

What is the characteristic of a uniform population dispersion?

Spacing is even, a common result of behavioral or territorial interactions

What is the relationship between high population density and parasitism?

High population density makes it easier for parasites to find hosts

What is the cause of clumped population dispersion?

Uneven distribution of resources in the environment

Which type of competition occurs between individuals of the same species?

Intra-specific competition

What is an example of inter-specific competition?

Lions competing with hyenas for food

Study Notes

Population and Community

  • A population consists of members of one species that live in a particular geographic area.
  • A community includes all the different species that live in a particular geographic area.

Population Dynamics

  • Population dynamics is the study of the factors that affect the increase, stability, or decrease of a population over time.
  • It is influenced by the number of additions to the population (births and immigration) and the number of reductions in the population (deaths and emigration).
  • Understanding population dynamics is key to understanding the relative importance of competition for resources and predation in structuring ecological communities.

Population Size

  • Population size is the number of individuals present in a subjectively designated geographic range.
  • Ecologists estimate population size by counting individuals within a small sample area and extrapolating that sample to the larger population.
  • Small populations face a greater risk of inbreeding, are susceptible to random deaths, and are at a higher risk of extinction.
  • Large populations experience greater competition for resources as they approach carrying capacity, resulting in lowered fecundity and may degrade available habitat.

Population Density

  • Population density is the number of individuals per unit area or volume.
  • It can be measured using various sampling techniques, such as:
    • Counting individuals in a few representative plots of an appropriate size.
    • Counting indirect indicators, such as the numbers of nests, amounts of droppings, or signs of tracks.
    • Capture-mark-recapture method.

Population Dispersion

  • Population dispersion is the pattern of spacing among individuals within the geographical boundaries of the population.
  • Types of population dispersion:
    • Random: Spacing varies in an unpredictable way.
    • Uniform: Spacing is even, a common result of behavioral or territorial interactions.
    • Clumped: Individuals are aggregated in patches, a common response to uneven distribution of resources.

Density-Dependent Factors

  • Density-dependent factors are factors that influence the size and growth of a population depending on the density of the population.
  • Examples of density-dependent factors:
    • Competition: interference competition and exploitative competition.
    • Disease and parasitism: high population density makes the spread of disease easier to transmit.

Survivorship Curves

  • Survivorship is the percentage of an original population that survives to a given age.
  • Survivorship curves are plots of the numbers in a cohort still alive at each age.
  • Types of survivorship curves:
    • Type I: Curve is relatively flat at the start, reflecting low death rates during early and middle life.
    • Type II: Curve is intermediate, with mortality more constant over the lifespan.
    • Type III: Curve drops sharply at the start, reflecting very high death rates for the young.

Life History Adaptations

  • K-selected species or populations: adaptations that enable organisms to survive and reproduce with few resources.
  • r-selected species or populations: adaptations that promote rapid reproduction, such as increased fecundity and earlier maturity.
  • Traits or characteristics of K-selected species/populations and r-selected species/populations:
    • K-selected: high parental investment, low reproductive rate, and large body size.
    • r-selected: low parental investment, high reproductive rate, and small body size.

Factors That Regulate Population Growth

  • Factors that regulate population growth:
    • Density-dependent factors: influence the size and growth of a population depending on the density of the population.
    • Density-independent factors: influence the size and growth of a population regardless of the density of the population.

Learn the difference between population and community, and understand population dynamics, including the factors that affect population growth or decline over time.

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