Ecology of Communities

Questions and Answers

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?

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?

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?

A more diverse community Signup and view all the answers

In the context of the information provided, what does relative abundance measure?

The proportion each species represents of all individuals Signup and view all the answers

If two communities have the same species richness, what other factor must be considered to assess overall diversity?

Relative abundance of the species Signup and view all the answers

What can be inferred if one community exhibits high species richness but low relative abundance?

It may face ecological instability Signup and view all the answers

What does the species richness of a community specifically refer to?

The number of different species present Signup and view all the answers

What is a significant challenge when determining species abundance in a community?

Obtaining a large enough sample size can be difficult. Signup and view all the answers

How does DNA sequencing aid in species identification?

It compares DNA sequences to a reference database. Signup and view all the answers

What technique is commonly used to analyze microbial diversity?

PCR amplification and DNA profiling. Signup and view all the answers

Which factor was related to the highest Shannon diversity index in bacterial communities?

Neutral soils. Signup and view all the answers

What ecological benefit is commonly associated with higher species diversity?

Greater stability in community productivity. Signup and view all the answers

In the Cedar Creek Ecosystem Science Reserve experiments, which plots produced more biomass annually?

High-diversity plots. Signup and view all the answers

What was the result of introducing a tunicate to communities with varying diversity levels?

Higher-diversity communities were less resistant. Signup and view all the answers

What role does trophic structure play in communities?

It influences feeding relationships among organisms. Signup and view all the answers

Why are fractions of DNA analyzed in microbial diversity studies?

To measure sequence variations in ribosomal RNA. Signup and view all the answers

What was the correlation between Shannon diversity index and soil acidity in the studied samples?

Diversity peaks at neutral pH levels. Signup and view all the answers

What is a challenge faced when studying microorganisms in communities?

Their small size complicates sampling efforts. Signup and view all the answers

How does increased plant diversity influence community stability?

It enhances productivity throughout the year. Signup and view all the answers

What does the Shannon diversity index measure?

Species diversity and evenness within a community. Signup and view all the answers

What is a common outcome for diverse communities when facing new species introductions?

They can better compete for available resources. Signup and view all the answers

What role do decomposers play in a food chain?

They break down organic material from various trophic levels. Signup and view all the answers

What defines a species as a primary consumer in a food chain?

It directly feeds on primary producers. Signup and view all the answers

In the context of food webs, what is a nonexclusive consumer?

A species that has a diet consisting of multiple trophic levels. Signup and view all the answers

How is the diversity of a food web beneficial to an ecological community?

It reduces the chances of extinction among species. Signup and view all the answers

Which trophic level is directly fed upon by tertiary consumers?

Secondary consumers. Signup and view all the answers

What effect would an increase in the population of carnivores targeting zooplankton have on phytoplankton?

Phytoplankton abundance will decrease due to increased predation. Signup and view all the answers

What is the primary producer in the Antarctic marine food web?

Phytoplankton. Signup and view all the answers

What is the main function of arrows in a food web diagram?

To represent the flow of energy and nutrient transfer. Signup and view all the answers

Which term describes the position of an organism in a food chain?

Trophic level. Signup and view all the answers

How can complicated food webs be simplified for study?

By grouping organisms into functional groups or isolating portions of the web. Signup and view all the answers

In a food web, what is the role of predatory species like penguins and seals?

They transfer energy to higher trophic levels. Signup and view all the answers

What type of organisms are krill classified as in an Antarctic food web?

Primary consumers. Signup and view all the answers

Which of the following organisms would be considered a tertiary consumer in a food chain?

A large fish consuming small fish. Signup and view all the answers

Which of the following groups of animals primarily fulfill the role of decomposers?

Detritivores and bacteria. Signup and view all the answers

What happened to species richness when Pisaster was removed from the intertidal zone?

Species richness declined sharply due to mussel dominance. Signup and view all the answers

What conclusion can be drawn about Pisaster's ecological role?

Pisaster acts as a keystone species influencing community structure. Signup and view all the answers

In which scenario would species richness potentially decline further after the removal of Pisaster?

The death of a majority of Mytilus due to an invasive fungus. Signup and view all the answers

What is meant by 'bottom-up' control in ecological communities?

Nutrient supply limits the abundance of organisms at various trophic levels. Signup and view all the answers

What role do ecosystem engineers play in their environments?

They alter the physical environment, impacting other species positively or negatively. Signup and view all the answers

How does the removal of top-level predators affect the ecosystem?

It results in an increase in primary producers. Signup and view all the answers

What is indicated by a graph showing stable species richness with the presence of Pisaster?

Pisaster supports diversity by preventing biomass monopolization. Signup and view all the answers

Which term describes species that significantly alter their physical environment?

Ecosystem engineers Signup and view all the answers

What was the overall trend in species richness from 1963 to 1973 without Pisaster?

Plummeted and stabilized at a low level. Signup and view all the answers

What effect does bottom-up control have on ecological dynamics?

It leads to cascading effects through higher trophic levels. Signup and view all the answers

Which factor is a key element in top-down control of an ecosystem?

Predation rates Signup and view all the answers

What would be a consequence of adding nutrients to a bottom-up controlled ecosystem?

Increased biomass at various trophic levels. Signup and view all the answers

How do changes in predator abundance affect lower trophic levels in a top-down controlled ecosystem?

They can lead to fluctuations among herbivore and primary producer populations. Signup and view all the answers

What does the stabilization of species richness with Pisaster present suggest about species interactions?

Pisaster suppresses competitive exclusion by mussels. Signup and view all the answers

What is a primary reason that food chains are typically short?

Inefficiency of energy transfer through trophic levels. Signup and view all the answers

Which factor influences the length of food chains according to the energetic hypothesis?

The rate of photosynthetic production. Signup and view all the answers

How many trophic links were observed in tree-hole communities with low productivity?

One trophic link. Signup and view all the answers

What is the role of foundation species in a community?

To provide habitat or food and dominate key resources. Signup and view all the answers

What effect did the chestnut blight have on other tree species?

It allowed competing tree species to increase in abundance. Signup and view all the answers

What is a key distinction of keystone species compared to foundation species?

Keystone species exert control through their ecological roles rather than abundance. Signup and view all the answers

Which of the following statements about energy transfer efficiency is accurate?

Only a small fraction of energy (approximately 10%) is passed to the next trophic level. Signup and view all the answers

In the experiments conducted on tree-hole communities, what condition decreased food chain length?

Reducing energy input through leaf litter. Signup and view all the answers

What defines the term 'foundation species'?

Species that are abundant and play a critical role in the structure of a community. Signup and view all the answers

Which ecological role is exemplified by the sea star Pisaster ochraceus in intertidal communities?

It acts as a keystone species by controlling mussel populations. Signup and view all the answers

What factor limits the size of carnivores at higher trophic levels?

The metabolic demands of larger body size. Signup and view all the answers

Why do most studied food webs have chains consisting of five or fewer links?

As a result of energy transfer inefficiencies. Signup and view all the answers

Which mechanism is directly responsible for the increases in diversity seen when a foundation species is removed?

Reduction in competitive pressure from the foundation species. Signup and view all the answers

What is the impact on herbivores when a foundation species like the American chestnut is removed?

Unchanged herbivore populations due to alternative food sources. Signup and view all the answers

What does the energetic hypothesis predict about food chains in highly productive environments?

They should be longer due to increased energy availability. Signup and view all the answers

What is the main outcome when colonists increase the abundance of a species on an island?

It reduces the chance of extinction for that species. Signup and view all the answers

Which factor correlates with the number of species at equilibrium according to MacArthur and Wilson's model?

The island's size and distance from the mainland. Signup and view all the answers

After fumigating islands, what trend was observed regarding the number of arthropod species?

Species numbers increased over time towards pre-fumigation levels. Signup and view all the answers

In the experiment, which island was observed to recover the fastest after fumigation?

The island closest to the mainland. Signup and view all the answers

What happens to the exact species composition on an island over time despite the stabilization of species numbers?

It can change, although total numbers stabilize. Signup and view all the answers

What was the role of the two control islands during the study on species recovery?

To maintain constant species numbers as a baseline. Signup and view all the answers

Which of the following is NOT a factor that influences species numbers at equilibrium in the island equilibrium model?

Migration patterns of terrestrial animals. Signup and view all the answers

What methodology was used to initially assess the arthropod species on the islands?

Identifying and counting all species manually. Signup and view all the answers

What are two significant factors that contribute to latitudinal gradients of species richness?

Climate and evolutionary history Signup and view all the answers

Why do tropical communities tend to have higher species richness compared to temperate or polar communities?

Tropical communities are affected by fewer disturbances over time. Signup and view all the answers

Which of the following factors is NOT correlated with species diversity in terrestrial communities?

Temperature variations Signup and view all the answers

What has historical observation pointed out regarding the abundance and diversity of species in different latitudes?

Tropical regions generally show greater abundance and diversity of life. Signup and view all the answers

How can past disturbances like glaciations affect species richness in different communities?

They limit opportunities for new speciation. Signup and view all the answers

Which statement best explains the reason for a higher tree species count in tropical regions compared to temperate regions?

Favorable climate conditions enhance tree growth in tropics. Signup and view all the answers

What concept explains the observed increase in species richness over evolutionary time in tropical communities?

Tropical communities have had longer time periods for evolution. Signup and view all the answers

Which of the following observations has been confirmed regarding the diversity of animal species across different latitudes?

Brazil contains significantly more ant species than Alaska. Signup and view all the answers

How does potential evapotranspiration relate to vertebrate species richness in a community?

Higher potential evapotranspiration typically correlates with greater species richness. Signup and view all the answers

What does the species-area curve suggest about larger geographic areas?

They typically have more diverse habitats and thus support more species. Signup and view all the answers

According to the island equilibrium model, what happens to the immigration rate as the number of species on an island increases?

It decreases due to increased competition among species. Signup and view all the answers

What effect do smaller islands generally have on species diversity compared to larger islands?

They typically have lower immigration rates and higher extinction rates. Signup and view all the answers

Which statement accurately describes the relationship between rainfall and species richness in North America?

Species richness correlates positively with rainfall, up to a certain point. Signup and view all the answers

What hypothesis can be derived from the observation that species richness increases with island size in the Sunda Islands?

Larger islands support a higher number of ecological niches. Signup and view all the answers

What does the intersection point of the immigration and extinction curves represent in the island equilibrium model?

The predicted equilibrium number of species on the island. Signup and view all the answers

How does habitat fragmentation on smaller islands typically affect species?

It reduces available resources, leading to higher extinction rates. Signup and view all the answers

In the context of species interactions on islands, what is competitive exclusion?

Existing species are outcompeted and driven to extinction by newcomers. Signup and view all the answers

What is a significant consequence of rising sea levels on island ecosystems?

Decreased land area leading to potential declines in species populations. Signup and view all the answers

What primary factor influences the number of bird species on the islands of Malaysia?

The size of the island and its available habitats. Signup and view all the answers

Why do immigration rates decrease as more species colonize an island?

Because fewer new species are likely to survive competition. Signup and view all the answers

What prediction can be made about species richness on a newly formed island?

It will increase rapidly until it reaches a maximum and then stabilize. Signup and view all the answers

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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Description

This quiz explores the attributes of ecological communities, focusing on species diversity and feeding relationships among species. You'll delve into concepts like species richness and the influence of certain species on community structure. Test your understanding of these fundamental ecological principles.