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Questions and Answers
What is the primary distinction between dispersal and dispersion in the context of population distributions?
What is the primary distinction between dispersal and dispersion in the context of population distributions?
When conducting area- and volume-based surveys, which factor is NOT typically considered when defining the boundaries for sampling?
When conducting area- and volume-based surveys, which factor is NOT typically considered when defining the boundaries for sampling?
What is a key advantage of conducting multiple surveys when estimating population parameters?
What is a key advantage of conducting multiple surveys when estimating population parameters?
What method is best suited for populations that are more mobile, such as larger animals, during surveys?
What method is best suited for populations that are more mobile, such as larger animals, during surveys?
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Which of the following statements about line-transect surveys is incorrect?
Which of the following statements about line-transect surveys is incorrect?
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What is the main purpose of a mark-recapture survey?
What is the main purpose of a mark-recapture survey?
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What equation is used to estimate the population size (N) in a mark-recapture survey?
What equation is used to estimate the population size (N) in a mark-recapture survey?
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When might indirect counts be used in population estimation?
When might indirect counts be used in population estimation?
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Which of the following is a method of indirect counting?
Which of the following is a method of indirect counting?
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What is a potential limitation of area-based or line-transect surveys?
What is a potential limitation of area-based or line-transect surveys?
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What primarily limits the distribution of populations?
What primarily limits the distribution of populations?
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Which of the following describes a fundamental niche?
Which of the following describes a fundamental niche?
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What does geographic range indicate about a population?
What does geographic range indicate about a population?
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What is abundance in the context of population characteristics?
What is abundance in the context of population characteristics?
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What type of data can ecological niche modelling utilize to predict species distributions?
What type of data can ecological niche modelling utilize to predict species distributions?
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Which statement accurately describes density in population distributions?
Which statement accurately describes density in population distributions?
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Which factor is not considered when determining an organism's niche?
Which factor is not considered when determining an organism's niche?
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How can climate change affect habitat suitability?
How can climate change affect habitat suitability?
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What does clustered dispersion typically arise from?
What does clustered dispersion typically arise from?
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What is a realized niche?
What is a realized niche?
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What distinguishes dispersal from migration?
What distinguishes dispersal from migration?
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What challenge is associated with predicting the spread of invasive species?
What challenge is associated with predicting the spread of invasive species?
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Which type of dispersion is least common in nature?
Which type of dispersion is least common in nature?
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Why might individuals not occupy all locations within their geographic range?
Why might individuals not occupy all locations within their geographic range?
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What role does dispersal play in ecology?
What role does dispersal play in ecology?
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Which of the following patterns of dispersion describes individuals spaced uniformly?
Which of the following patterns of dispersion describes individuals spaced uniformly?
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Which of the following statements about population density is true?
Which of the following statements about population density is true?
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What describes the relationship between habitat suitability and population growth?
What describes the relationship between habitat suitability and population growth?
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How does population density affect individual survival?
How does population density affect individual survival?
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What is the common measure of dispersal that quantifies how far individuals move from where they are born to where they reproduce?
What is the common measure of dispersal that quantifies how far individuals move from where they are born to where they reproduce?
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Which method is NOT commonly used to quantify the dispersal of individuals?
Which method is NOT commonly used to quantify the dispersal of individuals?
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What factor is believed to potentially explain the relationship between population abundance and geographic range?
What factor is believed to potentially explain the relationship between population abundance and geographic range?
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Why are lifetime dispersal distances significant for understanding population growth?
Why are lifetime dispersal distances significant for understanding population growth?
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How far can songbirds typically spread from their birthplace per generation?
How far can songbirds typically spread from their birthplace per generation?
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What was the average travel distance per year for the European starling after its introduction to NYC?
What was the average travel distance per year for the European starling after its introduction to NYC?
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What is the relationship between population abundance and geographic range generally observed in various species?
What is the relationship between population abundance and geographic range generally observed in various species?
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What is one common reason for unexplained variation in the relationship between abundance and geographic range?
What is one common reason for unexplained variation in the relationship between abundance and geographic range?
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What happens to population size as geographic range decreases?
What happens to population size as geographic range decreases?
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How does body mass relate to population density?
How does body mass relate to population density?
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What is dispersal limitation?
What is dispersal limitation?
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What does a habitat corridor do?
What does a habitat corridor do?
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In an ideal free distribution, what do individuals choose based on?
In an ideal free distribution, what do individuals choose based on?
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What typically influences the use of high-quality habitat?
What typically influences the use of high-quality habitat?
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What benefit do high-quality habitats often provide?
What benefit do high-quality habitats often provide?
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What usually happens when the per capita benefit of a high-quality habitat reduces?
What usually happens when the per capita benefit of a high-quality habitat reduces?
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What happens in a situation where individuals are absent from a suitable habitat?
What happens in a situation where individuals are absent from a suitable habitat?
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What is a common result of clearing a habitat corridor in ecosystems?
What is a common result of clearing a habitat corridor in ecosystems?
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What is the rescue effect regarding habitat quality and population persistence?
What is the rescue effect regarding habitat quality and population persistence?
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What does the study of ideal free distribution predict about species distribution in habitats?
What does the study of ideal free distribution predict about species distribution in habitats?
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Why might a population show a consistent decrease in a habitat despite an overall suitable environment?
Why might a population show a consistent decrease in a habitat despite an overall suitable environment?
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Study Notes
Reminders
- No seminars next week (Remembrance Day)
- Poster presentation — week of November 25th
Lecture 11: Population Distributions (BIOL 203)
- November 8, 2024
Learning Objectives
- Explain why population distribution is limited to suitable habitats
- List five important characteristics of population distributions
- Describe methods to estimate population distribution properties
- Explain the relationship between population abundance/density, geographic range, and adult body size
- Explain why dispersal is essential for colonization of new areas
Key Concept
- Population distribution is limited to ecologically suitable habitats
The distribution of populations is limited to ecologically suitable habitats
- A habitat is a place or physical setting where an organism lives
- Determined by the organism's niche (range of abiotic and biotic conditions it can tolerate)
- Abiotic factors include temperature, humidity, and pH
- Biotic factors include predators, parasites, and competitors
Two types of niche:
- Fundamental niche — range of abiotic conditions a species can live in
- Realized niche — includes biotic factors which may limit a species' distribution
Determining suitable habitats
- Patterns of distribution suggest only certain habitats are suitable
- Example: Monkeyflowers (Scarlet, Lewis')
Ecological niche modelling
- Generally, the more suitable the habitat, the larger a population can grow within that habitat.
- Allows prediction of species distributions (useful for invasive species, climate change).
- Use historical data/data from other populations to determine suitable habitat conditions
Modelling the spread of invasive species
- Example: Chinese bushclover (Lespedeza cuneata)
- Introduced in 1800s and displaced native plants
- Data from Asia used to predict potential distribution in North America
Difficulties with ecological niche modelling
- Assuming historical conditions accurately predict suitable habitat in new environments
- Example: Raccoon (Procyon lotor) — vastly different realized niches in different locations
Habitat suitability and climate change
- Current suitable habitats can predict species responses to climate change
- Example: Fish in the North Sea - climate change increased water temperature, leading to increased species richness
Concept check
- Define fundamental and realized niche
- Explain possible reasons for the difference between fundamental and realized niches
Population distributions have five important characteristics
- Geographic range
- Abundance
- Density
- Dispersion
- Dispersal
Geographic range
- Total area covered by a population
- Not every location in geographic range may be occupied
- Factors impacting range include: climate, topography, soil, vegetation, other factors
- Includes areas occupied through the organism's entire life history (e.g., migratory species)
- Endemic species — restricted range increase sensitivity to natural disasters
Abundance
- Total number of individuals within a defined area
- Example: Number of rainbow trout in a lake
Density
- Number of individuals in a unit of area or volume
- Ecologists use this to examine habitat capacity to sustain individuals.
- Too high a population density results in lower growth rates/survival
Dispersion
- Spacing of individuals within a geographic range
- Three patterns: clustered, evenly-spaced, random
Dispersion (Clustered)
- Individuals aggregate in discrete groups
- May be due to social groups (flocks of birds) or resource clustering (bugs under logs)
- Offspring often cluster around parents
Dispersion (Evenly spaced)
- Individuals maintain uniform distance from neighbors
- Territories common cause for even spacing (e.g., pika)
- Competition common cause for even spacing (e.g., plants)
Dispersion (Random)
- Individuals' position is independent of other individuals
- Not very common in nature
Dispersal
- Movement of individuals from one area to another
- Distinct from migration
- Mechanism for colonizing new suitable habitats and avoiding high competition/predation risk
Concept check
- Why aren't all locations in a species' geographic range occupied?
- What is the difference between dispersal and dispersion?
Estimating population size
- Direct method — census
- Indirect method — surveys (e.g., counting subset of population)
- Methods: area-based surveys, line-transect surveys, mark-recapture surveys
Area- and volume-based surveys
- Scientists define boundaries and count all individuals within
- Size depends on organism density
- Example: cm³ of soil for bacteria, m² for reef corals
Line-transect surveys
- Scientists count individuals as they move along a line
- Many variations (length, number of transects)
Mark-recapture surveys
- Collect, mark, and return individuals to a population
- Second collection happens later
- Proportion of marked individuals informs population size
Indirect counts
- Use methods like tracks or droppings to estimate population
- Relative measure of population size
Quantifying dispersal of individuals
- Need to know the source of individuals
- Mark-recapture methods useful (e.g., ear tags, radio transmitters)
- Fluorescent dye on pollen
Lifetime dispersal distance
- Average distance individuals move from birth to reproduction
- Used to estimate how fast a population can expand its range
- Examples: European starling's rapid spread across the US, birds
Concept check
- Why use surveys instead of censuses to measure animal populations?
- List and define the methods for quantifying population size
Population abundance and geographic range
- Populations with higher abundance may have larger geographic ranges
- This correlation observed for plants, mammals, birds, and protists
- Example: Birds in North America
Population abundance and geographic range (continued)
- Cause of correlation debated
- Possible causes include resource availability, change in habitat use, or reproduction/survival
Population density and adult body size
- Population density generally negatively correlated with body mass
- Related to space and resource availability
Concept check
- What is the relationship between population abundance and geographic range?
- Define the relationship between population density and adult body size
Dispersal is essential to colonize new areas
- Essential for population dispersion
- Barriers including time, substantial barriers, and inhospitable habitats can limit dispersal
- Humans facilitate dispersal (e.g., commensal species)
- Habitat corridors — favorable areas aiding dispersal between habitats
Testing the importance of habitat corridors
- Example: pine forests in South Carolina
- Researchers cleared forest patches and analyzed dispersal among plants and insects
Ideal free distribution among habitats
- Individuals ideally move to best-quality habitats
- However, high density in best habitats means fewer resources
Ideal free distribution (continued)
- Per-capita benefit often decreases with increasing population in quality habitats
- Individuals distribute based on per-capita benefit, ensuring equal quality among habitats
Ideal free distribution (continued)
- Individuals may not always know of other habitat options
- Fitness influenced by more than just resources
- Predators, occupied territories
The effects of habitat quality
- High-quality habitats often result in more reproductive success.
- Habitats may serve as dispersal sources to habitats of lower quality
The effects of habitat quality (continued)
- Example: Blue tit birds in downy and holm oak forests
- Population persistence due to migration between suitable habitats (rescue effect)
Concept check
- Why are some species absent from continents with suitable habitat?
- How do habitat corridors influence dispersal?
- What does an individual seek to optimize in ideal free distribution?
Next class
- Population growth and regulation (Chapter 11)
- No seminars next week (Remembrance Day)
- Poster presentation — week of November 25th
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Description
Test your knowledge on the distinctions between dispersal and dispersion, various population survey methods, and the principles behind mark-recapture surveys. This quiz covers key concepts in population ecology, sampling techniques, and survey methodologies.
