The Never Ending Struggle Flashcards
How does liverwort defend itself?
By using oil glands that produce terpenoids that are toxic
Why is it hard for plants to produce defence compunds?
Photosynthesis can usually supply enough carbon to synthesize compounds such as terpenoids (2,6 g of carbon)
But it is harder to synthesize alkloids because the nitrogen intake of a plant is limited (5,2g for alkaloids)
What is the cause of these defence costs?
The plant has to choose between growing or defending itself
It can also affect symbiotic relationships because these can choose not to form one if the plant isnt protected enough
What does mounting a defence against attack require?
The production of chemicals and erection of structural barriers which places a constraint on the plant because it diverts energy and recources away from growth and development
What is the growth-differentation balance hypothesis?
This hypothesis is based on the premise that there is a trade-off between growth and differentation processes (defence) in plants.
It predicts that rapidly growing plants will have low levels of defensive chemicals bc making new leaves means there is little carbohydrates left over to manifacture expensive chemicals
How does defence place a constraint on the plant?
It diverts energy and resources away from growth and development
How do plants adapt in a environment where there is more competition?
They will favour growth over defence. Defences that would be activated are induced ones and low concentration ones
What is the optimal defence hypothesis?
A plant with an evolutionary history of high herbivory will prioritize the production of defensive compounds at the expense of growth. According to this:
-young leaves will be well-defended since they are of greater value for the plant (they can still photosensitize a lot compared to older leaves)
-roots have lower levels of defence chemicals due to them not being attacked by herbivores most of the time
What is the enemy release hypothesis?
Following their introduction to a new geographical region, plants experience a reduction in attack by the natural enemies with which they have co-evolved
Because of this, they suffer less damage and increase in size and fecundicity (fertility potential in populations) in contrast to the neighbouring plants
What is the competitive ability hypothesis?
Freedom from natural enemies and the relaxation of defences enables the plant to invest their resources in improving their competetive ability.
What is the novel weapon hypothesis?
Some highly invasive plants become dominant because they posess novel chemicals to which their new, native neighbours have not been previously exposed
What is the problem with studies that look at plant defence against herbivores?
They sometimes dont look at the difference between generalist and specialist herbivores
What is the the problem with quantitative defences?
They are expensive to produce, even though they help both againt generalist and specialist herbivores (trichomes or tannins)
What is the problem with qualitative defences?
They are cheaper but specialist insects often adapt to them (alkaloids and glucosinolates)
What is the shifting defence hypothesis?
The evolutionary shift from quantitative defence to qualitative defences by plants invading a new geographical area
What is the plant apparency hypothesis?
The kind of chemical defence a plant has against herbivores and pathogens depend on how easily the plant can be discovered by enemies
-Trees are very apparent ->they invest in quantitative defences: mechanisms that are robust enough to deal with more frequent and consistent attack
-Plants that appear on a scene after disturbance (fire) are less apparent ->they invest in qualitative defences: glucosinolates, alkaloids and cardenolides
What is associational resistance?
Plants that become less apparent to herbivores bc they grow intermingled with other species
Why are trees that are mixed with others less suspectable to attack?
-the other trees conceal the host tree (bc they are taller)
- the presence of non host trees disrupts visual or olfactory cues used by insects to locate their host
How do plants that grow on an island with low herbivory or parasite densities adapt their defences?
They reduce their investment in defence
How was the plant apparency theory refuted?
-the researcher found that the theory was right about the amount of defences activated
-she also found that the less apparent trees suffered way more herbivory and damage that the unapparent ones
-the variability of herbivory was also the same
-> there is a strong correlation between the amount of resources a tree invested in defence ant the level of damage it suffered
->a plants investment in defences was not the result of differences among species an apparency, but to differences in the cost/benefit ratio of those defences
