Herbivore Offence and Plant Defence

Question 1

Explain the diversity of herbivores

Answer 1

1/4 of all plant and animal species combined are phytophagous (plant feeding) insects. herbivores consume about 18% of net primary production

Question 2

What is another way to ask why the world is green?

Answer 2

why do herbivores not eat all the available plants

Question 3

What is a potential argument that ended up being wrong about why herbivores do not eat all the available plants

Answer 3

herbivores have evolved to not eat all the plants because it would counter to the “good of the species”
BUT wrong because evolution doesn’t plan/look at the future and are not actually interesting in conserving resources

Question 4

What are the two modern explanation categories to answer why the earth is green

Answer 4

1. bottom up
2. top down

Question 5

Evaluate top down control

Answer 5

remove predators and compare with control.
predict herbivore number increase and consume more vegetation.
difficult to remove all predators!

Question 6

What do they commonly use to test top down control

Answer 6

enclosure experiments, vegetation is usually taller inside than outside because remove herbivores

Question 7

Results of evaluating top down control

Answer 7

removal of predators does not result in complete destruction of plants, therefore top-down effects are part of explanation, but not sufficient

Question 8

What are the 3 types of plant defence

Answer 8

1. structural
2. chemical
3. biotic

Question 9

What is the principle of evaluating bottom up control

Answer 9

plant defence, that plants don’t want to be eaten

Question 10

Examples of structural defences

Answer 10

spines, trichomes (fine hairs on plants, protective barrier), thick cuticles on leaves

Question 11

Examples of chemical defences

Answer 11

toxicity toward herbivore (nightshade alkaloids causing hallucinations) and behavioural deterrence due to unpalatability (ex. ghost peppers)

Question 12

What is the difference between constitutive and induced defences

Answer 12

constitutive defences = present all the time
induced defences = unregulated when the plant is attacked

Question 13

Advantages of constitutive and induced defences

Answer 13

constitutive = no lag time
induced = energy saving, can be sense by neighbours to also start defence, have higher specificity than constitutive

Question 14

What does biotic defences mean and an example

Answer 14

plants recruit their herbivores natural enemies and reward them with food or shelter. natural enemies include predators or parasitoids
ex. bullhorn acacia, ants

Question 15

How may the bottom up affect drive diet specialization

Answer 15

plants will develop defences which lower herbivore populations and can drive the evolution of diet specialization, most herbivores cant eat most plants

Question 16

What is the nutrient ratio problem

Answer 16

many insects have more N in their bodies than the plants they are eating, animals succeed more with more nitrogen consumed

Question 17

Why can poor quality food keep herbivore populations low

Answer 17

because it requires more resources and energy to be used to allocated more food and processing rather than using those resources and energy to reproduce

Question 18

SOOOO why is the world green

Answer 18

while top-down and bottom-up both contribute, bottom-up processes are the most important in maintaining a green world

Question 19

instead of asking why is the sea blue, we really want to know…

Answer 19

why isn’t the sea green

Question 20

Why is euphotic zone a reason for the sea not being green

Answer 20

the layer where light can penetrate, photosynthesis can not occur below this zone, explains why below volume cannot be green

Question 21

why is seaweed an example of why the sea cannot be green

Answer 21

it is limited to near land and shallow areas because needs to be anchored to the ground

Question 22

Why are freshwater systems often green with plants/floating autotrophs but not oceans (2)

Answer 22

1. scarcity of nutrients = iron relatively insoluble in oceans and tend to be low concentration in bioavailable forms as more away from land (other nutrients can limit growth too)
2. biological pump = dead phytoplankton and zooplankton and feces sink and cannot be recycled, in the euphotic zone it effectively pumps out nutrients which keeps concentrations low and limits growth