3) Angus McIntosh Flashcards
types of plant damage
- Types of damage: Leaves, buds, roots and saps - more preferable to insects/animals because that’s where the most proteins and nutrients are - new growths.
plant compensations for damage
- reduced death of plant parts: dropping leaves sooner
- mobilizing stored carbs - stored in roots, tubers, stems
- reduced competition and self thinning - top leaves shading bottom leaves - shed leaves to maximise photosynthesis - rearrange posistion of leaves
- chnage allocation of photosynthate in leaves to make sure they don’t get eaten.
types of defences
- toxic/bad taste: terpens, phenols, tannins
- insect hormones mimics and blockers
- protinase inhibitors
- physical defences - tough and difficult to eat plants.
chemical defences nz: Rimu - large proportion are nasty things that herbivores that don’t want to eat - 12% terpenes, 24% tannins
theory: investment in chemical defense
- relationship between how much is invested in chemical defense and released growth rate
- as investment in defense occurs they benefit by having a higher growth rate
- something with a low maximal growth rate, the more it invests in defense the better it does.
- something grown high is only a minimal growth rate
- there is a humped relationship - why? if you’re slow growing you will be around for a while so its worth putting energy into defense.
- a fast growing plant may not put energy into defense because they are getting out of the herbivore zone faster
- trade off: energy into defense and grow slowly, no enegry into defense and grow fast - can’t do both.
specialist herbivores and co-evolution
- butterfly feeds on the nettle - specialist herbivore and co-evolution
generalist herbivores - polyphagos
- even the generalist herbivore is selective about what it feeds on - how generalist herbivores can be damaging.
impact on vegetation
- a study on deer exclosure plots - deer cannot get in. monitored and compared the exlosure with deer outside in terms of soil and inverts
- found that ground layer wasn’t much different but browse layers are more abundant comapred to the outside
- dramatic chnage to herbivores due to vegetation
- why such a big influence? lack of co-evolution the plants were well desgined to deal with existing herbivores but not an introduced herbivore
- unable to adjust quickly so community structure changed.
how similar are the responses of plants to herbivores in comparison to the responses of animal prey to predators?
- both involve a trade off between defences, being fast and no defences or slow with defences, slow growing
- fundamental differences in handling time and search time. herbivores live in the presence of their food
- predator prey cycles but unlikely to get with plants because there are usually a lot of plants
- plants can’t run away
- plant can regrow
What controls the strength of interactions like trophic cascades?
- its possible the terrestrial world is green becuse its prickly and tastes bad
- plants can defend themselves well. why is the world? because lots of resources everywhere but is it because of top down interactions or because the world is prickly and tastes bad?
are wet trophic cascades stronger?
- meta analysis of all experiments on all different tri-trophic levels
- in most systems predators cause declines in herbivores
- biggest declines in lake bottom and marine benthic communities
- not big in terrestrial communities -> suppression in herbivores should increase plants
- should be more plants compared to the control because we removed herbivores - less reduction in plants than expected - probably because plants can defend themselves well and stop them from getting eaten.
Why might aquatic cascades be stronger?
- maybe because algae are not so well defended
- primary producers are more edible and less defended
- in aquatic systems HSS might be more correct
What factors influence the effect of top-down and bottom-up forces?
- Number of trophic levels
- Defence of the primary producers
- Availability of resources (ie., bottom-up can limit topdown)
- Position in food chain
- Presence of intraguild predation
- Predatory generalists vs specialists (next)
diversity
Diversity - when we talk about it we talk about richness - the no. of species there and relative abundance - distribution across a community.
effects of predation on commuities
why was different algae cover happening in different pools?
- Interested in how the herbivores affected the diversity of plants on the rocky shore and the primary producers are the algae.
- Two main types - greens (littorina and enteromorpha) - palatable and the chondrus which is unpalatable because it’s tough.
- different cover types - If you add littorina that had relatively few of them then snails reduced the cover of the green palatable alga pretty quickly. Bloom of sea lettuce and then that went away and left limited coverage
- If they took littorina out fo the tide pools where it had been abundant, enteromorpha cover increased dramatically - green alga and it increased it pretty quickly.
- Why when you add littorina why does enteromorpha disappear? It’s being grazed. When you take them away, the palatable one dominates - high cover.
- The chondrus is most abundant in the control pools - why isn’t it present in the other pools? There is a herbivore, the herbivore is eating down the palatable algae and leaves space for chondrus to grow. The herbivore is suppressing the competitive dominant by grazing. Herbivory can change patterns of cover because it alters the dominance of organisms in a community.
- In the absence of herbivory the enteromorpha dominates because when you remove littorina, entermorpha dominates.
changes in influences of littorina grazing
- Tide pools and exposed platforms altered the numbers of littorina in the pools. Overtime keeps the densities.
No littorina and then increased them to 250 per msq. So a hump shape pattern in the tide pools.
Where there is no littorina why is species richness likely to be low? Species richness of algal species.
Because one species is dominating - enteromorpha dominates. Increasing snails means increasing herbivory and the snails uspress the enteromorpha (more palatable competitive dominant) which means more room for chondrus to grow.
On the other side of the curve with lots of snails - they eat the alga down. Even the unpalatable one struggles.
Why does littorina density vary in the tide pools? The number of rocks, rocks producing hiding places for predators - crabs etc. determines the number of predators which determines the number of herbivores.
On exposed rock platforms as she increased the number of snails the littorina density declined. Completely different pattern of effect of the herbivore. The exposed platform and tide pool are different because when the tide is on the wave platform, the waves wash over and damage soft alga. Anything damaged by waves struggles to live on the exposed platform. Tide pools are protected a lot more. Big difference between the amounts of disturbance between the two habitats.
If the exposed platforms are more disturbed, how can you explain the pattern of algal species platform change with grazing.
Why with low numbers of littorina do we have heaps of species? The waves are affecting which algal species can be there, and the pattern of competitive dominance has changed - enteromorpha cannot be dominant because it’s vulnerable to the wave disturbance. Algae like chondrus are. Disturbance may increase species richness. When you add snails, they graze the rest of the enteromorpha.
- Tide pools are an example of predator mediated coexistence.
Exposed platforms - disturbances controlling that.
indirect interactions
- where one species affect another via their effect on the third species
- more than 2 species interacting
- a trophic cascade is an axample of indirect interactions
- examples: the salt alkes and lion-zebra-grass.
the beetle, ant and plant foodweb
- negative interactions from beetles to ants to herbivores to plants
- but by influencing the ants and herbivores, predatory beetles have negative indirect effects on the plants. because they decrease ants, releasing herbivores, which eat more plants.
- direct positive effect between the plant and ants because of the mutualisms.
keystone predation - example of indirect effects - pisaster food web
- all other species apart from mussels are benefiting
- negative competitve affect between mussels, chitons, limpits and barnacles
- starfish decreasing the abundance of mussels decreases the strenght of the negative direct effect
- so a positive indirect effect to all other species.
exploitation competition - potential indirect affect
- consumer 1 - stronger competitor
- negative effect on resource because they are decreasing it
- negative indirect or inferior competitor
apparent competiton - indirect competition
- where two prey (consumers) share a predator
- depending on the predators preference and relative abundance of the two prey species, there can be an indirect effect of one consumer on the other consumer
- the indirect effect is mediated by the predator making it appear as though they are competing.
- increase in C1 (because C1 providing resource to predators) and more C1 = more predators, which means predators prey on C2, C2 will decrease -> this makes it look like they compete but they have the same predator.
example of apparent competition - aphids and ladybugs
- fertilisation increases the number of grass aphids so you get more ladybugs, so number of nettle aphids decrease because they eat nettle aphids
- shared predators - apparent competition
- i.e. increase in grass aphid population decreases nettle aphid population becasue they share a predator
- increase in abundance of A1 (grass) leads to increase in population of its predator H1 (grass aphid)
- increase in abundance of H1 equals increase in predator population
- abundance of the top predator leads to an increase in population of rate of predation on H2
interaction modification
- where one species modifies the effect on another, influecning a thrid interaction
- just behavioural - scaring ecology of fear. no one eating anyone
- trout scare stoneflies which has a positive indirect on the mayflies because trout are decreasing effects of the stoneflies.
complex indirect effects: mistletoe
- mutualism between birds and the mistletoe
- negative effects: stoats and rats eating bellbirds and tui nestlings and egg. possums browsing on mistletoe
- possible negative indirect effect of stoats and rats on mistletoe: mistletoe could suffer if they lose pollinators by killing birds
complex indirect effects: pond food web
- salamander eat large daphnia
- large daphnia outcompete small daphnia. two daphinia species compete for same resources.
- phantom midge eat small + daphnia
- midge depends on precense of salamander in the pond
- positive indirect effect because salamander eat large daphnia - regulating population so small daphnia don’t get outcompeted. therefore also positive indirect effect on phantom midge because more resources to survive.
- ponds with salamander - large daphnia low and small daphnia high
- ponds without salamander - small daphnia absent, no phantom midges
- salamander have positive indirect effect on small daphnia - predation reduces population growth of large daphnia
- indirect interaction between phantom midge and salamander - indirect commensilism - because interaction is beneficial to midge but nuetral to salamander.
comsumptive links within foodwebs
draw them on
- cannabalism
- omnivory - feeidng on the herbivore and autotroph
- intraguild predation - feed on herbivores and something at the same trophic level
modules in food webs
- tri-trophic chain
- omnivory
- exploitative competition (consumer sharing two predators)
- apparent competition (two herbivores sharing a predators)
