Lecture 5 - interactions between organisms

Question 1

5 types of network interactions

Answer 1

1) herbivores and plants; defence strategies
2) ant plant mutualism
3) nutrient cycling (mycorrhizas and soil microbes)
4) plant pollination by insects, birds and bats
5) seed dispersal by birds and mammals

Question 2

what are the types of herbivory and what is most common?

Answer 2

• insects (most common)
• vertebrates
• funghi
• pathogens

Question 3

what is important in regulating trophic dynamics?

Answer 3

the interaction of herbivores and young leaves of tree seedlings - it determines herbivore population sizes and/or seedling persistence

Question 4

what dominates consumption of biomass in rainforests?

Answer 4

herbivores - major impact on plants

herbivory in temperate forests is nothing compared to rainforests

Question 5

how can be impacts on plants be observed (examples)

Answer 5

obvious - caterpillers and grasshoppers

hidden damage - sap sucking insects - result in plant growing slower

Question 6

types of defences against herbivory?

Answer 6

1) physical e.g. spines of stinging
2) chemical e.g. toxic bark
3) leaf defences

Question 7

when does most damage to leaves occur?

Answer 7

when they are young - leaves of shade tolerant species live for years yet 75% of lifetime damage occurs during the first few weeks that leaves are expanding

Question 8

6 examples of different leaf defence strategies

Answer 8

1) leaf toughness - high fibre content
2) chemical defences e.g. tannins
3) rapid leaf expansion to minimise damage
4) synchronous leaf production to satiate herbivores
5) delayed greening of young leaves
6) extra floral nectars and ant defence

Question 9

why are leaves vulnerable when they are expanding?

Answer 9

there is no lignin or cuticle - no rigid structure

Question 10

describe delayed greening

Answer 10

• energy losses are reduced by delayed development of chloroplasts
• sometimes look red/purple due to anthocyanin
• less attractive/nutritious to herbivores (less chlorophyll = less nitrogen)
• cost of delayed greening is forfeited photosynthate
• more prevalent among understorey plants where photosynthesis is limited by shade

Question 11

what are myrmecophytes and describe the relationship

Answer 11

plants that live in a mutualistic association with a colony of ants

• ants protect leaves in exchange for a home and food
• ants will aggressively attack both vertebrate and invertebrate herbivores
• plants provide extra floral nectaries, food bodies and nesting sites (domatia)

Question 12

describe the mutualistic relationship of macaranga bancana

Answer 12

• pioneer rainforest species
• obligate relationship with heart gaster ants
• plants colonised as saplings
• queen seals herself inside shoots and lays her effs
• plant provides starchy food bodies on the undersurface of stipules
• ants squirt formic acid on intruders

Question 13

describe the triptrophic relationship with macaranga bancana

Answer 13

The ants farm scale insects of the genus Coccus in the hollows of the stem and feed on the honeydew that these sapsuckers secrete.

Question 14

describe kursar and coley (2003) experiment

Answer 14

• looked for correlations of defences
• classified traits into two syndromes:
  1) well defended young leaves (defence syndrome)
  2) rely on rapid expansion to minimise vulnerable period (escape syndrome)
• not always discrete classes but a continuum
• investigated two closely related inga species which exist

Question 15

what were the results from the kursar and coley experiment

Answer 15

• each species has evolved a different suite of adaptations in response to herbivore pressure
• l.goldmanni = defence strategy - had ant defence - leaf defence chemicals more bioactive against herbivores
• l.umbellifera = escape strategy - delayed greening, synchronus flushes, less effective chemical defence and no ant defence
• both plants coexist due to their different defence mechanisms