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Questions and Answers
Which scenario best illustrates indirect commensalism?
Which scenario best illustrates indirect commensalism?
- A predator consumes a prey species, directly decreasing its population size.
- Beavers create habitats that benefit beetle populations, while the beavers are unaffected. (correct)
- A plant releases chemicals that inhibit the growth of nearby plants.
- Two bird species compete for the same nesting sites, limiting both populations.
How can the presence of a keystone species influence species diversity within a community?
How can the presence of a keystone species influence species diversity within a community?
- By directly increasing the population size of all species within the community.
- By reducing the likelihood of competitive exclusion, allowing more species to coexist. (correct)
- By intensifying competitive exclusion, leading to a decrease in species richness.
- By creating uniform environmental conditions, favoring a single dominant species.
In the context of apparent competition, what is the primary mechanism driving the negative impact between two competing species?
In the context of apparent competition, what is the primary mechanism driving the negative impact between two competing species?
- Increased herbivory or predation on one species due to the presence of another species that benefits the predator. (correct)
- One species directly preys on the other, reducing its population size.
- Direct competition for the same resources, such as food or habitat.
- Mutualistic interactions between the two species that inadvertently harm both populations.
What is the key difference between direct and indirect interactions within an ecological community?
What is the key difference between direct and indirect interactions within an ecological community?
Consider a scenario where a predatory fish is introduced to a lake ecosystem. The fish primarily preys on a zooplankton species, which in turn feeds on algae. What is the most likely indirect effect of introducing the predatory fish?
Consider a scenario where a predatory fish is introduced to a lake ecosystem. The fish primarily preys on a zooplankton species, which in turn feeds on algae. What is the most likely indirect effect of introducing the predatory fish?
In the study by Orrock et al. involving Brassica nigra and Nassella pulchra, what role did the mammals play in the apparent competition between the two plant species?
In the study by Orrock et al. involving Brassica nigra and Nassella pulchra, what role did the mammals play in the apparent competition between the two plant species?
How might a keystone predator influence the distribution and abundance of other predator species in an ecosystem?
How might a keystone predator influence the distribution and abundance of other predator species in an ecosystem?
Paine's research on intertidal food webs revealed a relationship between species diversity and the proportion of predators. What was the key finding of this research?
Paine's research on intertidal food webs revealed a relationship between species diversity and the proportion of predators. What was the key finding of this research?
In the context of ecological studies, what is the primary advantage of focusing on the strongest trophic links within a food web?
In the context of ecological studies, what is the primary advantage of focusing on the strongest trophic links within a food web?
How did Paine define strong interactions within a community, and why is this concept important in food web studies?
How did Paine define strong interactions within a community, and why is this concept important in food web studies?
What is the most significant outcome of distinguishing between weak and strong interactions in a food web, as demonstrated by Tscharntke's study of wetland reeds?
What is the most significant outcome of distinguishing between weak and strong interactions in a food web, as demonstrated by Tscharntke's study of wetland reeds?
What is a key characteristic of early food web studies, and why was this approach adopted?
What is a key characteristic of early food web studies, and why was this approach adopted?
Consider a scenario where a particular fish species in a freshwater ecosystem consumes both algae and small insects. How would this mixed diet likely be represented in a detailed food web?
Consider a scenario where a particular fish species in a freshwater ecosystem consumes both algae and small insects. How would this mixed diet likely be represented in a detailed food web?
Ecologists are studying a forest ecosystem and observe that the removal of a specific beetle species leads to a significant decline in the population of a particular tree. Which of the following conclusions is most justified based on this observation?
Ecologists are studying a forest ecosystem and observe that the removal of a specific beetle species leads to a significant decline in the population of a particular tree. Which of the following conclusions is most justified based on this observation?
In a study of a grassland ecosystem, researchers identify several species of grasses, herbivores, and predators. Which approach would best help them construct a food web that highlights the most critical interactions for maintaining the grassland's structure?
In a study of a grassland ecosystem, researchers identify several species of grasses, herbivores, and predators. Which approach would best help them construct a food web that highlights the most critical interactions for maintaining the grassland's structure?
How might the removal of a predator that specializes on fly larvae and parasitoid wasps (as seen in the Phragmites food web) impact the community structure?
How might the removal of a predator that specializes on fly larvae and parasitoid wasps (as seen in the Phragmites food web) impact the community structure?
In Paine's experiment involving the removal of Pisaster sea stars, what was the most significant observed ecological consequence?
In Paine's experiment involving the removal of Pisaster sea stars, what was the most significant observed ecological consequence?
What crucial information is needed to effectively study the influence of intertidal snails on the diversity of intertidal algae?
What crucial information is needed to effectively study the influence of intertidal snails on the diversity of intertidal algae?
Which of the following best describes the effect of Littorina snails on algal communities, considering the different algal species?
Which of the following best describes the effect of Littorina snails on algal communities, considering the different algal species?
In a tide pool ecosystem, what ecological relationship exists between green crabs (Carcinus maenus) and Littorina snails?
In a tide pool ecosystem, what ecological relationship exists between green crabs (Carcinus maenus) and Littorina snails?
How does varying snail density affect algal diversity in tide pools?
How does varying snail density affect algal diversity in tide pools?
What is the likely outcome in a tide pool where seagulls, a key predator, are removed from the local ecosystem?
What is the likely outcome in a tide pool where seagulls, a key predator, are removed from the local ecosystem?
Consider a scenario where a new invasive species of algae, highly preferred by Littorina snails, is introduced into a tide pool ecosystem. What is the most likely short-term effect on the native algal community?
Consider a scenario where a new invasive species of algae, highly preferred by Littorina snails, is introduced into a tide pool ecosystem. What is the most likely short-term effect on the native algal community?
In an intertidal zone, a disease drastically reduces the population of Carcinus maenus (green crabs). Predict the most likely long-term impact on the Littorina littorea (snail) and algal populations.
In an intertidal zone, a disease drastically reduces the population of Carcinus maenus (green crabs). Predict the most likely long-term impact on the Littorina littorea (snail) and algal populations.
In the Eel River food web, how do predatory fish influence algal densities?
In the Eel River food web, how do predatory fish influence algal densities?
Why are cleaner wrasses considered a keystone species on Red Sea coral reefs?
Why are cleaner wrasses considered a keystone species on Red Sea coral reefs?
What is the primary role of native ants in the fynbos of South Africa, and how does this relate to their keystone species status?
What is the primary role of native ants in the fynbos of South Africa, and how does this relate to their keystone species status?
How does the displacement of native seed-dispersing ants by Argentine ants affect seedling recruitment in the fynbos?
How does the displacement of native seed-dispersing ants by Argentine ants affect seedling recruitment in the fynbos?
Which of the following scenarios best illustrates a mutualistic keystone species interaction?
Which of the following scenarios best illustrates a mutualistic keystone species interaction?
What ecological principle is demonstrated when the removal of cleaner wrasses from a coral reef leads to a significant reduction in fish species diversity?
What ecological principle is demonstrated when the removal of cleaner wrasses from a coral reef leads to a significant reduction in fish species diversity?
In the context of the Eel River food web, how would an increase in the population of predatory fish likely affect algal densities, assuming other factors remain constant?
In the context of the Eel River food web, how would an increase in the population of predatory fish likely affect algal densities, assuming other factors remain constant?
Consider a community where a particular species of beetle helps to aerate the soil through its burrowing activity, which in turn benefits plant growth. This beetle also serves as a primary food source for several bird species. If the beetle population declines drastically due to habitat loss, what is the most likely consequence for this community?
Consider a community where a particular species of beetle helps to aerate the soil through its burrowing activity, which in turn benefits plant growth. This beetle also serves as a primary food source for several bird species. If the beetle population declines drastically due to habitat loss, what is the most likely consequence for this community?
Flashcards
Food Web
Food Web
A summary of the feeding relationships within a community.
Indirect Interactions
Indirect Interactions
Interactions between species in a community that are not direct, such as when one species affects another through a third species.
Keystone Species
Keystone Species
Species whose feeding activities significantly control community structure.
Mutualism
Mutualism
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Early Community Study Approach
Early Community Study Approach
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Strong Interactions
Strong Interactions
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Interaction Strength
Interaction Strength
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Phragmites australis
Phragmites australis
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Indirect Commensalism
Indirect Commensalism
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Beavers and Beetles example
Beavers and Beetles example
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Apparent Competition
Apparent Competition
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Brassica/Nassella Example
Brassica/Nassella Example
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Keystone Effect on Diversity
Keystone Effect on Diversity
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Predators and Diversity
Predators and Diversity
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Predator-Prey Dynamics & Diversity
Predator-Prey Dynamics & Diversity
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Pisaster Removal Experiment
Pisaster Removal Experiment
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Algal Diversity Study
Algal Diversity Study
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Snail Herbivore Preference
Snail Herbivore Preference
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Littorina's Impact on Algae
Littorina's Impact on Algae
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Snail Grazing Effects
Snail Grazing Effects
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Crabs, Snails, and Seagulls
Crabs, Snails, and Seagulls
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Effect of Predatory Fish on Algae
Effect of Predatory Fish on Algae
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Fish as Keystone Species (Rivers)
Fish as Keystone Species (Rivers)
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Keystone Species Characteristic
Keystone Species Characteristic
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Mutualist as Keystone
Mutualist as Keystone
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Cleaner Wrasse as Keystone
Cleaner Wrasse as Keystone
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Seed-Dispersing Ants
Seed-Dispersing Ants
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Impact of Argentine Ants
Impact of Argentine Ants
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Seedling recruitment
Seedling recruitment
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Study Notes
- Food webs summarize the feeding relations in a community
- Indirect interactions between species are fundamental to communities
- The feeding activities of a few keystone species is able to control the structure of communities
- Mutualists can act as keystone species
Introduction
- Feeding relationships are easily documented interactions in communities
- Early studies of communities focused on describing who eats whom
- These feeding relationships are called food webs
Community Webs
- Early work on food webs concentrated on simplified communities
- Feeding relations are complex, even in "impoverished faunas"
- Simplified food webs are more manageable to study than food webs of diverse communities
Detailed Food Webs
- Winemiller described feeding relations among tropical freshwater fish at 2 sites
- Food webs are represented in various ways
- Webs include only common species
- Webs exclude the weakest trophic links
- The most comprehensible webs focus on the strongest trophic links
Strong Interactions
- Paine suggested the feeding activities of a few species may have a dominant influence on community structure, these are strong interactions
- The criterion for a strong interaction is the degree of influence on community structure
- Recognizing interaction strength can affect how a food web is depicted
Phragmites Food Web
- Tscharntke studied wetland reed food webs, also know as Phragmites australis
- Reeds are attacked by a fly Giraudiella inclusa
- The fly is attacked by 14 parasitoid wasp species
- Predators specialize on eating fly larvae and consequently on parasitoid wasps interactions
- This allows easier determination of species with significant influences
Indirect Interactions
- Direct interactions (competition, predation, etc.) between two species do not involve intermediary species
- Indirect interactions are the effects of one species on another through a third species
- Trophic cascades, indirect commensalism, and apparent competition are examples of indirect interactions
Indirect Commensalism
- One species indirectly benefits another species (through a third species) while it is neither helped nor harmed
- Beavers fell cottonwood trees, which then produce stump sprouts
- Herbivorous beetles (Chrysomela confluens) prefer consuming high-nutrition sprout leaves
- Beetles grow larger, faster, and utilize defensive compounds found in those leaves
- Beavers have a positive effect on beetles through cottonwood trees
Apparent Competition
- Negative effects between two competitors who share a predator or herbivore may occur
- One species may facilitate populations of a predator of a second species
- Orrock et al. studied apparent competition between Brassica nigra (exotic) and Nassella pulchra (native)
- Brassica shelters mammals which feed on surrounding vegetation
- This increases herbivory on Nassella
Keystone Species
- Feeding activities of a few species, called keystone species, have inordinate influences on community structure
- Keystone species reduce the likelihood of competitive exclusion, their activities increase the number of species that can coexist in communities
- Some predators can increase species diversity
Food Web Structure
- Paine found as the number of species in intertidal food webs increased, the proportion of the web represented by predators also increased
- A higher proportion of predators produces higher predation pressure on prey populations, promoting higher diversity
Experimental Removal of Sea Stars
- Paine removed top predator, Pisaster, from intertidal food web and monitored it for over 2 years
- The control plot remained with a diversity of 15 species
- The removal plot dropped to a diversity of 8 species
- After Pisaster removal, the plot was dominated by mussels and gooseneck barnacles
- Pisaster is is considered to be a keystone species because without it, the community collapsed
Snail Effects on Algal Diversity
- To study the influence of intertidal snails on the diversity of intertidal algae, you must know:
- Herbivore food preference
- Competitive relationships between plant species in the local community
- Variance in feeding preferences and competitive relationships across environments
Study of Littorina Littorea
- Lubchenco studied Littorina littorea
- Snails preferred small, ephemeral, tender algae (Enteromorpha spp.)
- Snails did not prefer tough perennial species (such as Chondrus)
- Tidepools with high densities of Enteromorpha had low snail density, vice versa
- Without Littorina, Chondrus is competitively displaced
Snails and Crabs
- When snails are present in high densities, Littorina grazes down Enteromorpha, releasing Chondrus from competition
- Green crabs (Carcinus maenus) prey on young snails, preventing juveniles from colonizing tide pools
- Populations of Carcinus are controlled by seagulls
Variations in Snail Density
- Low snail density indicates Enteromorpha dominates the tide pool
- Medium snail density indicates competitive exclusion is eliminated, and algal diversity increased
- High snail density means the feeding requirements are high enough that snails eat both preferred and less-preferred algae
- Algal diversity is decreased
Fish as River Keystone Species
- Power investigated whether California roach and steelhead trout significantly influence food web structure
- It was found that predatory fish decrease algal densities
- Low predator density increased midge production
- Increased midge feeding pressure on algal populations occurs
- Fish act as keystone species
Mutualistic Keystones
- Mutualists can act as keystone species
- Keystone species have a high impact on community structure, despite low biomass
Cleaner Fish
- Many fish species on coral reefs clean ectoparasites from other fish, showing mutualism
- Cleaner wrasse can remove and eat 1,200 parasites per day
- When wrasses disappear or are removed, a 24% median reduction in fish species diversity occurs
- When wrasses appear or are added, a 24% median increase in fish species diversity occurs
- Cleaner wrasse is a keystone species on Red Sea coral reefs
Seed Dispersal Mutualists
- Christian observed native ants disperse 30% of shrubland seeds in the fynbos plant communities of South Africa
- Seed-dispersing ants bury seeds in sites that are safer from predators and fire
- Argentine ants have displaced many native ant species that disperse large seeds
- Substantial reductions in seedling recruitment occur by plants producing large seeds
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Description
Explore indirect commensalism, keystone species, and apparent competition. Differentiate between direct and indirect ecological interactions. Examples include predatory fish and intertidal food webs.
