Marine Biology: Trophic Cascades Quiz

Questions and Answers

All members of a food web are equal in abundance and on their relative effects on one another.

False

Explain the reasoning to why 'all members of a food web are equal in abundance and on their relative effects on one another' is false.

Some species, which are not as abundant as some other species, can have large effects on the structure of their ecosystems.

Every member of a food web is the prey of another member of the food web.

False

Why are the mussels in Mukkaw Bay able to quickly cover the rockface in Paine's experiment?

Starfish feed on mussels, so when the starfish were removed the mussels no longer had a predator and their populations grew unchecked. Signup and view all the answers

How did the green world hypothesis differ from the 'bottom-up' view?

The green world hypothesis explained that the number of herbivores is also limited by predators from the top down. Signup and view all the answers

Imagine a simple food chain: Grass -> Grasshoppers -> Mice. If snakes that eat mice are added to this ecosystem, how would you redraw the food chain to represent this change?

Grass -> Grasshoppers -> Mice -> Snakes Signup and view all the answers

After the snakes are added, would you expect the amount of grass to increase or decrease? Explain your reasoning.

The snakes will cause a reduction in mouse populations, leading to an increase in grasshoppers that will then eat the grass. Signup and view all the answers

In 1997, which species is the apex predator in the food chain?

Killer whales Signup and view all the answers

Draw two diagrams that show the food chains for the control and experimental plots. Include interactions among predatory beetles (if present), ants, caterpillars, and piper plants.

Control: piper plants -> ants -> caterpillars; Experimental: piper plants -> caterpillars -> beetles. Signup and view all the answers

What statement do Letourneau and Dyer's results support?

Adding beetles reduced ant numbers and triggered a trophic cascade that decreased the mean leaf area left on plants. Signup and view all the answers

Do the results of the Letourneau and Dyer experiment support or refute the green world hypothesis? Explain your answer.

The experiment supports the green world hypothesis because changes in plant leaf area were caused by predators controlling herbivore numbers from the top down. Signup and view all the answers

Study Notes

Food Web Dynamics

Not all members of a food web have equal effects on one another; some species can significantly influence ecosystem structure despite lower abundance.
Apex predators are positioned at the top of food webs and typically do not have predators themselves.

Keystone Species

Removal of keystone species (e.g., starfish) can lead to dramatic declines in biodiversity; mussels proliferated when their predator was removed in Paine's experiment.
After the starfish removal, species diversity in the ecosystem decreased from 15 to nearly all mussels, indicating the crucial role of keystone species in maintaining ecological balance.

Green World Hypothesis vs. Bottom-Up View

The green world hypothesis posits that herbivore populations are regulated by predation, challenging the bottom-up perspective that emphasizes resource availability as the main control factor.

Food Chain Dynamics

Introducing snakes to a simple food chain (Grass -> Grasshoppers -> Mice) modifies it to Grass -> Grasshoppers -> Mice -> Snakes, illustrating the impact of predators.
The presence of snakes would likely lead to a decrease in mouse populations, resulting in an increase in grasshoppers, which would then consume more grass.

Apex Predators

In the 1997 ecosystem scenario, killer whales were recognized as apex predators, playing a significant role in controlling other population sizes in marine food webs.

Trophic Cascades

Adding predatory beetles to food chains resulted in reduced ant populations, triggering cascades affecting plant health by decreasing leaf area.
The experiment conducted by Letourneau and Dyer supports the green world hypothesis, demonstrating that top-down predation by beetles impacts herbivore (caterpillar) populations and subsequently plant health.

Summary of Experimental Results

Control plots showed stability with no significant changes in species diversity, contrasting with experimental plots where the removal of predators led to ecological imbalances.
Key interactions among species, including predatory relationships, highlight the interconnectedness of food web dynamics.

Description

Test your knowledge about trophic cascades and the role of keystone species in marine ecosystems. This quiz will challenge your understanding of food webs and the relative impacts of different species on their environment. Get ready to delve into the intricacies of marine biology!