W13: Biocontrol (CO2 & Climate Change) [Dr. Nic]

Question 1

CO2 attributes? (3)

Answer 1

• Industrial revolution caused CO2 levels to skyrocket.
• Effect of increased CO2 was that there was increased global temperature, due to the greenhouse effect (i.e., it’s getting warmer & warmer).
• Decrease in precipitation also occurred.

Question 2

What does climate change mean for biocontrol? (6)

Answer 2

• Systems diagram showing the different interactions between climate change, plant invaders, weed biological agents & ecosystem impacts.
• Climate change affects plant invaders & weed biological control agents.
• Climate change increases (+) plant invaders.
• Climate change increases (+)/decreases (-) weed biocontrol agents.
• Weed biocontrol agents may increase (+)/decrease (-)/no effect (0) plant invaders.
• Plant invaders decrease (-) ecosystem impacts.

Question 3

Why do we have elevated CO2? (4)

Answer 3

• Increased by 50% (200ppm) in 50 years time.
• Plants balance CO2 uptake & water loss.
• Elevated CO2 increases CO2 uptake with the same/less water loss (water use efficient).
• Reallocation of resources.

Question 4

Eg of the effects of elevated CO2 on plants?

Answer 4

Opuntia stricta.

Question 5

Opuntia stricta attributes in relation to elevated CO2? (11)

Answer 5

• Distributed predominantly in northern South Africa.
• Palnts are grown in CO2 growth chambers at different CO2 levels to determine how they would respond (this is an attempt to mimic predicted CO2 levels).
• Increase in WUE as you move from current CO2 levels (400ppm) to future CO2 levels (600ppm).
• Allows plants to persist in drier environments as WUE increases (indicated by camel).
• No change in # of cladodes.
• Relative change in the total cladode area.
• Increase in biomass (get heavier from 400-600ppm).
• Specific cladode area/specific leaf area decreased from 400-600ppm.
• Increase in the cladode hardness (allows them to be more resilient to herbivory & harsh weather conditions).
• Increase in biomass of spines (spinescence), which increases defence.
• Increase in tannins (lignification).

Question 6

Cladodes?

Answer 6

= modified stems that fulfil the purpose that the leaves usually would in other plants.

Question 7

Invasion implications? (2)

Answer 7

• Allows these plants to persist in more arid environments (due to being water-use efficient).
• Plants tend to be larger & more vigorous (helps with defence).

Question 8

Elevated CO2 effects/Results of elevated CO2? (6)

Answer 8

Elevated CO2
|
Range expansion
|
Greater biomass
|
Tougher & greater mechanical defence
|
Decreased plant quality
|
Less effective biocontrol

Question 9

Plant responses to elevated CO2? (4)

Answer 9

• Decrease in N content in leaf.
• Increase in C: N ratio (dilution effect).
• Defence compounds increase, so increased defence.
• Similar to Opuntia stricta trends.

Question 10

Biocontrol implications? (2)

Answer 10

• Plants are less nutritious for plants.
• Increased defence.

Question 11

Egs of biocontrol implications? (2)

Answer 11

• Dactylopius sp. (cochineal).
• Aquatic plants.

Question 12

Dactylopius sp. (cochineal) attributes in relation to biocontrol implications? (6)

Answer 12

• At high CO2 levels, mortality rates increased for crawlers (couldn’t settle on plant).
• About 30% survival (i.e., few could settle on plant).
• Took 2 weeks & longer for maturation of the insect.
• No difference in female body mass & offspring number produced.
• Fitness significantly decreased.
• As C:N ratio increased, female fitness decreased.

Question 13

Opuntia stricta response to increased CO2 & cochineal herbivory? (3)

Answer 13

• Increased C:N ratio (dilution effect again!!).
• Decreased N content in plants.
• Carbon in plants stays constant, but N decreases.

Question 14

Cactus response to cochineal? (3)

Answer 14

• Plants at 400ppm CO2 had more plant mortality that those at 600ppm CO2.
• Specialist insects had high mortality with elevated CO2 due to decreased nutrient quality, compared to generalists who were not affected.
• Elevated CO2 negatively affects insect herbivores by changing plant nutrient dynamics (relates to N content & midgut changes, perhaps?).

Question 15

What about the interactions of temperature & CO2? (7)

Answer 15

• Not many studies on this.
• Open to interpretation, as long as you are able to back it up.
• Think about the benefits & effects of high temperatures to both pants (weeds) & agents.
• Think about the benefits & effects of elevated CO2 to both plants (weeds) and agents.
• Consider the general trend.
• Integrate Dr. Blair’s section on the effects of high temperatures & elevated CO2 with phenology, & conclude as to how they will affect biocontrol (i.e., implication on biocontrol).
• Overall, will it be good or bad for biocontrol in the long run? Back up your answer.