Structure, Stability and Trophic Cascades

Question 1

What does species richness mean?

Answer 1

Diversity

Question 2

What does complexicity mean?

Answer 2

Number of links

Question 3

What does interaction strengths mean?

Answer 3

How strong are the interactions e.g. prey preference, attack rates

Question 4

When does instability happen?

Answer 4

If there is a highly connected web OR a very large web

Unstable:

𝜎_(𝑖𝑛𝑡𝑒𝑟𝑎𝑐𝑡𝑖𝑜𝑛−𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ) √𝑆𝐶>1

Question 5

What did May conclude?

Answer 5

No distinction among predation, competition and mutualism

BUT

he used randomly generated interactions and not real biological ones

Question 6

When is stability lower?

Answer 6

For predator-prey networks with more realistic food web structure

When there is lots of weak interactions

Question 7

How do predators change plant biomass?

Answer 7

Density:

• predators eat herbivores = fewer herbivores
• fewer herbivores = lower pressure on plants
• lower pressure on plants = more plant biomass

Behaviour:

• predators scare herbivores = herbivores stop feeding or move to a safer habitat
• herbivores not feeding = lower pressure on plants
• lower pressure on plants = more plant biomass

Question 8

What are some negative indirect effects on lower trophic cascades of predator loss?

Answer 8

Loss of plant diversity and biomass

Loss of plant community structure

Loss of herbivore diversity

Eutrophication and hypoxia of water bodies

Services loss - freshwater, tourism, recreation, nutrient cycling, carbon capture