Lecture 8 - Interactions Flashcards
Aquatic life eats what percentage of world plant productivity?
More than 80%
Terrestrial animals eat what percentage of world plant productivity?
10 - 20%
Who eats plants?
Eating plants is taxonomically restricted
Only a few mammals taxa eat plants (hoofed animals and primates)
Birds only eat fruits and seeds
Only 9/26 insect orders eat plants
Only one third of beetles are herbivores.
What processes are involved with eating plants?
Mechanical and Chemical
Explain the mechanical processes associated with eating plants.
Mechanical devices such as teeth fragment the tissue and break cell walls.
Leaf feeders have specialised teeth
omnivores and fruit feeders have generalised teeth
Explain the chemical processes associated with eating plants.
Vertebrates rely mostly on large microbes
Specialised organs: Rumen (ruminants) Foregut sacs in some primates Sacculated colon, e.g. horse Caecum (= appendix)
Not everything can be digested, the success depends on:
a large volume of microbial fluid
time taken in the gut
% indigestible
How do insect herbivores digest plant material?
They rely on microbes
They reduce the living material in the gut
They only eat some plant species (few generalists, mostly specialists that feed on 1, or a few closely related plants)
They possess specialised enzymes
They have low digestion time
What mechanical defences do plants possess?
Spines, prickles, thorns Structural properties Leaf toughness Tree bark Trichome (small outer hairs) Hooked, sharp hairs and sticky glands
What are digestible reducers?
They are a plant defence mechanism. Digestible reducers make plant cell walls indigestible to animals.
What is the role of Cellulose / hemicellulose?
80-90% of dry wt
Support of cell walls
Slow microbial digestion
What is role of lignin?
Lignin Binds to cellulose ‘Woody’ parts Indigestible Bind enzymes & puncture gut
What is the role of tannin?
Tanning protein binding
Astringent taste, e.g. tea
Cytoplasmic defence
Large molecules
What is the role of Silica?
Cell wall strength
Tooth wear
Common in grasses
What are the differences in composition between plant and animal tissue?
Plant tissue has just 1/10th of the Nitrogen that animal tissue has, therefore it optimises N intake as it is required for the formation of proteins.
Describe chemical toxins.
Chemical toxins are specifically targeted and not dosage dependent. They are a qualitative defences meaning they are present in small amounts and are effective against all but specialist herbivores. They are hugely diverse.
Plants concentrate defences in valuable resources such as leaves and roots.
What is plant apparency?
Plant apparency refers to the fact that some plants cannot hide to avoid discovery due to being obvious such as trees. These plants therefore focus on generalised protection, quantitative defences, lignin and tannins in trees and silica in grass.
Other plants are difficult to find so they are preyed on by specialist herbivores so produce specific qualitative defences such as toxins.
What must happen for coevolution to occur?
Genetic variation for both plant and insect
Each species must act as a selective force on the other
Each species must respond to selection.
What is Batesian mimicry?
It is polymorphic
Accurate
predators learn from experience
What is Mullerian mimicry?
It is general
predators learn by shared experience and the costs are shared.
