Lecture Five - Food webs and trophic cascades I

Question 1

What is the first law of thermodynamics?

Answer 1

Energy can neither be created nor destryed, only transformed.

Question 2

What is the ecological pyramid?

Answer 2

As you increase the trophic level, you decrease in biomass and the amount of energy passed up through the ecological pyramid deacreases incrementally.

Question 3

How do producers and consumers interact?

Answer 3

Tertiary consumers eat secondary consumers eat primary consumers eat producers.

Question 4

What is a trophic cascade?

Answer 4

Predators suppress the abundance of their prey.

• When removed, the trophic level below increases.

Essentially, the alteration of one species in an ecosystem will affect all those who are connected to it (directly and indirectly) in the food web.

Question 5

Explain the green world hypothesis.

Answer 5

Predators reduce the abundance of herbivores allowing plants to flourish.

• Many strategies exist to reduce herbivory.

Highlighted the role of top-down effects (predation).

Many critisizms to this theory, including the fact that plants have their own defence systems, particular plants will not be a part of a herbivours diet etc.

Question 6

What is the top down and bottom up effects?

Answer 6

The bottom-up model of community organisation proposes a unidirectional influence from lower to higher trophic levels.

• In this case, presence or absence of mineral nutrients determines community structure, including abundance of primary producers.

Question 7

What are the euphototrophic and profundal zones?

Answer 7

Euphototrophic zone is where light can penetrate water in an aquatic environment and allows for photosynthesis to occur.

• Photosynthesis > Respiration.

Profundal zone is where there is not enought light penetration to allow for much photosynthesis.

• Photosynthesis < Respiration.

Question 8

What are the two main chains of organisms in an ecosystem?

Answer 8

Grazing and detrital (eat dead things).

Question 9

What is biomanipulation?

Answer 9

Modification of an aquatic foodweb to enhance grazing by zooplankton to control algal biomass.

Enhance grazing by zooplankton to control algal biomass.

Putting things back into an ecosystem - Top up control.

Biomanipulation - ‘Top Down’ control of water quality.

Nutrient Reduction - ‘Bottom Up’ control of water quality.