Chapter 16: Species Abundance and Diversity
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How did the reduction of prairie dog populations impact plant communities in North American prairies?

  • It led to an increase in plant diversity due to reduced soil disturbance.
  • It shifted the dominant plant species towards those more resistant to burrowing animals.
  • It had no significant impact because other burrowing animals filled the ecological role.
  • It eliminated a dynamic influence, potentially reducing opportunities for plant colonization and diversity. (correct)

Which of the following statements best describes the relationship between human-caused disturbance and species diversity?

  • High levels of human-caused disturbance generally lead to declines in species diversity. (correct)
  • High levels of human-caused disturbance consistently increase species diversity due to the creation of new niches.
  • Human-caused disturbance has no predictable effect on species diversity.
  • Moderate levels of human-caused disturbance always maximize species diversity.

What is the general trend observed in bird species richness in urban landscapes as land use intensity increases?

  • Bird species richness consistently increases with increasing land use intensity.
  • Land use intensity has no predictable effect on bird species richness.
  • Bird species richness consistently decreases with increasing land use intensity.
  • Bird species richness peaks at intermediate levels of land use intensity. (correct)

In the context of urban ecology, what factor primarily contributes to the potential for substantial levels of bird diversity in some urban landscapes?

<p>The presence of varied habitats and resources despite urbanization. (D)</p> Signup and view all the answers

Considering the effects of disturbance on species diversity, which of the following scenarios would MOST likely result in the highest level of biodiversity in a temperate grassland?

<p>A moderate level of controlled burning and grazing to create habitat heterogeneity. (B)</p> Signup and view all the answers

Which of the following best explains how spatial variation in nutrient availability contributes to environmental complexity?

<p>It creates diverse niches that support the coexistence of different species. (C)</p> Signup and view all the answers

Based on the information, how does increased nutrient availability typically affect plant and algal species diversity?

<p>It decreases diversity as light becomes the primary limiting resource. (C)</p> Signup and view all the answers

What did Jordan's study in the Amazon forest reveal about the organization of forest diversity?

<p>Forest diversity is influenced by both a high number of species within communities and variation in soil influencing the number of communities. (D)</p> Signup and view all the answers

How might atmospheric nitrogen deposition impact ectomycorrhizal fungus diversity?

<p>Decrease fungal diversity. (C)</p> Signup and view all the answers

According to Tilman's research, what factor directly influences the coexistence of freshwater diatoms?

<p>The ratio of silicate and phosphate in the environment. (A)</p> Signup and view all the answers

How does soil heterogeneity contribute to the diversity of plant communities?

<p>By creating a variety of niches that different plant species can occupy. (D)</p> Signup and view all the answers

What can be inferred about the relationship between environmental complexity and species diversity?

<p>Environmental complexity accounts for a significant portion of species diversity. (B)</p> Signup and view all the answers

In environments with high nutrient availability, what factor tends to become the most limiting resource for plant and algal growth?

<p>Light. (C)</p> Signup and view all the answers

How might a shift from primarily aboveground fruiting bodies to belowground growth in ectomycorrhizal fungi impact nutrient cycling in an ecosystem?

<p>It would promote greater carbon sequestration within the soil. (B)</p> Signup and view all the answers

If an Alaskan study found a decline in ectomycorrhizal taxa along a soil nitrogen gradient that corresponded to a decline in soil pH, what could be a potential explanation for this correlation?

<p>Elevated nitrogen levels may inhibit the growth of certain acid-tolerant ectomycorrhizal species. (B)</p> Signup and view all the answers

In the context of the intermediate disturbance hypothesis, which of the following scenarios would MOST likely lead to the highest level of species diversity in a community?

<p>An intertidal zone with occasional, moderate wave action. (C)</p> Signup and view all the answers

How does the scale of observation influence the definition and perception of disturbance in ecological studies?

<p>Different spatial and temporal scales alter the perception of what constitutes a disturbance and its ecological impact. (A)</p> Signup and view all the answers

If an ecosystem is in a state of equilibrium, what is the primary mechanism maintaining this balance?

<p>The balance of opposing forces. (C)</p> Signup and view all the answers

Based on Sousa's study, how does boulder size influence disturbance levels and species diversity in intertidal zones?

<p>Boulders of intermediate size support the greatest diversity due to intermediate levels of disturbance. (A)</p> Signup and view all the answers

In the context of disturbance ecology, which of the following factors would NOT be considered a source of disturbance in an ecosystem?

<p>Consistent and predictable seasonal changes in temperature. (B)</p> Signup and view all the answers

How can human activities alter the natural disturbance regimes in ecosystems, and what are the potential ecological consequences?

<p>Human activities can either increase or decrease disturbances, potentially altering species composition and ecosystem function. (B)</p> Signup and view all the answers

Which of the following scenarios would likely result in the highest Shannon-Wiener diversity index (H')?

<p>A community with many species, each represented by a roughly equal number of individuals. (B)</p> Signup and view all the answers

In a rank-abundance curve, what does a steeper slope indicate about the community structure?

<p>Less species evenness and a community dominated by a few abundant species. (C)</p> Signup and view all the answers

How would you calculate the proportional abundance of the ith species?

<p>By dividing the number of individuals in the <em>ith</em> species by the total number of individuals of all species. (A)</p> Signup and view all the answers

Based on MacArthur's study of warblers, which of the following forest structures would likely support the greatest diversity of warbler species?

<p>A forest with multiple layers of vegetation from the ground to the canopy. (B)</p> Signup and view all the answers

What is the 'paradox of the plankton'?

<p>The observation that many phytoplankton species coexist in relatively simple environments despite competing for the same resources. (A)</p> Signup and view all the answers

Which of these tide pools has a greater species richness?

<p>Tide pool A (C)</p> Signup and view all the answers

What is the relationship between environmental complexity and species diversity?

<p>Species diversity increases with environmental complexity. (D)</p> Signup and view all the answers

If Community 1 has 5 equally abundant species and Community 2 has 5 species, one of which is much more abundant than the others, which of the following statements is most accurate?

<p>Community 1 has higher species diversity than Community 2. (D)</p> Signup and view all the answers

Which statement best describes the typical relative abundance of species within a community?

<p>A few species are very abundant, a few are very rare, and most are moderately abundant. (A)</p> Signup and view all the answers

What two factors define species diversity in a community?

<p>Species richness and species evenness. (C)</p> Signup and view all the answers

Preston's work with species abundance resulted in the concept of the lognormal distribution. What does a lognormal distribution of species abundance typically look like?

<p>A bell-shaped curve when abundances are plotted on a logarithmic scale. (B)</p> Signup and view all the answers

How does sample size affect the observation of lognormal distributions of species abundance?

<p>Larger sample sizes are more likely to fully capture the lognormal distribution, including rare species. (A)</p> Signup and view all the answers

Which of the following best describes a 'guild' in ecological terms?

<p>A group of organisms that exploit the resources of their environment in a similar manner. (D)</p> Signup and view all the answers

What does 'species evenness' refer to within the context of species diversity?

<p>The relative abundance of different species in a community. (B)</p> Signup and view all the answers

How does the concept of 'life-form' relate to the concept of 'guild'?

<p>Life-form is a term describing a combination of the structure and growth dynamics of a plant, similar in concept to a guild's functional role. (D)</p> Signup and view all the answers

Which of the following statements accurately reflects the relationship between sampling effort and the observed lognormal distribution?

<p>Increased sampling effort is crucial for revealing the complete lognormal distribution by capturing rare species. (C)</p> Signup and view all the answers

Flashcards

Community

Association of interacting species inhabiting a defined area.

Community Structure

Attributes like number of species, relative species abundance, and species diversity.

Guild

Group of organisms that make their living in a similar way.

Life-form

Combination of the structure and growth dynamics of a plant.

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Species Abundance

Few species are very abundant, few are very rare, most are moderately abundant.

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Lognormal Distribution

Graphs abundance of species as frequency distributions, intervals are twice the preceding one, plotted on a log2 scale, bell-shaped curve.

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Species Richness

Number of species in the community.

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Species Evenness

Relative abundance of species.

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Grassland Disturbance

Animals like prairie dogs create disturbance in grasslands by burrowing and altering vegetation.

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Disturbance and Diversity

High levels of disturbance, like deforestation or pollution, generally decrease biodiversity.

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Urban Biodiversity

Cities can support surprisingly diverse populations of species.

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Bird Diversity in Urban Areas

Bird diversity tends to be highest in areas with a mix of natural and human-modified landscapes.

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Soil Nitrogen Impact

Ectomycorrhizal fungi decline with increased soil nitrogen and decreased pH.

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Environmental Complexity

Environmental complexity can account for a portion of plant species diversity.

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Intermediate Disturbance

Diversity is highest at intermediate disturbance levels.

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State of Equilibrium

A state where environmental conditions are relatively stable, maintained by opposing forces.

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Disturbance

Forces that disrupt environmental conditions, varying by organism and scale.

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Connell's Disturbance Theory

Proposed that high diversity results from constantly changing environmental conditions due to disturbance.

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Intermediate Disturbance Effect

High diversity occurs when there's enough time for colonization between disturbances, preventing competitive exclusion.

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Sousa's Boulder Study

Study of algae and invertebrates on intertidal boulders showed intermediate disturbance (boulder size) leads to greatest diversity.

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Algal Niches

Algae niches are greatly influenced by the availability and ratio of essential elements.

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Diatom Coexistence

Coexistence of diatoms depends on the silicate:phosphate ratio.

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Nutrient Variation

Spatial variation in nutrients creates diverse phytoplankton growing conditions.

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Field Patchiness

Patchiness in nitrogen and moisture affects plant structure.

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Soil Variation

Variation in soil influences the number of plant communities.

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Nutrient Enrichment

Increased nutrients decrease plant and algae diversity, with light becoming the limiting resource.

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Nitrogen Deposition

High nitrogen levels decrease fungal diversity.

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Species Diversity

A quantitative measure that reflects how many different species there are in a community and how evenly distributed the individuals are among those species.

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Shannon Wiener Index

A quantitative index used to measure species diversity in a community.

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Rank-Abundance Curves

Graphs that display the relative abundance of each species in a community, ranked from most to least abundant.

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Environmental Complexity & Diversity

Species diversity generally increases as the physical structure or variety of habitats in an environment increases.

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Foliage Height

The range of vertical distribution of foliage (leaves) in a forest.

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Paradox of the Plankton

The question of how so many species of phytoplankton can coexist in a simple environment with limited resources.

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Study Notes

  • Chapter 16 discusses species abundance and diversity
  • It covers how species abundance is distributed, what defines species diversity, how it is affected by environmental factors, and the role of disturbance.

Introduction

  • A community is an association of interacting species inhabiting a defined area
  • Community structure includes the number of species, their relative abundance, and species diversity
  • A guild is a group of organisms living in a similar way, such as seed-eating animals in the desert
  • Life-form refers to the combination of a plant's structure and growth dynamics, similar to a guild

Species Abundance

  • There are regularities in the relative abundance of species in communities, regardless of the ecosystem
  • A few species are very abundant, a few are very rare, and most are moderately abundant.
  • Preston studied relative abundance and developed the concept of commonness and rarity distribution.
  • Preston graphed abundance of species in collections as frequency distributions
  • Each interval on the graph is twice the preceding one, plotted on a logâ‚‚ scale, forming a bell-shaped curve
  • In most lognormal distributions, only a portion of the bell-shaped curve is apparent
  • Sample size has a large effect on the shape of this curve
  • Significant effort is needed to capture rare species

Species Diversity

  • Species diversity is defined by species richness and species evenness
  • Species richness: the number of species in the community
  • Species evenness: the relative abundance of species
  • The Shannon-Wiener index (H') is used to quantify species diversity: H' = -Σ(pi * loge pi)
  • H' is the value of the Shannon-Wiener diversity index
  • pi ​is the proportion of the i-th species
  • loge​ pi is the natural logarithm of pi
  • s is the number of species in the community
  • Rank-abundance curves plot the relative abundance of species against their rank in abundance
  • Greater species evenness is indicated by a lower slope, and less evenness by a steeper slope

Environmental Complexity

  • Species diversity generally increases with environmental complexity or heterogeneity
  • MacArthur found that warbler diversity increased as vegetation stature (foliage height) increased
  • Many studies have shown a positive relationship between environmental complexity and species diversity
  • The paradox of the plankton describes phytoplankton communities that consist of many species competing for the same nutrients in relatively simple environments
  • Coexistence of freshwater diatoms depends on the ratio of silicate and phosphate
  • Diatoms vary in phosphorus uptake rate
  • The ratio of silicate to phosphate varies across a lake, affecting diatom dominance
  • Spatial variation in nutrient and particulate concentrations varies in bodies of water
  • Nitrogen and moisture vary across fields
  • Spatial variability affects plant community structure
  • Jordan found the relationship between vegetation and soils affects the diversity of the Amazon rain forest
  • A large number reside within most tropical forest communities
  • Soil variation influences the number of communities
  • As nutrient availability increases, species diversity of plants and algae declines
  • Light becomes the single limiting resource
  • Species most effective at competing for light become dominant
  • High atmospheric nitrogen deposition leads to declines in fungal diversity
  • This may reflect shifts from aboveground fruiting bodies to belowground growth
  • A study in Alaska found a decline in ectomycorrhizal fungal taxa along a soil nitrogen gradient, corresponding to a decline in soil pH

Disturbance and Diversity

  • Intermediate levels of disturbance promote higher diversity
  • A state of equilibrium is when environmental conditions remain relatively stable and is maintained by opposing forces
  • Most environments are subject to disturbance
  • Disturbance varies with organisms and environments, and is difficult to define
  • It is important to consider the spatial and temporal scale when analyzing environmental disturbance
  • Abiotic forces such as fire, hurricanes, and floods are sources of disturbance
  • Biotic factors such as disease and predation are other sources
  • Human-caused disturbances also affect the environment
  • The intermediate disturbance hypothesis states high diversity is a result of constantly changing conditions
  • High and low disturbance reduce diversity
  • Frequent, intense disturbances will reduce diversity

Application

  • Human-caused disturbance is widespread and is leading to declines in diversity in some locations
  • Deforestation and pollution can decrease the natural biodiversity that is found in healthy ecosystems
  • Thousands of species are threatened with extinction
  • Urban environments are diverse
  • Typically 80% of the population in developed countries lives in cities
  • Urbanization can reduce bird species richness and evenness, but in some landscapes, substantial levels of diversity exist
  • Bird species richness peaks with intermediate land use intensity

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Chapter 16: Species Abundance and Diversity (PDF)

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Explore species abundance distributions, species diversity definitions, environmental influences, and the role of disturbance. Understand commonness and rarity, factors affecting diversity, and the intermediate disturbance hypothesis in communities.

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