Population Density and Dispersion
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Questions and Answers

Which of the following factors would LEAST likely influence the dispersion pattern of a population?

  • The distribution of resources.
  • The specific carrying capacity of the environment. (correct)
  • Territoriality within the population.
  • Social interactions among individuals in the population.

A researcher is studying a population of fish in a lake. Which approach would provide the MOST accurate estimate of population size?

  • Counting the number of fish caught by local fisherman over a season.
  • Visually estimating the number of fish in a small section of the lake and extrapolating to the entire lake.
  • Using the mark-recapture method. (correct)
  • Estimating population size based on the amount of algae present in the lake.

Suppose you are studying a population of plants in a field. You divide the field into several plots, count the number of plants in each plot, and calculate the average density. Which condition would MOST improve the accuracy of your estimate of the total population size?

  • There are a small number of plots.
  • The plots are located in areas with the highest plant density.
  • The field has a homogenous habitat. (correct)
  • The plants are evenly distributed throughout each plot.

In a mark-recapture study, 200 fish are captured, marked, and released back into a lake. A week later, 150 fish are captured, and 30 of them are marked. Using the mark-recapture formula, what is the estimated population size of the fish in the lake?

<p>1000 (A)</p> Signup and view all the answers

Which of the following scenarios would MOST likely lead to a clumped dispersion pattern?

<p>Social behavior that keeps individuals in groups. (C)</p> Signup and view all the answers

Instead of directly counting a population of snakes, a researcher counts the number of shed skins in the area. Which population characteristic is the researcher MOST directly estimating?

<p>Density (A)</p> Signup and view all the answers

What is the MOST significant limitation of determining population size and density by simply counting all the individuals within a population's boundaries?

<p>It is often impractical or impossible to count all individuals. (B)</p> Signup and view all the answers

A population of deer lives in a forest. Which factor is LEAST likely to be considered an abiotic factor affecting the population's density?

<p>The number of predators in the forest. (D)</p> Signup and view all the answers

In the mark-recapture method, what does the assumption that 'marked and unmarked individuals have the same probability of being captured' primarily ensure?

<p>The sampling method accurately reflects the true proportion of marked individuals in the entire population. (D)</p> Signup and view all the answers

If a researcher using the mark-recapture method finds that none of the individuals captured in the second sampling are marked, what is the most likely conclusion?

<p>The population size is much larger than initially estimated, or the marked individuals have left the area. (C)</p> Signup and view all the answers

How does emigration primarily affect a population's density and distribution?

<p>Decreases density in the original population and can lead to the establishment of new populations. (D)</p> Signup and view all the answers

Which scenario would most likely lead to a uniform dispersion pattern in a plant population?

<p>Release of chemicals that inhibit growth of nearby individuals (D)</p> Signup and view all the answers

What is the primary ecological benefit of clumped dispersion for animals like wolves?

<p>Increased efficiency in capturing prey or enhanced defense (A)</p> Signup and view all the answers

In the context of population dynamics, what is the difference between density and dispersion?

<p>Density measures the number of individuals, while dispersion describes their spatial arrangement. (C)</p> Signup and view all the answers

Assuming all other conditions are met, how would increasing the number of marked individuals in the initial sample affect the accuracy of the mark-recapture method?

<p>It would increase the accuracy by providing a larger proportion of marked individuals in the population. (B)</p> Signup and view all the answers

How do biotic and abiotic factors interact to influence patterns of dispersion?

<p>Abiotic factors set the stage, while biotic interactions influence the specific spacing of individuals. (C)</p> Signup and view all the answers

Which of the following scenarios illustrates the impact of immigration on population dynamics?

<p>A population increases in size as new individuals arrive from a neighboring area. (C)</p> Signup and view all the answers

How might seasonal changes influence emigration patterns in a dolphin population?

<p>Dolphins might emigrate to follow food resources or avoid harsh weather conditions. (D)</p> Signup and view all the answers

Using the mark-recapture method, if s = 200, n = 50, and x = 10, what is the estimated population size (N)?

<p>1000 (D)</p> Signup and view all the answers

Which scenario best exemplifies territoriality as a factor influencing dispersion?

<p>Lions maintaining exclusive hunting grounds by warding off intruders (B)</p> Signup and view all the answers

How do mortality and emigration differ in their impact on population size?

<p>Mortality removes individuals through death, while emigration removes individuals through movement. (D)</p> Signup and view all the answers

What is the effect of clumped dispersion on competition among individuals within the group?

<p>It increases competition for resources within the clump. (A)</p> Signup and view all the answers

How does the mark-recapture method account for potential errors introduced by births and deaths during the sampling period?

<p>By ensuring that the resampling interval is short enough to minimize births and deaths (A)</p> Signup and view all the answers

Flashcards

Population

A group of individuals of a single species living in the same area.

Population Density

The number of individuals per unit area or volume of a population.

Dispersion

The pattern of spacing among individuals within a population.

Sampling Techniques

Methods used by ecologists to estimate population size when counting all individuals is impractical.

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Indicator of Population Size

Signs like nests, tracks, or droppings used to estimate population density.

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Mark-Recapture Method

A technique for estimating wildlife population sizes by marking individuals and recapturing them later.

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Homogeneous Habitat

A habitat where conditions are uniform, making sampling more accurate.

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Population Boundaries

Defined limits of a population, which can be natural or investigator-defined.

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Population Size (N)

The estimated total number of individuals in a population based on sampling data.

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Formula for N

N = (s × n) / x, where s is marked, n is recaptured, and x is marked recaptured.

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Sampling Interval

The time between the first and second capture in mark-recapture studies.

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Assumptions of Mark-Recapture

Marked and unmarked individuals must have equal capture chances and mix completely back into the population.

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Endangered Species

Species at risk of extinction; Hector’s dolphins are an example.

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Immigration

The influx of new individuals into a population from other areas.

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Emigration

The movement of individuals out of a population to other areas.

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Factors Affecting Population Density

Birth, death, immigration, and emigration influence population size and density.

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Clumped Dispersion

Individuals are grouped in patches due to environmental factors or social behaviors.

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Uniform Dispersion

Evenly spaced individuals often due to territorial behavior or resource competition.

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Random Dispersion

Unpredictable spacing of individuals with no strong interactions among them.

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Territoriality

The defense of a bounded physical space by individuals against others.

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Biotic Factors

Living components that affect population dynamics, such as predation and competition.

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Abiotic Factors

Non-living physical factors that can influence populations, like weather and soil conditions.

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Study Notes

Population Density and Dispersion

  • A population is a group of the same species in a shared area, relying on similar resources and interacting.
  • Population boundaries are defined by area relevant to the species and study question (e.g., an island, a county).
  • Population density is the number of individuals per unit area or volume.
  • Population dispersion is the pattern of spacing among individuals within a population.

Density: Determining Population Size

  • Population size and density can be determined by counting all individuals if practical (e.g., sea stars in a tide pool).

  • Sampling methods are used for populations too large or difficult to count.

    • Counting in sample plots (e.g., oak trees in a square area), then extrapolate.
    • Using indicators like nests or tracks.
    • Mark-recapture method (Figure 53.2)

  • Scientists capture, tag, and release individuals.

  • A second sampling is conducted to find the ratio of tagged to untagged.

  • Formula: (x/n) = (s/N); N = (s*n)/x

  • Population size estimates are most accurate with more sample plots.

  • Population size depends on the environment conditions during the sampling period.

Dynamic Density

  • Population density changes due to births, immigration, deaths, and emigration.
  • Birth and death rates universally influence population size.
  • Immigration and emigration may have strong effects (e.g., 15% of Hector's dolphin populations migrate annually).

Dispersion Patterns

  • Clumped dispersion: Individuals grouped together in patches (e.g., plants, fungi, animals).
  • Uniform dispersion: Individuals are evenly spaced, often due to competition (e.g., plants secreting chemicals).
  • Random dispersion: Position of each individual is independent of others in the absence of attracting or repelling forces (e.g., wind-dispersed plants).

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Description

Explore population ecology: density, dispersion, and size determination. Learn about direct counts, sampling methods, and the mark-recapture technique for estimating population sizes. Understand how ecologists study and measure populations in diverse environments.

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