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Questions and Answers
What are the two main components of species diversity in an ecological community?
What are the two main components of species diversity in an ecological community?
- Species abundance and ecological stability
- Species richness and food web complexity
- Species richness and relative abundance (correct)
- Species adaptation and environmental resistance
Which community would be considered more diverse according to ecologists' definitions?
Which community would be considered more diverse according to ecologists' definitions?
- A community dominated by one species
- A community with equal representation of all species (correct)
- A community with only one species present
- A community where one species is substantially more abundant than others
How is the Shannon diversity index calculated?
How is the Shannon diversity index calculated?
- Adding the species count to the total abundance
- Multiplying species richness by relative abundance
- Using the formula: H' = -Σ(pi * ln(pi)) (correct)
- Dividing species richness by total number of individuals
What would a higher value of the Shannon diversity index indicate?
What would a higher value of the Shannon diversity index indicate?
In the context of the information provided, what does relative abundance measure?
In the context of the information provided, what does relative abundance measure?
If two communities have the same species richness, what other factor must be considered to assess overall diversity?
If two communities have the same species richness, what other factor must be considered to assess overall diversity?
What can be inferred if one community exhibits high species richness but low relative abundance?
What can be inferred if one community exhibits high species richness but low relative abundance?
What does the species richness of a community specifically refer to?
What does the species richness of a community specifically refer to?
What is a significant challenge when determining species abundance in a community?
What is a significant challenge when determining species abundance in a community?
How does DNA sequencing aid in species identification?
How does DNA sequencing aid in species identification?
What technique is commonly used to analyze microbial diversity?
What technique is commonly used to analyze microbial diversity?
Which factor was related to the highest Shannon diversity index in bacterial communities?
Which factor was related to the highest Shannon diversity index in bacterial communities?
What ecological benefit is commonly associated with higher species diversity?
What ecological benefit is commonly associated with higher species diversity?
In the Cedar Creek Ecosystem Science Reserve experiments, which plots produced more biomass annually?
In the Cedar Creek Ecosystem Science Reserve experiments, which plots produced more biomass annually?
What was the result of introducing a tunicate to communities with varying diversity levels?
What was the result of introducing a tunicate to communities with varying diversity levels?
What role does trophic structure play in communities?
What role does trophic structure play in communities?
Why are fractions of DNA analyzed in microbial diversity studies?
Why are fractions of DNA analyzed in microbial diversity studies?
What was the correlation between Shannon diversity index and soil acidity in the studied samples?
What was the correlation between Shannon diversity index and soil acidity in the studied samples?
What is a challenge faced when studying microorganisms in communities?
What is a challenge faced when studying microorganisms in communities?
How does increased plant diversity influence community stability?
How does increased plant diversity influence community stability?
What does the Shannon diversity index measure?
What does the Shannon diversity index measure?
What is a common outcome for diverse communities when facing new species introductions?
What is a common outcome for diverse communities when facing new species introductions?
What role do decomposers play in a food chain?
What role do decomposers play in a food chain?
What defines a species as a primary consumer in a food chain?
What defines a species as a primary consumer in a food chain?
In the context of food webs, what is a nonexclusive consumer?
In the context of food webs, what is a nonexclusive consumer?
How is the diversity of a food web beneficial to an ecological community?
How is the diversity of a food web beneficial to an ecological community?
Which trophic level is directly fed upon by tertiary consumers?
Which trophic level is directly fed upon by tertiary consumers?
What effect would an increase in the population of carnivores targeting zooplankton have on phytoplankton?
What effect would an increase in the population of carnivores targeting zooplankton have on phytoplankton?
What is the primary producer in the Antarctic marine food web?
What is the primary producer in the Antarctic marine food web?
What is the main function of arrows in a food web diagram?
What is the main function of arrows in a food web diagram?
Which term describes the position of an organism in a food chain?
Which term describes the position of an organism in a food chain?
How can complicated food webs be simplified for study?
How can complicated food webs be simplified for study?
In a food web, what is the role of predatory species like penguins and seals?
In a food web, what is the role of predatory species like penguins and seals?
What type of organisms are krill classified as in an Antarctic food web?
What type of organisms are krill classified as in an Antarctic food web?
Which of the following organisms would be considered a tertiary consumer in a food chain?
Which of the following organisms would be considered a tertiary consumer in a food chain?
Which of the following groups of animals primarily fulfill the role of decomposers?
Which of the following groups of animals primarily fulfill the role of decomposers?
What happened to species richness when Pisaster was removed from the intertidal zone?
What happened to species richness when Pisaster was removed from the intertidal zone?
What conclusion can be drawn about Pisaster's ecological role?
What conclusion can be drawn about Pisaster's ecological role?
In which scenario would species richness potentially decline further after the removal of Pisaster?
In which scenario would species richness potentially decline further after the removal of Pisaster?
What is meant by 'bottom-up' control in ecological communities?
What is meant by 'bottom-up' control in ecological communities?
What role do ecosystem engineers play in their environments?
What role do ecosystem engineers play in their environments?
How does the removal of top-level predators affect the ecosystem?
How does the removal of top-level predators affect the ecosystem?
What is indicated by a graph showing stable species richness with the presence of Pisaster?
What is indicated by a graph showing stable species richness with the presence of Pisaster?
Which term describes species that significantly alter their physical environment?
Which term describes species that significantly alter their physical environment?
What was the overall trend in species richness from 1963 to 1973 without Pisaster?
What was the overall trend in species richness from 1963 to 1973 without Pisaster?
What effect does bottom-up control have on ecological dynamics?
What effect does bottom-up control have on ecological dynamics?
Which factor is a key element in top-down control of an ecosystem?
Which factor is a key element in top-down control of an ecosystem?
What would be a consequence of adding nutrients to a bottom-up controlled ecosystem?
What would be a consequence of adding nutrients to a bottom-up controlled ecosystem?
How do changes in predator abundance affect lower trophic levels in a top-down controlled ecosystem?
How do changes in predator abundance affect lower trophic levels in a top-down controlled ecosystem?
What does the stabilization of species richness with Pisaster present suggest about species interactions?
What does the stabilization of species richness with Pisaster present suggest about species interactions?
What is a primary reason that food chains are typically short?
What is a primary reason that food chains are typically short?
Which factor influences the length of food chains according to the energetic hypothesis?
Which factor influences the length of food chains according to the energetic hypothesis?
How many trophic links were observed in tree-hole communities with low productivity?
How many trophic links were observed in tree-hole communities with low productivity?
What is the role of foundation species in a community?
What is the role of foundation species in a community?
What effect did the chestnut blight have on other tree species?
What effect did the chestnut blight have on other tree species?
What is a key distinction of keystone species compared to foundation species?
What is a key distinction of keystone species compared to foundation species?
Which of the following statements about energy transfer efficiency is accurate?
Which of the following statements about energy transfer efficiency is accurate?
In the experiments conducted on tree-hole communities, what condition decreased food chain length?
In the experiments conducted on tree-hole communities, what condition decreased food chain length?
What defines the term 'foundation species'?
What defines the term 'foundation species'?
Which ecological role is exemplified by the sea star Pisaster ochraceus in intertidal communities?
Which ecological role is exemplified by the sea star Pisaster ochraceus in intertidal communities?
What factor limits the size of carnivores at higher trophic levels?
What factor limits the size of carnivores at higher trophic levels?
Why do most studied food webs have chains consisting of five or fewer links?
Why do most studied food webs have chains consisting of five or fewer links?
Which mechanism is directly responsible for the increases in diversity seen when a foundation species is removed?
Which mechanism is directly responsible for the increases in diversity seen when a foundation species is removed?
What is the impact on herbivores when a foundation species like the American chestnut is removed?
What is the impact on herbivores when a foundation species like the American chestnut is removed?
What does the energetic hypothesis predict about food chains in highly productive environments?
What does the energetic hypothesis predict about food chains in highly productive environments?
What is the main outcome when colonists increase the abundance of a species on an island?
What is the main outcome when colonists increase the abundance of a species on an island?
Which factor correlates with the number of species at equilibrium according to MacArthur and Wilson's model?
Which factor correlates with the number of species at equilibrium according to MacArthur and Wilson's model?
After fumigating islands, what trend was observed regarding the number of arthropod species?
After fumigating islands, what trend was observed regarding the number of arthropod species?
In the experiment, which island was observed to recover the fastest after fumigation?
In the experiment, which island was observed to recover the fastest after fumigation?
What happens to the exact species composition on an island over time despite the stabilization of species numbers?
What happens to the exact species composition on an island over time despite the stabilization of species numbers?
What was the role of the two control islands during the study on species recovery?
What was the role of the two control islands during the study on species recovery?
Which of the following is NOT a factor that influences species numbers at equilibrium in the island equilibrium model?
Which of the following is NOT a factor that influences species numbers at equilibrium in the island equilibrium model?
What methodology was used to initially assess the arthropod species on the islands?
What methodology was used to initially assess the arthropod species on the islands?
What are two significant factors that contribute to latitudinal gradients of species richness?
What are two significant factors that contribute to latitudinal gradients of species richness?
Why do tropical communities tend to have higher species richness compared to temperate or polar communities?
Why do tropical communities tend to have higher species richness compared to temperate or polar communities?
Which of the following factors is NOT correlated with species diversity in terrestrial communities?
Which of the following factors is NOT correlated with species diversity in terrestrial communities?
What has historical observation pointed out regarding the abundance and diversity of species in different latitudes?
What has historical observation pointed out regarding the abundance and diversity of species in different latitudes?
How can past disturbances like glaciations affect species richness in different communities?
How can past disturbances like glaciations affect species richness in different communities?
Which statement best explains the reason for a higher tree species count in tropical regions compared to temperate regions?
Which statement best explains the reason for a higher tree species count in tropical regions compared to temperate regions?
What concept explains the observed increase in species richness over evolutionary time in tropical communities?
What concept explains the observed increase in species richness over evolutionary time in tropical communities?
Which of the following observations has been confirmed regarding the diversity of animal species across different latitudes?
Which of the following observations has been confirmed regarding the diversity of animal species across different latitudes?
How does potential evapotranspiration relate to vertebrate species richness in a community?
How does potential evapotranspiration relate to vertebrate species richness in a community?
What does the species-area curve suggest about larger geographic areas?
What does the species-area curve suggest about larger geographic areas?
According to the island equilibrium model, what happens to the immigration rate as the number of species on an island increases?
According to the island equilibrium model, what happens to the immigration rate as the number of species on an island increases?
What effect do smaller islands generally have on species diversity compared to larger islands?
What effect do smaller islands generally have on species diversity compared to larger islands?
Which statement accurately describes the relationship between rainfall and species richness in North America?
Which statement accurately describes the relationship between rainfall and species richness in North America?
What hypothesis can be derived from the observation that species richness increases with island size in the Sunda Islands?
What hypothesis can be derived from the observation that species richness increases with island size in the Sunda Islands?
What does the intersection point of the immigration and extinction curves represent in the island equilibrium model?
What does the intersection point of the immigration and extinction curves represent in the island equilibrium model?
How does habitat fragmentation on smaller islands typically affect species?
How does habitat fragmentation on smaller islands typically affect species?
In the context of species interactions on islands, what is competitive exclusion?
In the context of species interactions on islands, what is competitive exclusion?
What is a significant consequence of rising sea levels on island ecosystems?
What is a significant consequence of rising sea levels on island ecosystems?
What primary factor influences the number of bird species on the islands of Malaysia?
What primary factor influences the number of bird species on the islands of Malaysia?
Why do immigration rates decrease as more species colonize an island?
Why do immigration rates decrease as more species colonize an island?
What prediction can be made about species richness on a newly formed island?
What prediction can be made about species richness on a newly formed island?
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Study Notes
Species Diversity
- Species diversity includes species richness (number of different species) and relative abundance (proportion of each species).
- Example communities may have the same species richness but differing relative abundances; community may appear less diverse but could have a lower Shannon diversity index.
- The Shannon diversity index quantifies diversity, using species richness and relative abundance; higher values indicate greater diversity.
Challenges in Measuring Diversity
- Determining species numbers can be difficult due to rare species and challenges in identification, particularly in microorganisms.
- DNA sequencing helps identify species by comparing genetic material to reference databases.
- Molecular tools are increasingly used to assess microbial diversity due to their small size making them hard to count.
Community Stability and Diversity Benefits
- Higher plant diversity leads to increased productivity and stability within communities, allowing better recovery from environmental stressors.
- Long-term experiments demonstrate that diverse plant communities produce more biomass than single-species plots.
- Communities with high diversity are more resistant to the establishment of invasive species.
Trophic Structure
- Trophic structure refers to feeding relationships among organisms, forming a food chain connecting primary producers to consumers, and decomposers.
- Each organism occupies a specific trophic level in this chain, which illustrates energy transfer in an ecosystem.
Food Webs
- Food chains are interconnected, forming complex food webs; each species may interact at multiple levels.
- Examples found in specific ecosystems such as the Antarctic pelagic community highlight primary producers and various predator relationships.
Food Chain Length
- Food chains typically have short lengths, usually five or fewer links, constrained by energy transfer inefficiency.
- The energetic hypothesis suggests higher productivity supports longer chains in ecosystems.
Species with Large Impact
- Foundation species, such as certain trees and algae, significantly shape communities by providing habitat and resources; their removal often alters community dynamics.
- Keystone species, like the sea star Pisaster ochraceus, maintain community diversity through their ecological roles rather than abundance; their removal can lead to decreased species richness.
Experimental Evidence on Keystone Species
- In rocky intertidal zones, removing sea stars led to increased mussel populations, which dominated and eliminated other species, reducing overall diversity.### Keystone Species and Species Diversity
- Pisaster is identified as a keystone species, affecting community dynamics beyond its numerical abundance.
- In the control scenario with Pisaster, species richness ranged from 17 to 20 species from 1963 to 1973.
- The experimental scenario without Pisaster resulted in a dramatic decline in species richness, plummeting from 17 to approximately 2 species and remaining stable at that low level until 1973.
Ecosystem Engineers
- Organisms that modify the physical environment significantly are termed ecosystem engineers.
- Beavers exemplify ecosystem engineers by altering landscapes through tree felling, dam building, and pond creation, converting forests into flooded wetlands.
- Foundation species, like trees, also act as ecosystem engineers by modifying environments to create habitats for various other species.
Bottom-Up and Top-Down Controls
- Community organization is influenced by interactions across trophic levels, classified into two types of controls: bottom-up and top-down.
- Bottom-up control: Organism abundance is limited by the availability of food/nutrients at lower trophic levels. Altering lower level biomass can propagate changes up the food web.
- Top-down control: Organism abundance at each trophic level is controlled by the abundance of consumers at higher levels. Predators regulate herbivore populations, which, in turn, affects plant/algal abundance.
Practical Applications of Trophic Control
- In ecosystems, adjustments to trophic levels can enhance environmental health, such as improving water quality in lakes with excessive algal blooms.
- Removing top predators (e.g., killer whales) leads to increased primary carnivore (sea otters) populations, reducing herbivores (urchins) and fostering primary producers (kelp).
- Case study: Ecologists improved Lake Vesijärvi’s water quality by removing roach fish to reduce cyanobacterial blooms and stocking pike perch to establish a new predator level, successfully clearing the water.
Monitoring and Continuous Management
- Long-term monitoring is essential to maintain water quality and ecological balance, particularly after restoring trophic levels in impacted ecosystems.
Biogeographic Factors Influencing Diversity
- Diversity in biological communities is impacted by both local species interactions and large-scale biogeographic factors.
- Latitude and area are two significant biogeographic factors affecting species diversity.
Latitudinal Gradients
- Species richness is generally greater in tropical regions compared to temperate or polar areas.
- Historical observations by Charles Darwin and Alfred Wallace noted higher biodiversity in the tropics during the 1850s.
- A plot in tropical Malaysia can contain over 150 tree species, while a similar plot in Michigan usually has 30.
- Over 1,000 species of ants are found in Brazil, but only 13 species in Alaska.
- Evolutionary history contributes to diversity; tropical communities have more time for speciation due to less frequent major disturbances compared to temperate regions.
- Climate factors, specifically sunlight and precipitation, drive higher diversity in tropical areas; evapotranspiration rates correlate with species richness.
Area Effects
- Alexander von Humboldt recognized the species-area curve in 1807: larger geographic areas typically host more species.
- The diversity of habitats within larger areas supports increased species richness.
- Studies in areas like the Sunda Islands show a direct increase in bird species with larger island size.
Island Equilibrium Model
- Islands serve as practical models for understanding species diversity due to their isolation and defined boundaries.
- Robert MacArthur and E.O. Wilson developed the island equilibrium model, which balances species immigration and extinction rates.
- As species numbers on an island increase, immigration rates decline, while extinction rates rise due to competition.
- Smaller islands have decreased immigration and increased extinction rates due to fewer resources.
- Proximity to mainland enhances immigration rates and decreases extinction risks for species on islands.
Experimental Validation of the Model
- Research on mangrove islands in the Florida Keys demonstrated that larger and closer islands had higher species diversity.
- After fumigating certain islands to eliminate arthropods, species numbers gradually returned to pre-fumigation levels, with closer islands recovering faster.
- Control islands that were not fumigated maintained their species counts, confirming the model's predictions of recovery dynamics.
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